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[
"How did our ancestors survive before glasses?"
] |
[
false
] |
[deleted]
|
[
"You're thinking of life expectancy ",
", which is not the same as one's total ",
". ",
"It's simply a myth that people didn't get old in ancient times. It's a myth that possibly originates in a confusion about ",
" lifespans. In those times, infant and child mortality was extremely high, so the total ",
" life expectancy at birth was very low; but if you were lucky enough to live into adulthood in medieval times, you could expect to live to the age of 60-70. And that's just the average.",
"You still had a lot of things, like infections, that you could kill you. On the other hand, diseases like cancer and heart disease such as atherosclerosis (two of the main causes of age-associated death in modern times) were rare, so lifespan-wise there was actually a benefit to living before the age of obesity and processed food.",
"So back to the question: People did grow old, and presumably a lot of them had to suffer from poor eyesight, with no chance of correcting the problem until the invention of glasses in the 13th century. If you go back to pre-historic times, it's conceivable that near-sightedness would hamper you ability to survive, especially since you would be more accident-prone or possibily less aware of obvious dangers.",
"But humans are social, empathetic animals, and for thousands of years we have been taking care of each other, even our weakest individuals. I'm not an anthropologist, but I think someone incapacitated by lack of sight would likely be taken care of by the rest of the family or tribe, if one was around. So I don't think it necessarily was so terrible.",
"And remember, up to a certain degree of near-sightedness (my gut feeling is between -2.0 or -3.0 diopters), you can get by quite well being nearsighted. Even with a high degree of myopia (I'm currently at -6.75), it's not like you can't recognize your surroundings, or people, or dangerous situations. In a hunter-gatherer society you would be crap at hunting animals, but you might be really good at building dwellings out of mud and straw."
] |
[
"Let me ask you a similar question: what happens to animals with bad eyesight? Birds, predators, or rodents with bad eyesight? Either the eyesight deficit is severe enough that it results in their death (as other posters have said) or the deficit is not severe enough to affect survival. ",
"Now the question is: how vital was good eyesight to survival for our ancestors? Well, that depends on which ancestors you're talking about. You can imagine a hunter would have a hard time hunting game if he couldn't see. But a gatherer or a \"priest\" would be able to get by. And once agriculture became widespread, the need for perfect vision lessened. "
] |
[
"One thing that I am surprised has not been mentioned yet - Myopia is more common in societies that do close work as children. ",
"Here is ",
"a source",
" (I am sure someone else can find a better, or even refuting source) that shows that children who do lots of close work (reading, writing, etc.) developed myopia at an increased level relative to those who did less. ",
"I seem to remember, (but did not look for/find a source) that a gene was found that was closely linked to myopia, and that this gene was found in equal proportions in aboriginal australians and non-aboriginal australians. However, the percentage who showed signs of myopia were significantly skewed toward the non-aboriginal part of the study. ",
"Also, here is an unreferenced bit from wikipedia about myopia",
"Near work causes the lens of the eye to focus (accommodate) excessively, leading to a spasm of the ciliary muscles surrounding the lens of the eye. Prolonged ciliary muscle spasms eventually lead to the elongation of the eye resulting in myopia. ",
"So perhaps our ancestors with myopic genotypes did not express myopic phenotypes because of how they lived.",
"Edit- Spelling, also, it turns out the source I cited determined that there was not a direct link between time spent at close work and myopia, but still suggested a correlation. (which != causation)"
] |
[
"Could solar panels have an effect on the average climate temperature"
] |
[
false
] |
Do solar panels produce heat or do they reduce heat due to absorbing light?
|
[
"Solar panels absorb heat. But the electricity they make will end up being converted into back into heat eventually. "
] |
[
"I see thanks "
] |
[
"Although solar panels absorb photons from the sun that typically would have dissipated as heat in the earth's environment, the proportion of earth's surface area covered in solar panels is so small that the effect is negligible."
] |
[
"If the higgs field is what gives thing mass, is there a field that gives things charge?"
] |
[
false
] |
I saw a similar image to where they said mass increases to the right and charge increases towards the top (doesn't work entirely but sort of)(in one of those videos explaining the higgs boson). They also said something along the lines of "mass is a property given by the higgs field". And so I wondered if there is some field giving the particles their charge. If so, does it have a particle associated with it, like the higgs field has the higgs boson?
|
[
"The electromagnetic field, which is quantized as the photon."
] |
[
"Simply put, no. The value of the electric charge is put in by hand in the Standard Model. It is not generated by a field.",
"It is true that there is an electromagnetic field, but this field only carries the forces between charged particles; it does not generate the charge in the first place."
] |
[
"To understand the distinction, it is important to understand how the Higgs mechanism gives particles mass. A particle like the electron gets its mass from the product of two terms: the strength with which it interacts with the Higgs field, and the value of the Higgs field that fills space.",
"The first of these -- the strength with which the electron and the Higgs field interact -- is a parameter in the Standard Model that is very much like electric charge; it is a number that we have to put in by hand. (It is different from charge in that charge is associated with a symmetry, but that is irrelevant here.)",
"But the value of the Higgs field that fills space arises from the equations governing the behavior of the fields, and, in fact, this value changes over time: in the early universe, this value was zero and the electron was massless, and now this value is non-zero and the electron has a mass.",
"So the difference is this: both the electric charge and the Higgs-matter coupling constant are parameters that have to be put in by hand, and which do not change over time. The Higgs-matter coupling constant is not, by itself, the origin of mass; this requires the non-zero value of the Higgs field, and there is no analog of this at play with electric charge."
] |
[
"Why do our hair colors change (greying/white hair) when we grow older or are stressed?"
] |
[
false
] |
I've always wondered about this phenomenon. It seems kind of odd that people grey as they grow older as hair does not seem, to require a lot of energy to maintain. Can someone explain why this happens? And how does stress factor into people greying faster?
|
[
"According to a recent article in the Federation of American Societies for Experimental Biology (sorry, no link, subscription site):",
"Oddly enough, your follicles produce three things simultaneously: melanin, which gives your hair its natural colour, hydrogen peroxide (as part of the follicle's normal oxygen intake cycle), and the enzyme catalase, which breaks down said peroxide into hydrogen and water almost as soon as it forms. As you age, your catalase production decreases, leaving more peroxide hanging around in the follicle, which bleaches out the melanin colouring in your hair proteins. Your keratin turns to its neutral-state colour, which is a semitranslucent silvery-gray.",
"And btw, psychological stress doesn't \"cause\" gray hair. Stress can sometimes (rarely) cause ",
", which means the thicker, darker hair can stop growing, leaving the already-gray remainder more prominent, but it won't cause the hair to actually change colour, per se. Some health issues, like insufficient B12 intake, smoking or thyroid problems may accelerate the graying process. Genetic predispositions also come into play, which is why caucasians generally tend to go gray earlier and more completely than, say, Asians."
] |
[
"How come there isn't some way of shampooing with catalase to stop the formation of peroxide?"
] |
[
"Primarily because catalase is an intracellular enzyme and needs to be in the cells producing the keratin/melanin at the base of the hair shaft. The hair is being produced by the follicles deeper in the scalp, so the catalase enzyme can't get down to where it would need to be effective. Also, it's a LOT cheaper to dye your hair than it would be to ",
"produce catalase and ship it stably",
". 30C is 86F, which is higher than ambient room temperature, so you'd have to ship the product in a warmed container truck and in a warmed bin at the pharmacy. Compare that expense to the convenience/cost of hair dye."
] |
[
"Why didn't the human ribcage evolve to to completely surround our torso?"
] |
[
false
] |
Our backside seems well protected, but our stomach and other organs don't have that protection. What gives?
|
[
"Evolution doesn't perfect living beings, it just optimizes them for reproduction. Basically, if a better ribcage doesn't result in more babies, it doesn't get passed on. An unprotected backside results in fewer babies, so those with protected backside pass on those genes."
] |
[
"I believe that if the entire torso was surrounded and bound by a \"full\" ribcage it would cut down on the ability of the ribcage to expand fully during the inhalation and exhalation cycle. Biomechanically if the rest of the spine was connected dorsally and ventrally by more ribs, lateral movement and rotation would also be limited. Lateral flexing and rotation in the thoracics (where the ribs are attached) is much more limited than in the Cervical and Lumbar spine, where ribs don't exist.",
"Edit: for spelling"
] |
[
"Plus it allows for the expansion of a woman's belly... reproductive efficiency, if people did evolve the \"full ribcage\" you want it would stop woman from being able to bear children efficiently."
] |
[
"Question of Genetics/Evolution?"
] |
[
false
] | null |
[
"In other words, if a homogeneous culture such as Iceland were moved to the equator, even if they continued the \"pure\" blood line, they would adapt/evolve to their environment and gain darker skinned mutations over a very very long time, even if the original gene (which allowed for/was caused by the mutation in humans long long ago) from long ago wasn't present in current Icelandic people today?",
"There is always a certain amount of genetic variation between people. It might not be much, but even among relatively homogeneous populations, some people will have darker or lighter skin, more or less webbing between their fingers, slightly faster or slower metabolism, and things like that.",
"There's also generally not a single mutation that happens, turning something on or off. Mutations happen all the time, and evolution happens due to a more gradual trend towards something happening more or less. In the case of skin tone, it's all about small mutations changing how much melanin is produced. We all produce it, but people with darker skin just produce more.",
"Now, natural selection works through a process whereby some of those traits will make somebody more or less likely to survive long enough to have children and raise them to the point where they can take care of themselves.",
"If you moved the population of Iceland to the equator and trapped them there, a certain proportion of them would develop skin cancer due to the increased UV levels. In aggregate, the people who had darker skin would tend to get less skin cancer, and thus would survive longer. The people with lighter skin tend to die younger, and thus the average skin tone of the population as a whole would become darker. The average genetic makeup would become one keyed for higher melanin production.",
"But again the natural variation comes into play. When the average skin tone is slightly darker, the variation in the population is around that skin tone. Some will have lighter skin than average, and some will have darker. The people who are at the darker end of that variation would again be more likely to survive to have children due to being more resilient to the UV radiation, and the people at the lighter end would be more likely to die due to skin cancer. So again the average skin tone gets darker.",
"Over the generations, this leads to the former Icelandic population developing noticeably darker skin."
] |
[
"First there is no such thing as pure or homogeneous in genetics. Every population has genetic variations between individuals. Otherwise everyone would look like identical twins.",
"When some people in Iceland moved to Ecuador evolution will favor slightly darker skinned individuals. Also in time some mutations will occur to darken their skins more and people with these mutations will also be favored by evolution. Over time population will get darker and darker skinned in each generation. Mutations causing this can be completely different than other darker skinned populations elsewhere in the world since that part is random."
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"For more information regarding this and similar issues, please see our ",
"guidelines.",
"/r/AskScienceDiscussion",
"Please see our ",
"guidelines.",
"If you disagree with this decision, please send a message to the moderators."
] |
[
"Do the vaccines prevent Covid from damaging your brain?"
] |
[
false
] | null |
[
"It’s well known that COVID infection can lead to mental issues, and even apparently mild infections can lead to long term lingering mental problems.",
"The presence of numerous psychiatric symptoms are also highlighted in many reviews ... The most frequently disclosed are low mood, mood swings, hopelessness, heightened anxiety, sleep/wake cycle dysregulation and neurocognitive disturbances including brain fog, difficulties with memory, concentration and executive function. ... up to two-thirds of hospitalized patients with Covid-19 may show clinically relevant cognitive impairments that impact their quality of life and daily functioning 4 months after hospital discharge",
"--",
"Mind long COVID: Psychiatric sequelae of SARS-CoV-2 infection",
"The vaccines prevent COVID-driven brain effects in two ways. Most obviously, the vaccine prevent infections very effectively. If you’re not infected with COVID, you don’t get COVID symptoms, including the so-called “long COVID” effects that include mental symptoms.",
"But even in the relatively rare breakthrough cases, vaccinated people are significantly less likely to have long COVID symptoms in general, and that includes the mental symptoms. ",
"Vaccination (compared with no vaccination) was associated with reduced odds of hospitalisation or having more than five symptoms in the first week of illness following the first or second dose, and long-duration (≥28 days) symptoms following the second dose. Almost all symptoms were reported less frequently in infected vaccinated individuals than in infected unvaccinated individuals, and vaccinated participants were more likely to be completely asymptomatic, especially if they were 60 years or older.",
"—",
"Risk factors and disease profile of post-vaccination SARS-CoV-2 infection in UK users of the COVID Symptom Study app: a prospective, community-based, nested, case-control study",
"Commentary on the above paper: ",
"Vaccination reduces risk of long Covid, even when people are infected, U.K. study indicates",
"By 120 days, vaccination reduced the long COVID symptoms (mean (SD) ST score in the vaccination group 13·0 (9·4) vs. 14·8 (9·8) in the control group … Furthermore, vaccination reduced both disease impact on patients’ lives … COVID-19 vaccination lowers the severity and life impact of long COVID at 120 days among patients with persistent symptoms.",
"—",
"Efficacy of COVID-19 Vaccination on the Symptoms of Patients With Long COVID: A Target Trial Emulation Using Data From the ComPaRe e-Cohort in France",
" (Preprint study)",
"Commentary on the above paper: ",
"People Who Are Vaccinated and Get COVID-19 Are Half as Likely to Have Long-Term Symptoms",
"A neurologist’s opinion: ",
"Another Reason to Get a COVID-19 Vaccine: Avoiding Brain Damage"
] |
[
"We are not going to know the answer to that for decades. I personally have gotten back to normal after a month in the ICU back in April (pre-Vaccine); but I'm participating in five studies working frantically to try and answer exactly that question. For now? We just don't know."
] |
[
"I have one important question that I’d like answered. Does this said damage repair itself over time, do you ever get back to baseline, like pre Covid? Asking in general, like a normal healthy persons body."
] |
[
"What exactly happens when you get the wind knocked out of you?"
] |
[
false
] |
Have had it happen a few times to myself as a kid or adult playing sports. Basically after watching that video, it made me think what exactly is going on internally that makes you not able to breath?
|
[
"It hurts to get hit in the abdomen."
] |
[
"It hurts to get hit in the abdomen."
] |
[
"Your diaphragm is temporarily paralyzed so your lungs can't expand/contract normally."
] |
[
"Is it actually possible to discover an element that \"isn't found on the periodic table\"?"
] |
[
false
] |
That line, which occurs in basically every sci-fi movie involving aliens ever, always bothered me. My high-school-science understanding of elements was that their identity is determined by the number of protons, and at some point too many protons = instant decay into smaller elements. That gives us a pretty limited range of possible elements, and I thought we'd already named the hypothetical ones at the upper end. PS. Not sure if this violates the "no hypotheticals" guideline, and if so, I apologize.
|
[
"Well, we need to wait for theory to catch up. You're right that all that defines an element is the number of protons in its nucleus. We haven't ever created anything with more than ",
"118 protons",
" yet, and they're all just temporarily named for the Latin version of the number of protons.",
"Our simulations and models aren't very good yet at predicting what the behavior would be of heavier elements, but some have predicted an ",
"'island of stability'",
" where some heavy elements could actually be stable for reasonable amounts of time (days, years, millions of years). Right now that's all theoretical though."
] |
[
"The main argument is whether the \"island of stability\" will be \"relatively stable\" as in lasting for days/years/long enough to use them for whatever, or \"relatively stable\" as in \"oh wow, this one lasted for a whole minute! That's millions of times longer than that other isotope did!\". Mostly depends on which theoretical models you think is correct, since we can't confirm anything by experiment right now. "
] |
[
"It's written as a way for \"scientists\" to express that something is completely alien, written by people who haven't had chemistry since high school. ",
"For one thing, in theory the periodic table expands as necessary. When I learned it, there were only 108 elements \"on the periodic table,\" though the tables we had would often go to 112 just to finish the transition metal row. Now we've discovered up to 116, though many periodic tables will put 117 and 118 to finish the Halogen and Noble gas elements of the row. ",
"A better written scientist would say \"made of an alloy we've never seen before\" or \"appears to be some kind of ceramic that isn't like anything I've ever seen\" [etc] "
] |
[
"How can a person have ADHD AND Schizophrenia when they’re believed to have opposite ‘causes’?"
] |
[
false
] |
ADHD is believed to be caused by a lack of dopamine (and/or noradrenaline) in the brain. Schizophrenia is believed to be the excess production of dopamine, the opposite. So how can somebody have both? Could it be that those who have both produce an excess amount of dopamine, but not enough noradrenaline (another cause of adhd)? Is there anything different/interesting about people who get adderall induced psychosis/schizophrenia?
|
[
"I don't know how much agreement there is on the dopamine assumptions here. The causes of schizophrenia remain very much a mystery beyond \"probably associated with this increasingly long list of genes\" and although anti-psychotic medications and anti-ADHD medications frequently target one or several of the multiple different types of dopamine receptors, they target different sets of dopamine receptors from each other. They also target a bunch of ",
" receptors. ",
"Neurons involved in dopamine signaling are distributed throughout the brain, sometimes in clumps and sometimes in dispersed patterns, and we really have extremely limited understanding of what most of them, and the networks they are part of, are doing. More recent evidence also shows that many (most?) neurons produce/receive more than one type of neurotransmitter, which adds another layer or three of complexity to what might be going wrong in any given neuropsychiatric disorder.",
"Adderall-induced psychosis (or psychosis induced by any other drug) is usually temporary. Schizophrenia is a lifelong condition for most people and involves multiple symptoms in addition to psychosis."
] |
[
"The leading theory on the mechanism of adhd is more to do with dopamine receptor level or function, than not having enough dopamine itself. ",
"Another theory is that the molecule that transports dopamine doesn't work effectively or there isn't enough produced.",
"Schizophrenia is theorised to be due to neural pathways being over sensitive to dopamine. Where these neural pathways contain dopamine receptors with very low thresholds for dopamine activation. So very little dopamine is required to cause activation. ",
"It's like when you're in a noisy environment and you think you can hear your name being called. But when you look around you see nothing.",
"And lastly, both adhd and schizophrenia are quite hereditary.\nIf you have ADHD (like I do), there is a 60% chance of one of your parents having it. Schizophrenia is too, however this it isn't a guarantee that a person will get it either. It is quite dependent on your situation.",
"My mum has bouts of schizophrenia, we give her lots of love and attention, she receives treatment and after not long, she's back to being her wonderful self.",
"Hope you found my response enlightening.",
"James.\nADHD scientist (Biotechnologist)"
] |
[
"Re: Adderall induced psychosis.\nIn most cases it tends to happen when a person takes too high of a dosage and doesn't get enough sleep.",
"Some times it occurs if the person is on other medication as well. Such as SSRI or antidepressants.",
"But this can also happen as a quirk of a person's mental health at the time.",
"I'd look into the first two points first though. And always discuss with a doctor before making any changes to medication."
] |
[
"Does the IFR of an infectious disease change with time?"
] |
[
false
] | null |
[
"It can change significantly once better treatments are discovered. For example, the fatality rate for HIV was nearly 100% before antiretroviral therapy was developed. Now it is a manageable chronic infection. You also have to take timing into account, as well as age groups. With COVID for example the fatality rate for children is the same as the flu, while for the elderly it is 10-100x more deadly. Interventions like vaccination also reduce the severity of the disease where you may still get infected, but the fatality rate drops by 10 fold or more."
] |
[
"Yes it does imagine this oversimplified situation. A disease kills 10% of people who have a gene which makes them susceptible while just infecting everyone else. At first it kills 10% of people but after it's killed 50% of the people with the gene it now only kills 5% of the total population."
] |
[
"Absolutely correct. These situations are mind bogglingly dynamic with many thousands of variables affecting outcomes."
] |
[
"What natural phenomenon used to occur back in prehistoric times that we wouldn't see now?"
] |
[
false
] | null |
[
"There are doubtlessly quite a few, here's a start:",
"Komatiitic flows",
". These are a type of volcanic flow involving low-silica magnesium-rich lava. Komatiites had a distinctive composition, were high-volume, very high tempearture and low in volatiles. They used to produce large sheets and are associated with nickel deposits. Their production required the earths mantle to be hotter than it currently is. Most are af Archean age (> 2.5 billion years) with a few slightly younger stragglers.",
"Another obvious one would be ",
"Banded Iron Formations",
", especially Algoma types. BIFs are laminated sedimentary deposits rich in iron oxydes, and the source of most iron production today. These were related to the great oxygenation event and are pretty much all formed in the Proterozoic (2.5 to 0.54 billion years ago.)",
"Planetary glaciations of the ",
"\"Snowball Earth\"",
" type. Imagine the icecaps growing all the way past the tropics and meeting at the equator ... Latest one ended about 580 million years ago, and we haven't seen another one since.",
"A comprehensive list could undoubtedly be done, but it would require work..."
] |
[
"Coal formation.",
" It can still happen, but the Carboniferous era was pretty much a one-shot deal for producing useful amounts (>90% of total reserves) of high-quality coal.",
"Lycopsid trees (which incidentally look like something by Dr. Seuss) had just invented lignin, a major polymer in modern wood. It took a while for decomposers to fully catch up and figure out how to break down this new polymer fast enough to keep up. Enormous amounts of dead trees that could not rot piled up until they were buried or burned in massive forest fires. Quite a lot of coal started out as charcoal from those forest fires of dead rot-proof trees.",
"Decomposers eventually learned to keep up with lignin, and it's still around as part of the wood in every form of plantlife you'd consider a tree. Nothing like the Carboniferous will ever happen again unless trees invent a new inedible polymer."
] |
[
"Extremely large lakes held back by continental ice sheets (Lake Agassiz, etc.), and catastrophic flooding related to the draining of similar lakes (the great Missoula floods that created the scablands of Washington).",
"https://i.ytimg.com/vi/xOqy_IeQ6b0/hqdefault.jpg",
"https://en.wikipedia.org/wiki/Missoula_Floods"
] |
[
"How much power does a charger plugged into a wall use if any at all?"
] |
[
false
] |
No device plugged in.
|
[
"Depends on the quality and design of the particular charger. A good design with quality parts will sip so little power that it's essentially nothing, a bad design can have substantial draw and just dumps the power into the room as heat.",
"To get a very rough idea of how much energy is drawn, touch the charger after it's been sitting idle for a while. If it's cold it's likely drawing close to zero power, if it's warm it's somewhat inefficient, if it's hot it's very inefficient and you should replace it ASAP for safety concerns alone.",
"If you're interested in the actual numbers you're going to have to get your hands on a device that can measure AC current and do a direct test."
] |
[
"Wouldn't going by the Watts in, Watts out measure be a good way to see how efficient it is under 0 load as well? If it takes in 20 watts under max load and outputs 15 watts (like my tablet charger) that means it is of high efficiency to begin with. If it is something like a lot of laptop power bricks where they can take in 250-300 watts and only output 90 (hp laptop brick) that is a lot of heat being outputted under load so wouldn't it be safe to assume that it draws a lot of idle power as well? (even if it is still rather low)",
"Just a bit of speculation as I've never tested that, but seems somewhat logical "
] |
[
"The operating efficiency isn't necessarily correlated directly with the standby draw, but it would be pretty funky to find a design that is efficient in one case but not the other. ",
"If it is something like a lot of laptop power bricks where they can take in 250-300 watts and only output 90 (hp laptop brick)",
"That would be an astoundingly bad power brick. An operating efficiency of ~36% is completely unacceptable from a major consumer product, ",
" can design a better supply than that and I don't know much at all about supply design. I think you're mistaking the max power draws with the actual operating draw, dumping 160 watts to heat is mind-boggling.",
"To get more solid answers you would really need to get your hands on a watt meter and check it yourself. There's just too many variables to consider and still make concrete statements without some specific example to reference."
] |
[
"Why is it that there is no planet that orbits the sun in the opposite direction to the other planets?"
] |
[
false
] | null |
[
"All the planets in our solar system would have emerged from what's called a 'proto-planetary disk'. This was a fairly flat disk of gas (largely H and He) and dust (solid stuff, including rock-making stuff and, at farther distances, solid ices). The planets inherited how they orbit from the direction in which the disk rotated, which would have been about the same as the spin direction of the sun.",
"There are several observed cases where the one planet in the system rotates in almost the opposite sense to the sense in which the star is rotating (or at least in which the sense of the orbit and the sense of the star's spin are at some large angle relative to each other). In these cases the system went through some sort of violent upheaval or maybe the star somehow had a different spin than the proto-planetary disk. This topic is a hot area of ongoing research."
] |
[
"Here's a good video using a rubber sheet to simulate a gravity well: \n",
"Gravity Visualised (Youtube)",
"At around 2:45 the teacher adds a bunch of marbles in opposite directions, and through collisions they self-select one direction to orbit the well. As other commenters have mentioned, this happens because one bunch of marbles has more angular momentum than the other one, so they end up with just that preferred direction."
] |
[
"The tl;dr here is that almost everything in the solar system is spinning because the matter it is made of was always spinning in some small way. That kind of momentum doesnt just go away. There is no force that makes planets rotate or orbit — it's just the energy from the formation of the solar system still being expended. The exceptions in our solar system are Venus and Uranus, both show evidence of being in massive collisions."
] |
[
"Why do states of matter exist?"
] |
[
false
] |
I can't seem to find a straight answer as to why distinct states of matter with boundaries (boiling point, melting point) between them exist and not a continuum of states. I'm guessing it has to do with specific bonding energies and such and it makes sense when you think of say a solid structure breaking up to form a liquid or water, with hydrogen bonds, boiling - but what about a liquid with very negligible intermolecular forces boiling, why is there a distinct point of equilibrium between liquid and gas.
|
[
"This is a really good question, and ultimately comes down to the concept of ",
"criticality",
". Criticality in day-to-day systems such as liquids and gasses is quite complicated, but the idea can be understood fairly well with a simpler system, the Ising model of ferromagnetism.",
"The basic idea of the Ising model is that you have a collection of magnetic moments which point either up or down at any given moment. They generally want to point the same direction as their neighbors, but as long as there is any energy in the system they'll flip back and forth more-or-less randomly as the temperature allows.",
"What we find in such a system is that at high temperatures there is no large-scale organization. There may be some small correlation between the spin at one point and the spin of its neighbors, but this correlation disappears as soon as you look at spins with a significant separation. At low temperatures, we find that the whole lattice of spins is likely to be in the same position, with a few spins possibly reversing for a moment, but only ever temporarily.",
"One might expect that, while these descriptions apply to extremely high or extremely low temperatures, there would have to be a smooth transition between them for temperatures in between. In fact, this is not the case. The system undergoes a clear, demonstrable phase-change at a precise temperature, known as the Curie temperature.",
"To understand ",
" critical behavior occurs requires more advanced mathematics, and I'm not personally familiar with the theory."
] |
[
"When you have a collection of matter, there exists different types of interactions between the constituents of that collection. For example gravitational attraction, coulombic interaction, spin-spin interactions, etc. All of these interactions have a characteristic energy associated with them, and furthermore, each interaction directs the system toward a specific configuration. In the case of ferromagnetism for example, the ferromagnetism directs the magnetic moments of neighboring ions to align in parallel.",
"So the important thing here is that each of these interactions has their own characteristic energy. For example, ferromagnetism's characteristic energy is called the Curie Temperature. Phase changes typically occur when the temperature of a system passes through the temperature associated with the characteristic energy of a particular interaction. If there are multiple interactions in a system, each with their own characteristic energies, that system can experience multiple phase transitions, at least one associated with the characteristic energy of each interaction present.",
"P.S. If you know the characteristic energy of an interaction (let's call it E), then you can get a ",
" of where a phase transition will occur using E = kT, where k is boltzmann's constant and T is temperature."
] |
[
"Tell me again how this is not a continuum.",
"You can lead a horse to water...",
"I think the problem is that while your answer is technically correct and perhaps appropriate for a well informed audience, it misrepresents the important aspects of what happens in large interacting systems. There are ",
" changes in behavior as parameters (particle number, temperature, pressure, etc) are changed. Yes, they are indeed fundamentally not truly discontinuous, but that point must be understood ",
" with an understanding of why interacting systems undergo sharp changes."
] |
[
"What is Area 51?"
] |
[
false
] | null |
[
"Area 51 is a facility in the United States for testing military aircraft."
] |
[
"Does it has anything related to programming?"
] |
[
"No."
] |
[
"Why do software updates require me to restart my computer/phone? Why can't the update install properly with the device turned on?"
] |
[
false
] | null |
[
"In 99% of cases, they don't, except in a couple of specific cases.",
"Your computer is currently running a bunch of software, which we'll divide into two major sets. For example, you'll have your web browser, email client, music player, chat clients and other stuff running. These programs are so called \"user mode\" programs. They run inside the operating system, which (typically) keeps them isolated from each other, and handles stuff such as file access, access to draw to screen, access to the internet, and a bunch of other things. The operating system is also responsible for giving them time to do computation, as all of these programs are given small amounts of time in turn to be able to run on your 1-4 processing cores. ",
"Updating a program requires it to be restarted so that the operating system can load in the new code. This is required because in the update, stuff moves around. Data which the program expected to be located at address X will now be located at address Y, and other stuff like that. Updates to these will not require a system restart though; they can be closed, at which point the operating system will unload them, and then re-opened after they have been updated, at which point you'll be running the latest version.",
"Your operating system itself is basically a program though, although this program is what we call a \"kernel mode\" program. This is a special type of program that has unrestricted access to the system and can do anything, i.e. write any memory, control low-level switches, and write to hardware. If we tried to do anything like that from a user-mode application, the operating system would kill us for doing naughty stuff (side note, we can sometimes trick the OS into not killing us. This is called a kernel-mode exploit, and allow a malicious program to basically control your system or steal any data from your system).",
"Recall that I said that you need to re-start a program in order to update it. The operating system is running right at the lowest level, hence to update it, we need to restart the whole system so that the new code can be loaded in. You might ask \"well, why can't we just restart the operating system part?\". Recall that user mode applications run ",
" the operating system. If we kill the operating system, all of the user mode tasks will die too. Even if they didn't restarting the operating system would have cleared all the operating system's data (such as what processes are running, what files are open etc), so the programs wouldn't be able to run anyway (as the operating system wouldn't be aware they were running).",
"Now, some of this has been a bit of a white lie (sort of how they teach you science at primary school, then secondary school says \"lol that was all a simplification, here's the real stuff\" and so on). With some smartness, we can actually update in-place, but it requires support by the program. Since all data has shuffled around, we can't just update the code and hope, but we can make the program start a new copy of itself, send the data across (which the new copy will put in the new places), then kill the old one and pretend that nothing happened. It is also possible for the operating system to do this, and this is what tools such as ",
"kSplice",
" attempted to fix.",
"While this works (and removes downtime), it can be risky though. What if you miss some data for example? The program is then half consistent, and may run perfectly until the time that it requires the data you forgot to copy, then it will either do something undefined or crash. This is bad if a user-mode program does it, but could be catastrophic if a program does it.",
"So, basically, to sum up. You don't, apart from in a few cases. A normal program can be restarted by itself to load the updated copy, which doesn't require restarting the operating system. If you update the operating system, you need to reload that though, which requires a reboot, except if you really, really carefully design a system to cope with it."
] |
[
"Some operating systems, such as Linux, can update all software without restarting. Windows hasn't had significant market pressure (the driving force behind it's progression) to gain this ability. While rebooting can be disruptive it is a quick and easy method to supplant new code and dependencies while ensuring the operating environment remains stable."
] |
[
"Memory management is a weird one in this case. Most of the memory management is done by the runtime that is used by the program (i.e. libc). This is a shared library that is loaded by each program when it starts, and provides a bunch of useful functions to the program. Most of these just really streamline the interface between the operating system and the program, and are for stuff like opening files, getting the system time, and quite a lot of other useful stuff.",
"One of these functions is ",
"malloc",
", which is a method to allocate memory. This is the meat of the memory allocator. It handles where the free memory is, where the used memory is, and decides where to put stuff when you request more memory. This is done in user-land and is purely a part of the programming language's standard library.",
"There is a mechanism, however, to request memory from the operating system. On Linux, this is the ",
"mmap",
" syscall...I'm not sure what it is on Windows. This is more for requesting large chunks of memory to be allocated, and more concerns itself with virtual address mapping, and setting up the hardware components like the MMU etc. Your programming language's memory allocator (e.g. ",
"malloc",
") will use this in order to map large blocks of memory that it can then allocate itself.",
"This is required because in systems with virtual memory, writing to an unmapped memory location will cause a crash, so you need to ask the operating system to map some memory for you, which you can then use.",
"Anyway, I'm sort of circling the point of this post at the moment. The memory allocator inside your programming language's standard library (i.e. ",
"malloc",
" in libc) can be replaced without rebooting...currently running programs will use the old version and programs that you start after updating will use the new version. There's no clash from having two memory allocators because they work in completely different address spaces.",
"Updates to the OS memory allocator (i.e. ",
"mmap",
") will require a reboot...but that's because you've just changed your kernel more than anything."
] |
[
"Why do we see intricate patterns when pressing down on closed eyes?"
] |
[
false
] |
[deleted]
|
[
"The photoreceptors in our eyes normally respond to light wavelengths. However mechanical forces can also slightly activate these same photoreceptors. So by pressing on your eye, it activates the receptors so you see “lights” just as if light was causing you to see lights"
] |
[
"Could it damage your eyes as well? I used to do that all the time when I was a kid in class because I was so bored. I would open my eyes again and my eyesight was all wacky until it went away."
] |
[
"OK, thanks for this response. I was always scared that I messed up my eyesight and that I was gonna go blind. Well here I am now wearing glasses but it is most likely that I have glasses because it runs in the family lol. "
] |
[
"Statistical polls vs. election results."
] |
[
false
] |
[deleted]
|
[
"Statistics like these can be very misleading. It depends on the area they polled, the economic group, age group, ethnic group. The odds D would win are very hard to determine due to a very small amount of info. They would need to do a broader poll for the best results. I know you're in Iceland so maybe there aren't many differences between geographical areas, but in America polls like these must be taken with a grain of salt."
] |
[
"It has been too long since I took a statistics course in college, so I'm not going to make a fool of myself and explain it incorrectly. But ",
"here",
" is a reference that might help!",
"Perhaps a kindly statistician will come by and offer his/her input!"
] |
[
"It has been too long since I took a statistics course in college, so I'm not going to make a fool of myself and explain it incorrectly. But ",
"here",
" is a reference that might help!",
"Perhaps a kindly statistician will come by and offer his/her input!"
] |
[
"If the Moon is slowly moving away from us, what will happen to the Earth when this actually happens?"
] |
[
false
] |
It seems the moon is moving farther and farther away from the Earth every year. When the moon is no longer in orbit, what will happen to the Earth and the moon?
|
[
"The Moon will never leave orbit. Its track widens at a rate of only a few centimeters per year, and given current rates of change, the Earth will become tidally locked with the Moon (keeping the same face constantly toward each other) long before it can to leave orbit. At that point its orbit will stop expanding, so we'll still have the Moon when the Sun expands into a red giant and engulfs us in its last days."
] |
[
"Ok so no death caused by the tides running amok. But definite death by a bloated sun. Gotcha!"
] |
[
"The bloating sun is only the first of our concerns, i for one want to see the andromeda collision. "
] |
[
"Why do propeller planes often have their wings located above the fuselage while jets have the wings located in the middle or below the fuselage?"
] |
[
false
] | null |
[
"These are called \"high wing\" and \"low wing\" designs, respectively. There are plenty of both low-wing and high-wing variations of small prop planes, but jet airliners are almost always low-wing. There are a lot of reasons why an airplane might use one or the other; I'll give a few examples.",
"Part of it simply has to do with the fact that low-wing designs are more practical for ",
" planes. For example, it's easier to do maintenance on the wings and engines when they're lower to the ground. Similarly, the rear landing gear is typically attached to the wings, and if the wings are low then the gear struts can be smaller and lighter. ",
"Also, a low-wing design is potentially safer in the event of a crash. The wings and engines can absorb some of the impact, and afterwards, passengers can use the emergency exits to exit via the wings. In a high-wing airplane, the wings could potentially collapse on top of the fuselage if they were over-stressed.",
"Finally, small prop planes are often flown under Visual Flight Rules, which means the pilot is navigating by simply looking around -- just like when you drive a car. This means it helps to have good visibility below you in all directions, especially when landing. Commercial airline flights are done \"on instruments\", which means visibility is less critical.",
"There are probably plenty of other reasons involving the structural engineering and aerodynamic aspects of aircraft design, which I'm not nearly qualified enough to talk about. But here are some answers to similar questions I've found:",
"https://aviation.stackexchange.com/questions/701/what-are-the-pros-and-cons-of-high-wing-compared-to-low-wing-design",
"https://aviation.stackexchange.com/questions/6319/why-do-almost-all-military-transports-have-high-wings-and-civilian-transports",
"https://www.quora.com/Why-do-some-airplanes-have-low-wings-and-others-have-high-wings",
"https://groups.google.com/forum/#!topic/sci.aeronautics.airliners/QBkLXKD8x08"
] |
[
"Also, high wing designs are often popular in smaller propeller aircraft, thus resulting in the two following points.",
"2.Small a/c often fly off-field ( that means they land on random roads and clearings) and a high wing helps avoid collisons with road signs, fences, rocks, bushes, small annoying children, most things really."
] |
[
"This is a super thorough answer, but I just wanted to contribute that there are quite a few exceptions to OPs stipulation.",
"The B52: ",
"https://upload.wikimedia.org/wikipedia/commons/d/d0/Usaf.Boeing_B-52.jpg",
"The B17:\n",
"http://www.warbirdsnews.com/wp-content/uploads/X-Boeing-B-17-Aluminum-Overcast.jpg",
"The Beechcraft King Air:\n",
"http://www.coloradoprivatecharter.com/assets/Uploads/fleetIMG-KingAir250.jpg",
"The Anatov AN-48: ",
"http://imgproc.airliners.net/photos/airliners/1/8/9/1404981.jpg?v=v40"
] |
[
"Did the Fukushima meltdown in Japan cause any far-reaching damage? Was the ocean poisoned, has it affected any other countries?"
] |
[
false
] |
My friend claims that the meltdown essentially poisoned the whole ocean, and that fish everywhere are diseased... Also, we in America have reason to fear the effects of the meltdown. Currently, I don't believe we have any reason to fear -- in regards to nuclear exposure or whathaveyou. Please inform me.
|
[
"I would start with the World Health Organization Preliminary Dose Assessment on the Fukushima Accident and the events that transpired as a result of the 3/11 earthquake",
". In terms of worldwide, they clearly state that committed doses are very low outside of Japan. For thyroid, the worst dose is to infants near the plant receiving as much as 20 Rem (200mSv), but to the rest of the world they state dose rates of less than 10mRem (0.01mSv). These are ",
"Committed Dose Rates",
", so they represent total exposure received over the time the radioisotope was present in the body. This is preliminary data, but outside of Japan the dose rates are not going to be enough to be of an issue. There are also reports and individuals who believe that the massive scale of the evacuation costed more lives than radiation would have if they just let people inside certain boundaries stay at their homes.",
"Also, to add some anecdotal evidence, I was working at Columbia Generating Station at the time, and I believe we were the first plant to detect any radioactive material from Fukushima in the US. We detected iodine, and I cannot recall the amount, but it was not enough to set off any of our on-site contamination monitoring systems. We detected it when doing radiation surveys of HVAC filters (where dust and particulate can gather and concentrate), and noticed slightly elevated iodine levels, but the iodine ratios (The ratio of I-131 to I-133) were not indicative of a release from our unit, and was indicative of a release from a unit which shut down about 5-7 days prior. We saw elevated rates for a short period of time then they came down. That was the most we witnessed from Fukushima. As I said, it wasn't enough to set off on-site contamination detectors (and radon on people's clothes from home or from work leeching in is enough to do that), and it was causing no false indications on any of our monitoring equipment, and no elevated dose rates on our personal dosimeters.",
"The US doesn't have any real, physical, health based reason to fear what happened at Fukushima. There ARE studies of fish and bio-accumulation of Cs-137 in the aquatic wildlife off the coast of Fukushima (and I'm having trouble finding one right now), but it is not consistent. The last study I read found a few sets of outlier fish with several orders of magnitude greater activity. I'm not sure as to the magnitude of effects on the local environment. As for the whole ocean, there are models of dispersion paths in the water, and over long enough time the amount of radiation is negligible compared to what is already in the water, and it would dilute itself, but that's speculation on my part and I think dispersion models should be best left to environmental experts."
] |
[
"Doses from nuclear accidents often depend heavily on the various factors. The type of reactor, nuclear material in question, wind direction, wind strength, wind stability, etc... \nIn general, doses from nuclear accidents tend matter most to those very near the reactor and downwind due to airborne gamma doses. ",
"To calculate doses to aquatic biota, it would require a bit more of a detailed calculation than what we typically have models for. Additionally, the effects of water distribution and shielding will also need to be taken into account. ",
"For people in America, there are some excellent measurements of just how much radiation made it to the pacific shore. All of the dose calculations that I've seen have been orders of magnitude below what we usually get every day from natural sources like cosmic radiation or ever-present sources in the ground. ",
"Note: I'd like to give you a much more detailed answer (calculations and estimates included) but I've found myself struggling (12AM EST). Others feel free to answer, but I should be back tomorrow if no-one else pitches in."
] |
[
"Thanks for the reply."
] |
[
"If I set my water temperature to 50 deg celsius and have a shower why does the bathroom fill with steam, as this is half of the boiling point?"
] |
[
false
] | null |
[
"Boiling and evaporation are different processes. Evaporation can happen at any time from the ",
" of the liquid, while boiling is a bulk process where all the liquid may turn to gas. This is why you get the bubbeling when boiling, as gas bubbles are formed below the surface and rise. ",
"Evaporation increases with higher temperatures because the energy in the liquid is randomly distributed between the water molequles, giving some of them high enough energy to evaporate from the surface. The reason there is so much steam when you shower is that the evaporation only happens from the surface of the liquid. Small droplets have a large surface area compared to the volume, so naturally this allows for a lot of evaporation. "
] |
[
"Technically what you are seeing is not steam, but still liquid water. Actual steam (as in, water gas) is invisible. Google is being unhelpful in finding the standard image reference, but if you get a kettle really boiling you will see an inch or so gap between the spout and the clouds. That gap is steam, the rest is still water. "
] |
[
"That's for example the same reason why your washed clothes actually dry as well. And I might add that if u for example freeze your wet clothes and put them out in the Winter, they will be dry at some point in time although it might take a while. As far as i remember the correct term was sublimation."
] |
[
"What compels a liquid to be relatively incompressible?"
] |
[
false
] |
When I learned about phases, I learned the good ol' rule of thumb that solids are of constant shape and volume, liquids are variable shape and constant volume, and gases are of variable shape and volume. While what I've since learned of the molecular lattice that comprises a solid seems to account at a high level for a solid's constant shape, I find myself stumped when it comes to reasoning why a liquid has a constant volume. Surely it can't be gravity alone since we've seen plenty of videos of astronauts drinking water. Is it air pressure? If so, wouldn't that predict that all liquids become gases at zero pressure?
|
[
"The interaction between molecules can be thought of as a short range attraction (1/r",
" and a really weak repulsion (1/r",
" This is due to the fact that molecules have a dipole electrical moment (e.g. water has more negative charge towards the oxygen and more positive towards the hydrogens). In equilibrium, it's the dipole attraction that holds it together. When you try to compress a liquid, the short range repulsion prevents it from compressing."
] |
[
"They still have an induced dipole moment.",
"http://en.wikipedia.org/wiki/London_dispersion_force"
] |
[
"How does this apply to liquids which do not have a dipole electrical moment?"
] |
[
"How absorbent is our skin?"
] |
[
false
] |
I know it has to be somewhat absorbent since our fingers get all wrinkly if they stay in water too long. But what's the level of absorbency?
|
[
"Not my field, but I ",
" taken painter training. Pretty much ANYTHING that gets on you will absorb through your skin to a degree, especially organics. For example, if you get oil-based paint on yourself, you do ",
" want to use paint thinner to get it off because your skin WILL absorb it, and you WILL cause yourself nerve damage. It's much better to just wait a month for it to flake off on its own, or scour the shit out of yourself with an SOS pad.",
"It's actually pretty scary how much exposure to toxic chemicals painters get, even with respirators and enforced long-sleeves. I also know that the more absorbent areas of skin are eyes, nose, mouth and groinal regions. Basically, anything with a pseudo-mucus-y membrane is extra absorbent. As a result of all this exposure, painters are number one in just about every ailment you can imagine when it comes to typical tradesmen, especially nerve and digestive stuff. Absorbed VOC interactions with ciggs and booze also make nicotine and alcohol addictions extra-special common amongst painters.",
"Also, as someone who used to browse erowid for fun: Some people ",
" take advantage of the skin absorbency thing for drug use. Of course, you probably knew that, what with nicotine patches and birth control patches and all. Also, a fun fact I learned when studying MK-Ultra: The guy that discovered LSD discovered it on accident when he touched some and absorbed enough through his fingers to lose the entire rest of his day to hallucinations."
] |
[
"Your dead skin layer (Stratum Corneum) is basically a keratin layer that is great for keeping out small particles (microbes, dust, dirt, etc). When it comes to things like water, it's fairly resistant (when you get into a pool your body doesn't absorb water until your cells start popping) up to a point where (I believe mass action, someone correct me if I'm wrong) it starts pushing through that layer's cracks and into your epidermal/dermal layers. At some point your cells would start to pop if you never got out (probably many hours, closer to a day). I'm sure there's a gruesome picture of this on the internet.",
"As far as things like \"organic solvents\" or, anything that has a relatively non-polar structure (e.g. CCl4) will absorb into your cells much more quickly because your cell membranes are sort of like little semi-charged fat (lipid) oceans when you get down to a molecular level. So they are effectively water proof (unless they have ports/holes for water to move in and out of) but more susceptible to \"fat like\" molecules. Steroids would be a good example of fat like molecules that you can use topically.",
"I'm not positive about this, but I'd go out on a limb and say that keratin is a relatively non-polar molecule and so water beads up well (like a waxed car) at least to a point while fat like molecules (like a slice of bologna on a car) eats right through to the inside."
] |
[
"DMSO ",
"http://en.wikipedia.org/wiki/Dimethyl_sulfoxide",
" can act as a transdermal shuttle."
] |
[
"Ask Anything Wednesday - Physics, Astronomy, Earth and Planetary Science"
] |
[
false
] |
Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...". Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists. Please only answer a posted question if you are an expert in the field. . In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for . If you would like to become a member of the AskScience panel, . Past AskAnythingWednesday posts . Ask away!
|
[
"Yes. NASA has planned both a ",
"flyby",
" and ",
"lander",
" mission for Europa. Since it takes years both to design a mission and then fly to Jupiter, it will be quite a while before we see the results of either mission (assuming funding continues). ",
"Currently, various companies are working on a design for a submersible robot to explore Europa's under-ice ocean.",
"Edit: fixed grammar"
] |
[
"He sees the object appear green. The reason for that is that while the wavelength of the light gets shortened, the frequency remains the same. The reason that wavelength changes is because the speed of light in water is lower than in air. Frequency doesn't change is due to the simple fact that when waves cross medium boundaries, their frequency is unaltered. This is true for waves on a string and is true for light. "
] |
[
"Are we planning any missions to explore Europa or Enceladus, the two ice moons with potential subsurface oceans?",
"Edit: Post Cassini missions to be more specific"
] |
[
"If a star’s color is determined by it’s temperature (the bluer the hotter) then why aren’t any stars for an example green or purple? (Only red, orange, yellow and blue)"
] |
[
false
] | null |
[
"Light from a star is combination of light of many wavelengths. A hotter star produces more low-wavelength high-energy photons, which are more on the blue/violet/ultraviolet end of the spectrum. However, it also produces lots of infrared/red/orange/yellow/green photons. The colour you see is a mix of all these wavelengths.",
"The Sun actually has its peak emission in green light (although there's some semantic issues in defining peak emission, but that's not critical here). But it produces enough red, orange, and yellow that these all combine to look sort of yellow-white.",
"A really hot star might have a peak in the violet, but it produces so much over the rest of the ROYGBIV spectrum that it ends up looking white or bluish instead, depending on how hot it is.",
"Here",
" is a nice pic from wikipedia showing the Sun's emission. You can see the Sun emits light all across the whole visible range."
] |
[
"Here",
" is a nice pic from Wikipedia showing the colour of an idealised black-body as a function of temperature. While the sun is not an idealised black-body it is very close. This image shows that no star could ever appear green as a function of temperature."
] |
[
"Yes. The ratio of intensities across the visible range approaches a constant as the temperature goes to infinity. Things keep getting brighter, but the color impression (if you are sufficiently far away to not damage your eyes...) doesn't change any more."
] |
[
"Are drugs addictive in nature or does the addiction depend on the individual consuming it?"
] |
[
false
] | null |
[
"Well both really. Addiction can be based on a feeling that someone or animal gets from consuming drugs so it's psych0logical that they want and strive for that feeling so they keep taking drugs. But also it can be physical as you in keep taking pain killers and your body gets used to having the dose and you eventually need more or your body can't function without it, you go through withdraw."
] |
[
"Read this and ask a more specific question, that is simply too broad ",
"http://en.wikipedia.org/wiki/Substance_dependence",
" . "
] |
[
"To elaborate on this, the body and brain will attempt to maintain homeostasis. So when the drug stimulates a particular receptor or process, the receptor will often be downregulated, less of the neurotransmitter involved will be produced or countervailing processes will be enhanced to compensate. As an example, alcohol acts as a depressant, which means that excitatory processes in the brain are enhanced to maintain balance. Thus more alcohol is needed to overcome the new balance. Additionally, in cases of chronic administration, a certain level of alcohol is necessary to maintain the balance. Hence, when alcoholics go through withdrawal, they often suffer seizures due to the now out of balance excitatory and inhibitory processes."
] |
[
"What are some of the harmful off-target effects of CRISPR gene editing?"
] |
[
false
] | null |
[
"That just means that it can cut DNA that it isn't instructed to cut by the guide RNA. Off-target is literally saying it has its effect (cutting DNA) on the wrong 'target'."
] |
[
"Normal CRISPR-Cas9 has guide RNA ",
"that gets specificity",
" from the PAM, the base seed sequence (about 11 nucleotides out of the 20), and the upstream sequence (remaining 9). However, 1-2 nucleotide mismatches in the upstream sequence are tolerated by the system, and can result in cleavage. ",
"So when designing a CRISPR-Cas9 guide RNA, you need to design one that 1. Targets a sequence in the gene you want to break, 2. Is unique in the genome, and 3. Doesn't have other sequences in the genome that are only 1-2 nucleotides different from it. ",
"There are alternatives, such as nickase Cas9 mutants, which basically use two 'complementary' guide RNAs to nick both sides of a DNA strand -- these have pretty much 0 off target effects. "
] |
[
"What could be some factors that interfere with the precision though? Normally I would think about CRISPR as having a surgically-precise \"targeting system\" for DNA sequences."
] |
[
"Does your blood type affect your health in any way (except in the case of transfusions and transplants)"
] |
[
false
] |
For instance, gives you a resistance to certain diseases? Certain drugs are more or less effective? Anything else? (I know those with sickle cell anemia are more resistant to malaria, but it's not a blood type and it's a disease in itself)
|
[
"Superb answer, very informative, should be used as a model answer.",
"Another interesting area is haemotology and the different risks for venous clots according to blood type ",
"http://www.ncbi.nlm.nih.gov/pubmed/21103665"
] |
[
"Superb answer, very informative, should be used as a model answer.",
"Another interesting area is haemotology and the different risks for venous clots according to blood type ",
"http://www.ncbi.nlm.nih.gov/pubmed/21103665"
] |
[
"There may be some relationship between A-antigens and influenza, B-antigens and gram-negative bacteria. ",
"Wiki: ABO blood group system"
] |
[
"What makes some people faint at the sight of blood? For that matter, what makes people faint because of things they see?"
] |
[
false
] | null |
[
"Here is one cause of fainting.",
"http://en.m.wikipedia.org/wiki/Vasovagal_response",
"Specifically \"simultaneous enhancement of parasympathetic nervous system (vagal) tone and withdrawal of sympathetic nervous system tone\" which leads to a precipitous drop in blood pressure which causes a standing person to lose consciousness. Why exactly the sight of something sets off such a reaction I don't think is fully understood. "
] |
[
"To further add to this description, a basic grounding in physiology might help.",
"The general concept is that your sympathetic system is responsible for maintaining your body when you are active, whereas the parasympathetic system relates to your body at rest.",
"What does this mean exactly? When you are active, say running around, your body wants more blood to your muscles/lungs/brain due to the increased demand placed upon them. As such, the sympathetic system kicks in and causes vasoconstriction (shrinking of your blood vessels) to increase blood pressure.",
"Let's talk vice versa. You just ate a giant steak and are sitting on the couch. Your body's parasympathetic system engages. This results is vasodilation throughout your extremities (increased blood vessel size --> lower pressure) and redirects blood to your digestive system, thus conserving energy and focusing on digestion. It also slows your heart rate which yet again causes a lowering of blood pressure.",
"There is obviously more to each system than this description, but should provide an accurate summary insofar as each's effect on blood pressure is concerned."
] |
[
"The evolutionary (ultimate) explanation is that a decrease in blood pressure at the sight of one's own blood decreased the likelihood of bleeding out. Those of our ancestors who had this adaptation (of a decrease in blood pressure at the sight of their own blood) had more offspring than those who did not."
] |
[
"Which circumstances must be present to have a tidal locked planet/moon?"
] |
[
false
] |
I just watched the newest video of were they say, that planets which circle red dwarfs in an inhabitable distance would be too close to the star and therefore tidal locked, just like the moon is tidal locked to our earth. ( ) So, which circumstances must be present, that such a tidal lock develops? Why are for instance moons like (surrounds Jupiter) or (surrounds Saturn) not tidal locked?
|
[
"When the bodies orbit close together, tidal forces are stronger and locking is easier. Small, irregular moons far away from their planets don't get locked as these forces are much weaker (and probably disturbed by other moons). See Wikipedia for a longer explanation with examples ",
"https://en.wikipedia.org/wiki/Tidal_locking"
] |
[
"So first: your picture of Himalia is actually a picture of Iapetus, a moon of Saturn (and is tidally locked).",
"Second, in the case of both Himalia and Phoebe, they both orbit quite a bit farther from the planet than the larger moons. Unlike gravity, the tidal force scales as the inverse of the distance ",
", so it's a lot weaker as you move outwards even a little. This prevents locking of distant moons.",
"For some exact numbers, Himalia orbits an average of 11 million km from Jupiter, quite a bit farther than the big four of Io, Europa, Ganymede, Callisto (0.42, 0.67, 1.07, and 1.88 million km, respectively). ",
"Similarly, Phoebe orbits 13 million km from Saturn - compare that to Titan, which orbits Saturn just 1.22 million km. If we round that off to a factor of 10, that mean the tidal forces that Phoebe feels are 10",
" = 1000 times weaker than what Titan feels. There's also the added weirdness that Phoebe orbits retrograde, in the opposite direction of the big moons and Saturn's rotation."
] |
[
"While it is true that a planet in the habitable zone around a red dwarf star would end up tidally locked to the star, that planet could be a gas giant and have its own moons. One of those moons, if it is large and has its own atmosphere, could be habitable as its proximity to the planet would at worst have it tidally locked to the planet, and not the star."
] |
[
"Can erbium be used to stop a nuclear reaction?"
] |
[
false
] |
I saw on periodicvideos that erbium is a nuclear poison. It was described as killing any nuclear fission dead. If that is true, at what scale can it do this. Is it possible to produce a sort of safety kill switch for nuclear reactors? Or is the amount of erbium required just too massive? Or is there a reaction that makes this unfeasible? I had never heard of a nuclear poison before.
|
[
"The particular situations you're referring to (fission reactors or weapons) rely on chain reactions involving neutron-induced fission. Neutron-induced fission reactions often release more neutrons, which can further cause more fission, and so on.",
"If you are able to remove neutrons from the system, for example by absorption, you can \"poison\" the chain reaction and stop it from continuing.",
"Certain materials have very high probabilities to capture neutrons, and once those neutrons have been captured, they no longer contribute to the fission chain reaction."
] |
[
"Short answer, poisons do work and are used to control and stop nuclear reactors. Erbium can be used. Other poisons are more common."
] |
[
"Boric acid, more specifically. Borax generally refers to sodium tetraborate."
] |
[
"Question about working in the space program"
] |
[
false
] |
[deleted]
|
[
"I have a physics degree (BS) and work in the space program, so I can probably give you an idea of what to expect. The most important discriminator here is whether you want to actually work in physics research or intend to use the degree as means to access a career in the space field. The former is quite limited, with the latter approach giving you the greatest possibility of getting your foot in the door.",
"I started working for a contractor doing work on the ISS robots soon after I graduated. My work has primarily been in developing and using simulators, engineering and operations analysis, flight software test and verification, etc. None of this is directly dependent on having a degree in physics, but neither was I particularly hampered by not having an engineering degree. The physics degree has come in handy for some particular projects, but overall the job is less dependent on the specifics of your degree than it is on your ability to do proper analysis. If you know your basic statistics and data analysis techniques you'll be fine.",
"Now, there is a major aspect of the space program that you will need exposure to that is not part of physics curricula, and that is systems engineering. ",
" that happens here takes place in the context of systems engineering, and if you wish to advance to any position of authority you'd be well advised to make sure you take electives out of the engineering department that will give you an idea of what it's all about. I really wish I had.",
"As for other people with physics degrees that I work with, one has become a bit of an expert in math modeling and has done a lot of work on Guidance, Navigation, and Control simulations as well as robotics simulation. Another chose to go into management. He was at one time (many years ago) my supervisor, and last I heard from him he was director of a software development contractor. Others are working as test engineers in an orbiter avionics integration test facility. ",
"So, I hope you get the idea that there isn't a single type of job that having a physics degree qualifies you for. It instead gives you the opportunity to explore a wide variety of different jobs that all have the potential to give you that \"I helped make that happen\" feeling. For me, I get that feeling every time I see video of the ISS, because my work helped put it together. If there's anything I can help you with just ask."
] |
[
"You can get involved with various space telescope programs with a physics background. Engineering might be better for your aspirations, particularly aerospace engineering. That's not to say that you can't do it with physics, of course. Does your school have an engineering physics program?"
] |
[
"I know this is a vague answer, but NASA is huge and has people working in many, many different fields. As you study physics, you will probably be attracted to one specific area or another, and whatever it is, NASA will probably have some research in that area.",
"I would strongly encourage you to apply for an internship at NASA to see what working there is like (I had an internship there, it was awesome). Here are a few links to look at:\n",
"http://www.nasa.gov/centers/glenn/education/LERCIP_GRC.html",
"\n",
"http://intern.nasa.gov/",
"When I interned at NASA (Glenn Research Center), I was in a small branch where most of the work was done by materials scientists, but there were a few physicists there. One was working on modeling Lunar dust and Mars dust and determining how to prevent it from impacting future missions. Another physicist studied the effects of solar radiation and atomic oxygen exposure on various satellites, including Hubble."
] |
[
"What theories present in Walking with Dinosaurs have been debunked by now?"
] |
[
false
] | null |
[
"Hi tjoolder thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
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" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
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[
"Paleontology"
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"For more information regarding this and similar issues, please see our ",
"guidelines.",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"How much force is behind a gasoline explosion at five feet, and what would it do to a human?"
] |
[
false
] | null |
[
"Cars don't explode like they do in the movies. It's actually pretty hard to have a gasoline explosion with a car because gasoline has to be in it's vapor form to burn, mixed with air in the right proportions (there's a range: upper and lower flammability limits). Really, the only way to get close to a Hollywood style explosion is by crushing the gasoline tank rapidly so that the gasoline sprays out quickly, vaporizes, and mixes with air and ignites."
] |
[
"The first link below details blast effects, building damage, injuries, levels of protection, stand-off distance, and predicting blast effects.",
"http://www.fema.gov/pdf/plan/prevent/rms/426/fema426_ch4.pdf",
"The second is a masters thesis about blast profiles and two primary methods of determining them, reviewed for use in the creation of a computer program for calculating blast pressures which serves as a\ndesign tool to aid engineers or analysts in the study of structures subjected to explosive air blast.",
"http://scholar.lib.vt.edu/theses/available/etd-043099-163540/unrestricted/AJMKCTHESIS.PDF"
] |
[
"There's a mythbusters where they do this exact set up with different chemical reactions at different distances and also underwater. From what I remember being underwater past 10 or so feet with a gasoline explosion you'd be fine, so the movies are actually true to a point. I don't remember the exact science but I hope that helps. It's entertaining at least."
] |
[
"Why does rocking make people sleep faster/better?"
] |
[
false
] |
I always have the best naps when I'm on a rocking chair or on a boat, is there some sort of chemical released in the body when moving back and forth in a wave-like motion?
|
[
"Hey guys, please only post if you have relevant experience and can answer follow up questions!"
] |
[
"As far as I know there is no neurotransmitter directly released by rocking your body, nor by any simple physical movement of the body.",
"It is thought that rocking back and forth mimics what our parents may have done (rocking us as infants) and thus is a learned association. Learned associations are very common in our every day lives, and the classic example is Pavlov's dogs. If you are not familiar with this, please see (",
"http://psychology.about.com/od/classicalconditioning/a/pavlovs-dogs.htm",
"). So what I am saying is that as an infant your parents rocked you back and forth and you learned to associate this motion with feeling good and then eventually with falling back asleep. So now as an adult you can use this learned association and rock yourself back and forth and thus tell your body to relax and sleep.",
"Specifically which neurochemicals are involved? I am not 100% sure and I wouldn't want to steer you in the wrong direction. I can tell you that melatonin is strongly associated with signaling your brain to sleep, and is tied to your body's circadian rhythm (the internal body clock that is regulated by light). Likely there is also a change in the transmission of norepinephrine (regulating arousal), dopamine and serotonin (to alter your mood and make you more relaxed, happy and stress-free).",
"There are also probably other contributing factors to your sleepiness at those times. Rocking back and forth on a rocking chair, or on a boat, generally happens during a relaxing time (on vacation or something), or in the sun (which can warm our bodies and makes us sleepy). There is also something about repetitive signals, be they sounds, visual cues, or bodily movements, that can lead to an almost hypnotic reaction. I do not know about hypnosis and would recommend looking at this review article (if you have access at a library or university or something): ",
"http://www.nature.com/nrn/journal/v14/n8/full/nrn3538.html"
] |
[
"I've actually read about this while I was studying hypnosis.",
"What I know about this is merely the physical process, so I don't know if any sort of chemical is released to the body",
"While you rock a person it creates a loss of equilibrium, this loss of equilibrium makes the person relaxed and makes it easier to fall asleep. It is even said that it sort of creates a trance like state. (If you are interested, there also even some inductions related to hypnosis that involve this loss of equilibrium. Not rocking, but only falling backwards for instance.) Oh! And besides this it is also a rhythmical movement, which it can also stimulate relaxation. ",
"But I think that what it is also said here about the classical conditioning is related. You link the rocking with relaxing situations and it also makes it easier.",
"So I think we can conclude that loss of equilibrium, rhythmical motions and classical conditioning help the process of falling asleep. "
] |
[
"[AskScience AMA Series]: I AMA late-stage Ph.D. student in management, with research interests spanning intelligence and personality testing in selection, interviewing, newcomer socialization and early turnover, and job attitudes. AMA"
] |
[
false
] |
My opinions may be somewhat personally biased (like my beliefs about nature/nurture in intelligence), but I am familiar with the literature and will try to present both viewpoints where appropriate. Consider my field the intersection of psychology and business, describing/explaining/predicting/controlling cognitions attitudes and behaviors at work. I have taught classes in human resource management and organizational behavior, but am equally well-versed in more macro topics of business strategy and organization theory (i.e. "Why do organizations exist in the first place?") Please don't ask me personal questions along the lines of: "Can you tell me how to nail this job interview?", or "Why is my boss such a moron?" Alrighty then
|
[
"What do you think about personality questionaires, Meyer-Briggs for instance?",
"Any opinion on the Peter principle or Parkinson's laws?"
] |
[
"I am for them as a selection measure, but not the Meyers-Briggs. As noted in another comment it:",
"a) forces people into dichotomous personality \"types\", rather than allowing for within-trait variation on a continuum, which treats meaningful variance as error. This is problematic, because a 49% score on extraversion-introversion is treated as the same as a 3% score. ",
"b) the MBTI isn't very predictive for major work outcomes, so it has pretty low utility anyway. ",
"c) the MBTI doesn't in my opinion fully capture the whole aspect of \"what people are\". If that question, as well as \"how do people differ\", is the goal of personality psychologists, it kind of fails on both accounts. This is to say that of all the variation in adjectives we can describe people, a factor analysis of these adjectives (something like 17,000 is what Gordon Allport started with back in the 1930's), you don't get the Meyers-Briggs traits, but rather the Big Five personality traits of Extraversion, Agreeableness, Conscientiousness, Openness to Experience, and Emotional Stability/Neuroticism. These traits account for much more variance in the many adjectives, have higher predictive utility, and don't suffer from the dichotomization issue. Some say there is a sixth factor trait, honesty-humility, but most people just use the five.",
"Most other personality inventories may be cool for fun, but I wouldn't recommend their use in a selection situation. An interesting new trend is using structured interviews to measure personality, as opposed to a paper-and-pencil questionnaire. Since in an interview, there aren't any stems on which to answer, some say that an interview makes people think more on the spot, and therefore they can't fake, and therefore their \"true self\" shines through a bit more. ",
"No major opinion on the Peter Principle, except to say that the intelligence-performance relationship is moderated by job complexity, with lower validities at higher levels of complexity (Hunter & Hunter, 1984), which does support that idea. ",
"As for Parkinson's laws, I hadn't heard of it until just now, but the wiki for that page makes me simply think that if the purpose of a business is to make a profit (not always to maximize profits, but an optimal one given their resource and capability constraints), then this law makes obvious sense. "
] |
[
"I'm pretty interested in I/O psychology but as an undergraduate im still conflicted as to what I'd like to study in grad school. Any readings you can recommend to me to get an in-depth description of your field?"
] |
[
"Need help identifying this fungi/mold/spore thing."
] |
[
false
] |
[deleted]
|
[
"My notpron skills tell me it is ",
"Rhizopus oligosporus",
". Aww, they're ",
"adorable",
". "
] |
[
"Good try, but that image is labeled incorrectly. That's not what ",
" actually looks like, ",
"this is",
"."
] |
[
"It looks to be some kind of a bread mold thing. I'll have a look through my copy of Mushrooms Demystified, but its going to ask me for microscopic evidence.",
"It looks kind of like maybe ",
", as I'm guessing it should be something familiar or important. I'm too tired to track down an exactly matching pic right now. Good luck, report back."
] |
[
"Why does the water froth and bubble when I'm cooking pasta and leave the top on the pot?"
] |
[
false
] |
[deleted]
|
[
"When you're cooking pasta, some of the starch and protein in the flour comes out into the cooking water.",
"The surface tension of the water is increased by the addition of starch and protein from the pasta, so the bubbles formed by violent boiling don't burst as quickly, and the froth forms. As the froth forms, it develops an insulating layer that begins to trap heat in the water, making the boiling even more violent, which makes the froth more substantial, and this ends with a boil-over.",
"The effect is amplified but not created by the lid, because the lid helps trap heat in the air above the boiling water, causing the violent boiling to begin earlier. You can still get boil-over in an open pot, but the heat from the burner needs to be higher."
] |
[
"The pressure increase from an unsecured lid is trivial; it's why the lid bumps and rattles at a boil."
] |
[
"Is the froth (which is made from protein if i understand you correctly) stabilized by the higher air temperature with the lid on? (like when baking a baiser) "
] |
[
"How do bacteria and other microscopic organisms become anti-biotic resistant and what happens if one becomes completely resistant?"
] |
[
false
] |
Bacteria and other microscopic organisms become resistant to different types of antibiotics. Is it possible that there will be no more treatments and bacteria will become completely immune? If so, are there anyways to reverse what has happened and the bacteria again becomes susceptible to antibiotics?
|
[
"Most antibiotics act by binding and inhibiting the activity of a specific bacterial enzyme. This requires the antibiotic to diffuse through the surface of the cell and reach its target enzyme. Bacteria can resist the effects of antibiotics through a number of mechanisms. Some common mechanisms are:",
"1) The enzyme itself can mutate so that the antibiotic can no longer bind. ",
"2) The bacteria may produce a molecule capable of binding the antibiotic and neutralizing it before it can reach its target.",
"3) Cell membrane transporters on the bacteria may pump the antibiotic out of the cells before it can reach its target enzyme.",
"Bacteria can acquire these resistance mechanisms two ways:",
"1) ",
" mutation- Through the process of DNA replication and repair mistakes are made that conferred resistance. This is most common for the first mechanism I mentioned, and is a relatively slow process. ",
"2) Plasmid borne resistance- The bacteria took up a plasmid (a piece of circular DNA) from another bacteria that carried genes for resistance to one or more types of antibiotic. Plasmid borne resistance is particularly worrying as it allows resistance to may different types of antibiotics to spread rapidly between unrelated groups of bacterial pathogens. ",
"There are hundreds of enzymes in even the smallest bacterial genome, each of which can be inhibited in several unique ways. In this sense, \"complete resistance\" to antibiotics is practically impossible. Much more likely, however, is for a bacteria to acquire enough plasmids and ",
" mutations to become resistant to the relatively small pool of antibiotics we've developed so far. ",
"With regards to the reversibility of the process, antibiotic resistance is not wholly without cost to the bacteria. Plasmids cost energy to maintain, and mutated versions of enzymes are usually less efficient than their wild-type equivalents. When the selective pressure of antibiotics is lessened, it's common to see bacteria drop plasmids and undergo reversion mutations. In other words, we can stop antibiotic resistance by using them less. ",
"I simplified quite a bit, but hopefully that helps!"
] |
[
"recombination ",
"Prokaryotes do not have recombination. ",
"due to recombination [...] mutations occur",
"Mutations and recombination have nothing to do with each other. Recombination shuffles alleles, decoupling them, and allowing selection to happen on individual genes, rather than whole chromosomes. ",
"Can this be prevented? Not really.",
"Phage therapy and biotherapy work via the red queen effect."
] |
[
"\"is it possible that there will be no more treatments?\"",
"Even if bacteria become completely resistant to all known antibiotics, we can still probably treat them with a bacteriophage - a virus that kills bacteria. It was used in the past as a therapy, particularly in the Soviet Union I believe, and presents something of a more attractive option since the virus can evolve as fast or faster than the bacteria can to evade it. ",
"The differences between eukaryotes (like us) and prokaryotes (like bacteria) also means it's essentially impossible for a bacteriophage to then evolve to attack humans instead.",
"Why don't we use them now? Regulations usually. Since each bacteriophage attacks only 1 species of bacteria, the best way to treat a non-specific infection would be to simply use a \"phage cocktail\" of many different bacteriophage - the problem is that each individual virus species must undergo separate approval testing, and that is incredibly expensive. ",
"I expect that initially a phage specific to MRSA will be developed as a therapy though."
] |
[
"What is caffeine used for in the organisms that produce it?"
] |
[
false
] | null |
[
"The coffee tree uses it as a poison. Caffeine in high doses is lethal which is why the coffee tree produces it. We are able to consume coffee due to our enormous size. The tree uses is as a deference mechanism against insects which are incredibly tiny, making the caffeine an effective bug repellent. "
] |
[
"Caffeine in plants acts as a natural pesticide, it can paralyze and kill predator insects feeding on the plant. High caffeine levels are found in coffee seedlings when they are developing foliage and lack mechanical protection In addition, high caffeine levels are found in the surrounding soil of coffee seedlings, which inhibits seed germination of nearby coffee seedlings, thus giving seedlings with the highest caffeine levels fewer competitors for existing resources for survival. ",
"Caffeine has also been found to enhance the reward memory of honeybees, improving the reproductive success of the plant"
] |
[
"Worldwide popular psychoactive drug caffeine is a plant alkaloid, and also a vasoconstrictor in humans. Caffeine (1,3,7-trimethylxanthine), among other methylxanthines, is a known pesticide, and this is thought to be its natural function in plants In humans, the stimulant effect is caused by caffeine’s ability to antagonize adenosine receptors, meaning it binds these receptors in a way to stop them from functioning. Theophylline, identical to caffeine except with one less methyl group is much better at antagonizing these receptors, but it isn’t as effective as a pesticide as caffeine, meaning that the adenosine receptor antagonism exhibited by caffeine probably isn’t responsible for its pesticide activity because more species of plants accumulate caffeine over other related alkaloids. It’s thought that caffeine’s pesticidal behavior is due to its ability to inhibit phosphodiesterases, enzymes that break phosphodiester bonds. Specifically the toxic effects are from it keeping cyclic adenosine monophosphate (cAMP) from being converted into adenosine monophosphate, a nucleotide in DNA and RNA. ",
"Coffea isn’t the only genus to accumulate caffeine and other related xanthine alkaloids. Several other genera are known to contain caffeine including Camelia (tea), Ilex (maté), Paullinia (guarana), Cola (cola nut), Cacao (chocolate), and Citrus (oranges, lemons).",
"Although the enzymes in these plants necessary to produce caffeine may be slightly different, the pathway is largely the same, xanthosine is converted to caffeine. Largely studied with the usage carbon-14 labeling and RNAi enzyme knockouts, xanthosine is methylated to 7-methylxanthosine. The ribose is then hydrolyzed off. Then N-methyltransferases will add methyl groups to the different nitrogens to produce different alkaloids. If nitrogens 1,3, and 7 have a methyl group attached, it is caffeine. The enzyme that catalyzes the first reaction in the biosynthetic pathway of caffeine is very specific, it only catalyzes the methylation of xanthosine. The same goes for the second methylation catalyzed by the enzyme 7-N-methyltransferase. However, the next methylation is caused by an enzyme that is not as specific as the other two enzymes. It can methylate both the 3 and the 7 nitrogen. Also, this can happen before 7-methylxanthine is converted to theobromine, which can lead to other related products being formed like paraxanthine and methyluric acids. The enzyme that converts theobromine to caffeine, 3,7-dimethylxanthine N-methyltransferase (caffeine synthase), has a higher substrate specificity to paraxanthine than theobromine. However, plants like coffee and citrus don’t produce much paraxanthine at all, caffeine synthase is used in plants primarily to produce caffeine from theobromine.",
"I have read studies for all the information I've said that I'm not citing here, dm me if you want to know about them. I am currently applying for research money to study caffeine synthase, I want to know why it isn't as selective as the other enzymes involved in synthesizing caffeine."
] |
[
"What is the most primitive organism that can get addicted to drugs?"
] |
[
false
] |
[deleted]
|
[
"I love this question because it allows me to post the following paper:",
"Time flies like an arrow. Fruit flies like crack? by J Hirsh",
"As opposed to the human population, addiction to drugs of abuse is not a great problem in insects, at least as far as we are aware. Nonetheless, the fruit fly, Drosophila melanogaster, has recently shown potential as a model organism for molecular genetic studies of response pathways to several human drugs of abuse, including cocaine, alcohol, and nicotine.1,2,3 These studies are possible since these drugs induce motor behaviors in insects that are strikingly similar to those induced in higher animals. In addition, repeated drug exposures result in plastic changes in responsiveness; tolerance to alcohol,4 and reverse tolerance, or sensitization, to repeated exposures to cocaine.1 Sensitization is of interest in that it represents an animal model for a long-lasting behavioral change that appears linked to the long-lasting drug craving in animals and humans,5 and also has potential links to mental disorders such as schizophrenia.6 Here we will focus on studies of sensitization in Drosophila, emphasizing an unexpected link between sensitization and the circadian gene family.",
"It’s a fun read",
"https://www.nature.com/articles/6500020",
"So based on this we can say with good confidence that flies can get addicted to crack-cocaine ",
"(Please also note that the title is a ‘garden ",
"path sentence’ which I find hilarious)"
] |
[
"Yes but organisms need a certain level of complexity to be addicted (not just dependent). They need to be able to perceive the lack of the thing they're not getting and want it which is a question of consciousness, and also need enough neural complexity to sensitize to the substance. If you're a squid with one neuron, well you're not going to form any synapses as a result of taking crack."
] |
[
"I'd would assume it extends downwards on the size scale as well. The smallest living organism that can be addicted to a substance is likely only limited to our delivery and measurement tolerances.",
"Addiction is essentially just leveraging natural impulses after all isn't it? It's been over thirty years since Deviance and Conformity for me and my further studies went into another direction. Honest question and no impugnment on the social sciences."
] |
[
"How do supermassive black holes reach their size?"
] |
[
false
] |
Let's make a few presumptions: Black holes are remnants of massive stars. The Eddington limit states that a star can only reach a few hundred solar masses at max. A "newborn" black hole would only have a few hundred solar masses at max. So the only way for supermassive black holes to reach their size would be to consume other bodies. However, due to time dilation, masses approaching the event horizon of any black hole would freeze in time to our perspective, thus making it impossible for any black hole to gain mass. And even if that is not a problem, most objects approaching a black hole would be slingshotted away simply because space is huge and a black hole is relatively tiny. How does it work IRL? In which part am I wrong?
|
[
"So first of all, this is an active area of astrophysics research and no one knows the full answer, but we ",
" know a lot more than you assume.",
"First of all, we see black holes merge, quite regularly in fact!, thanks to the gravitational wave detector called ",
"LIGO",
". ",
"The first such merger was detected in 2015",
", and we have seen enough of these by now that some basic statistics of the sample exist and it turns out black hole mergers are more common than originally thought! ",
"However, there are questions that still remain on if these mergers are common enough to explain how you get a supermassive black hole from these. Two main problems come to mind:",
"While we see stellar-sized black holes out in the universe, and supermassive black holes, we have a real dearth of ",
"\"intermediate\" mass black holes",
" (like, a few hundred to a few thousand solar mass ones). Presumably, if you start off with the small ones just merging like crazy, you should see a lot of these in the universe, but we just don't right now. It is worth noting that LIGO says they have found the first intermediate mass black hole, when two ~80 solar mass ones merged to combine a >100 mass black hole... but it's really unclear how common this is as yet.",
"We actually ",
" understand the final merger process between two supermassive black holes (SMBHs), called ",
"the final parsec problem",
"- basically they should stall out roughly a parsec apart rather than merge together. However, we know that they ",
" merge, so questions abound! (Note: we have never directly detected a supermassive black hole merger because LIGO is not sensitive at that frequency. However, we believe SMBH mergers are more common than the ones LIGO detects, because galaxies merge all the time.)",
"Finally, I will point out because of all this, some astronomers think it's possible that SMBHs are actually from ",
"primordial black holes",
", which would basically be mass fluctuations in the very early universe that then became the SMBHs we see today. I personally kinda like this idea because it explains the mass gap well, but this theory has a lot of work (theoretically and observationally) that still has to be done, versus we can probe the growth of black holes now with current tech and set limits/rates from that.",
"I hope this answers your question!"
] |
[
"This was super helpful for me, thanks!",
"It's super crazy to know that we just flat out don't understand how black holes can bypass the parsec problem, I hadn't heard of that!",
"Are you aware of current research around this subject?"
] |
[
"The simplest solution is to introduce a third black hole. This allows for much more complex gravitational dynamics including (rare) scenarios where two of the BHs get put onto a close orbit (from which they can then lose energy via gravitational waves) while the third gets slingshotted away.",
"Alternatively, you can try to model more complex interactions between the BHs and the material near them e.g. including the effects of radiation pressure or magnetic fields to see if that introduces additional ways that energy can be transferred away from the BHs.",
"Yet another possibility is that actually, supermassive black holes never do merge! We can't always image the centres of galaxies with enough resolution to tell whether there is a single source there or multiple - it could be that galaxies with rich merger histories end up containing multiple BHs."
] |
[
"Would gravity alone make the planets face themselves with the same side towards the sun? (Like a ball on string)"
] |
[
false
] |
My understanding is that if you rotate an object around a certain axis outside that object (orbit) then it tends to face the same direction towards that axis. Also common experience with a ball attached to a string tells me that it should behave this way since there's only one force acting on it (as gravity acts on the planet).
|
[
"This is an effect called ",
"tidal locking",
" and yes, gravity alone is responsible for this. It is a little like a ball on a string, actually.",
"As two objects attract each other, it can create a small elongation of a planet or moon towards the acting body. In exaggeration, think of the moon being pulled into an egg shape due to the earth's gravitational pull. The same effect happens to the earth too, and this is what causes tides. Due to gravity alone, this elongation can slow or speed up a planet's rotation as the body it is orbiting tries to \"pull\" this bulge back such that the \"egg\" points towards the body it is orbiting, creating a torque to keep the rotation in check . Of course, this takes a lot of time, but eventually you can end up with a case such as the moon, which always has the same face towards us. It works best in strong gravitational situations where this effect is exaggerated, such as mercury, which rotates 3 times for every 2 orbits. It is the same kind of effect and I believe given enough time, mercury would become tidally locked like the moon to the earth.",
"As for all the planets, they all have this effect to a certain extent, but very lightly and other factors such as their moons or other activity can overcome this effect.",
"As for the simulation you showed, I don't know how they made the planets act as they did. Given an object which is solid, and can not be deformed, it would maintain its rotation it was given initially. If the orbit does not change that is. I will have a think to how they made the simulation act like that.",
"Hope this helped at least a little bit."
] |
[
"The effect starts immediately, yes. It, however takes time as tidal locking is applying a torque to the planet, thats all. This torque alters the rotation speed of the planet slowly to match its orbital speed. The same way a car applies torque to its wheels, it doesn't mean that the car immediately reaches its top speed. These forces placed on the solar system take billions of years to take effect, hence no planet in our solar system, not even mercury is tidally locked perfectly. It works a little like a ball on a string, but not exactly. The string still needs to apply a rotation to the ball in order to keep it facing you, similar how this bulge applies a torque to a planet to make it face the sun. Difference is that it happens in less than a second for a ball."
] |
[
"Thank you! Sounds like you'd also agree with this sentence - \"If the bodies of the solar system were set up with just orbital speeds (no spin) they would always point (face) to their nearest attractor (neglecting the other gravitational forces)\"\nIf so then do the astronomers count the spin of the body as zero or not zero? Because in my understanding all there is, is an rotation around an outside axis and there is no spin at that moment. Although looking at it from the outside it may look (for the naive observer) like it follows some path ",
" has a spin, but all it really does is a simple a rotation around an outside axis (orbit). "
] |
[
"Does the perceived size of the moon actually increase as it moves from the horizon to overhead? Or is it just an optical illusion?"
] |
[
false
] |
I'm in a bit of a bet with my wife. She swears the moon is bigger in the sky when it's near the horizon and gets smaller as it gets higher. I've told her it's the same size, but only looks bigger because of the difference in perspective. Once it is higher up, there is more empty sky surrounding it which makes it seem smaller, but if you held a ruler at arms length during both phases, it would occupy the same diameter.
|
[
"You win the bet. The moon does ",
" larger to the eye near the horizon, but it's an illusion. Images like ",
"this one",
" allow a direct comparison of the apparent size of the moon at different points above the horizon and show that it's constant. "
] |
[
"Yeah, but there's no correlation between its apparent size and position in the sky."
] |
[
"The Moon illusion is an optical illusion which causes the Moon to appear larger near thehorizon than it does higher up in the sky. This optical illusion also occurs with the Sun andstar constellations.",
"https://en.m.wikipedia.org/wiki/Moon_illusion"
] |
[
"What is the responsible thing to do with the Hubble Telescope when it is decommissioned?"
] |
[
false
] |
Should we disassemble it and bring the pieces back down to earth to avoid wasteful debris in space?
|
[
"That's really not an option. There are essentially two choices:",
"1: De-orbit the telescope so it falls into the atmosphere and burns up in a controlled way. The mirror is large enough that it will survive and reach the surface of the Earth, so you don't want it coming down somewhere you can't control. ",
"2: Boost the telescope's orbit so that it won't fall into the atmosphere. Hubble would not contribute meaningfully to the amount of debris in space, and it's large enough to always know where it is and avoid it. This also opens the possibility that one day in the future, it could be serviced and brought back into operation, though there are no concrete plans to do that."
] |
[
"I feel compelled to add, that Hubble is still an active observatory and continues to produce world class science. It's probably going to operate through at least 2025, and might go longer. It's our best window to the ultraviolet spectrum and that capability will not be superceded or replaced until AT LEAST 2040. In fact, it just launched it's largest program ever, to study the ultraviolet light of young stars, called the ULLYSES program. ",
"https://hubblesite.org/mission-and-telescope/hubbles-ullyses-program"
] |
[
"No, not yet, but it is fully expected to (I hear). It entered safe-mode because of a coding error in some new routines they are using to prolong gyroscope life, using 3 gyros to slew the telescope and then 1 to keep it pointed. They've identified the problem, and will fix it soon."
] |
[
"Why humans and most living things on earth are symetrical? (2 legs, 2 arms...)"
] |
[
false
] |
I mean, even my nose and mouth are right in the middle of my face, not on a side, why is that?
|
[
"Now that that's out of the way, there are multiple ways to approach this question. One interpretation of your quesiton would be, ",
" My hunch would be yes, but first let me take another angle at it, based on evolutionary history.",
"Most animals that you can think of (fish, birds, worms, spiders, humans, etc.) are members of an evolutionary group called ",
"Bilateria",
". Almost all bilateral organisms belong to this group, and are descended from a single bilaterally symmetrical animal of some kind. They have, for the most part, inherited their ancestor's pattern of symmetry (starfish, sea urchins, and sea cucumbers are members of this group, but have evolved radial symmetry secondarily). Therefore, most animals are bilaterally symmetrical because off common descent.",
"Admittedly, this is only a partial explanation. It brings us back to the ",
" question: what is so great about bilateral symmetry? Why are bilateral animals the most numerous on Earth, rather than radial?",
"Wikipedia says",
" it may have to do with something called cephalization: the trend for animals to evolve heads. When you move purposefully in a certain direction, like a shark rather than a jellyfish, one part of your body is in front and another part is in back. In order to navigate your environment most effectively, sensory organs such as eyes, ears, or antennae (and the brain which interprets sensory information) should be in the front -- pointed toward where you are going.",
"For an animal to orient itself in its environment, it needs to make sense of where things are located. I've already said there is a front and back to the animal, but gravity also causes a natural axis of up and down. That axis will be most useful if our animal keeps its body oriented so it has a \"back\" and a \"belly,\" otherwise where objects or stimuli appear to be relative to the animal will change moment to moment. If the animal has a front and a back, and a top and a bottom, one side of the body will always be \"left\" and the other always \"right\". This may have lead to the evolution of two anatomical sides to the ancestral bilaterian.",
"But we don't really know for sure..."
] |
[
"To add to this, a ",
" of cephalisation seems to be the reason that ",
" organisms (",
") do ",
" show this type of symmetry - they are either ",
" or ",
".\n",
" is like a ",
", the animal is ",
", regardless of where it is cut from. Scientists think that this may be advantageous for sessile organisms since they can catch food in all directions, while remaining attached to one spot. "
] |
[
"Simply put, symmetry in development is easier to regulate than asymmetry. When cells start to differentiate, they do so based on concentration gradients of various signal proteins. So if signals are produced from the center of an organism, a single genetic network is all that's necessary to create symmetrical body parts. Asymmetric body plans necessarily require more complex underlying genetic networks and signaling between cells, and so are less likely to evolve."
] |
[
"Is the danger of loud noise related to absolute noise or noise above ambient white noise?"
] |
[
false
] |
I got to thinking about this because I got an air cleaner fan and now need to keep my computer volume at a higher level to get the same amount of noise when the white noise from the fan is also going. Does white noise cancel out the dangerous effects of sound or does it add on or do nothing? For a practical example, could a big ass white noise generator at the shooting range supplant earplugs?
|
[
"Sound doesn’t cancel out like that. If you have your music louder to hear it over the white noise, then the music is actually louder. ",
"In a shooting range adding a loud white noise generator would just raise the ambient sound level. Or if it was louder than the gun shots, would mean everyone would need to wear hearing protection from the white noise generator even if they weren’t firing guns. "
] |
[
"It is the absolute pressure of the sound that damages your body. Not the relative amount. For instance adding 10dB of extra sound to a 100dB existing sound would make the absolute sound level 110dB. Shortening your allowed exposure time from 15 minutes to less than a minute. But at those danger levels, your ears will already be hurting.",
"http://dangerousdecibels.org/education/information-center/decibel-exposure-time-guidelines/"
] |
[
"Thanks! "
] |
[
"How does the drug Adderall calm and let an ADHD patient focus?"
] |
[
false
] | null |
[
"\"ADHD drugs fall into a class of medications known as stimulants. ADHD stimulants boost levels of two neurotransmitters, or chemical messengers in the brain, known as dopamine and norepinephrine. Dopamine is thought to play a role in memory formation and the onset of addictive behaviors, while norepinephrine has been linked with arousal and attentiveness.\"\nSourcehttp://",
"www.sciencedaily.com/releases/2006/06/060626091749.htm",
"\nLittle is actually know about why they work mainly that they do."
] |
[
"As a follow up, why does Adderall/Ritalin seem to calm down people with ADHD but speed up people without it?"
] |
[
"Amphetamines help anybody focus. "
] |
[
"What exactly would I need to do to turn heat into electricity?"
] |
[
false
] | null |
[
"You can do it directly with the ",
"Seebeck Effect",
" using a ",
"Thermoelectric Generator Unit",
".",
"The difference in temperature between the hot and cold side of the panel directly outputs electricity. This is one of the ways they generate power on deep space probes. They use a ",
"radioactive isotope",
" to create the heat, and the cold of space as the difference in heat. Extremely long life due to the half-life of the isotope, and the virtually unlimited cold of space.",
"This is how the ",
"Voyager Probes",
" are powered. They are still operating today, more than 40 years later."
] |
[
"A ",
"steam turbine",
" with an ",
"electric generator",
" would be a good start.",
"The heat is fed to a body of water in order to produce steam, which is fed into the turbine where the steam pressure forces the turbine to rotate and this rotation is what makes the generator generate electricity.",
"This is the basic mode of operation for most of our sources of electricity these days. The source of heat varies (coal, gas, nuclear fission), but it ultimately ends up with steam powering a turbine/generator combination."
] |
[
"First, you need a hot thing ",
". Heat's not enough: there must be a temperature difference to extract energy. This is the #1 problem that trips up amateur energy inventors.",
"Second, there are two basic strategies: ",
"a) If you heat and cool a gas it will expand and contract: you can use the gas pressure to drive a machine (a piston or turbine) connected to an electrical generator. ",
"Steam engines",
" are a common example.",
"b) You can use the relationship between electron motion and heat in a conductor to create electricity directly using a ",
"Thermoelectric Generator.",
"Third, there's a limit. Your machine cannot possibly generate more energy than the ",
"Carnot limit",
"), which depends on the difference in temperature between your hot thing and your cold thing. For temperature differences of a few degrees at room temperature, the limit is ",
"; for machines powered by fire, it can be 50% or more. This is the #2 problem that trips up amateur energy inventors."
] |
[
"Do extended-release pills release medicine at a constant rate, and how can they stay \"inside you?\""
] |
[
false
] |
I'm taking plenty of meds right now. One is a 12 hour pill. 1) Do pills release at a constant rate, or is it something changing like an exponential decay? 2) How do pills stay "in you" for 12 hours? Wouldn't your digestive system have expelled it by then?
|
[
"I'm having difficulties finding a specific reference for you, but the complete digestion process normally takes longer than 12 hours, I'm finding references up to 75 hours but 24-48 hours for an adult is expected.",
"Time release pills are designed to take a while to decay, this is usually a rate dependent on the surface area of the pill, technically as the radius and length of the pill decrease the surface area decreases, so it's likely the rate decreases with time. This is obviously assuming the pill is composed of the same material. But the digestive cycle includes a few different chemicals which could alter the rate as well."
] |
[
"Source",
": The pills often are made out of very slow dissolving materials or have tiny holes that the medicine can leak out very slowly. Others, like ",
"Adderall",
" have the drug in different salts which metabolize at different rates. Normally, when a drug is digested, the concentration of the drug in the blood jumps and then decays (though many factors change based on ",
"absorbance, distribution, metabolism, excretion of the drug",
". ",
"An extended released drug can even out the peaks and troughs of the blood concentration",
".",
"Interestingly, releasing an extended release formulation is a common pharmaceutical tactic to get longer market share once the original/non-extended drug loses patent protection and generics come out. Often though, it makes life much easier for a patient to be on a once or twice a day drug, and compliance goes up."
] |
[
"Wikipedia drugs pages have a side panel that can include \"half-life\". Many of the slow release drugs have a half life of 2 days or more, so that the concentration builds up over days, not hours. The level of drug presumably still oscillates, but there is no drug-free period. (You can often change the most-drug-in the system timing of 24-hour meds to suit your needs -- more in the morning when you are active, or if the side effects are bad, take it at night and sleep through the side effects -- not so easy with 12-hour ones.) "
] |
[
"Have whitening toothpastes improved measurably in recent years, or is it all hype?"
] |
[
false
] |
Has the effectiveness of whitening toothpastes improved measurably in recent (or not so recent) years, or is it all hype? What, if any, ingredients are responsible?
|
[
"Dental researcher here. Whitening toothpastes ",
" help. The abrasives only remove surface staining. The problem is that yellowed, deeply stained teeth have the underlying dentin as the problem. You need to penetrate all the way through the enamel layer, between all of the hydroxyapatite prisms to get to the dentin.The only thing proven absolutely to work is high concentration (10%+) of carbamide peroxide gel. This gel rapidly loses oxidizing/whitening power after the first 2 hours, but continues to work a bit after that. Whitening strips work OK, but the concentration isn't very high and the strips aren't custom made, so they don't always fit well. A professionally made tray molded from your teeth with 10% gel is the way to go. Make friends with a dental student. Any 2nd year can make one for you.\nA word of caution, pro-strength bleaching can cause sensitivity/pain problems, because the pain response is transmitted through dentinal tubules, and when they open up from bleaching, it can hurt for a couple of days. Pastes like Sensodyne with Calcium and Phoshoprus suspensions may help a bit. \nTL:DNR - whitening pastes don't really work for deep staining. Get a tray made by a dentist.\nEdit: You can also prevent stains in the first place by drinking tea, coffee, or soda through s a straw. May look silly, but you'll bypass your incisors altogether. Oh, and don't' smoke, duh."
] |
[
"Here in Australia, there's a consumer group called Choice that often reviews, compares, and calls out bad products (to paying customers, so as to remain neutral) in a clear and methodical (if not scientific) manner. They recently did a release that was on the news: ",
"http://www.smh.com.au/lifestyle/beauty/whitening-toothpastes-a-washout-choice-20120704-21g4u.html",
"It reviewed 17 toothpaste products ranging in price from $1.27 to $7.99 and broke down product claims such as \"advanced-whitening\", \"multi-action\", \"enamel-lock\", and \"micro-cleaning crystals\".",
"Choice found none of the whitening toothpastes investigated actually contained a bleaching agent required to physically alter the colour of teeth."
] |
[
"All toothpaste is abrasive, that's how it cleans the teeth. You can actually use toothpaste as a polishing compound. "
] |
[
"Hypothetical question regarding genetics and ageing"
] |
[
false
] |
Hi again, Been reading ageing and found that as we age, DNA mutations/damages accumulate from sources like free radicals, oxidative stress, UV rays, carcinogens, radiation, endogenous damage (replication errors, synthesis errors), etc. The average lifespan of an organism is dependent on how efficient and extensive DNA repair mechanisms are and to a lesser extent how long telomeres are/whether the organism expresses telomerase. For example, while rats may have longer telomeres than us, we have superior DNA repair mechanisms and succumb to ageing and ageing diseases like cancer at a much later age. Naked mole rats are unique amongst rodents for their presence of anti-cancer (and subsequently, anti-ageing) genes (p16 and p27) and can live up to the age of 30! Alright, so hopefully that is enough background information. On to my question. Hypothetically, if there was some sort of tool that took every single cell in your body and replaced its current mtDNA and nDNA with your original DNA from birth (undamaged and unmutated. your original genome) and also restored telomeres to their default amount, what would happen? Since every cell in your body originally had the same DNA and mutations and damage from the aforementioned sources have over time degraded your cellular DNA in varying amounts, I'd imagine this procedure would restore one's youth, no? Also, could someone more informed than me could discuss whether the scale of this sort of procedure would even be remotely possible? I believe it is possible to edit single strands of DNA in live organisms at the moment but this is considerably more massive an undertaking. Thanks for humoring my rather ignorant question :)
|
[
"Aging (I won't give in to your British spelling!) is remarkably complex and many unknowns still exist. There is a lot of aging theories that are DNA damage-centric, which is a definite core component to what's going wrong.",
"One of the core things going wrong in aging is your stem cell populations accruing too much DNA damage, and eventually dying off. Telomeres/telomerase are most present, comparatively, in these stem cells but they evolved to diminish because of how they can allow a cancer phenotype to form in such cells (again, due to DNA damage).",
"Coming to your question, if you magically did a spell that made all your DNA back to how it originally was (getting rid of all accumulated changes), you would definitely help to stop continued aging and also greatly decrease your future odds of cancer. However, depending on when you did this, you could have already lost a significant amount of your stem cells. ",
"For example, the main reason it's thought that hair goes gray is due to loss of melanocyte-producing stem cells. Reverting all your DNA back to normal wouldn't bring back those stem cells.",
"I emphasized that what your procedure was magical, because it can't happen. You'd have to know your original DNA composition and go in and somehow target individual base sequences in every cell, which could have any number of random mutations. The incredibly specificity needed and the scale would just be insane. ",
"Let me know if you have any other questions, although I'm far from an aging expert. "
] |
[
"Hello! Thanks for the reply!",
"I haven't heard much about the ",
"stem cell theory of ageing",
" and the linked Wikipedia article is rather short as well. I was not aware the \"main theory\" for why hair goes grey is due to loss of stem cells. However, I am very interested in this and would like to know more. Could you elaborate? For example, is there any way to restore/replace these stem cells? Where are they located? What controls/regulates them?",
"As to finding out your original DNA, aren't there some cells in the body that divide very infrequently or not at all? Even if not, perhaps the saved umbilical cord or baby teeth could provide the original genome. Regardless, I doubt finding the DNA is the largest problem and rather replacing all of your DNA is.",
"Thanks again for responding!"
] |
[
"You'd probably get more in-depth answers from someone in the stem cell or aging field, but I'll do my best.",
"[",
"http://en.wikipedia.org/wiki/Adult_stem_cell](This",
" article) is a good start to see all the main types of adult stem cells. You have these populations all over where large-scale cell growth/division is needed. I am pretty sure their numbers are determined during development. They divide asymmetrically, as in a stem cell divides into the same stem cell and one differentiated cell...meaning that the stem cell population stays the same as they replicate.",
"There are mechanisms that are able to induce increased levels of their division (I'm personally familiar with neurogenesis, which the article links to). But again, the original population is staying at the same level.",
"Like I said before, they have some of the highest levels of telomerase, and therefore have a fairly constant level of non-coding telomeres on the ends of their chromosomes. Most of your other cells do not have any telomerase, and therefore lose telomere DNA each time replication occurs (this is due to how the \"lagging strand\" gets replicated during division). Telomeres shield your actual genomic DNA from being lost during replication, which would otherwise signal to the cell to undergo apoptosis (via p53). ",
"Telomeres evolved as a mechanism to stop cancer. If they do not go away over time, your DNA would accrue a lot of mutations that would eventually greatly increase your odds for cancer. So, cells that have been through a lot of replications will eventually kill themselves as they deplete their telomeres as a means to prevent themselves from becoming cancerous.",
"This isn't true for stem cells, because of their telomerase levels. They are thus one of the more likely sources of cancer. There's been a lot of hype about cancer stem cells, so you might want to check them out too.",
"My point is there is a constant fight between cancer and aging, and these are some of the main players in it. People love to talk about telomeres and how they are the secret to stop aging, but forget that we evolved to have them diminish for a reason. In your scenario, instead of targeting EVERY single cell (which would never happen), it may make more sense to try and target/revert these stem cell populations back to normal, as they are the sources of all the rapidly dividing cells and they are most likely to have a lot of mutations. ",
"To answer your final question, I'm sure there would be sources of your more original DNA...and that the replacement part would be the much more difficult part. I'm almost more inclined to say that replacing the entire nucleus with your replacement tissues' nuclei would be a more logical approach then going in and changing all the mutations individually. "
] |
[
"How does moment of inertia mesh with inertial reference frames?"
] |
[
false
] |
Disclaimer: I am not a physicist, or a scientist of any kind, it's just something I'm fascinated with. I just haven't been able to wrap my mind around this question. I don't need the math, just the concept that explains it. In physics, I understand that there is no privileged frame of inertial reference. You can pick any object in space-time and it can claim to be at rest relative to the rest of the universe, and all the physics still work fine. I get this in principle. But this also means that if you were on the outer ring of a space station, spinning enough to generate an equivalent to 1G of gravity, isn't it impossible for you to claim that the space station is at rest from your point of reference? If it were (meaning that the entire universe would appear to be orbiting you), there would be no force holding you against the outer wall of that ring, and the universe itself would appear to be orbiting you at speeds far greater than possible by general relativity. It seems to me there is no frame of reference that really allows for the spinning space station to be at rest. Does the concept of inertial reference points even work with rotational inertia?
|
[
"Rotating frames are not inertial. If you review the theory you'll see the transformations between inertial frames do not include time-dependent rotations.",
"Moreover, this has nothing to do with inertia of any kind, and so with the moment. This is pure kinematics."
] |
[
"Thanks! If I'm reading you right (I'm a complete noob at this), then the answer to this question:",
"Does the concept of inertial reference points even work with rotational inertia?",
"... is \"No?\""
] |
[
"You mean angular velocity, not rotational inertia. Inertia has units of mass, it's not what you want. In that case, the answer is no."
] |
[
"What is the current state of light based computing? What are the problems holding us back?"
] |
[
false
] |
I know the idea of light based logic has been around for decades and researched for just as long, but I hear little about it. With Moore's law starting to get caught up in physics problems, it seems like the logical way forward. Has light based computing even been prototyped? Is there no currently visible way forward? Whats holding us back?
|
[
"I don't know what the current state of doing actual computing with light is. I suspect \"far off. Very.\"",
"However, the field of silicon photonics is heating up like crazy right now. The distinction here is that we're only talking about the communications tech between the standard silicon chips, not changing how those chips do compute.",
"Presently, 100 Gbps optical network links are rolling out, and 400 Gbps is in development, with 1-2 Tbps in research. The neat thing about silicon photonics is that it seems like it's in a similar position as early SSDs: every reason to believe that once this stuff gets going, it's going to comes down in cost hugely over the next few years, while getting faster and smaller incredibly quickly.",
"So this is starting as network links in expensive data centers and super computers, but it likely will eventually end up as a new connectivity approach replacing interconnect technologies like DDR and PCIe for connecting together your CPU, GPU & RAM inside your computer. These are already running into limits of how much bandwidth they're capable of shoving over ordinary wires. (PCIe 4.0 hits 16 Gbps per lane, and has enough trouble carrying that much bandwidth even 20 inches that they had to pay special attention to \"retimers\" in the spec, which are little chips that essentially act as repeaters.)",
"So light is going to show up first as interconnect, before it becomes compute (if it ever does?)"
] |
[
"A couple of critical issues with optical computing that rarely get mentioned:",
"Photons are huge compared to electrons, and generally the devices that manipulate them are bigger than the photons themselves. A MOSFET for manipulating electrons can have a gate dimension of 0.5 nm and still be much bigger than the electron. An optical modulator for doing something similar with photons will have to have dimensions of at least a couple microns.",
"Optical computing, at least in the areas where it has big advantages in \"processing power\", is essentially analog computing. For example, with a clever arrangement of lenses an optical computer can essentially calculate a fourier transform in a few nanoseconds. But the result is analog, subject to errors due to thermal noise and so on. It might still be a powerful tool, but there are compromises to be made."
] |
[
"The problem with using light to do computing is basically ",
"\"fan out\"",
". How many follow on gates can you drive with the result of a given logic operation. This problem partly became the reason ",
"tunnel diode logic",
" never took off in the 1960's. Even though it had the promise of gigahertz clock rates back then. Light logic suffers the same problems. You would need a conventional photodetector-amplifier-LED/LASER to allow fan out. For each gate!"
] |
[
"Were there enough complex elements in the universe to support life 15 million years after the big bang?"
] |
[
false
] |
There's an currently posted over in suggesting that 15 million years after the big bang, the CMB would've been around the right temperature to support life throughout the cosmos, even on planets far away from their star. There's a lot of layman speculation about whether other conditions necessary for life such as complex elements were even around yet, so I was hoping a non-layman could shed some light on the viability of this theory.
|
[
"No. As dullertap said, stars didn't even form until ~200 million years after the big bang. Even then, there was only Hydrogen and Helium. All other elements are created by the processes within stars or during a supernova eruption.",
"The first generation of stars went supernova and spewed forth a variety of elements into space. Only then can you argue that the chemistry even existed for complexity. As Carl Sagan said, \"We are all made of star stuff.\"",
"The sun I believe is a 3rd generation star."
] |
[
"There were no stars at 15 million years after the big bang so there certainly would not have been any planets that would be capable of supporting life as we know it. The first stars were formed ~200 million years after the big bang. ",
"Source: ",
"http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question55.html"
] |
[
"TH OP's article has speculated that the CMB would be at the correct and reasonably narrow temperature range for water to be liquid at around 15 mill years ABB (after the Big Bang). But this particular factor in the creation and/or sustenance of life is just one of many. Oxygen possibly existed at that time but in such small amounts that its doubtful even a puddle would be able form. The other factors required for 'earth-like' life to appear (as opposed to Neutron star civs or Photospheric animals living on the edge of stars) are largely or entirely absent at that time. Mainly any of the higher level elements (except maybe in extreme trace amounts) but more importantly perhaps, time itself, time to evolve. Whilst our knowledge of that era is almost entirely theoretical it would still be stretching credulity to expect life to have sprung up from merely hydrogen and helium purely because the temperature was conducive."
] |
[
"Sunrise temperature dip?"
] |
[
false
] |
So my co workers & I watched the sun come up this Morning and observed the normal 5-10 degree drop & subsequent rebound of the temperature. After a little discussion it became clear no one has a good answer as to why this occurs. So my question is why does this happen?
|
[
"Radiational cooling of the atmosphere and ground has the most effect on the drop in nighttime temperature. The decrease in temperature continues for a short amount of time after sunrise because the input of energy from the sun has yet to equal the loss of energy from the ground and air. The temperature will begin to increase when the ground has received sufficient energy from the sun to begin warming the air.",
"This is a more detailed explanation."
] |
[
"Thanks it was my best guess I'm glad to know I was on the right track:)"
] |
[
"I don't know, but I will hypothesize.",
"I think the air at higher altitudes is heating up first due to the way the sunlight hits the atmosphere. This causes the air to rise, pulling the air below it up to fill the void. Then, the air on the ground around you (to the west I guess) would move in to fill the air that moved up. If you have an open area around that doesn't have concrete/buildings/anything else that would retain the heat, that air would be cooler due to the heat island effect.",
"Or I could just be talking out of my ass."
] |
[
"Are the ideas behind the Singularity at all legitimate?"
] |
[
false
] |
I know that there is no definitive answer, but are singularitians complete jokes to all real scientists? Ive been reading Kurzeil's book and it seems sensible to me, but for all I know its the same thing as people fifty years ago predicting that we would live on the moon. I would love to hear some personal opinions from some scientists.
|
[
"Read Scott Aaronson discuss it ",
"here",
", with Eleizer Yudkowsky chipping in on the comments section. Pharyngula is ",
"quite harsh",
" in its criticism of Kurzweil's claims.",
"While 'real scientists' might accept the possibility of a singularity, it is such a distant possibility with so many uncontrollable degrees of freedom that the idea of devoting ones life to its pursuit seems to be in vain. The very notion of a singularity arose because of developments in computing, energy, genomics and nanotech over the latter half of this century, and I would guess that none of the scientists who made major contributions to these fields were directly motivated by the quest for a technological singularity."
] |
[
"My opinion is that Kurzweilians are afraid of death. ",
"The \"Singularity\" is a joke to nearly every scientist I know. With a rare occurence of \"eh, maybe someday?\""
] |
[
"The only thing we can reliably predict about the future is that people will be just as gullible there.",
"What pisses me off is that this guy speaks as some sort of authority... on the future. What the hell? Is this like some sort of... reality sci-fi for people?"
] |
[
"When light strikes a metal, a photon can excite an electron to leave. Does the metal ever run out of electrons?"
] |
[
false
] | null |
[
"No. While releasing more and more electrons, the Fermi level will become lower and lower, because the electrons with largest kientic energy will be ejected. This increases the work function of the metal until the energy of one photon is not sufficient to excite another electron to the vacuum level. At this point you have changed the potential of the metal significantly. So you could call the photoelectric effect self-inhibiting if the metal is not connect to an electron source.",
"edit: additions due to many questions going in very similar directions:",
"A: No. First, a solar cell usually doesn't operate using the photoelectric effect but using an interface between two different doped semiconductors (p-n junction). But that difference is not really relevant. The thing is that after leaving the photoelectric electrode (or the electron donor phase in the semiconductor) they travel towards an electron acceptor electrode. This creates a potential between these electrodes. If both electrodes are floating (i.e. not connected to any mass or ground which can neutralize potential, this potential will then counteract any further charge separation. However, in a solar cell powered circuit, the to electrodes are connected to each other by a load (for example a lamp). The electrons travel through that load, lose their potential energy and travel back to the donor electrode where they replenish the electron reservoir and more electrons can be excited. This is a continuous process and electrons are not \"lost\" somewhere in between.",
"A: A circuit as described above can also contain the ground as electrical conductor. This does not change the efficiency of a circuit or lead to changes in potential. The only importance is that the two opposite poles of the load and the two opposite electrodes of the photoelectric element or solar cell are connect to the same potential each. You can do that directly, or can put the ground in between ONE leg. Not both, because then you would short the solar cell and not be able to power the load.",
"A: No. Even though the loss of electrons is formally an oxidation, the metal does not become oxidized because it will regain the electrons on one way or the other before that many electrons are lost so that a chemical process would set in. The removed electrons do not belong to a specific atom within the metal, but are rather shared between all atoms in an electron \"sea\" where they can freely move (hence the electric conductivity of metals).",
"But you can make chemical reactions more or less likely by applying a potential (voltage) to the metal. This is what is used in electrolysis or active passivation of metals. In principle you can tune the reactivity by lowering or increasing the energy of the most energetic electrons in the electron \"sea\", making it harder or easier, respectively, for oxidizing agents (e.g. O2, H",
" ) to remove electrons from the metal."
] |
[
"Yes, this is called the photoelectric effect; Albert Einstein won the Nobel Prize in physics for understanding it. It is the basis for solar power, although photovoltaics is a bit more complicated than the photoelectric effect.",
"If too much charge is removed from a solid, the remaining charges start to repel each other and you get a ",
"Coulomb explosion",
".",
"edit:",
" the answer to OP's question is \"no.\" My \"yes\" refers to whether the photoelectric effect occurs, which it does."
] |
[
"I agree with him by saying that a Coulomb explosion will happen before the metal runs out of electrons. The smaller the particle (metal cluster) the more likely a Coulomb explosion becomes because the free energy difference of lattice formation is smaller compared to a bulk metal.",
"edit: I just did a little bit of research and Coulomb explosions can also happen locally with ultra-short high energy laser pulses. But it doesn't change my initial answer that in a bulk a Coulomb explosions will not happen likely. Before that could happen the metal will get the emitted electrons back, either by arc formation to the \"collector\" (the emitted electrons have to go somewhere) or by the generated electron gas itself. In that case you would generate a stationary (in time) electron density in the vacuum above the metal surface where the rate of electron emission equals the rate of electron absorption from the gas.",
"TL;DR: Yes, Coulomb explosion is a real thing but is unlikely to happen for a bulk metal. In any case, the metal would never completely run out of electrons."
] |
[
"Is it possible for a living organism to evolve in a different wavelength from visible light?"
] |
[
false
] | null |
[
"It would have to be ",
" transparent to visible light. That's so implausible we can dismiss it out of hand. The glass in your windows is very, very transparent, but you don't have any trouble seeing it."
] |
[
"This question has been removed because highly speculative in nature. Exceedingly imaginary hypotheticals often invite non-scientific speculations.",
"For more information regarding this and similar issues, please see the ",
"FAQ."
] |
[
"Well, nature has gotten sort of ",
"close",
".",
"Problem is, a lot of the things animals need to be made of happen to reflect visible light."
] |
[
"How to find x,y,z rotations between two given coordinate frames (or planes)?"
] |
[
false
] | null |
[
"The rotation matrix that maps between these coordinate systems is given by ",
"R",
" = ",
" • ",
"’",
",",
"where ",
" is the unit vector in the i",
" direction in the unprimed coordinate system, and ",
"’",
" is the unit vector in the j",
" direction in the primed coordinate system."
] |
[
"Sorry, what are i and j? x and y? "
] |
[
"i and j are indices that represent x, y, and z."
] |
[
"Why can foxes eat raw chicken while we cant, and how did we eat meat before we could cook it?"
] |
[
false
] |
the title says it all
|
[
"People don’t get sick every time they eat raw meat. We cook food to mitigate that risk, and it helps with nutrient absorption. I met a health inspector who said he’d rather eat raw chicken than unwashed vegetables."
] |
[
"Also, foxes don't store the chicken in the fridge for a week before they eat it. Eating a freshly killed chicken is a lot less dangerous (from a food poisoning perspective) than eating a chicken breast that's been sitting around for days."
] |
[
"It is very unusual for a disease to be transmissible between species. Humans have made many dangerous diseases that are transmissible between species from centuries of living in close proximity to domesticated animals.",
"It should be noted that decaying meat is dangerous because of decomposers like botulism that produce extremely potent poisons. Animals that eat decomposing meat have ways to deal with these poisons.",
"Somewhat related, humans in the Americas did not domesticate as many animals as humans in the Old World. There were significantly many more disease spread from the Old World to the Americas than the other way around because of this. Here's an ",
"interesting video",
" on the subject."
] |
[
"How do Sperm Whales find Giant squid?"
] |
[
false
] |
They dive to extreme depths to find the squid but how do they actually locate them? Do they use sonar or smell or some other sense to hone in on them? I imagine its pitch black down there and the ocean is huge so it blows my mind they are able to survive off such a strange and hard to get to diet.
|
[
"They don't solely eat giant squid- from what we can tell, they require about a ton of food per day, so they eat all kinds of fish and squid. That being said, giant squid are obviously the most well known prey item for sperm whales as far as humans are concerned, and likely a very desirable one for the whales, since its a high payout- one hunt equals a huge, energy rich meal, instead of swimming after numerous smaller things. They find them the way most cetaceans do; with echolocation. They don't have the characteristic \"singing\" that some of their filter-feeding counterparts are known for- instead, their large head (filled with fatty tissue) and their spermaceti organ (where the oil is that whalers seek, mostly in the past but still to a certain degree today) is used to amplify clicking sounds made by their nasal passages and a pair of clappers called \"monkey lips\". It appears that, as the sound bounces back to them, they use a pad of fat in their jaw that is attached to their inner ear to absorb and interpret the sound. They use this same system to make different clicks and sounds to communicate with other whales. Its even come.out fairly recently that they have certain series of clicks to identify different members of their clan- essentially, names. ",
"As far as hunting though, it can be broken down a little bit- if they send out a \"click\" and it bounces off the hard parts of a giant squid (like its beak), the amount of time it takes to bounce back tells the whale how far away it is. The \"shape\" of the wave tells it how large it is and what shape it is- and if you're a whale that means you now know what it is. Its been determined that they can find a relatively small squid up to a mile away- now imagine it was a big squid, or a school, and you had multiple whales hunting that can all hold their breath for over an hour. While I'm sure its difficult, it doesn't sound nearly as impossible as rooting around in the dark abyss with eyes that rely on light. They can essentially see down there with echolocation. ",
"We're still learning an awful lot about them (I read a paper about the function of their teeth just last week) so I'm sure that, even in the next 5-10 years, I could come update this answer with more info. Either way, I hope this explains it satisfactorily, but feel free to ask if you have more questions"
] |
[
"Wow, that’s just amazing."
] |
[
"It doesn't hurt that we think large deep-sea squid like the giant squid and the colossal squid are actually remarkably common.",
"Judging by how many squid beaks we find in the stomachs of almost every whale that's ever been cut open, the whales clearly don't have a hard time finding the squids."
] |
[
"Is there a way to calculate the amount of heat energy released during the oxidation of a certain amount of a certain substance?"
] |
[
false
] | null |
[
"enthalpy data is tabulated, if you know the combustion reactions of interest, you can work out the theoretical energy released by looking at the weighted sum of products and reactants.",
"practically reactions don't go to completion, so in a real scenario you would expect to typically get less.",
"all of this data should be given as heats of formation in an SI data book."
] |
[
"Are you trying to calculate ab initio or through experimental methods? There are ways to do both, but experimental will likely be a lot more accurate. Some form of calorimetry might be your best bet."
] |
[
"Yes, scientists have tabulated the energy released in kJ/mol or kJ/kg. Of course, variations in pressure, temperature, solvent and solute impurities, radiation, magnetic fields mean the value is never perfect, but for engineering/practical purposes it's good enough."
] |
[
"When you drop a pebble in water, you hear a sound wave, and you see ripples along the surface. Is the distance between the ripples on the surface the same as the wavelength of the sound wave?"
] |
[
false
] | null |
[
"What you hear is the soundwave as it travels through air. So it will have a different wavelength vs. traveling through water.",
"The waves you see are not indicative of the sound's wavelength. It is a physical reaction to the pebble breaking the water's surface and displacing water in a cycle."
] |
[
"The ripples you see on the surface of the water are not sound waves - they are ",
"gravity-capillary waves.",
" It is entirely different physics which govern them (gravity, surface tension) so there is no reason for them to by synced with the sound waves in either the water or the air."
] |
[
"Interesting question, and as others have pointed out, the answer is no. The mechanisms which create the ripples are different from those that create the sound. When a rock drops on the surface of a body of water, it will create three distinct sets of waves. The ripples are the gravity-capillary waves that another commenter mentioned (I have no expertise with these, so I will leave that alone). Those waves will travel as gravity waves, and their speed is determined by the depth of the water, among other things. The other sets are the sound waves that travel away from rock in the air or in the water.",
"The sound waves that leave in the air travel at 343 m/s. Franz",
" describes the sound wave sources as the object hitting the surface, the object itself vibrating after impact, the water droplets thrown up after the impact, those water droplets hitting the surface, vibrations of cavities open to the air, and bubbles popping on the surface. According to the paper, the vibrations of the object dominate at high velocity, while the vibrating air bubbles dominate at low frequencies. Impact sound also plays a role.",
"Underwater sound is also explored by Franz",
" He notes that the same mechanisms are important, and points out that the sound underwater is more directional than it is on the surface (the explanation for this has to do with wave interaction). This knowledge is actually very useful, and work by Pumphrey",
" on the sound generated by splashes of water and rain are now a key part of underwater acoustics.",
"[1] ",
"G. J. Franz, “Splashes as Sources of Sound in Liquids,” J. Acoust. Soc. Am., vol. 31, no. 8, pp. 1080–1096, 1959.",
"[2] ",
"H. C. Pumphrey, “Underwater sound produced by individual drop impacts and rainfall,” J. Acoust. Soc. Am., vol. 85, no. 4, pp. 1518–1526, 1989."
] |
[
"What (if any) differences exist between delta-9 THC derived from conventional sources vs delta-9 THC derived from hemp?"
] |
[
false
] |
The past couple years, delta-8 THC was being screwed as a legally produced alternative to conventional delta-9 THC products. Recently, I've seen new products marketed as containing delta-9 THC, somehow legalized under the same provision. What's the difference between this hemp-derived d9-THC and traditional d9-THC? Is there a chemical difference, like with delta-8? Is it solely a legal distinction? Is it a difference in production?
|
[
"No one seems to be answering your question, so let me provide some context: The reason D9 edibles are now legal is because those edibles are technically under the legal limit of 0.3% D9THC.",
"Some opponents say that the law also specifies that these hemp products must not be \"intoxicating,\" but obviously you could just eat a similar amount of hemp flower if you wanted. I believe that 3 grams of flower would be about 9mg of D9THC.",
"I cannot speak to the chemical make-up. Theoretically it should be exactly the same. Maybe there will be some impurities from the extraction process, but supposedly D9 is easier to extract than D8 or even CBD. But my point is that it is not legal because the chemical composition is different----only because of its source (hemp) and that the percentage is under the legal limit."
] |
[
"This goes even farther with edibles. As it is.3% by weight per the federal Farm laws including hemp regulation. Therefore you can make an edible that weighs 5g that has 15mg D9. Which is more than enough to get the occasional user pretty high. It usurps states rec and med laws a bit, but who cares. I think there is one state that has said you need 0% to sell it under Hemp regulation."
] |
[
"it is a super petty legal distinction. If you were to eyeball a hemp plant and a marijuana plant the \"lay person\" could not tell the difference. Untrained law enforcement cant tell the difference either and just think you have weed on you. They are two different plants but part of the same Cannabaceae family they are cousins lol so they produce and have similar qualities. Cannabis just has way higher concentrations of THC and if you look through the controlled subtances act they name our specific chemical compounds that are illegal and Delta-9 is one of them and Delta-8 is not lol"
] |
[
"Is there anything you can wrap around a magnet to block the magnetic field?"
] |
[
false
] |
[deleted]
|
[
"Magnetic shielding is made of materials with high magnetic permeabilities, like iron."
] |
[
"Nuclear magnetic resonance spectrometers (and magnetic resonance imagers) use a main superconducting electromagnet coil to generate a huge magnetic fields. Some of these instruments use \"active shielding\" which is a another superconducting magnet wound in the opposite direction to the main coil. This gives an opposing field that limits the stray field from the main coil. "
] |
[
"Yes, mu-metal is often used to sheild equipment that is sensitive to external magnetic fields"
] |
[
"Do freeze-dried fruits have the same nutritional value as fresh fruits?"
] |
[
false
] |
Are freeze-dried fruits less nutritious than fresh fruit? Is there any kind of damage that the freeze-drying process does? I'm not talking dried, sugared fruits, I mean just pure fruit freeze-dried.
|
[
"This question depends heavily on how one defines ",
". If you mean specifically the inorganic mineral content, then the answer is flatly yes, freeze-dried fruits have the same inorganic mineral content as fresh fruits. On the other hand if you are more interested in the content of various organic compounds in the fruits, such as organic vitamins, antioxidants, or sugars, the answer becomes slightly more complex.",
"The freeze-drying process simply removes water from the tissue, so it should have no direct impact on the either the inorganic or organic components ",
". The process sort of locks in what is there by removing the water, which may have otherwise fostered an environment in which degradation of the organic compounds would have been more favored. However, it is also important to note that many nutritionally-relevant compounds continue to be synthesized in fruit throughout the ripening process, and freeze-drying would also put a halt to that. ",
"I think most people probably do not know how freeze-drying actually works, so here is a quick overview: Fruit samples are frozen to some temperature well below the freezing point of water, and are then placed under a high vacuum. We are all familiar with the melting and boiling points of water, but what we often fail to appreciate is that these points are also dependent on pressure; 0°C and 100°C are the respective melting and boiling points for water only at 1 atm. If we increase or decrease the pressure, those points change. For example, this is why boiled foods often include \"high altitude instructions\", which will say something along the lines of \"boil 4 minutes longer.\" Why? At higher altitudes there is lower atmospheric pressure, meaning the water boils at a lower temperature, which means you need to cook your food longer to compensate. Back to freeze-drying: in a high enough vacuum (i.e. low enough pressure) solid frozen water will actually be unable to melt into the liquid phase, but will instead ",
" directly to the gas phase. You have probably observed this phenomena in carbon dioxide, which exhibits this behavior at normal atmospheric pressures. So-called ",
" goes directly from a solid to gas, and in the freeze-drying process the water is behaving as a dry ice.",
"In freeze-drying, the water is removed in a low energy system through the process of sublimation. Because no additional energy is added, no additional reactions altering the nutritional contents of the fruit (or other food). Compare that to heated drying (or even cooking!), where energy is added and water leaves through boiling, a system favoring additional chemical reactions. These reactions may well destroy some of the desired nutritional components, though on the other hand they create other compounds with desired properties, such as flavor."
] |
[
"No. Only the water is sublimated. ",
"Imagine the evaporation of spilled orange juice, which contain lots of water soluble compounds and works well as an analogy to our dried fruit. Even at normal atmospheric pressure the water will eventually evaporate, leaving behind a sticky mess of what had been the water soluble compounds, including vitamins and sugars. The water left, but they did not.",
"The processes of sublimation, boiling, or even evaporation, involve transfer of individual molecules from one phase to another. We describe water as a solvent dissolving other solutes when there are sufficiently excess water molecules capable of surrounding the solute particle. This means that solutes cannot piggy-back on individual water molecules as they make the phase transition. Instead, they are left behind."
] |
[
"Couldn't removing water also remove some of the water soluble vitamins?"
] |
[
"As the solar system orbits the galactic center, why does it have a helical precession?"
] |
[
false
] | null |
[
"That's not ",
"precession",
", precession happens to a spinning body. The Earth spins, it's an oblate spheroid with water and a Moon, so its rotational axis rotates with a 26,000 year period - that's precession.",
"The solar system bobs up and down through the galactic plane over a period of 60 million years, but there's not a helical motion as shown in that video. For that to happen the solar system would have to be orbiting something that's orbiting the galaxy, and to have a period like 26,000 years, it would have to be pretty noticeable."
] |
[
"The reason it bobs is that the mass in the Galaxy is located not just in the center, but throughout the disk. So when the Sun is in the midplane of the Galaxy, it's at a lower gravitational potential than when it's above or below the midplane. When it's out of the midplane, the disk pulls the Sun back toward it, creating an oscillation."
] |
[
".",
"I don't know why this keeps coming up, but there seems to be a large segment of the occult/conspiracy subculture that has become very fixated on this idea. Planets orbit around the Sun. The Sun orbits around the center of the Galaxy. It makes absolutely no difference whatsoever",
" what the orientation of the ecliptic (the plane in which the planets orbit) is with relation to the Galactic plane. The Sun does have an up-and-down oscillation in and out of the Galactic plane, but there's no possible way (edit: actually if it happened to have an epicyclic frequency equal to the vertical oscillatory frequency, and both were much shorter period than the full orbit, you would get something similar to a helical shape, but none of that is the case for our Sun) for it to follow a helical path. Additionally, stars in orbit of the Galaxy do not necessarily have regular oscillations-- they can change depending on the local gravity field.",
"[1] Technically there's a difference but it's far too small to have a measurable effect."
] |
[
"Why do humans feel hot/heat up when we exercise?"
] |
[
false
] |
Whenever I'm running, after about 30 minutes I feel so much hotter than when I started. Is my body actually heating up, or am I just feeling hotter? Also, why is this happening? Wouldn't this mean that we're inefficient at converting energy into momentum? Is there an evolutionary significance to this? Thanks!
|
[
"Cellular respiration is exothermic, meaning that the process of supplying energy to run a cell releases energy. When you exercise, your muscle cells do a lot of respiration to produce the chemicals that cause muscles to contract, and that contraction in turn is exothermic. Essentially, cell respiration is a very slow and controlled combustion. The by-products are H2O and CO2, where the carbon comes primarily from sugar and fat."
] |
[
"Like most physical processes, moving your muscles produces waste heat, which increases your temperature. ",
"Yes, we are not capable of 100% efficient transfer of energy into momentum; neither is any other macro-scale physical process in the universe."
] |
[
"In order to maintain your body temperature you begin to sweat, as the evaporation of sweat lets you cool down. Yeah, you are getting really a bit hotter while doing sports.",
"As to efficiency: Your body gets more efficient in doing certain processes warm, than doing them at his normal temperature. Warming up before sports can increase your efficiency up to 7%."
] |
[
"What drives the molecular change in catalytic enzymes?"
] |
[
false
] |
The example I'm specifically thinking of is the F1 domain of the ATPase, which creates ATP from the proton motive force. The translocation of protons causes rotation of the the F1 domain subunits. Which drives a conformational change between tight, loose, and open binding conformations and these have different affinities for ATP My question concerns the driving force for ATP synthesis. I read that there is a low gibbs free energy of for the reaction which means it'll happen spontaneously. Does this mean that in the tight conformation the ADP & Pi are held close so that there is less steric clash if they combined to form ATP. Basically I understand the mechanism used by the protein by I don't understand why it drives ATP production.
|
[
"tight conformation the ADP & Pi ",
"That's pretty much the idea. The ADP and Pi are pushed so close together (in just the right conformation) that they can't help but react. "
] |
[
"yes, the energy transmitted from the PMF via conformational changes is what forces the atoms past the small energy barrier - it is almost like snapping together building toys (K'Nex, Lego, etc)",
"edit: not all enzymes function in this fashion; they are many, many different protein-catalyzed reactions"
] |
[
"Chemical reactions ",
" occur by molecules bumping into each other; pushing them into each other is not very different. (which you can also do at the macroscopic scale; some reactions require high pressures)"
] |
[
"Why do dogs chase their own tails? Do they not realize its part of them?"
] |
[
false
] | null |
[
"There was not a single meaningful sentence in that entire article (this is not exaggeration). That is ",
" piece of garbage and \"woo\" I have ever read. In no conceivable way does it belong in ",
"/r/askscience",
". "
] |
[
"There was not a single meaningful sentence in that entire article (this is not exaggeration). That is ",
" piece of garbage and \"woo\" I have ever read. In no conceivable way does it belong in ",
"/r/askscience",
". "
] |
[
"You piqued my curiosity so I moseyed on over to JStor/Pubmed/Google and looked for papers on cats/dogs and consciousness and didn't find anything useful. The behavior of cats/dogs suggest (strongly) that their tails are used in emotion and base feelings that can comprise the subconscious.",
" It follows that the movements of their tail are not conscious at times, perhaps they can think \"Tail move left!\" and it responds, but more than likely a lot of movement is unconscious.",
"As such movement of something they didn't control while they look at it could result in a response of \"Hey that's not me, but it's close to me and looks like something good to pounce on!\".",
"And they pounce. (Or chase).",
"(Related (no mention of pets, just connection to unconscious emotion): Unconscious Emotion - Piotr Winkielman and Kent C. Berridge)",
" Another theory is that boredome and lack of enough exercise leads cats/dogs to become overstimulated when playing around, they forget/don't care it's their tail and just chase it for exercise and fun!",
"I like to think they know but pretend not to, just for giggles ",
"I work in Drug Target - siRNA (Microbiology) so take what I say with a grain of salt since I didn't study behaviorism."
] |
[
"My seven year old asked this: if Mercury suddenly didn't exist (for example if it were towed away from our solar system somehow) would that have an effect on the Earth?"
] |
[
false
] |
I'd like to expnad on this question. Would the removal of any of the planets would have an effect on Earth. Obviously, removing the Moon would have drastic consequences - but do the other planets and asteroids have much effect on Earth's orbit? Also kind of related: could we ever mine enough material from the Moon or the asteroid belt to make a noticable difference to the Earth - Moon system?
|
[
"Gravitationally not really, since Mercury is pretty small and pretty far away (the far away part being most important). Doing some back of the envelope calculations, the gravitational acceleration of Mercury at Earth's average distance from it is about 10",
" g. That's ",
" of the acceleration from gravity at Earth's surface. To put it in terms of something a seven year old would understand better, it would take about ",
" to speed up to walking pace at that acceleration. Not very influential gravity-wise :)"
] |
[
"I'm sorry, but isn't that acceleration relevant when we talk in astronomical time?"
] |
[
"Not exactly, because on astronomical time scales you're still dealing with astronomical distances. Even 100 m/s is pretty minuscule when you have to travel distances in space."
] |
[
"During embryogenesis how do cells know where to go and what to differentiate into?"
] |
[
false
] |
How does an individual cell know where it should go, what all proteins it should produce, when and along which axis it should divide and when it should die(if required)? Was this perfected with trial and error during evolution? Can we study how multicellularity evolved by looking at how a zygote becomes a multicellular organism?
|
[
"This is a GIGANTIC QUESTION. Let's see...\n1. An individual cell knows what to do, in general, from a combination of internal (cell autonomous) and external signals. Cells, when made from parental cells through mitosis, can have different proteins within its cytoplasm and nucleus than its sister cells through differential partitioning. Cells can also receive signals from neighboring cells (paracrine or juxtacrine) or from cells much further away (endocrine). It is often a combination of internal and external signals that determines what genes are being expressed within a cell, and it is differential gene expression (along with interaction with the microenvironment) that ultimately leads to the sorts of development you're talking about."
] |
[
"Thanks for the answer. During cell division how is it determined which cell gets what all components of the parent cell? "
] |
[
"So, except for some cases (like the formation of a human egg), one daughter cell doesn't get ",
" the components of the parent cell. Rather, it gets a different concentration of something compared to the other cell. That something could be:\n-mRNA\n-transcription factor(s)\n-signaling molecule(s)\n-etc.",
"For example, in fruit flies, high concentrations of mRNA coding for bicoid are kept tethered to the anterior portion of the oocyte, and upon fertilization and cell division, daughter cells in the anterior area of the oocyte (now embryo) get a large amount of bicoid mRNA, whereas daughter cells in the posterior portion of the embryo get very little. ",
"Here's",
" a wikipedia page on that, and ",
"another",
" with some other examples."
] |
[
"If dopamine is released into our brains when we eat foods we like, what is released when we eat foods we think taste bad?"
] |
[
false
] | null |
[
"I believe what matters more is the specific pathway in the brain which is activated. ",
"Dopamine is a neurotransmitter associated with the Ventral Tegmental Area and Substantia Nigra, which have a couple major projections. One of those projections is called the meso-limbic tract, which communicates pleasure signals to the Nucleus Accumbens. A variety of sensory signals might activate this sensation. Food - in particular, tasty bits - certainly do.",
"In terms of bad tastes, this adds a whole nother dimension, because it must first become associated with unsavory connotations. (I think food and sweets are more innately associated with pleasure, although I'm not sure). There is another pathway recruited for this, and I believe it involves the amygdala and gustatory cortex. Both of those most likely use your more traditional Glutamate and GABA neurotransmitters. ",
"Overall, the brain uses a variety of signal carriers or neurotransmitters to translate electrical messages into chemical, back into electrical messages. However, it's more so the pathway and pattern of modulation that connotes specific responses. Dopamine often gets associated with strictly pleasurable emotional gunk. That's why people tattoo it above their ass cracks. In reality it's just another neurotransmitter that might as well be associated with functions of any of the other pathways it's associated with. e.g. Fine motor movements in the meso-cortical tract (I think)"
] |
[
"I don't believe what ",
"/u/badasswizard",
" said is correct. GABA is an inhibitory neurotransmitter, which I would take a guess at saying that it inhibits the activity in the amygdala due to it's anti-anxiety properties (of GABA and GABAergic drugs such as alcohol and benzodiazepines).",
"But to answer your question, neurotransmitters can't be \"traditional\" because that doesn't make sense."
] |
[
"One easy way to think about this that doesn't require explaining multiple different pathways within the brain (which are definitely important but needlessly complex in this case) is to think in one level above the neurotransmitter level. As has been mentioned previously, the effect of dopamine is entirely dependent on the receptor that it binds to.",
"With that being said, when looking at the reward pathway in the brain, one needs to look at firing rates of dopaminergic neurons. There is a basal level of firing of these dopaminergic neurons that will occur in an animal experiencing nothing pleasurable or unpleasurable. In the case of a rewarding stimulation, you see increases in the firing rate of these neurons which in turn leads to an increase in dopamine being released. However, in the case of a noxious stimulation, you see the firing rate actually decreases and you see a lower amount of dopamine relative to the basal level. Thus, you have a \"set point\" of normal dopamine that can be increased or decreased following a stimulation like good or bad food, which in turn encodes the valence of the food.",
"Here is a paper that demonstrates how firing rates can be modified through training (though it does not compare pleasure vs noxious, the results suggest that firing rates are modulated in both upward and downward directions):\n",
"http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1564381/"
] |
[
"What kind of experiments do astronauts do in the ISS?"
] |
[
false
] | null |
[
"Come on man, first result from googling 'experiments on ISS.'",
"http://en.m.wikipedia.org/wiki/Scientific_research_on_the_International_Space_Station"
] |
[
"Eh well now at least you can post a more specific question if you'd like."
] |
[
"fuck. thank you though"
] |
[
"Why isn't the Sun Blue?"
] |
[
false
] |
[deleted]
|
[
"There are two things going on here.",
"The peak in color associated with the temperature of something is given by Wien's displacement law:",
"https://en.wikipedia.org/wiki/Wien's_displacement_law",
"If you plug in the temperature of the surface of the sun, 5777K, it says the peak should be at about 500nm, which is about green. Now keep in mind that that doesn't mean the sun should look green. If you look at this image:",
"https://en.wikipedia.org/wiki/Planck%27s_law#/media/File:Black_body.svg",
"The sun has a curve very similar to the 5000K, just nudged a bit to the left. So you can see that even though it peaks at green there is a LARGE portion of all the other colors because the curve is broad and green is right in the center. This means that, in space, our sun appears to be essentially white.",
"Now, I say \"in space\", because on earth our sun appears to be more yellow. The reason for this is the same reason the sky is blue. Light travels in a straight line (ignoring GR). If there was no atmosphere, you would not be able to \"see\" any sky, as no light would reach your eye unless you're looking directly at our planet's light source (i..e the sun). The only way light can reach your eye when you're looking at an \"off sun-to-you angle\" is if it takes a bit of a pinball path, bouncing and scattering off things along its way, thus taking it off the direct line between light source and your eye. Thus the light we see when we look up in any direction other than directly at the sun has reached us by scattering off something. Scattering off what? The atmosphere.",
"If you look at the graph I linked, not all colors in the rainbow are scattered by the molecules in our atmosphere the same. In fact, the more to the left a color is (i.e. the higher the energy of the photons), the more vigorously they scatter. This is called Rayleigh scattering:",
"https://en.wikipedia.org/wiki/Rayleigh_scattering",
"What this means is that when light is coming from the sun to your eye, passing through the atmosphere, the blue light and part of the green scatters the most, and the reds the least. As a result the light that reaches us from angle that are not directly looking at the sun are mostly blue and the light coming directly from the sun has been \"robbed\" of a lot of blue and some green. This means on the surface the sun appears yellower/redder than it does in space (where it appears white). The more atmosphere the light has to pass through the greater the effect, which is why when they sun comes at shallow angles, and thus traverse through the most atmosphere to reach you (i.e. a sunset/sunrise), you will see the sun as redder and find the colors in general bleed/diffuse more around the sun, as more scattering has occurred."
] |
[
"The flame example is misleading you a bit. It is true that hot gas molecules don't emit a smooth blackbody spectrum, because the emission spectrum of an object is the product of the ideal blackbody spectrum and its absorption spectrum. Many people forget about the second part, i.e. Kirchhoff's law of thermal radiation, and they just assume you are dealing with something close to an ideal blackbody. As a result, hot gases emit spectral lines rather than a continuous spectrum and they can have a variety of colors depending on where those lines cluster. For the flame, the light is also coming from chemiluminescence rather than thermal excitation, but regardless it still emits in sharp lines.",
"But if we look at the sun, we do see (more or less) a continuous blackbody curve, just like with hot soot. That is because the sun isn't a gas, it is a plasma. And plasma absorbs all frequencies. The sun isn't a perfect blackbody, because it is partially transparent too. But since the sun is so thick, you only see light from a finite depth range known as the photosphere. The temperature varies a little over the photosphere, so instead of one blackbody curve at one temperature you have to integrate the contribution of different layers up. But the end result is something ",
"very close to an ideal blackbody curve at 5777 K",
".",
"tl/dr - The sun is a plasma, which is a much better blackbody than a gas, so it emits something close to an ideal blackbody curve."
] |
[
"Not quite! Scroll down to the bit on the frequency-dependent formulation in the wiki page you linked. The constant there doesn't fit c=fλ with the Wien's law constant.",
"The deal is that for the power/flux/intensity distribution, you're really plotting dP/dλ, where P is your power or whatever. If you plot dP/df instead, you get a different peak, because you're looking at a different differential."
] |
[
"Have we ever had any evidence that light travels faster than 299,792,458 m/s?"
] |
[
false
] | null |
[
"Well, a lot of physics experiments are capable of testing the speed of light, insofar as they would go haywire if the speed of light changed. So, basically any optics experiment that anyone is doing anywhere. And if the speed of light changed suddenly, we'd also see an alteration in the apparent motion of the planets. We'd also have a suddenly different time lag to various spacecraft around the solar system."
] |
[
"There have been plenty of attempts to detect light or anything else traveling above ",
", but no solid evidence has ever been found of anything doing so."
] |
[
"Thanks! What's the most recent test?"
] |
[
"How common are diamonds really?"
] |
[
false
] |
I hear a lot on Reddit about how diamonds are actually fairly common, but are marketed as being rare and special in order to command higher prices - much higher than the value added by mining, refining, cutting etc (which I imagine is significant in itself - after all, an uncut diamond just looks like a cloudy rock). I hear also that de Beers artificially restricts supply to the same end. How true is this? And how common are diamonds really in terms of crust abundance? Thanks!
|
[
"I think diamonds are rare in any sort of absolute sense. From wiki, 26 (metric) tons of diamonds are mined annually (valued at about $9 billion) and about 100 tons are synthesized yearly with a total of 900 tons of diamonds mined in human existence (and as 1 ton of diamonds can make 5 million 1-carat diamond rings). Granted most probably aren't the right shape or clarity, but by weight you would have enough diamonds mined for 4.5 billion couples to give each other 1-carat diamond rings. If you compare this to say gold where there's been about 165 000 tons mined in human history, you'll see its not that much diamond (even accounting for gold being about 6 times denser than diamond, there's about 30 times more gold that's been extracted). ",
"However, I wasn't able to find #s on production of other gem stones, but I wouldn't be surprised if other cheaper gemstones (e.g., emeralds, sapphires) are much rarer than diamonds. I guess diamonds being the hardest material available, and the marketing of deBeers (convincing the western world your supposed to pay two months of your salary to buy a rock for your fiancée) probably drives up the price significantly. The price is definitely inflated and not strongly linked to the cost of mine ownership or costs of extracting diamonds from the ground, but from a near monopoly existing and making the money they can."
] |
[
"Try not to use lmgtfy in this subreddit. (His link is a google search of \"de Beers Monopoly\")."
] |
[
"Try not to use lmgtfy in this subreddit. (His link is a google search of \"de Beers Monopoly\")."
] |
[
"Do consuming meat with cancer have any effects on human body?"
] |
[
false
] |
Is there any after effects in consuming meat or fish that has a tumor?
|
[
"There is no evidence at all to suggest it would in humans. Moreover, there's little to no theoretical basis to suspect it would either. As far as we're concerned, it's just the same old bit of meat to be broken down and digested.",
"Cancers ",
" be transmissible, however - even when eaten. Tasmanian devils are particularly famous in the zoological and veterinary worlds for succumbing to a contagious cancer known as Devil Facial Tumour Disease (",
"DFTD",
"), which, once caught, can result in a 100% fatality rate. Usually this is transferred from one individual to another when they bite each other, during displays of aggression, though it also thought that some transmission may occur when healthy tasmanian devils scavenge the corpses of infected brethren and/or share another animal corpse also being fed upon by an infected individual. Cancer cells get into the mouth of a healthy devil and before too long they take seed and grow. It's pretty horrible - once this contagious cancer reaches a tasmanian devil population, the population rapidly collapses, and DFTD continues to be the leading cause of their continued decline (hence their endangered status).",
"Contagious cancer are also present in syrian hamsters, and one is sexually transmitted in dogs (see ",
"CTVT",
").",
"Cancer has also, in ",
" cases, been documented being transmitted person-to-person. Typically, these occur either: i) following organ transplant, where neoplastic (cancerous) cells have been accidentally transferred from an undiagnosed donor (who did have cancer, unknown to health professionals) to a healthy recipient - in about 1/3rd recorded cases, the transferred cancer cells evade the immune response in the donor causing them to develop cancer; or ii) when cancerous cells arising during pregnancy cross from mother to child in the womb during development.",
"So given humans ",
" pick up cancers from their environment, could we, like the devils, eat one into our system? Thanfully, no. The main reason why cancer is so 'successful' as a disease is because, unlike most diseases, it's ",
" cells that turn against you. Your immune system has difficulty recognising cancer cells from normal cells as they are both ",
". Your immune system however has no trouble at all distinguishing between your cells and those from another species, and so the risk to you from eating an animal tumour is practically zero.",
" ",
" ",
" ",
" "
] |
[
"Late to the show, but Devil Facial Tumor transmits because of MHC ",
"downregulation",
" that prevents the Tasmanian devil’s immune system from recognizing and destroying the foreign cancer cells. In the lab, we can engineer that immune evasion by directly impacting immune system development. We use that to grow human tumors in mice, so they’re in a cell culture dish.",
"Missing from the OP comment is that ",
" a tumor is a particularly violent process for the cancer cells to undergo. Mechanical disturbance of chewing followed by very low pH exposure and bombardment with digestive enzymes would destroy the cancer cells. There is also no route for the cancer cells to move from the digestive tract into the blood or other tissues. Not even highly metastatic disease would have any luck here, as cancer cells can have difficulty surviving the metastatic process even when they’re theoretically able. ",
"Now, there certainly exists MHC downregulation in human tumors as a mechanism of immune evasion. We also know humans with cancer have measurable quantities of circulating tumor cells before the cancer has even established metastasis. More critical, I would say, is that humans aren’t in the habit of biting each other, or performing any action that could feasibly transfer the tumor cells to each other. Because of that, there’s really no mechanism by which we would practically transfer cancer from one person to another.",
"But yeah, eating an animal tumor is definitely not going to do anything."
] |
[
"So is limited genetic diversity the reason that it's a problem in Tasmanian devils?"
] |
[
"Do satellites orbiting the earth have to compensate for the sun's gravity?"
] |
[
false
] | null |
[
"I'm assuming that you are using the word \"compensate\" to describe controlled maneuvering or station keeping, since satellite orbits are inherently affected by anything in the universe with mass -- some more than others... ",
"Orbits are commonly described and predicted by varying fidelity of propagators, a few of which are detailed ",
"here",
". To maintain an orbit, you're going to use a control scheme based on orbit predictions that are routinely updated by observation.",
"A commonly used propagator, SGP4, accounts for \"secular and periodic variations due to Earth oblateness, ",
", gravitational resonance effects and orbital decay using a simple drag model...\"",
"However, the simplest model, the two body, uses only earth's gravity. ",
"Whether you care about the sun's gravity depends on your required fidelity and available computational power."
] |
[
"Yep. It's also worth mentioning that the deviations caused by the Sun's gravity might be small compared to those caused by atmospheric drag, the moon's gravity, the Earth's oblateness, or even by solar radiation pressure. Which factors are most impactful depends on the specific orbit (altitude, orientation, etc) and on the timeframe of the mission."
] |
[
"Acceleration due to gravity of earth (or any object very near the earth) due to the sun is 0.0006g. That would be a rounding error compared to the acceleration due to gravity of a satellite due to the earth itself."
] |
[
"Is our solar system in a group of other stars of approximately the same age?"
] |
[
false
] |
Since our sun and solar system was formed from a massive cloud of swirling dust and gas, are we aware of other stellar 'cousins' (relatively) in our same part of the Milky Way. Have astronomers been able to identify a batch of stars born about when our Sun was. It seems most of the 'Goldilocks' planets are locates quite far away. Is these any reason there couldn't be an Earth 2.0 in our local region of space?
|
[
"Short answer - we have \"cousins\", but they're not likely to be near us anymore, and not particularly good candidates for Earth-like planets.",
"A molecular cloud might form hundreds of stars all in one spot. As the radiation from the stars dissipates the cloud, you're left with an \"open star cluster\".",
"However, the cloud was turbulent, and that means that the stars that formed inside it all have random velocities. Blowing away the gas also means there's less gravity in the cloud, and the cloud was pretty loosely bound to start with. So an open star cluster isn't really bound together by its own gravity - the random motions \"win\", and it'll start to drift apart over time. It'll downgrade into a \"moving group\", and eventually it'll just mix into the rest of the star in the Milky Way.",
"Our Sun has been around for about 5 billion years, and it takes about 200 million years to orbit the Milky Way. So we've gone around the Milky Way enough times that things are pretty well mixed. Our \"cousin\" stars are likely all spread out around the Milky Way.",
"Some people have tried to spot stars that could have come form the same \"stellar nursery\" as our Sun, based on their age and chemical composition. There's been at least one decent candidate, but it's really hard to tell, because all stars of the same age and mass are pretty similar.",
"However, there's no reason why we should particularly expect Earth-like planets around these stars. Our \"cousin\" stars would have all sorts of random masses, so you'll have a few big blue stars that burned quickly and went supernova billions of years ago, a large number of tiny red dwarfs slowly burning away, and some stars like our Sun in the middle. This is true any time we get star formation, so any other cloud is pretty much just as likely as our own originating molecular cloud to produce stars with Earth-like planets."
] |
[
"Thank you for your excellent and very informative reply."
] |
[
"To answer the 1st question, if there are other stars around the same age as our sun; yes, there are. All stars in the same star class (If I remember correctly, our sun is a G type star) should have similar ages. There are lots of stars in that same class \"near\" us. (i'm talking under 100 light-years, still far, but small in the grand scale of the galaxy)",
"As for the second question, there are more factors that go into what we know makes a \"Goldilocks\" planet than the star type it orbits. You have to take in the consideration of the size and age of the planet, (from what we know, life-sustaining planets need to have a molten core, which is why age matters) how far from the star the planet is, to the gravitational effects other bodies in the system have, which all add up to make these planets extremely rare."
] |
[
"If a gorilla lifted weights, would it improve its physique?"
] |
[
false
] |
Why do humans need to lift weights a lot to look strong, and gorillas can naturally strut around with muscles?
|
[
"It is almost certain that Gorrillas and other similarly muscled primates have large muscles because of their different hormone profiles. I searched for a citation that specifically talked about Gorilla hormones but came up lacking. However, ",
"here is a study along similar lines",
" that discovers a mutation in the myostatin gene (a powerful negative regulator of muscle size) correlates in time with anatomical changes towards human-like features. There are likely many other similar changes.",
"The comments here that suggest that Gorillas have a lot of muscle because of their physical activity are way off the mark. The assumption underlying these responses is that Gorilla's muscles are essentially the same as ours, but they just use them more and thus they grow to such sizes. It's easy to see how this is wrong just by looking at natural bodybuilders. The largest natural bodybuilder does not look anything approaching inhuman. Also consider male gymnasts that work out 6 days a week for many years doing extreme bodyweight movements and they never reach anything approaching a Gorilla's proportions. ",
"Professional bodybuilders on the other hand, can and do reach sizes that look inhuman. The key here is their modified hormone profile that supports massively greater amounts of muscle."
] |
[
"Natural bodybuilders are bodybuilders who aren't using any performance enhancing drugs. Or at least, they're able to pass the best tests we have for detecting PEDs :)"
] |
[
"The comments here that suggest that Gorillas have a lot of muscle because of their physical activity are way off the mark. The assumption underlying these responses is that Gorilla's muscles are essentially the same as ours, but they just use them more and thus they grow to such sizes.",
"Yes - this is absolutely correct. Humans lose muscles to save energy if those muscles are not needed. Gorillas live in hareem based mating systems and many males never mate. Sustaining such a high level of musculature is necessary for male-male competition.",
"An even more interesting example is male oragutans. Male orangs have two adult morphs - a 'flanged' territorial morph where males mateguard females and a non-territorial morph where males sneak around and try to consort on the sly with females. When male orangutans find an area with many females and no male they become ",
"'flanged'",
" and almost double in weight and musculature - no weightlifting necessary. It's one of the closest things in the animal kingdom to a Pokemon evolution...",
"On the other hand, it is likely that if Gorillas lifted weights they would show some muscle gain (and become even bigger)... as I very much doubt habitual-use muscle gain/loss is exclusive to humans. However, as far as I am aware, this has not been tested for gorillas specifically! "
] |
[
"How small of an object can an electron microscope detect?"
] |
[
false
] |
Would it be able to see specific atoms, molecules. Bonus Question: What is the smallest electron microscope that can be built while maintaining its primary function? Is there a way to develop nano cameras that can help us see what happens at the molecular level?
|
[
"The reason that electrons are used is that they have a much smaller wavelength than visible light, so can give a higher resolution. You can detect anything on the order of nano-meters or so, (so yes, we can see molecules) but this does vary depending on the method used, ie; scanning, transmission, etc. "
] |
[
"There are actually various types of electron microscopes. By around 100,000x magnification a standard Scanning Electron Microscope tends to get a bit blurry, so it can't image down to the level of atoms. But the center image ",
"here",
" is probably a Transmission Electron Microscope image, and those dots are individual atoms of Si. (Well, they are the silicon lattice.) ",
"They tend to be moderately large, although ",
"not huge",
". You need to have a very good focus and control of the beam and it's easier to do that with some room. Plus a lot of SEMs pack multiple instruments into one machine, such as different detectors, and squeezing it together would make that much more difficult (expensive) for no particularly good purpose. So it generally isn't done. ",
"But you could probably build one more compactly...I don't know the lower limits. "
] |
[
"Interesting site ",
"http://scaleofuniverse.com/",
"Zoom in enough and it gives you a visual display of how small the optical vs the electron microscopes can see."
] |
[
"Why can you cause a more forceful impact if you \"flick\" your finger as opposed to simply extending it?"
] |
[
false
] |
Is it something to do with muscle tension? The thought entered my head and it's been bothering me all day.
|
[
"This is really a mix of biology and physics...Basically, F = ma (force = mass x acceleration). When you are flicking your finger you build up maximum muscle tension before the finger begins to move giving it maximal acceleration also maximizing the force. When you extend your finger the acceleration is less because the tension is variable across the motion."
] |
[
"A flick has more momentum then a slow extension, if you finger collides with something it will impart some momentum to that something. So if you flick something there is more momentum to impart during a collision than if you have a slow extension. (The physics term for this is impulse)",
"Or are you asking what the kineseological difference is between a flick and a slow extension?"
] |
[
"I was asking more about the kineseological difference, which ",
"/u/KarlOskar12",
" explained. Thanks, though!"
] |
[
"Tar/asphalt being liquid, How come roads don't repair themselves."
] |
[
false
] |
I assume because it takes to long. So, if left long enough would it fix itself and how long would it take.
|
[
"The asphalt binders used in modern flexible (asphalt concrete) pavements are very viscous at the normal temperatures that the pavement was designed for. Also, the asphalt binders themselves make up only a small portion of the volume of the pavement, with the vast majority of the material being aggregate.",
"Pavements fail in many different types of ways. There is fatigue cracking, rutting, potholes, and low-temperature shrinkage cracking just to name a few that affect flexible pavements. Many of the failure modes also occur because of failures in the material underlying the pavement surface. These types of failures would not be fixed by any flow of the asphalt in the pavement.",
"So to answer your question, no pavements do not fix themselves. Asphalt is too viscous in most situations to really fill in defects, doesn't comprise enough of the material, and most of the failures would not be fixed from this flow anyway.",
"Source: Pavement analysis and design class"
] |
[
"Given enough time could it fix it's self, It was that tar drip experiment that got me thinking about it, even if it took 20 years, Would a crack seal?"
] |
[
"Well, as you may remember from that experiment, the flow rate is ",
" slow. As well, ~95% of the material is aggregate although I must admit to insufficient materials knowledge to really know how that would affect flow. Perhaps another with expertise can help here.",
"Still, I think it is fair to say that cracks ",
" self-healing eventually in a lab setting over a sufficiently long timeline. In the real world it seems obvious that the flow rate is too slow and temperature variation damage and other environmental effects far outstrip the rate of settling."
] |
[
"Why was the gold rush specifically located in north western United States and not north eastern?"
] |
[
false
] | null |
[
"The Gold Rush was actually primarily in the southwestern US. The reason is quite simple. The Rocky Mountains have a large number of rich gold deposits. Similar gold deposits are not as common in the eastern US.",
"Also, the term Gold Rush was coined to describe the increased migration of people to both mine the discovered gold as well as supply them with good and services. As the northest was already heavily populated there would be no need for a ",
" to mine the gold and supply the miners."
] |
[
"It has to do with where gold forms; usually at tectonic boudaries. ",
"/u/Gargatua13013",
" mentioned a few in Canada associated with ",
"greenstone belts",
". There was also a gold rush in ",
"North Carolina that started in 1799",
". Romarco Minerals owns a gold property in South Carolina known as the ",
"Haile Gold Mine.",
" There was another famous gold rush in South Dakota known as the ",
"Black Hills gold rush",
". They based the show ",
" on it.",
"I think one of the big reasons the CA gold rush was so popular was because it coincided with the American idea of manifest destiny and that you could make tons of money by going out west to these nondeveloped gold deposits."
] |
[
"Indeed - and interestingly enough, the very same prospectors who outlined the gold play in California also were involved in most of the other plays as well. The Lode gold deposits around Virginia City, Nevada, were found by prospectors on the way back from California.",
"It's always a bit fun to be on site at a staking rush. We had one a few years back in the Temagami area in northern Ontario when a large tract of interesting land was opened up to mining. A pal of mine had his usual bunch of suspects were there waiting for sun-up and the official launch of the race (back then a claim required 4 claim posts around lots of a given size following a certain protocol to be recognized as valid) - typical prospectors all: old, wheezing, hungover and smoking a cigarette to the last one of them. 15 minutes before go-time, a school bus hired by a rival pulled up: ",
" other guy had hired a track and field team in racing snowshoes which were all fit and hale... Guess how that one turned out? Those days are gone now, it's all online staking..."
] |
[
"In the ISS, how do astronomers keep the station clean?"
] |
[
false
] |
Dust (food, human dead cells...) stay in there. Do they "hoover" the environment? Which technologies do they have to do it?
|
[
"They have filters that scrub particles from the air, and they also have (what must be an oddly ironic name considering what is on the other side of the walls), a vacuum. ",
"Astronaut #1 : Hey, where did you put the vacuum?\nAstronaut #2 : I left it outside.",
"EDIT: Found YouTube clip .. ",
"https://youtu.be/-IGfeWACp4k"
] |
[
"First of all, thay are astronauts and cosmonauts. ",
"Cmdr Chris Hadfield and some other crew membwr explianed ir in one of NASA youtube video that they clean themselves periodicly to cause less dead skin, sweat. And hair loss. They eat food through packages or in liquid form. And what ever leftover floats thay catch it with utensils then eat it too. Deinking water is same. ",
"The dust we know doesnt exist inside ISS. Because there is no soil. Except in lab racks. Which is isolated. \nWhatever cargo comes from Earth gets to bo cleaned before launch. As do people. "
] |
[
"I just visited the European Astronaut formation centre in Cologne recently and they mentioned cleaning the ISS as a regular, planned activity. Excess dust is hazardous in such environments and the task of cleaning is taken quite seriously.",
"Don't quote me on it but I remember something like a full day a week goes to cleaning duties."
] |
[
"If the Universe is an outdoor pool, is the CMB the pool walls or simply the edge of a sphere within the pool corresponding to our 13.8 bn years eye sight? Could there be many such spheres in the pool, none of them seeing the actual pool walls?"
] |
[
false
] |
The heart of my question is the cosmic microwave background (CMB). I know what it is (thank you Internet), but what does it represent? Is it the end of what we see, or an actual border (but then: a border of what?). If it's just the end of lightspeed vision, could there be a number of universes happily dangling around in a greater area (the "pool")? Then comes the (I think) unanswered question: what is all this composed of? The Universe sphere we know well. What about the space between the spheres? What about the pool walls?Beyond the pool walls? I apologize for the semantics, these are hard concepts for me to grasp. Thank you!
|
[
"This is actually a very good question with not a simple answer.",
"Here is a graphic",
" of the history of the Universe. Between the beginning and the region marked \"Afterglow Light Pattern\", the universe was opaque to light. Any photons emitted by matter were almost instantly reabsorbed by other matter, so no photons could travel freely. At the point marked \"Afterglow Light Pattern\", the universe cooled to the point where the matter no longer interacted strongly with the photons, so the light was free to escape. Sometimes we call this \"the surface of last scattering\".",
"The Cosmic Microwave Background is the light that escaped at this moment. The CMB, in your pool analogy, isn't the walls of the pool - it's the water itself. The CMB permeates all of space as the remnant of the light that escaped from the surface of last scattering.",
"So, where does the surface of last scattering fit in with your pool analogy? The surface of last scattering is the most distant part of the pool you can see. Looking at great distances also means looking back in time. As well look farther and farther into the Universe, we see older and older galaxies. If we could look all the way back, we see the surface of last scattering, because we can't see anything from before then (when the Universe was opaque)."
] |
[
"Thank you very much for taking the time to write this; I enjoyed reading it. I think the main part I missed was that looking far away also means looking back in time. If we have a (radio?) telescope powerful enough to look as far as possible (well, not \"look far\" but \"receive from afar\"), then we see the first bit of light ever produced. And Every Point Everywhere, all at the same time (more or less), produced its first light ever. So looking at the CMB is not looking lightyears into the distance. It's looking 13.8 billion years (years as in Time, not Distance) into the past.",
"I googled some more while you answered and I have more info than I can digest in a short time. I'll keep digging out of curiosity. My main takeaway to get back to the pool analogy:",
"I am at a point in the pool. It costs me \"years\" to explore around me. After I expend all my 13.8 bn years, I cease to be able to see further in the water. I can now map the sphere I explored around me, and the CMB is the limit I will never see past. This does not give me information on what else is in the pool, or whether there is a pool at all.",
"Thank you very much, tvw."
] |
[
"\"This does not give me information on what else is in the pool, or whether there is a pool at all.\"",
"Exactly! we just can't tell, maybe we will never be able to.",
"There are some studies looking for patterns in the CMB that might indicate a collision with other spheres, but nothing conclusive (or even persuasive imho) so far."
] |
[
"How is original antigenic sin a negative for the host?"
] |
[
false
] |
[deleted]
|
[
"Provided the original epitope remains a part of the mutated virus (even in a lower percentage of the viral protein expressed) then a secondary response will always be faster than the initial infection response. I mean to say that T memory cells will respond more quickly to a previously encountered Ag than an initial immune response can be generated. This will have a stepwise increase in B cell activation, plasma cell activity and IgG production and circulation. This could all be a waste of time if the viral genome has mutated enough that the previous epitope is no longer a significant part of the infection process. If that is the case the albeit fast and aggressive secondary immune response will have limited effect on the total circulating viral population. On the other hand in a reasonably healthy individual multiple Ag's are responded to simultaneously on a regular basis. If there is still original epitope presented by viral cells it could allow the secondary immune response to delay the onset of viral infection long enough for a primary response (initial T and B cell activation, IgM production and later IgG, memory cell specialization,etc.) to a new epitope of the mutated virus to have a synergistic effect, allowing for higher efficacy to the total immune response. "
] |
[
"Great this made the most sense, thanks! "
] |
[
"No, if the original epitope could no longer be recognised then an immune response would have to be raised against whatever epitopes were now present. That is how pathogens that rapidly change their surface proteins avoid the immune system. "
] |
[
"If a light is shined through purple tissue paper, does the light shining through the paper have increased energy because it's purple?"
] |
[
false
] |
This question came up in my AP Chemistry class, and I couldn't give a satisfactory answer
|
[
"No, if you shine white light on an object and purple light is transmitted that means several colors have been absorbed by the object. In the case of purple it would likely be the lower energy visible wavelengths (green through red) or maybe just green through orange with some red left over. Overall there is less energy in the light that is transmitted.",
"However the average energy might be greater as the long wavelengths were removed, skewing things toward higher energies."
] |
[
"What about blue light? Would that increase the energy level?"
] |
[
"Without looking at the actual transmission or absorbance spectrum it is hard to say exactly what the paper does. It could just allow through purple wavelengths (around 450 nm), or purple and blue and red, or red and blue, or anything in between. If it is letting out something that looks purple to us it likely has a higher average energy (but less total energy as explained before).",
"Or do you mean what happens if you shine a blue light through instead of white light?"
] |
[
"Why does a body orbiting another body lose energy, getting ever so slowly closer to each other?"
] |
[
false
] |
[deleted]
|
[
"I think you're greatly overcomplicating things by trying to think of everything in terms of particle exchange, which really isn't that useful a way to think about physics unless you're trying to calculate how particles scatter off each other.",
"Consider the electric field of a charged object, both close to and far away from that object. If the object accelerates, the electric field around it has to change to account for this, but the information that the electric field has changed can only propagate at the speed of light, so there's this disturbance in the electric field moving outward from the charged object at light speed.",
"Now consider the same scenario but with a gravitational field. The geometry of space around the object depends on its energy density, and if its energy density changes then the geometry changes, but the information that it's changed can only propagate outward at the speed of light. So when two objects are constantly accelerating around each other, they are constantly emitting gravitational radiation, to update the rest of the universe that the geometry has changed. Through this mechanism orbits slowly decay.",
"For an electron moving in a circle in a magnetic field, it loses energy due to synchrotron radiation and inspirals."
] |
[
"If your assertion is that gravitational radiation has no energy, that's simply incorrect."
] |
[
"If your assertion is that gravitational radiation has no energy, that's simply incorrect."
] |
[
"In theory, is the number of elements infinite?"
] |
[
false
] |
I know that there are 98 naturally occurring elements, but more have been artificially produced. I do realize that most of the synthetic elements are very unstable and decay almost instantaneously, but is there an upper limit on the largest atom physically possible?
|
[
"Some versions of the nuclear shell model, which describes the various nuances and patterns of stability and nuclear structure do predict 'islands of stability' away from the main stability line. In some instances these are in the super heavy region, though there is inevitably going to be a practical limit. In theory, yes, you can cram together an absurd amount of neutrons and protons and call it a nucleus, but even our current 'heaviest element' has a half-life of under 1ms.",
"The liquid drop model in particular is useful for describing heavy nuclei, amongst other things; the end result of any model however, is always going to show that the electrostatic force is prevalent. It's just a matter of how long the mass of protons and neutrons remains in tact before you consider it too unstable to be mentioned."
] |
[
"Depends by what you mean exactly by \"physically possible\". Does it mean \"has a half life longer than 5 minutes\"? If not, then what?",
"Anyway, guessing at what you actually mean, then no there is not an upper limit except in practice. As the electrons in the various quantised energy shells get further away from the nucleus on average, the forces that hold it in place get weaker. This is why there is a continuum of half-lives observed, as the likelihood of their escaping these forces increases further. Let me know if you want further clarification."
] |
[
"There is a limitation caused by the diminishing effect of",
" the residual strong force/nuclear force",
" as nuclei gets bigger. Any atom larger than lead is unstable as far as we know.",
"At distances larger than 0.7 fm the force becomes attractive between spin-aligned nucleons, becoming maximal at a center–center distance of about 0.9 fm. Beyond this distance the force drops essentially exponentially, until beyond about 2.0 fm separation, the force drops to negligibly small values.",
"At short distances (less than 1.7 fm or so), the nuclear force is stronger than the Coulomb force between protons; it thus overcomes the repulsion of protons inside the nucleus. However, the Coulomb force between protons has a much larger range due to its decay as the inverse square of charge separation, and Coulomb repulsion thus becomes the only significant force between protons when their separation exceeds about 2 to 2.5 fm."
] |
[
"What is the minimum mass required for a celestial object to become spherical in shape?"
] |
[
false
] |
Moons, planets, and stars are usually spheres and many asteroids tend to be big rocks. How massive does an object have to be before nature makes it a sphere? And why do large masses become spherical?
|
[
"AFAIK the smallest ",
" moon in the solar system is Mimas (about 3.8 x 10",
" kg), although it slightly tidally distorted ovoid by Saturn's gravity.",
"Planets are round because their gravitational field acts as though it originates from the center of the body and pulls everything toward it. With its large body and internal heating from radioactive elements, a planet behaves like a fluid, and over long periods of time succumbs to the gravitational pull from its center of gravity. The only way to get all the mass as close to planet's center of gravity as possible is to form a sphere. The technical name for this process is \"isostatic adjustment.\" ",
"source"
] |
[
"Yes presumably, but putting number on it is difficult (read: I don't know how to do it). The amount needed will depend upon material properties (icy bodies are less strong than rocky), planetary temperatures (radioactive heating promotes flow), etc."
] |
[
"I guess that ",
"water droplets",
" count as objects too. In this case I guess it's mostly surface tension holding the droplet together, not gravity."
] |
[
"Before there were beds, where did bedbugs live?"
] |
[
false
] |
Did they come from outside? Also, why have they made a "comeback" after being pretty rare for so long? I got curious after living in LA and encountering them in about every cheap hotel and friends house I stayed at...
|
[
"Bedbugs have ",
" to feed on human blood, while we sleep. ",
"Bedbugs were originally bat bugs. Their ancestors lived in caves, on bats (where most of their kin still live), and when our ancestors moved into caves, they jumped down onto us. A few found us where we slept. Those that did prospered on our blood as we prospered.",
"When they moved onto us, many things would have had to change for these bat/cavemen bugs. The platelets in our blood, for example, are wider than those of bats, and so the mouthparts of the bedbugs had to widen so that they wouldn’t clog up with blood. Their mouthparts changed in length, too, because of the thickness of our skin, a thickness through which their mandibles must meander to find blood vessels. Their activity patterns changed, too. Bat bugs feed during the day, when the bats are sleeping. Bedbugs, well, they had to feed at night, when we were sleeping.\nBedbugs changed so much in moving onto us, in fact, that now they are stuck. They can’t easily go back — and why would they want to? They ride us wherever we might lead them, which, it turns out, is all around the world.",
"Source"
] |
[
"There used to be a class of pesticides in common use in the US that effectively controlled bed bugs (and lice and scabies) for the majority of the 20th century. Those chemicals were banned due to human and environmental side effects, and so now those bugs have made a major comeback. ",
"You've got some facts mixed up. The pesticides that worked for most of the 20th century are all useless now, not because of the EPA, but rather because bedbugs evolved a resistance to them. Evolution is to blame for the comeback. There is an EPA-banned pesticide (Propoxur) but it was only available since 1959 and isn't the reason why bedbugs were previously under control."
] |
[
"On one hand, that's super creepy...on the other it's also super interesting.",
"Slightly worsened by the fact that they are ",
" the worst thing to feed on us or live on us...but hey, I'm all for showing some bugs the world. "
] |
[
"Why didn't Tevatron see conclusive evidence of the Higgs?"
] |
[
false
] |
I'm writing a report on the Higgs evidence. I have seen data that suggests Tevatron ruled out a Higgs with mass roughly 157 to 180 GeV. If this is true, why couldn't Tevatron see significant evidence of a Higgs with mass ~126 GeV? Surely this lower mass would be easier to create and therefore easier to rule out? A source would be great if possible.
|
[
"The answer to your question is contained in ",
"this",
" plot. Between 157 and 180 GeV the higgs is massive enough to begin decaying to WW and ZZ, which are a much easier to identify signature than when the higgs decays to bb."
] |
[
"To use a familiar (if technically incorrect) term, the problem was its signal-to-noise ratio. The Tevatron has a much lower peak luminosity compared to the LHC; ",
"this abstract",
" states that \"an excess of [background] events\" prevented them from establishing the 126 GeV Higgs to a 5-sigma certainty.",
"The most probable decay for the 126 GeV Higgs is that of a bottom-antibottom quark pair.",
"source",
" Unfortunately, there are many other decays that can produce a bottom-antibottom pair, so it is necessary to gather a massive amount of data to eliminate errors. To gather data on such a large number of collisions requires a very high beam luminosity, and a good probability of producing Higgs decays. My understanding is that this probability increases at higher energies because of the high mass of the Higgs - correct me if I'm wrong.",
"Although the Tevatron was able to produce Higgs decays, it was not able to produce them in numbers sufficient to overwhelm background events and lower energy decays - not to a 5-sigma certainty, at least.",
"source"
] |
[
"As far as I know, the lower limit comes not from the Tevatron but from the e+e- collisions at LEP2. ",
"Also, you are correct that the Higgs production cross section (essentially the probability of producing Higgs bosons) depends on the center of mass energy of the collision (see for example table 1 in this paper: ",
"http://arxiv.org/pdf/1008.3162v2.pdf",
"), so the LHC produces way more Higgs bosons than the Tevatron."
] |
[
"Apart from Pluto being small what made them decide to change the status of the planet?"
] |
[
false
] | null |
[
"The same thing that happened last time planets got demoted.",
"Back in the early 19th century they discovered 4 of some of the largest asteroids, and they called them \"planets\". This situation persisted for nearly 4 decades, but then they started discovering more asteroids. First a few, then after a couple years they were detecting dozens per year. It became obvious that the first 4 asteroids weren't just quirky members of the family of planets, they were fully representative members of a much different population of bodies, and their designation was adjusted accordingly (though asteroids are still called \"minor planets\" to this day in astronomy).",
"In the case of Pluto the delay was much longer, but the same thing happened. Starting around the 1990s we started discovering that there were kuiper belt and trans-Neptunian objects (KBOs and TNOs) which were much larger than we had anticipated they would be, some of them even as large or larger than Pluto. It then became obvious that Pluto wasn't truly a representative member of the rocky or gaseous planets but instead it along with Charon and Triton were members of a large family of TNOs. Icy bodies in the outer Solar System that were up to 1000 km or more in radius. Eris, for example, is practically the same size as Pluto and has a somewhat similar orbit (highly elliptical and inclined).",
"As to why we don't simply consider every notable body to be on an equal level of importance, that's a somewhat complicated question. Partly it's just because it's hard to memorize large numbers of things, and there are already as many TNOs as there are planets."
] |
[
"This situation persisted for nearly 4 decades",
"It was a little over 5 decades. Ceres was discovered 1801, but the term \"minor planet\" didn't come into fashion until 1854.",
"Charon and Triton were members of a large family of TNOs.",
"To be clear, Triton probably was a member once, but has since been captured by Neptune and is now considered just a moon, not a TNO."
] |
[
"Answer compiled from Wikipedia articles on ",
"Pluto",
", ",
"IAU definition of ",
" and the ",
"Scattered Disc",
":",
"After 1992, Pluto's status as a planet was questioned following the discovery of several objects of similar size in the Kuiper belt. In 2005, Eris, a dwarf planet in the scattered disc (a distant circumstellar disc on the edge of the Solar System that is sparsely populated by icy small solar system bodies) which is 27% more massive than Pluto, was discovered. This led the International Astronomical Union (IAU) to define the term \"planet\" formally in 2006, during their 26th General Assembly as a celestial body which:",
"is in orbit around the Sun,",
"has sufficient mass to assume hydrostatic equilibrium (a nearly round shape), and",
"has \"cleared the neighborhood\" around its orbit (this is the criterion that Pluto does not meet).",
"This definition excludes Pluto and reclassifies it as a dwarf planet."
] |
[
"Are the effects of gravity instantaneous across the universe?"
] |
[
false
] |
Please correct me on any of the following if I am wrong: Let's say I convert some energy in to mass. Before it was mass, it did not have any mass, so it did not have gravity, nor was it affected by gravity. After it became mass, it does have gravity. Are the effects of the "new" gravity that this mass created prevalent throughout the whole universe, or does gravity travel at a certain speed? If it is instantaneous, would it be possible, when our technology is advanced enough, to communicate via gravity? If we had sensitive enough instruments that could cancel out the gravitational noise, would it be possible?
|
[
"No, changes in gravitational fields propagate outward at the speed of light. This is most directly verified by ",
"measuring changes in Earth's gravitational field due to the sun versus the sun's position in the sky",
". It can also be inferred astronomically, for example due to decays in pulsar orbits from gravitational radiation. However, you're incorrect in your assumption that massless forms of energy do not gravitate. They do."
] |
[
"That's what light is: a propagation of electric and magnetic fields."
] |
[
"Because that's how fast information can propagate in this universe."
] |
[
"How would a space elevator tether actually be put in place?"
] |
[
false
] |
Most people know the basic idea of a . I've never actually read anything on how they'd get the cable in place though. "Dropping" it from the space end seems like it would be overly expensive, you'd have to launch all of the cable up there first. Also once it starts skimming the atmosphere that would cause all sorts of problems. Starting from the ground up just seems impossible. Attaching the whole tether to a rocket and launching it seems like the best way, but that also sounds horrifying.
|
[
"I think this is probably one of the (many) problems that currently makes space elevators impractical. My thought is to start by launching a rocket into geosync orbit carrying a spool of small cable and then using a projectile of some sort to launch the end of the cable back to Earth. Once it's back on Earth, you could use climbers to add additional strands to the cable, gradually building up the cable's cross section and using the spacecraft carrying the spool to adjust its altitude to keep the center of mass at geosync orbit. But even a small cable would be extremely heavy to initially lift because you need tens of thousands of miles worth of cable to get started, and the thinner your initial cable is, the longer it will take to build it up to a useful size."
] |
[
"Several issues exist with the concept, one being that the cable has to be incredibly strong and there has to be a lot of it. I remember seeing a documentary which calculated the strength requirements which could be met by some advanced materials (not in the quantities required yet currently). ",
"Cheap launch concepts are a hot topic in research with some fascinating ideas being proposed recently, one I found really interesting is the Lofstrom loop - a really good video about it ",
"https://www.youtube.com/watch?v=J1MAg0UAAHg",
". ",
"The reality is that 50 years ago it cost an insane amount to launch to orbit, now it's much cheaper, and it's going to get a lot cheaper as well. I think if we had the material to provide the required strength, getting a space elevator into position would be a much lesser challenge in comparison. "
] |
[
"Strong enough and light enough. That would have to be one hell of a rocket to haul it in to space, not to mention the aerodynamics of the tether. ",
"I know we don't have the proper material yet. People are saying carbon nanotubes are close but not quite good enough. I was just curious about the construction bit"
] |
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