question stringlengths 3 301 | answer stringlengths 9 26.1k | context list |
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how does a random function work? | A random number generator like the one typically used by a computer to generate random numbers isn't actually random. It is what is known as a *pseudo-random number generator*. It generates numbers according to a certain algorithm that first is initialized with a value called *seed*. For different seed values, different pseudo-random sequences would be produced. Your computer will usually use something like the current time as seed to initialize the pseudo-random number generator. And then you get these pseudo-random numbers that seem to be random, even if they aren't. For most purposes, this is good enough.
A certain category of pseudo-random number generators are known as *cryptographically secure pseudo-random number generators*. These are algorithms that conform to certain requirements that are hard to ELI5, but the basic and most important idea is that one can't predict what the next number would be even if you know the entire sequence up until now.
For certain applications where truly random numbers are needed, special hardware devices are used that can generate random numbers by using physical processes that are unpredictable (random) by the laws of physics. | [
"A random function is a type of random element in which a single outcome is selected from some family of functions, where the family consists some class of all maps from the domain to the codomain. For example, the class may be restricted to all continuous functions or to all step functions. The values determined b... |
why can some brands completely rip off other brands designs on certain products? | Per a quick google search, they are often lawsuits for this. However, I’d hazard a guess that court costs and lawyer fees are factored in before moving forward. Generic copy at Walmart maybe only profits 40k$, but the lawsuit would cost 200k for both sides. It’s now a loss to sue and not worth moving forward. Adidas sued Walmart for infringing on their 3 stripe design a while back and won. Those shoes now have 4 stripes.
Edit:changed a letter | [
"Designer branding is sometimes associated with a higher quality of manufacture and a higher price. The ownership and display of such products of quality is frequently marketed to suggest that the wearer will automatically embody a personal characteristic of quality by association. Designers have identified this an... |
does convolution of signals have an intuitive explanation like the water-flow example for voltage and current? | Have you heard of convolution reverb?
Basically, you take an impulse response from, say, a cathedral, and then you can convolve it with any sound signal to make it sound as if it were in the cathedral.
So i guess a convolution is kind of like an echo. A bit like sonar - when there is something x-metres away, you'll get a corresponding spike on the impulse-response when the echo comes back. | [
"In the \"water-flow analogy\", sometimes used to explain electric circuits by comparing them with water-filled pipes, voltage (difference in electric potential) is likened to difference in water pressure. Current is proportional to the diameter of the pipe or the amount of water flowing at that pressure. A resisto... |
the definition of “literary theory” | I suppose there isnt one definition but a literary theory woukd be a way in which yoi can understand/interpret literature.
For example you could read a text in a feminist or post colonial way and theyre both literary theories.
Or you could theorise on what literature itself is, for example literary theorist Roland Barthes discusses the role of the author in literature. | [
"As a consequence, the word \"theory\" has become an umbrella term for a variety of scholarly approaches to reading texts. Many of these approaches are informed by various strands of Continental philosophy and of sociology.\n",
"A theory is a contemplative and rational type of abstract or generalizing thinking ab... |
Mistakes Germany made on Russia | Wall of text- I'm sorry but it's a really complex answer that I've already really pruned down.
I'm going to direct your attention to a frequently underappreciated aspect of the historiography- differing conceptualisation of warfare at an operational level. Under appreciation for this level of history stems from a Western lack of appreciation of it's intricacies, and an often excessive reliance upon German Generals and sources who sought to rationalise their defeat in the terms of tactics and strategy- simply put, they argued that German generals and armies were constantly tactically superior to their enemies, and Hitler is responsible for all strategic mistakes. This rather conveniently ensures former German generals were freed from having to admit they made mistakes, and allowed them to keep their lucrative lecturing tours. that the German army deployed a somewhat complex operational method at this time was conveniently forgotten.
'the Wehrmacht is generally portrayed as immensely superior in every aspect...its failure are ascribed to adverse climatic conditions, the sheer size of the USSR, overwhelming soviet numbers, hitler's mistakes...everything...except superior Red leadership and combat performance.(1)'
Following the end of the first world war and the Russian civil war, Stavka (the Russian high command) recognised that the traditional division of warfare between tactics and strategy was outdated, and that a gap existed between these. Tactics had come to be associated with divisional combat downwards, while strategy was a question of Army Groups and High Command. Operational level technique exists in this gap, and the relationship between all of these levels is implicitly interlinked as it's first proponent, Aleksandr Svechin pointed out 'tactics make the steps from which operational art leaps; strategy points out the path.' The operational level of warfare deals with this path, and is best described as being
'Concerned with the disruption of the enemy's overall cohesion on a large scale, preventing him from accomplishing his aims and breaking up his organisation and control of higher formations. destruction of large enemy groupings is achieved as a result of the disruption of his plans, timetabled and ability to organise over a wide area and in great depth (i.e. 300-500KM).(2)'
These concepts were outlined initially outlined in the Russian manual PU-36 (field manual-'36) and detailed two key concepts, deep battle, and Maskirovka. The great purge (or as the Russians prefer to call it 'the events of 1936-8') saw the rejection of these ideas for a more traditional approach, but they were rapidly re-introduced with PU-42. Maskirovka is a term describing camouflage, concealment, deception, signals counter-intelligence and surveillance methods and has no accurate English translation, just note that it was the means by which the Russians aimed to achieve surprise, and that Russian doctrine views the surprise as a 10X force multiplier- one man with it, is worth 10 without.
Deep battle was a term utilised to describe what we would call blitzkrieg, but carried out on a far larger scale. A Russian Army group (called a 'front') would be devided into two unequal halves. the first, representing 1/3 was called a pinning group, and was responsible for holding the frontline when it was static, carrying out spoiling attacks etc. this allowed for the major concentration of resources into 'strike groups,' representing 2/3 of the forces deployed. these were divided into shock armies and mobile groups
Shock armies were essentially break-in formations, heavily provided with infantry support tanks, engineers and artillery. they would punch a hole in the initial defences through overwhelming concentrations of force and firepower.
these openings would then be exploited by mobile groups- composed of tank armies equipped with anti-tank guns, mechanised infantry, self propelled guns and medium tanks such as the t-34. these would develop the break-in into a break out and exploit deeply.
It is important to understand the scale of these operations, and the interlinking of them. A series of shock armies would engineered several break-ins of about 12-15 km width, with about 16-20km between each of them. These break-ins would have a depth of about 10-15 km, which would then be rapidly exploited by the mobile groups, sacrificing some combat power to complete the break out. These formations were then expected to drive deeply to a depth of 100-200km. They would screen surrounded German units, who would then be reduced by hard-marching shock armies as the mobile groups conducted a mobile defence against German counter-attacks.
The most important aspect to remember is Maskirovka, all of these offensives were to be mounted in the utmost secrecy. Briefing were carried out in the third period (more on this later) Orally only, and just 5-10 days or so before the attack to front commanders, who in turn briefed the subordinates. The fact that entire tank armies (seriously, the Russians had formations called tank armies) were able to entrain, move 100s of miles, detrain and then launch these huge assault with only days of preparation and acting on verbal orders hints at an often underestimated genius in the west for Russian staffwork, professionalism and the effectiveness of maskirovka.
For the Russians, the great patriotic war is divided into three periods, based upon how effectively these principles were deployed-
The first from the 22 June 1941- 18th November 1942 saw an endless period of defeats as the germans advanced rapidly. They destroyed 28 divisions, and reduced an additional 70 to 50% strength. These defeats eventually led to the re-introduction of the operational method outlined above in PU-42. severe mistakes were continuously made. a lack of maskirovka meant attacks failed to achieve surprise, lack of concentration, poor command and a lack of appreciation of the operational level of warfare allowed opportunities to slip away.
The second period was a slow and painful learning experience, lasting from 19th November 1942 to the end of '43. every aspect of their warfighting capability was overhauled- command, control communications improved, better combat support and service support. Better weapons and more of them, overhauled formation organisation etc. they still made mistakes, but they slowly learnt from them and showed an increasing capacity for waging war. encirclements, where they occurred, took a considerable amount of time to reduce, but the effectiveness of such methods was obvious, and formations fought deeper, and reduced the encirclements far quicker.
The third period from 1944-45 is simply awesome. They were not just conducting these massive offensives one at a time anymore, these huge operations were now interlinked, as one closed down, another was just in the process of opening up. The perfect example of this is Operation Bagration. another would be the vistula-oder operation, 'liberating' most of Poland in 17 days. Additionally they constantly achieved complete surprise and destroyed tactically superior German armies at every turn.
So yeah, it didn't really matter that the Germans were tactically superior when the Russians had perfected their operational method for the operational level of war, were able to mass huge numbers of troops, achieving complete surprise and overwhelming the enemy through systematic manoeuvre warfare, crushing every single enemy formation they met with superior material, generalship and staffwork.
References
Hastings, M., Armageddon, (London, Pan Books,2004)
Glatz, D.M., Soviet Operational Art (London, Frank Cass, 1991)
Harrison, R.W. The Russian Way of War (Laurence, University of Kansas press, 2001)
(1) Dick, C.J. 'The operational employment of soviet armour in the great patriotic war' In Harris J.P. and Toase F.N. eds Armoured Warfare (London, Batsford Ltd.,1990)
(2) Dick, C.J., 'Soviet Operation Art, Part 1' in International defence review, July 1988 | [
"As Russia's war losses increased, so did anti-German hysteria. They were held responsible for the disastrous course of the war and were accused of being spies and saboteurs betraying Russia. Anti-German measures reached a nadir with the government's so-called Liquidation Laws, of February 1915, authorizing it to e... |
Paper vs Electronics | To add to that, how much difference is there between an e-ink e-reader and an actual book? | [
"Electronic paper, also called e-paper, is a display technology designed to mimic the appearance of ordinary ink on paper. Electronic paper reflects light like ordinary paper and is capable of holding text and images indefinitely without drawing electricity, while allowing the image to be changed later. Application... |
How come Denmark ruled the Kalmar Union during 14-16 centuries, while Sweden was humongous in territory and Norway was considerably larger as well? | Well, first let's sort out what the Kalmar Union _was_ (and wasn't).
It was a personal union, where three different countries had the same monarch. All three Scandinavian countries had elective monarchies at that time, albeit with a preference for electing people within he same dynasties. So the nobles (or _stormän_, or jarls if you want to go even farther back) could elect and also dethrone kings. That alone tells you that the monarch was not that strong. The countries did not have strong central government. Besides power being held by local jarls, the church and its bishops had huge power and wealth. The countries had also been hit hard by the Great Plague int he 14th century, and the Hanseatic League of north Germany was the dominant trading power in the Baltic. Ok, so the king is fairly weak. Being in another country there's not even a theoretical chance of exercising direct control anyway.
So in the late 15th century Danish Margarethe comes along, and in very simplified terms, basically inherits Denmark, marries into Norway and gets herself elected as queen of Sweden on the condition of defeating their German king, which she does. Not bad! Not having any heirs of her own, she adopts her sister's daughter's son ~~Bogislav~~ now Erik of Pomerania, has him coronated in Kalmar and then an act of union is signed or something. We don't really know! The document we have doesn't have the correct seals on it, is on paper rather than the expected parchment, has amendments and crossed-out stufff and doesn't exist in six copies like it says it should, so interpretations have varied. It may be just a draft document, or it might be an attested copy of a summary of what was decided, which is why the seals aren't right - they're for the witnesses and not the original signers.. Anyway, the content makes it clear that the three countries remain three countries, with their own laws. But they are also bound to to assist each other in war.
So in short the monarch gets to collect taxes, appoint foged/fogde/fogds as local administrators and tax collectors, appoint clergy (the Vatican at that particular point is too weak to stop it), handle foreign policy and wage war. The latter bit is an important to the motive of taking up competition with the Hanseatic League. (at least according to historian Erik Lönnroth)
Anyway, Margarethe still continues as de facto ruler but with power being gradually transferred to Erik until her death (1412). Already 1410 Erik starts war for territory against Holstein (at the base of the Jutland peninsula) and then against he Hanseatic League, which, with breaks, would continue until the 1430s. In 1429 he also starts trying to claim the Sound Toll on all shipping in and out of the Baltic, which would ultimately become a Danish cash-cow all the way until the 19th century.
This isn't that much in the interest of Sweden and Norway though. Norway's selling fish to the Hansa, who have offices in Bergen. (Everyone's still Catholic, so fish on Fridays is a big deal, not to mention lent) and Sweden's shipping iron from Bergslagen down to Lübeck through Stockholm (nominally a Hanseatic city). They have much less to gain from picking a fight with the Hanseatics. Add to that, the Swedes are angry that Erik has been appointing Germans and Danes as _fogdar_ in the crown castles and estates, despite promises that only Swedish nobles would get those. Taxes are high as well.
Supposedly the Danish _fogde_ of Västerås, Jens Erikssøn, was super-cruel and forced pregnant women to work so hard they had miscarriages and other horrible things, according to the Swedsh chronicle of Engelbrekt, which is a highly biased source nobody really takes too seriously. But in any case, the figure Engelbrekt comes out of Bergslagen in 1434 and demands Erikssøn be replaced, but gets nothing. So he raises an army and takes matters into his own hands, forces Erikssøn out of his castle and executes him after a trial. The rebellion continues, with Engelbrekt and his men successfully laying siege to castle after castle until he's taken 14 of them, 2 in the then-Danish province of Halland before a truce is declared. At which point only the 7 strongest castles are still left in Sweden (plus the ones in Finland).
Anyway, in the peace negotiations they agree on only letting the king put foreigners in three castles, that he was required to listen to the advice of the national council (but not to follow it), and that there would be future discussions about taxes. Notably, Engelbrekt did not demand or appear to want to dissolve the union, but the secessionist tendencies nevertheless increased in Sweden. Engelbrekt passed away in 1436, and the Swedish nobles, considering Erik to have broken the treaty in a number of ways (including by intending to designate a relative as heir without any election) declared Erik deposed not long after that. The remainder of the history is a pretty messy back-and-forth of rules, but the short is that the Swedes pretty much do what they want while the Danish kings try to reclaim power, it breaks out into open hostilities under Sten Sture the Elder and then the Younger (no relation! the latter just took the former's name as a political statemnet). Initially these are however fought mostly between pro-and-anti-union Swedes rather than being the Sweden-vs-Denmark affair it became at the end.
Sten Sture the Younger is killed by the invading Danish king Kristian II, who takes Stockholm, has himself coronated as king of Sweden and then celebrates with the Stockholm Bloodbath, where about 100 anti-unionist Swedish nobles are executed. This leads to Gustav Vasa taking up the fight (bankrolled by the Hansa) and defeating the Danes, becoming king (1523) that's the formal end of the union. Vasa also converts the country to Lutheranism, confiscates church property and gathers power, and it's now you start to have a really strong central state both in Sweden and Denmark. Not long after Frederik I of Denmark decides that Danish nobles should have privileges in Norway as well, and it's now the union really starts transforming into the Kingdom of Denmark-Norway-where-Denmark-calls-all-the-shots. (However even as Sweden had started to pull away, Denmark-Norway signed a treaty in 1450 stating they'd have the same king 'in perpetuity', so one might also consider it to have started there)
Ho-kay, so that's the short version of the history of the Kalmar Union. As you can hopefully tell from the above, you can't really describe it as Denmark ruling the union, but rather a "king in Denmark" ruling the union. One with certain tendencies to put Denmark's interests first.
How could Sweden and Norway be dominated by Denmark despite being bigger? Well, first - territory doesn't matter, especially not when it's mostly empty, as was the case. Denmark was population-wise larger than Norway, and about the same as Sweden in 1400. More importantly though, Denmark _couldn't_ actually rule Sweden once Swedish opinion was firmly anti-Danish, as during the end of the Union. But up to the Stockholm Bloodbath there were a significant amount of pro-union Swedes, especially in the clergy. Roughly it started becoming more of a Sweden-vs-Denmark thing around 1500. Of course nationalist historiography in Sweden would long paint it all from the start as a grand war of liberation from a foreign oppressor rather than strife between pro- and anti-unionist Swedish factions.
The probable reason why the coronation and act of union (if there was one) was in Kalmar is because it was a conveniently-located coastal town, near the Swedish-Danish border (Blekinge province being Danish at the time), roughly equidistant from Copenhagen and Stockholm, with a royal palace and a cathedral. So a good spot for everyone except the Norwegians.
Finally as for why Copenhagen would be the seat of power, there's the simple fact Margarete was Danish. Sweden was the country she had least personal connections with. Copenhagen was closer to the continent, which she had plenty of aristocratic connections with. It was closer to other useful things like the Universty of Rostock, where Danes usually studied at that time. (Copenhagen and Uppsala Universities were founded in the 1470s) It was also much closer to the rival Hanseatic league, without them having as much influence as they did in Stockholm (which still has a medieval church just for Germans in the old town, to this day).
Sources: Any good Scandinavian general-history book will tell you all or most of the above, but I don't really know what to recommend in English. I like Alf Henriksson's book in Swedish though. There are some nice Danish books about Margarete in particular too (even fictionalized novels about her life).
I'm also taking the 'conventional' view and fallacy of viewing the union with the hindsight of its dissolution, in giving the period 1440-1520 short thrift. If you want to start getting more angles on the union history Gustafsson's ['A state that failed?'](_URL_0_) is a great place to start. | [
"The Kalmar Union (Danish/Norwegian/Swedish: \"Kalmarunionen\") was a series of personal unions (1397–1520) that united the three kingdoms of Denmark, Norway and Sweden under a single monarch. The countries had given up their sovereignty but not their independence, and diverging interests (especially Swedish dissat... |
how do we know what prehistoric life was like? | We have a good understanding of biomechanics, how the shape of bones, their growth and wear patterns, how ligaments were attached, and a lot of the details that tell us how the moved, how they ate and hunted. Teeth can tell you a lot about what sort of food an animal ate. The design of the head tells you how big their eyes, noses, and mouths were. Some bones have teeth marks, indicating that they were bitten by other dinosaurs.
Here's a review article [_URL_0_](_URL_0_) on Dinosaur Biomechanics
& #x200B; | [
"In addition, fossil remains of some hitherto undescribed prehistoric species have been found. The oldest comes from the Late Miocene (Tortonian, some 7 to 12 million years ago) of the Bahía Inglesa Formation in Chile.\n",
"The idea of prehistoric animals surviving into the present day was not new, but had alread... |
What was the fire rate of the matchlock musket, and how did it compare to wheel locks and flintlocks? | 16th century sources do indeed tend to be pretty unclear when it comes to firearm's rate of fire. Humfrey Barwick was a strong proponent of firearms at the end of the century and as such is probably represents the upper end of what might be expected in terms of fire rate. While serving as a mercenary for the French army he described a war meeting in which he overheard a nobleman claim that an arquebus could only be fired 10 times per hour. Some people apparently did think the fire rate was this low, but Barwick thought the man was daft and afterwards approached him offering to personally demonstrate shooting 40 times in one hour with a single piece. One shot every 1 minute and 30 seconds doesn't seem like much, but this seems to have only been the rate for long term fire over the course of an hour, which would have required occasionally cleaning the weapon, adjusting the match, and measuring the powder for each shot independently since a soldier at the time typically didn't carry 40 whole wooden cartridges at a time.
For short term rate of fire, later on in his discourse he described the maximum number of times that a soldier with a *musket* could shoot at an advancing army, which involved shooting once in the time it took the enemy to march (not running) 80 yards (presumably 60-90 seconds, he recommended making up the difference by shooting multiple bullets at a time as the enemy got closer). The fact that he says this is for a musket is significant because the 16th century musket was a very different beast compared to the muskets of the 17th and 18th centuries. It was extremely heavy with a longer barrel and a larger bore than later weapons and had to be supported by a forked rest while firing. Most troops at the time would have been armed with an arquebus or caliver, firearms which which were much lighter and had a much shorter barrel. Humfrey Barwick and Sir Roger Williams both wrote that the arquebus/caliver could fire twice as quickly as the clumsy musket could (though they prefered the latter because of its far greater force).
That would make the ideal rate of fire for the late 16th century arquebus/caliver: 30-45 seconds per shot max, 40 shots per hour sustained
And for the heavy musket: 60-90 seconds per shot max, 20 shots per hour sustained.
As far as how rate of fire compares to the wheel lock or flintlock. A matchlock is generally more complicated to load since it requires constantly tending the match to keep it burning as well as adjusting the match length as it burns down. In addition manuals on loading reccomends removing the match after every shot and holding it in the opposite hand so the soldier doesn't accidentally blow himself up while handling powder (loading could still potentially be done much faster if shortcuts are taken as demonstrated by [this reenactor with an arquebus](_URL_0_)). A wheel lock firearm did away all this but added the need to reset the spring with a specialized tool after every shot. As far as flintlocks go, most manuals and sources tend to give a maximum fire rate of around 3, maybe four shots per minute. As far as I know, even with greatly simplified drills reenactors tend to have a lot of difficulty reloading a full sized Napoleonic musket in under 20 seconds.
So to sum up, 16th century muskets did take a long time to reload, largely due to its size. A flintlock musket was generally quicker and easier to reload than a 16th century matchlock caliver (which was similar in length and weight) though probably not as much as you're saying. And there was more to reload speed than the type of lock. | [
"At the end of the 17th century, a flaw within the design of matchlock muskets became more apparent. Since the matchlock musket used a slow burning piece of twine known as a slow match, the twine sometimes would accidentally set fire to the gunpowder reservoir in the musket prematurely setting off all of the gunpow... |
what's a good source of hydration during a hurricane if water supply in stores is sold out? | The point is to stock up beforehand. Water comes out of your faucet for hundreds of times cheaper than in the store. | [
"To prevent casual use or misuse, the hydrant requires special tools to be opened, usually a large wrench with a pentagonal socket. Vandals sometimes cause monetary loss by wasting water when they open hydrants. Such vandalism can also reduce municipal water pressure and impair firefighters' efforts to extinguish f... |
why does canceling a credit card with a zero balance hurt my credit score | Assuming you have other credit and you have outstanding balances. Canceling increases your credit utilization %..
Lets say you have two cards and one has a balance
A:$50/$100
B: $0/$100
You are using 25% of your available credit.
You cancel card B
Your are now using 50% of your available credit.
Credit scores are a bit of a scam, they measure more your ability to keep paying than anything else... in fact most companies would prefer you keep paying your minimum and send them money for ever.
This is why the following can also hurt your score:
- Having TOO Much available credit, IE you have lots of cards with $0 on them but the total credit has become a risk in-case you snap and max them all at once.
- You have no credit cards, and have always payed for everything.. Even if you have good income, this can be a problem if they haven't been able to build a history of your reliability to pay.
If you have Netflix check if the movie [Maxed Out](_URL_0_) is still on their... it explains consumer debt fairly well. | [
"Because a significant portion of the FICO score is determined by the ratio of credit used to credit available on credit card accounts, one way to increase the score is to increase the credit limits on one's credit card accounts.\n",
"However, this law did not prohibit all forms of universal default. Credit card ... |
Do computer screens have a direct effect on our levels of melatonin? | The short answer is: yes, [computer monitors suppress the natural release of melatonin during the biological night](_URL_8_). But this is not unique to computer monitors -- *all* artificial and natural light that is bright enough suppresses melatonin, including blue and other colors of light.
Here is how melatonin release normally works. The brain contains a master circadian clock -- it is a group of a few thousand neurons called the [suprachiasmatic nucleus (SCN)](_URL_6_) in the hypothalamus -- that keeps approximately 24-hour time. This clock sends signals to many other brain regions, one of which is the pineal gland. As an aside, the signal takes a [rather crazy pathway](_URL_7_) via the superior cervical ganglion in the neck. As a result, people who have severed their spinal cord above this level (i.e., people with tetraplegia) [release no detectable melatonin at all](_URL_0_).
The SCN signals the pineal gland to release melatonin across the night. The timing of melatonin release (in the total absence of light) is variable between individuals, but it is typical for melatonin release to begin a couple of hours before bed and to end around wake time. Light exposure during the night causes the SCN to send a stop signal to the pineal gland, causing melatonin release to cease. [Once the light source is removed, melatonin release will ramp up again if it is still during the nighttime release interval](_URL_4_). No melatonin is released during the biological day, even in darkness.
So how bright does the light need to be to suppress melatonin? It turns out the circadian system is very sensitive to light. Using broad-spectrum white light, [dim indoor lighting is sufficient to cause 50% suppression of melatonin release](_URL_10_).
And what about the color of light? I often hear that it's just blue light that matters. This is not quite correct -- it's an oversimplification. The wikipedia passage you linked to is misleading in this respect. Let me explain why. The SCN receives light signals from a special population of cells in the retina, called [intrinsically-photosensitive retinal ganglion cells](_URL_5_), or ipRGCs for short. These cells are involved in sensing light for non-visual purposes, such as the circadian system and the pupillary reflex to light. It is possible to be visually blind yet still have this non-visual light-detecting system intact, but for some blind people this system is destroyed as well (e.g., if the eyes are removed), meaning the circadian rhythm is unable to be reset by light and runs at its intrinsic period (different between individuals and not exactly 24 hours).
The ipRGCs have their own photopigment called [melanopsin](_URL_3_) (which was only discovered in the last 20 years!), allowing them to detect light. The melanopsin molecule is most sensitive to blue light (around 460-480nm wavelength), which is where this idea that blue light is the only really important color of light for melatonin suppression comes from.
However, things are a bit more complicated than that. The ipRGCs *also* receive inputs from the cone/rod system, which is maximally sensitive to green light! I have drawn a simple schematic of the pathways [here](_URL_9_). As a result, the suppression of melatonin is achieved by a combination of rod/cone and melanopsin responses to light. For relatively short light pulses (up to minutes), the rod/cone system is highly responsive and [green light is just as effective as blue light for suppressing melatonin](_URL_1_). For longer exposures (hours or longer), blue light has the greatest effect. However, if the light is bright enough, any color light can suppress melatonin release.
There are some programs now (e.g., f.lux) that redden the screen at night, thereby reducing the blue content of the light. While I am not aware of any rigorous studies of these programs to date, they are based on sound scientific reasoning. Reducing the blue content of light at night will reduce (but not eliminate) the effect on the circadian system. This makes it easier to fall asleep for two reasons. First, there will be less suppression of melatonin, and melatonin helps sleep onset to occur. Second, light in the late evening and early night causes [delay of the circadian rhythm](_URL_2_), which pushes the brain's sleep onset signal and the release of melatonin back later into the night, which can cause insomnia on that night and subsequent nights. | [
"Interest lies in the fact that MDA and MDMA may not themselves be responsible for their neurotoxicity, as an intracerebroventricular injection does not appear to cause neurotoxicity. While many studies suggest excitotoxicity or oxidative stress as likely mechanisms, which may be an effect of MDMA itself, this has ... |
why do indian reservations have such high unemployment? | Very true and in case you have forgotten, the reservations were the tracts of mostly worthless land nobody wanted, far from civilisation. That should explain the dismal prospects ofvthe denizens. | [
"Native American reservation inequality underlies a range of societal issues that affect the lives of Native American populations residing on reservations in the United States. About one third of the Native American population, about 700,000 persons, lives on an Indian Reservation in the United States. Reservation ... |
how do motor boat engines not get water logged? | Same reason your car motor doesn't get water logged when you drive in rain or puddles.
The motor is not in the water. It's spins a shaft which is also attached to a propeller, that goes into the water. | [
"The Amphicar's engine was mounted at the rear of the craft, driving the rear wheels through a 4-speed manual transmission. For use in the water, the same engine drove a pair of reversible propellers at the rear, with a second gear lever engaging forward or reverse drive. Once in the water, the main gear lever woul... |
Are there any good book (for layman) about climate changes and their impact on the course of human history/prehistory? Hopefully with maps. | Although comprehensive only in the sense that it attempts to cover the whole globe across most of the seventeenth century, with special focus on the impact of the Little Ice Age and associated abnormal El Nino episodes, Geoffrey Parker's book *The Global Crisis* (2013) is a major contribution by a senior historian to efforts to integrate social, political and environmental history.
Parker's thesis is that climate change during this period is crucial to understanding the very widespread political turmoil of the 17th century, which "saw more cases of simultaneous state breakdown around the globe than any previous or subsequent age" – from the Thirty Years War and British civil wars to the Fronde, the downfall of the Ming dynasty, civil war in Mughal India, the overthrow of the African kingdom of Kongo, and the disintegration of the Polish-Lithuanian commonwealth.
Parker contends that the period was also marked by a sharp increase in the number of revolts, and more and longer wars than occurred in any comparable period before the 20th century, all accompanied by dearth and plague leading to massive mortality – which in turn led (as Hobbes suggested in *Leviathan*) to the feeling that
> "There is [now] no place for industry, because the fruit thereof is uncertain, and consequently no culture of the earth; no navigation, nor use of the commodities that may be imported by sea; no commodious building; ... no arts; no letters; no society. And, which is worst of all, continual fear and danger of violent death; and the life of man, solitary, poor, nasty, brutish, and short."
and which prompted the contemporary Welsh historian James Howell to conclude that:
> "God Almighty has a quarrel lately with all mankind, and given the reins to the ill spirit to compass the whole earth; for within these twelve years [1637-49] there have the strangest revolutions and horridest things happened, not only in Europe but all the world over, that have befallen mankind, I dare boldly say, since Adam fell, in so short a revolution of time ... [Such] monstrous things have happened [that] it seems the whole world is off the hinges."
Finally, although perhaps least persuasively, Parker also attempts to explain why Japan, pretty much alone among the major nations studied, escaped most of the problems caused by climate change in this period.
It's a very big book, but he writes extremely well and it flies by, if the subject matter itself grips you. | [
"Field Notes from a Catastrophe: Man, Nature, and Climate Change is a 2006 non-fiction book by Elizabeth Kolbert. The book attempts to bring attention to the causes and effects of global climate change. Kolbert travels around the world where climate change is affecting the environment in significant ways. These loc... |
reverse entropy | imagine you have a jar of marbles that you tip over. The marbles all go out in different directions, ricochet off of eachother, and settle. Now, you must put them back how they were before. How? That's impossible, that's so much data to somehow learn, which way each marble went and what it hit and how at what angle and so on to reach it's final resting spot.
imagine if you could look through time, though. You'd see the path that every single marble took and the way they scattered would look very apparent to you, like a tree with branches. You could easily tell how they got there and how to reverse it.
Reverse entropy is only possible by timetravel, but we cannot do that. As time advances, the past is braided, so to speak, into one singular universe, the universe we at this very moment are at the head of. In the future there's infinite possibilities but as we travel through the fourth dimension, we collapse/destroy all those universes into the one we right now are witnessing. The past is beyond our reach, and the future doesn't exist yet, or rather it exists in every infinite way. So we're kinda stuck in the present, just like how a 3D apple passing through a 2D world would only exist to the 2D world as that slice of 2D it is at that current time, we're that apple, and time is what we're passing through, and we can only experience the world as it is at this very moment we are advancing through it. And as such, it's not possible for us to go back and look how the marbles fell and scattered... But the secret to reversing entropy might hold the way to look back in time, and vice versa. Just like in that 2D world they have no concept of ALL of the apple in one physical 3D existence, only slices of it. They might have the cognition to imagine a 3D apple, just like how we humans have memory and forethought of the past and future, but it's really just a makeshift bandaid solution.
It's all very theoretical stuff. | [
"The linear entropy then is obtained by expanding ln \"ρ\" = ln (1−(1−\"ρ\")), around a pure state, \"ρ\"=\"ρ\"; that is, expanding in terms of the non-negative matrix 1−\"ρ\" in the formal Mercator series for the logarithm,\n",
"A reverse salient refers to a component of a technological system that, due to its i... |
how do companies like walmart profit from selling gift cards to other services when a gift card costs the amount of credit it's worth? | it is a strategy used to get people in the door, much like a sale, it is ok to not make as much money on one or two items because usually when people come in they buy more than they were intending to in the first place, it happens. so to get people in the door it is actually more profitable to sell some things at a reduced price or even at a loss if it means you are making more profit on other goods and or services | [
"In fact, many sellers could not qualify for a credit card Merchant account because they lacked a commercial credit history. The service also appealed to auction buyers because they could fund PayPal accounts using credit cards or bank account balances, without divulging credit card numbers to unknown sellers. PayP... |
Why are owls associated with intelligence? | To answer the former question: Athena was the protector of Athens. Athena had an owl because owls were abundant in Athens. There's a proverb that says "bring owls to Athens" for a pointless venture.
edit: I was answering the question of why owls are associated with the Greek goddess Athena. | [
"BULLET::::- Although owls are often associated with wisdom and intelligence, this is not universal, nor a timeless image. During the Middle Ages owls were seen as stupid and evil helpers of witches. In many paintings of Hieronymus Bosch the bird is seen as a symbol of stupidity and/or evil. The Dutch profanity wor... |
sound effects | Yes, sometimes they just go out to a shooting range or go out driving with a bunch of sound equipment.
Usually for movies they just buy the sound effects from someone who already did that and is selling all the sound effects.
Either way, studios end up with libraries of sound effects they use. | [
"A sound effect (or audio effect) is an artificially created or enhanced sound, or sound process used to emphasize artistic or other content of films, television shows, live performance, animation, video games, music, or other media. These are normally created with foley. In motion picture and television production... |
How important are cyanobacteria to *keeping* the earth's atmosphere oxygenated? | Indeed, they are very important. [Here](_URL_0_) is a Nat. Geo. article on this very topic (though they are talking about all phytoplankton, but just cyanobacteria). It's a bit old (2004), but still agrees with several other more recent sources I found. The short answer is that, yes, photosynthetic unicellular marine microorganisms (cyanobacteria being one of the most abundant) are very important for maintaining our atmospheric oxygen. | [
"While prokaryotic cyanobacteria reproduce asexually through cell division, they were instrumental in priming the environment for the evolutionary development of more complex eukaryotic organisms. Cyanobacteria (as well as extremophile Gammaproteobacteria) are thought to be largely responsible for increasing the am... |
is it true that if you eat human flesh your body will uncontrollably shake? if so, why? | It could happen, yes. It's due to a prion disease called Kuru: _URL_0_ | [
"In modern humans, necrophagy (eating of dead/decaying flesh) occurs rarely in most societies. This is likely an adaptation to the risk of disease, due to humans having lower levels of protective acids in the digestive tract, compared to species that are dedicated scavengers. Many instances have occurred in history... |
how is the sugar coating on sour candy so much different than table sugar? | From Wikipedia: *Sour sanding, or sour sugar, is a food ingredient that is used to impart a sour flavor, made from citric or tartaric acid and sugar. It is used to coat sour candies like Sour Patch Kids or to make hard candies tart, such as acid drops or SweeTarts.* It's not quite the same thing. | [
"Sugar candy is made by dissolving sugar in water or milk to form a syrup, which is boiled until it reaches the desired concentration or starts to caramelize. Candy comes in a wide variety of textures, from soft and chewy to hard and brittle. The texture of candy depends on the ingredients and the temperatures that... |
how are airplanes able to travel through the air despite being heavier than air? also, what exactly is jet propulsion? | Airplanes fly by generating lift. Their wings are shaped in such a way that when they are moving through the air, the air passing over the top of the wing is moving faster than the air moving under the wing. The faster that air moves, the lower pressure it has. Since the faster moving air on top of the wing has less pressure than the slower moving air on the bottom of the wing it generates lift and causes the plane to rise.
Jet engines work by taking in a large amount of air and compressing it into a small space. Fuel is then added to the compressed air and it is ignited, or basically blown up. The more air that can be pushed in and the more it can be compressed, the more powerful the explosion will be. The force of the explosion pushes out of the back of the jet engine causing forward thrust. In reality it creates more pressure pushing forward on the jet engine than at the rear of the jet engine, the thrust isn't actually pushing off of anything behind it. That's why boosters still work in space where there is no air. | [
"There are different approaches to flight. If an object has a lower density than air, then it is buoyant and is able to float in the air without expending energy. A heavier than air craft, known as an aerodyne, includes flighted animals and insects, fixed-wing aircraft and rotorcraft. Because the craft is heavier t... |
when you forget something, why does retracing your steps often make you remember? (such as going back to a webpage you closed or redoing the activity you were doing) | For me, it tends to be that something in what I was doing was the impetus for the thought to begin with. When that stimulus occurs again, the thought happens again in the same way it did initially. | [
"There are two theories that can explain directed forgetting: retrieval inhibition hypothesis and context shift hypothesis. The Retrieval Inhibition Hypothesis states that the instruction to forget the first list hinders memory of the list-one items. This hypothesis suggests that directed forgetting only reduces th... |
Is radioactive decay temperature-dependent? | Typically is not, the nucleus is so much smaller than the atom that it doesn't "care" what's happening around it (imagine a marble at the center of one of those giant human hamster balls). There are maybe a few small exceptions.
One could argue that the electron-capture mechanism (sometimes called inverse beta decay) depends on the probability of the electron being found in the nucleus, which depends on the lattice arrangement which depends on temperature. The difficulty with testing this is that the functioning of particle detectors for measuring decay also depends on temperature. There were a few studies purporting to find temperature dependence, [but a more precise study](_URL_0_) did not.
There's also the phenomenon that a superheated gas might have atoms that experience time dilation and appear to have slower decay rate. It's not feasible to make a gas that hot with current technology, but slower decay rates of nuclei have been observed in a particle accelerator. | [
"The mathematics of radioactive decay depend on a key assumption that a nucleus of a radionuclide has no \"memory\" or way of translating its history into its present behavior. A nucleus does not \"age\" with the passage of time. Thus, the probability of its breaking down does not increase with time, but stays cons... |
batteries: rechargeable vs disposable | Rechargable batteries have different chemistry from disposable batteries. And the different chemistries result in various pros and cons.
A NiMH AA has a voltage of 1.2, but an alkaline AA is 1.5. But most electronics tolerate these small differences.
A more significant difference for a user would be the problem of auto-discharge. Rechargeable cells like a NiMH, even when not plugged in, lose charge with time.
So while your remotes, mouse, and game controllers can utilize recharging cells, you should NOT use rechargables for something like an emergency-kit's flashlight which you store away for hurricane season, because chances are you won't be charging them periodically waiting for the unexpected to happen.
So there are legitimate reasons to use alkalines, but their use obviously is too common to be explained by those circumstances. My guess is selling disposable batteries is more profitable for them, or that people are too lazy, or both. | [
"A rechargeable battery, storage battery, secondary cell, or accumulator is a type of electrical battery which can be charged, discharged into a load, and recharged many times, as opposed to a disposable or primary battery, which is supplied fully charged and discarded after use. It is composed of one or more elect... |
why was microsoft criticised for bundling a browser and media player with their os, but is apple allowed to bundle a computer with their os? | Microsoft was leveraging its monopoly to put a much smaller rival out of business. | [
"The plaintiffs alleged that Microsoft had abused monopoly power on Intel-based personal computers in its handling of operating system and web browser integration. The issue central to the case was whether Microsoft was allowed to bundle its flagship Internet Explorer (IE) web browser software with its Windows oper... |
why do some nutrition labels read "total carbohydrates 30g" but sugars will say "sugars 22g"? | Sugars are a simple type of carbohydrate.
Fibre (cellulose) is technically a carbohydrate, but it is not digestible and has no direct nutritional value. It is therefore not included in the total carbohydrates of food. | [
"This is a list of sugars and sugar products. Sugar is the generalized name for sweet, short-chain, soluble carbohydrates, many of which are used in food. They are composed of carbon, hydrogen, and oxygen. There are various types of sugar derived from different sources.\n",
"Sugar is the generic name for sweet-ta... |
what do the schrödinger and dirac equations describe and what's the difference? | The Schrödinger equation (ih d/dt psi = H psi) is a very general statement about quantum mechanics: the phase of a state changes (it ”turns”, in a way) proportional to its energy. It can describe many different things as long as you use the correct H. Note that I’m NOT talking about the common formulation ih d/dt psi = -h^2 / 2m psi + V psi, which is the specific case for a singe nonrelativistic (slow) particle. The Dirac equation is another specific instance of it, describing relativistic (very fast) spin-1/2 particles (like electrons) and has spin and antiparticles built into it. | [
"the Schrödinger equation is turned into an integral equation. The \"in\" and \"out\" states are assumed to form bases too, in the distant past and distant future respectively having the appearance of free particle states, but being eigenfunctions of the complete Hamiltonian. Thus endowing them with an index, the e... |
English (Latin?) certainly made its view of left-handed people clear (sinister - left handed) but are there any cultures were left-handedness is seen as better than right-handedness? | You might try /r/Askanthropology. There may be someone here with the answer, but this other sub has a concentration of people with a background in comparative ethnography. | [
"Moreover, apart from inconvenience, left-handed people have historically been considered unlucky or even malicious for their difference by the right-handed majority. In many European languages, including English, the word for the direction \"right\" also means \"correct\" or \"proper\". Throughout history, being l... |
obama's new jobs bill. | You can read about it [Right Here](_URL_0_) from a previous ELI5. Cheers. | [
"The American Jobs Act () (H. Doc. 112-53) and (H.R. 12) is the informal name for a pair of bills recommended by U.S. President Barack Obama in a nationally televised address to a joint session of Congress on September 8, 2011. He characterized the proposal as a collection of non-controversial measures designed to ... |
what makes the noise in an engine? | Its either the engine lifter's noise, valve noise, the combustion, bearing noise, or the exhaust of the car itself you're talking about at the moment.
Vroom vroom. | [
"In recent years, the engine has developed a noise, referred to as \"The Squeak\". While the cause of this noise is not definitively known, it is presumed to come from the low pressure valve. There are no physical indications of scuffing, galling, or damage to components indicating a metal-to-metal contact. The squ... |
what is al qaeda fighting for? | Its not a simple answer because Al Qaeda is NOT a simple terrorist group.
The point of Al Qaeda, as laid out by Bin Laden, is not a single group with a single goal, but as the Arabic translation plainly tell us, to be "the base" for multiple related but not 100% similar groups, causes, and goals.
This is NO single thing Al Qaeda wants because the is NO single Al Qaeda. There's Al Qaeda in Iraq (now fracturing into AQI and ISIS), there's Al Qaeda in the Maghreb (AQM), Al Qaeda in the Arab Peninsula, also Al Qaeda in the Horn of Africa. The original Afghanistan franchise is also still present with the remnants of the Taliban in the Pakistan Tribal areas. Plus these franchises, literally they are franchises, they use the Al Qaeda name and sometimes share finances/fighters but they have semi-independent leadership and act towards separate goals.
Bin Laden states goals where many, but the usual demands in his fatwa videos included: Removal of US soldiers and sailors from Saudi Arabia, end of US support of Israel, the overthrow of several western friendly Middle East governments, and the replacement of them with a unified Islamic Caliphate or one super Arab-Muslim state in the gulf.
Others linked to Al Qaeda have also demanded the forced conversion of all non-Muslims, the replacement of civil law with Sharia religious law, the complete destruction of Israel, or for an Islamic Caliphate to extend beyond the middle east and conquer the world.
To accomplish these, Al Qaeda was supposed to be a linked network of terrorism support groups. The training camps in pre 9/11 Afghanistan hosted terrorists from all over the world. Al Qaeda would link financier X with group Y to move money. They would provide their franchise groups with better planning of attacks and strategy. You could share bomb makers. One guy learns an IED to defeat armored Humvees, Al Qaeda would hook up other groups with him. It was envisioned as a one stop terrorist super store/support line.
Each individual group had its own motivations, usually less about Islam and infidels, and more about seizing regional power and taking political control. Al Qaeda in Iraq talks a good game about hating Jews and Americans, but really they just bomb and kill other Iraqi Muslims so that AQI can get more political control over the west of Iraq. They couldn't care less about Al Qaeda in the Maghreb fighting in Libya or Algeria or the Taliban's fight in Afghanistan. Bin Laden simply built them a common support network for training, money, and strategy; but not a governing body where they vote on the general platforms of terrorism.
This split has only gotten bigger since most of the senior leadership have been killed or captured since 9/11. Al Qaeda is less about the spectacular overseas attacks (9/11, London bombings, Madrid train attacks) of which OBL and KSM were proponents and more about these regional franchises attacking regionally for regional gain.
**TL:DR** What exactly Al Qaeda wants depends on which Al Qaeda you are talking about. | [
"Al-Qaeda operates as a network of Islamic extremists and Salafist jihadists. The organization has been designated as a terrorist group by the United Nations Security Council, the North Atlantic Treaty Organization (NATO), the European Union, the United States, the United Kingdom, Russia, India, and various other c... |
why does styrofoam melt when it comes into contact with superglue/adhesives? | Super glue and other adhesives contain some organic solvents (e.g. acetone, ethyl acetate). Styrofoam is made from thousands of styrene molecules linked together. Styrene by itself really wants to dissolve in these organic solvents, but since so many of them are linked together it can't because it's simply too big. So instead of dissolving, you get melting effect. | [
"Two: Adhesion: Polyamide materials are basically high performance hot-melt adhesives. The adhesive properties of polyamide is what seals a chosen substrate. The type of adhesion is purely mechanical i.e. no chemical reaction takes place.\n",
"Hot-melt adhesives are as numerous as they are versatile. In general, ... |
how do services like pandora and spotify work | same way any business operates. sell it for more than you buy it.
if it costs $10,000 for Pandora to buy the rights for a song, and they play it on 1million users and get advertising $0.01 per play, then that's profit. | [
"Pandora (also known as Pandora Media or Pandora Radio) is an American music streaming and automated music recommendation internet radio service powered by the Music Genome Project. The service, operated by Sirius XM Satellite Radio, is available in the United States. The service plays songs that have similar music... |
putting down animals in zoo | Did you read the rest of the article? They explained exactly why they did it.
They didn't have the money to relocate the animals, and the new animals they were getting would have killed the old animals -- euthanasia makes a little more sense than a zoo snuff show.
It's more important to look at the population of the species as a whole than any one individual animal -- with regards to the species as a whole, the zoo was doing exactly what it should. | [
"Formerly the reptile house, Zoo At Home is a zone for pet animals. It was adapted with the assistance of Pets At Home. It is also currently home to the zoo's Madagascan giant jumping rats. As of September 2012 the area became the Animal Cafe, where visitors can eat as they watch the animals.\n",
"On 2015 it was ... |
why is it easier to fall asleep to background noise (radio, tv etc.) than just the plain dark? | This happens because when there's noise around us we feel that someone is near us.
Thus we feel safe and can let go of the tension and fall asleep.
This is an evolutionary thing and has been embedded in our DNA. Humans are primarily social animals and keep each other safe. | [
"Noise can make sleeping difficult on occasions, whether from snoring, talking and social activities in the lounge, people staying up to read with the light on, someone either returning late from bars, or leaving early, or the proximity of so many people. To mitigate this, some wear earplugs or eye-covering sleepin... |
how are amputees able to control the fingers in their bionic arm ? | The company I work at actually exclusively works on this!
/u/WashingtonFierce post is incorrect, we do not yet have commercial technology designed specifically to physically interact with the brain and detect limb movement. The amount of time, money, and risk is prohibitively monumental. Imagine being an ethics review board member having to review an experiment about splitting a subject's head open to insert a sensor that you may or may not know will work effectively and reliably unless you try.
/u/TheLazyD0G has more or less explained it correctly, and I can add some additional info.
* Your brain sends signals to nerves in the arm, and the nerves are connected to the arm muscles. What actually happens when your arm muscle contracts is a bunch of sodium and Potassium ions moving about the cell walls of your muscles. Since these ions have positive charges to them, their movement generates a very very tiny voltage. The two sensors that sit in the prosthetic socket and touch the forearm are sensitive enough to pick up this change in voltage. This concept is called [EMG](_URL_1_).
* [So depending on the voltage change, the sensors can detect how hard you're flexing, or even at all.](_URL_2_)
* [The way the hands are programmed are in that they cycle through different pre-set grip modes, and the patient can only open and close them in the different modes.](_URL_0_) The bebionic3, for example, you start out in Tripod grip (so you only close index, middle, and thumb) and can only close and open in that formation. You have to press the button on the back to change to Power grasp, and then you can only open and close them in a fist. You then have to press the button, AGAIN, to go into another grip, say Precision grasp, and then you can only open and close the thumb and index finger together. In a sense, they're just hand-shaped swiss army knives.
* The patient opens and closes them by flexing their limb in one direction or another. Imagine flexing your wrist towards your chest. That's close. Now flex your wrist away from you. That's open.
* This can get tedious (how many times did I have to press the button?) and can get frustrating if you make a mistake in a high-pressure situation (e.g. getting change into your wallet after the cashier hands it to you)
* The pattern recognition that /u/TheLazyD0G mentions attempts to use multiple (3+) sensors and machine learning to have the arm change the grip based on which hand gesture you trained it to do earlier. However, this concept is still bogged down by the hand's programming of only changing between different pre-set gestures.
* We have not yet achieved the level of fineness in detecting individual finger movements, largely to the concept of "Crosstalk". With the current size of these skin sensors, the region of muscle they observe can't distinguish whether a movement was for one finger versus another. Implantable sensors can theoretically solve this issue, but research into them so far have been very preliminary.
Let me know if you have other questions! | [
"The Lancet published a 2012 UPMC study of two 9 year quadriplegics being able to move a robotic arm by thought, to pick up objects, shake hands, and even eat. Wiring the brain around spine damage to restore arm and leg muscle function was successful using robotic arms controlled via an embedded computer to transla... |
I have a weird question about micro-gravity. | I'll attempt to answer part of this question seriously. I wouldn't know anything about the first two questions, but in terms of the third question you may be interested in [this nice Slate piece](_URL_1_) which has quite a bit of information.
In addition, you have several problems with radiation. Cosmic rays can damage male sperm -- not to the point of infertility, as many astronauts have conceived after sometimes extended stays in space -- but more importantly can seriously harm human fetuses. [Link.](_URL_2_)
Finally, female rats in microgravity have rather difficult labours. [Link, behind paywall.](_URL_0_) This doesn't bode well for humans, who have rather difficult labour already. | [
"The term 'micro' gravity refers to a gravitational state that is 'low' (i.e., 'micro' in the sense of 'small' and not necessarily a millionth of Earth's normal gravity) such that the influence of buoyancy on physical processes may be considered small relative to other flow processes that would be present at normal... |
why haven't we seen the us (and its partners in the fight against isis) engage in a siege of raqqah, the "de facto capital of isis"? | 1. Raqqa is surrounded by other territories controlled by Islamic State, so to surround it you need to fight IS on at least two fronts (both sides of the Euphrates).
2. Any effective form of siege could have to involve cutting off food, water, or electricity, which would result in massive civilian casualties and would be a PR disaster. Remember, IS is already surrounded by countries that are hostile to it, the softest of which is Turkey which still tries to prevent them from using the border. They manage to get weapons and soldiers despite this.
3. No one wants another war. America is tired from Iraq and Afghanistan, and Russia still has bad memories from Afghanistan and Chechnya.
4. Surrounding Raqqa would involve putting American troops in Syrian soil. America does occasional special forces raids into Syria (two that I can think of off the top of my head), but long-term troop deployments is something else entirely. It would be a diplomatic nightmare.
5. Raqqa is arguably not the most important city in the Islamic State. Their military equipment is spread everywhere, and the city of Mosul is larger and more important. Raqqa is only the capital because it is the first big city they captured.
6. There are already powerful groups fighting ISIS, including but not limited to: Jaysh al-Islam, the Army of Conquest coalition, Iraqi government, Syrian government, the SDF and New Syrian Army, Iraqi Kurdistan, YPG, PKK, FSA, and Hezbollah. For foreign governments, it is easier to simply support one of these groups with weapons or airstrikes. | [
"On 3 August 2014, ISIL captured the cities of Zumar, Sinjar and Wana in northern Iraq. Thousands of Yazidis fled up Mount Sinjar, fearful of the approaching hostile ISIL militants. The stranded Yazidis' need for food and water, the threat of genocide to them and to others announced by ISIL, along with the desire t... |
Was there any ethnic tension between Germans, Slovaks, Slavs, etc... in the early 1900's and leading into the second World War? If so, what was it like? | Of course there was. In the early days of Czechoslovakia, tensions between Czechs and Germans were a major issue that would later play a part in the months preceding the Second World War and the occupation of Czechoslovakia, and that would only be resolved until after the war. And even then only via the highly controversial Benes Decrees.
Germans have lived alongside Czechs (or Bohemians and Moravians, if you will) since the earliest days of a Czech state, colonizing parts of it from about the 10th century onwards in what we now call the Ostsiedlung - settling of the east. This was caused by both a growing population in German lands as well as local rulers actually welcoming and encouraging settlers to come to Bohemia.
However, after the Habsburgs had taken over some centuries later, Czech lands have been subjected to gradual Germanization and German culture as well as language became the norm for upper classes, politics and the like. This in turn led to the advent of nationalism and the Czech National Revival, a story that ought to sound quite familiar to many nationalities all over Europe around the 19th century.
Finally this leads us to the end of the Great War, and the dissolution of Austria-Hungary. The multiethnic monarchy had faced calls for independence or fair representation in politics from its constituent nations for quite a long time now, and the war had only postponed the resolution of these issues. Austria-Hungary did not survive, after the war, Czechoslovakia and others have declared independece and the empire soon ceased to exist.
This is where things get rather interesting. The idea of a Czechoslovak nationality is an artificial concept promoted by the leaders of the independence movement and future presidents Masaryk and Benes. It does have its roots in reasonable assumptions as the two groups have mutually intelligible languages, are close culturally and have lived in close proximity for centuries, but ultimately it was a calculated decision much influenced by the political situation.
You see, according to the 1921 census, there were 8 759 701 Czechoslovaks (roughly two million of which were Slovaks) and 3 123 305 Germans in Czechoslovakia, with other sizeable minorities such as Hungarians. This was a direct result of the newly independent country keeping its historical borders which, however, included the regions with a sizeable German population – Sudetenland.
The Germans had actually called for some sort of exclusion from this arrangement or self-determination, such as becoming a part of Austria – indeed, in the spirit of Wilson's Fourteen Points and the general post war atmosphere that allowed various peoples to declare their independence – but the Treaty of Saint-Germain-en-Laye ended their hopes as the lands of the Bohemian Crown were preserved in their historical shape.
In the two decades that followed, the relations between Czechoslovaks and Germans have deteriorated, albeit rather slowly at first. German was preserved as an official language in areas with a considerable German population, Germans were represented in the parliament, but on the other hand Czechoslovakia was ultimately a Czechoslovak nation and many policies reflected that, such as a clear preference for Czech officials in local politics.
An important point that I feel has to be made is that although this was at a time when Nazis were on the rise in Germany, Germans in Sudetenland were not yet particularly strong sympathizers of the new regime. Henlein's separationist Sudetendeutsche Partei only came under Hitler's major influence from 1937 onwards, two years after securing 44 seats in the chamber of deputies, more than any single Czech party, and 23 seats in the senate, tied with the agrarian party.
Germany portrayed the situation in Czechoslovakia as extremely untenable, Hitler made no secret of his ties to Henlein's party, with the Sudetendeutsche leader in turn exerting internal pressure on Czechoslovakia presenting mostly unacceptable demands including autonomy to the government. Besides overt political action, Germany also prepared for a military conflict if their demands were met.
Faced with the possibility of war and at the same time the less than ideal German situation in Czechoslovakia, France and Britain kept with their policy of appeasement, sided with Germany, and the Munich Agreement was signed in 1938 with the Czechs not having much say in the matter, ruling that Sudetenland would become a part of Germany.
In the end the Germans in Sudetenland were a minority with many of the problems this presents for those labelled this way, as well as for those who would form the majority. Centuries of tension did not help either, nor did the fact that they were not afforded the same treatment as other nationalities when it came to the collapse of the monarchy. However, Austria-Hungary was on the losing side of the war, the Czechs had only kept their historical borders, and although their relationship was often problematic, never subjected Germans to harsh treatment minorities sometimes suffer before the war.
That everything played out the way it did was a result of the build up to the Second World War by Germany rather than historical relations and ethnic tension between Germans and Czechs in a single country. | [
"After World War I, the population expanded with an influx of Gottscheers—an ethnic German population from Slovenia who were dislocated in the aftermath of World War I—and Irish, followed soon after by Italians. In April 1934, a large, 9,000-person boycott of Nazi Germany resulted in brawls between Nazi sympathizer... |
when did the storefront name of "arcade" go from being a kids' video-game hangout, to being an 18+ slot machine parlour? | It happened due to home gaming consoles.
Older redditor here. I used to play the quarter-munchers back in the days before everyone with teens or kids had at least a couple game consoles... and the earlier generations were really shitty. So you'd go to the "pinball arcade" to play games with much better features like actual voices, graphics that didn't look like potato-splats, and... pinball.
Fast forward to when the average 15 year old that finds they have an interest in electronic games has their own Steam account or PS4 or XBOne, and the biggest source of quarter-by-quarter funding for "arcades" dried up. So, with the exception of a few that feed our senses of nostalgia, they largely went out of business.
So the word "arcade" was ripe for repurposing... and they did that by assigning it to legal-gambling slot machines instead because a lot of gambling addicts and participants drop WAY more money into those machines so it's a viable business mode.
But why "arcade"? Before it was "video arcade" it meant "penny arcade", which meant coin-operated devices. With the exception that they now use bills or tokens instead, it's still currency-operated... and so the term still very much applies. | [
"The arcade was built by Watertown native Loveland Paddock and designed by architect Otis Wheelock. It was based on similar arcades built during that era in the United States and Europe. Shops occupied the bottom floor, while the upper floors were used for office space.\n",
"The name of the arcade version was a r... |
what is the difference between readings books (any kind) and reading various reddit articles/threads? | Reddit posts & articles are usually fairly short. There's not a lot of depth or nuance going on - especially the front page, which is full of image, memes and other such easily digestible things (not to mention all the articles that get commented on by people who never read the link).
A book, or long-form article requires more commitment & attention paid to it. It's able to express more complex ideas, commit more time to them & explore themes in more depth.
Having reddit as your primary reading source is like eating candy & stacks instead of eating a full meal. | [
"Reading, by definition, is the ability and knowledge of a language that allows comprehension by grasping the meaning of written or printed characters, words, or sentences. Reading involves a wide variety of print and non-print texts that helps a reader gain an understanding of the material that is being read. Read... |
Was Cato the Younger a Pleb or patrician? | > When Clodious , who was from a minor patrician family
*Minor*?! The *gens Claudia* was one of the largest and most prestigious patrician *gentes*, outstripped only in surviving patrician lines by perhaps the *gens Cornelia*. To call Clodius a member of a minor family is like calling the sun a little hot.
[You're completely misunderstanding what a plebeian (the singular of plebs is plebs, it's a collective singular) means.](_URL_0_) Patrician does not mean senator, and most senators were not patricians by far. Cato was a plebeian, like Cicero, Crassus, Pompey, Antony, Cassius, Lucullus, both Bruti, etc. The *gens Porcia* was a plebeian *gens*, and was heavily involved in the final stages of the Conflict of the Orders, during which members of the family passed several important *leges Porciae*, at least one of which protected soldiers on campaign from *coercitio* by extending *provocatio* to them | [
"The real Cato was much younger than his fictional counterpart appears: in 52 BC, the year the series opens, he was 43, seven years younger than Caesar. He was also not as contemptuous of plebeians as the series makes him: he established a provision of state-subsidised grain to poor Romans, and Cato was himself a p... |
Why did the Irish Rebellion in 1798 fail? | In short (don't have much time, so perhaps someone can expand on this)
1. Three of the United Irishmen's top brass were arrested on the eve of the uprising.
2. Artillery stationed in Ireland had been upgraded and increased in size. One Lieutenant was to describe that the 'Grapeshot (cannister) worked like a wonder'
3. The rising was more of a massive rural peasant riot that lacked proper cohesion and goals. While mobs would rise in a certain area, those with leadership abilities would come to the forefront, however their attacks were limited to local barracks etc
4. The United Irishmen were under-armed and were facing a fairly sizeable government army which had at it's disposal 9000 regular troops, 25000 militia and 40000 yeomanry (civilians with arms). The well disciplined regulars were more than enough to change the tide in a number of critical locations.
5. While the French did land in Co. Mayo I believe it was just too late, and once again it was a half hearted attempt like every other invasion of Ireland by Spain and France to support the nationalists. | [
"The Irish Rebellion of 1798 was assisted by a French invasion force under Jean Joseph Amable Humbert. The rebellion and the invasion failed. To secure control of Ireland, the Parliament of Ireland and the Parliament of Great Britain negotiated a merger of the two kingdoms. The Act of Union 1800 resulted in the for... |
why can paying off your student loans hurt your credit score? it seems like it would be a good thing. | Part of a credit score is being able to prove you can pay off debt, which requires having debt to begin with. That’s why people who have never had a credit card or loan generally don’t have good credit. Without any debt, you can’t prove you have the ability to pay it off, hence the lower score.
To summarize, lots of debt = bad / no debt = bad / some debt = good | [
"In coverage through established media outlets, many borrowers have expressed feelings of victimization by the student loan corporations. There is a comparison between these accounts and the college credit card trend in America during the 2000s, though the amounts owed by students on their student loans are almost ... |
What was the primary warship of the Indian Ocean before the advent of the modern period? | One particular aspect of maritime situation in the Indian ocean in the second half of fifteenth century which is often emphasized by scholars, is the *relative* peacefulness and *absence* of large scale naval conflicts. The accent here is really on the word *relative* as piracy was abundant and there was plenty of naval combat in the form of smaller neighboring states fighting each other, or a commercial center port subjugating its immediate surroundings.
But what you won't see, is the kind of power projection across the seas, sending combat fleets far way from home, or establishment of maritime empires backed by sea domination which you might associate with, for example Italian medieval merchant states. Again, before someone gets their pitchforks out, I am mostly referring to the *fifteenth century* and the setting in place in time of European arrival. It is quite possible somewhere back in time Indian ocean was full of such naval empires, I really wouldn't know.
The following consequence of such situation is that there really wasn't much large scale naval battles (like e.g. battle of Zonchio in 1499 in Mediterrenean) and for that matter, there were no clear large dedicated warships that might be considered an analgoue to European galleys, or later galleons or ship-of-the-line. And that's perfectly fine! In fact it is probably the Mediterrenean that was an outlier as in 14th century both England and France were raising their navies by commandeer and adapting merchant ships rather then having dedicated warships.
In those conditions, the naval fleets, when assembled, had usually consisted of a number of large merchant sailing ships taken for the occasion and filled with soldiers, augmented with a large number of oared vessels. Such combined fleet of smaller oared ships together with larger merchant ships were encountered several times by the Portuguese, in their fights at Hormuz, Chaul/Diu, Malacca, etc.
The smaller oared ships could vary in size (and have a mast with a sail, same as galleys) but were as a rule smaller then galleys as Portuguese often applied the term *fusta* to describe them, and *fusta* was a European type of small galley. if anything would be considered a warship of Indian ocean, it would be these oared vessels. Unfortunately, I can't find much information on them as they seemed to pass under the radar of most works.
The merchant ships, primarily propelled by sailing would be what you term dhows. That is if we are talking about the western part of the Indian ocean - the Arabian sea - where most ships were of this type. Most of the Portuguese descriptions (sorry for dealing with Portuguese sources, but it seems those are the main sources most of scholarship draws from. Hopefully the situation has changed and I am just out of date...) describe them as well built ships built, and particularly accent that they were built without nails (actually some sources disagree, but vast majority confirm) and instead either wooden pegs were used or the planks were sewn together, another interesting feature many sources agree with. By size those ships were just as big, and on more then one occasion even bigger then Portuguese naus they were up against. Yet unlike Portuguese ships it seems that the ship board artillery wasn't really a thing. Or it was, but the artillery it self was much weaker then the ones brought from Europe.
In the eastern part of Indian ocean, there was a considerable additional influx of SE Asian designs of such large ships, which Portuguese dubbed "junks" (juncos). Those had some Chinese influence in origins, but were actually heavily influenced by native SE Asian design. Unlike dhows, those are much more often described as having nails and in general had a different look and feel. They also had two side rudders instead of a stern rudder, a fact Portuguese wrote down with interest as they considered it a weakness in battle. They were also larger then Portuguese ships, and had multiple layers of planking which allowed some of those junks to resist even the largest cannon fire from Portuguese ships. The ships were still at a disadvantage against the Portuguese, and seems in the early days when Portuguese conquered Malacca they also succeeded in winning most of the few naval battles they had.
To conclude here are some of the 16th century (european) images of the ships. We are not sure if those are realistic first hand accounts or just imaginations of authors back in Europe.
[Ships of the Arabian sea: a dhow and a 9-masted large ship - 1519 ](_URL_0_)
[Ships from Java / SE Asia: junks - 1598](_URL_2_)
[Ship from SE Asia: jong/junk - 1613](_URL_1_) | [
"For the most of the 16th century, the Portuguese India Armadas and fleets, then the world leader navy of shipbuilding and naval artillery, dominated most of the Atlantic Ocean south of the Canary Islands, the Indian Ocean and the access to the western Pacific.\n",
"In the 1830s, the Portuguese Navy incorporated ... |
when i'm tired, every now and then i will go through bouts of extreme drowsiness where i can't even keep my head up and eyes open, but after about 5-10 minutes i am awake again and completely fine. what are these cycles and how do they work? | This can't be as abnormal as other posters are making it out to be. I experience the same problem sometimes if I did not get much rest the night before and I am doing something uninteresting. I try to think about how important it is that I stay awake in a meeting with my boss, for example, but sometimes I find it legitimately impossible to keep my eyes open, so I pinch myself ceaselessly until I wake up... | [
"The wake maintenance zone generally lasts 2 to 3 hours, during which one is less inclined to fall asleep. While potentially useful for completing urgent tasks, it may have a potentially unwanted side-effect of keeping one awake for several hours after the task has been completed. The hypervigilance and stimulation... |
suitjacket, sportcoat, and blazer? which situation calls for which jacket? | Sport coats have patterns, unlike blazers, which are solid and have contrasting buttons. Suit jackets are smooth, have tonal buttons, and should never be worn with anything other than matching suit trousers.
| [
"A sport coat, also called a sport jacket (sports coat or sports jacket in American English), is a men's lounge jacket designed to be worn on its own without matching trousers, traditionally for sporting purposes. Styles, fabrics, colours and patterns are more varied than in most suits; sturdier and thicker fabrics... |
why are so many large companies headquartered in minneapolis? | Minneapolis has a well educated population, the standard amenities of a major city, is a hub for a major airlines, has a high livability index, and still maintains a relatively low cost of living compared to other major cities. | [
"In 2011, the 20 largest U.S.-based companies by revenue were Walmart, ExxonMobil, Chevron, ConocoPhillips, Fannie Mae, General Electric, Berkshire Hathaway, General Motors, Ford Motor Company, Hewlett-Packard, AT&T, Cargill, McKesson Corporation, Bank of America, Federal Home Loan Mortgage Corporation, Apple Inc.,... |
why are b.c. (before christ) and a.c. (after christ) the reference points we have chosen to use for historical measure, as opposed to any other major historical event? | Nowadays you often see “BCE” which stands for “Before the Common Era.” “BC/AC” was just a handy reference since many Western historians were/ are Christian. | [
"BULLET::::- Dionysius Exiguus, Scythian theologian-mathematician, inaugurates at Rome the practice of using A.D. (Anno Domini) for calendar dates after the birth of Jesus Christ (who was actually born in 7 B.C. or later). Dionysius produces also his tables for computing the date of \"\"Cyclus Paschalis\"\" (\"East... |
if most psychopaths become psychopathic due to their childhood or a birth defect, why are most psychopaths male? | The debate about whether psychopaths are the result of nature vs nurture is still very much ongoing.
If and to the extent it is due to nature then the sex difference in psychopathy is likely to be due to the sexual dimorphism in the brain. Both women's and men's brains are mainly formed by estrogen, but the male estrogen is slightly different than the female estrogen because the estrogen in men is due to conversion of testosterone.
If and to the extent it is due to nurture then it is likely to be due to differences in how we raise boys vs girls. For example the amygdala - the center for emotions - is about 18% smaller for psychopaths. But newer research shows that the brain structure itself is due to the how we use the brain, especially in the formative years. The neural pathways we use as kids are the neural pathways that will dominate our brains as adults. Research shows that a young child dressed up as a boy receives less affection than a child dressed as a girl, and this will affect both personality development and brain structure. | [
"Psychopathy has been associated with commission of sexual crime, with some researchers arguing that it is correlated with a preference for violent sexual behavior. A 2011 study of conditional releases for Canadian male federal offenders found that psychopathy was related to more violent and non-violent offences bu... |
What problems was fascism intended to solve? | Hi there. There's always room for more discussion (and follow-up questions) but you might be interested in [this older answer of mine](_URL_0_) about the prelude to Mussolini's rise. [This great answer](_URL_1_) by u/Klesk_vs_Xaero is also great overview of Italy's descent into dictatorship
| [
"\"Fascism is the concentrated expression of the general offensive undertaken by the world bourgeoisie against the proletariat... fascism [is] an expression of the decay and disintegration of the capitalist economy and as a symptom of the bourgeois state’s dissolution. We can combat fascism only if we grasp that it... |
Why is it that the inside of fresh water pipes that feed houses don't need regular cleaning? | They are designed so that there are no blind ends or dead angles, where bacteria or deposit could build up. An example of how this failed was a case where the cooling system of a power plant had a blind end in their piping. *Legionella* bacteria found the place, made a little colony and then spread around the area with the mist from the cooling tower, infecting many people.
Second, tap water is chlorinated, even if it's pure at the source, exactly in order to avoid bacterial buildup. Small concentrations of chlorine are good enough to prevent growth, even if they can't be used for desinfection as such. A little ammonia is added, because when chlorinated, it forms more persistent nitrogen chlorides that retain the active chlorine in the water better than plain chlorine, which gives only a chlorine solution. If there's a breach of the integrity of the piping or a problem at the source, a "shock chlorination" is done to actually desinfect the pipes.
Even so, buildup is a thing. Fortunately, much of it is inorganic, like calcium and iron salts. Because it's washed continuously with water, it attains a pseudo-steady state where it releases little material into the water. However, over time, it can build up to such a point that it affects the water pressure. | [
"Moreover, because the acidic or basic drain cleaners themselves are washed down the drain, this contributes to pollution in the water supply. The heat generation can also soften plastic PVC pipes, and the pressure buildup by gas generation can cause older pipes to burst. Commercial chemical based solutions can cau... |
what makes our ears ‘clog’ in high altitudes and what makes them pop by yawning? | When you go from a lower altitude to a higher altitude, the ambient air pressure decreases. Because the air inside of your eardrum is semi-trapped (you can clear them) it expands as you go higher and puts pressure on the eardrum. When you yawn/chew/etc it helps open up the eustachian tubes that go from the backside of your eardrum to your throat and equalize the pressure.
Source: I have 2200+ skydives and had to clear my ears a lot. | [
"During a yawn, the tensor tympani muscle in the middle ear contracts, creating a rumbling noise from within the head. Yawning is sometimes accompanied, in humans and other animals, by an instinctive act of stretching several parts of the body, including arms, neck, shoulders and back.\n",
"A similar hypothesis s... |
Imagine an empty room with no windows/doors or any point of entry and escape with just a light bulb inside and a light switch outside. What will happen to light if I open the light for 10 seconds and turn the switch off? Will the brightness remains or will fade? Why? | The light will fade almost instantly. As the light strikes the wall, part of it is reflected and part of it is absorbed. The reflected light will bounce away from the wall until it hits another wall (or floor/ceiling) and then again, part of it is absorbed and part reflected. With every bounce the intensity of the remaining light decreases. And with the speed of light being very high compared to the size of an average room, there are many bounces in a short period.
Consider the following, we have a room with 10 meters between two walls and a light source at one end, shining a straight beam in the direction of the other wall. All walls are made of very high quality mirrors that reflect 99% of the incoming light. How much is left of a light pulse after 1 milisecond?
In 1 milisecond, light travels 300,000 meter, so that's 30,000 bounces. Each bounce reduces the intensity by 1%, so that means we have a fraction of 0.99^30,000 remaining: Approximately 10^-131. So after 1 milisecond, a thousandth of a second, any light will be completely gone. And that is in the scenario with very high quality mirrors. With regular walls only reflecting a small part of the incoming light, the intensity will become too small to detect in microseconds or even less. | [
"The width of the rooms is further subdivided into three sections of and this module determines the width of doors, windows and passages between rooms within the apartment. The wooden windows have two sets of nine movable slats that can be independently controlled to modulate the natural light in the room, they can... |
why are surgical gowns, masks, and gloves green or blue? | They used to be white. There's a sort of 'surgeon legend' about the green being used because it was easier to see in a surgical field (brightly lit + whites = too bright). But then also that green/blue is actually opposite red and makes it easier to see blood. But I think it's kind of one of those "was written down somewhere once" and became cannon type of things. Whether it's true or not. | [
"All gowns, other than the dress gowns of doctors, are made from black material. The dress gowns of Doctors of Philosophy and other doctors of this level (such as DBA, DArch and EdD) are made in claret, while those of higher doctors are made from scarlet cloth. For this purpose, the degree of Doctor of Medicine was... |
In medieval times, how long could a knight physically fight in a battle? The swords were heavy, the armor was heavy. Nutrition was poor. Could they last more than 30 minutes? | This doesn't directly answer the question, but I think you may be overestimating the weight carried/worn by a knight.
The average sword weighed somewhere around 3lbs, an M16 with full ammo weighs about 9lbs.
A suit of full-plate would generally weigh less than 60lbs (sometimes significantly less), such armor was also custom fitted and designed to be relatively easy to wear with little strain. A full set of modern combat gear tops 60lbs, and is "one-size fits most". | [
"BULLET::::- According to the given statistics, the Knight had a size advantage of 1 inch and 10 lbs; roughly equal by the standards of Deadliest Warrior matchups. However, the Knight's gear was 50 lbs heavier.\n",
"BULLET::::- According to the given statistics, the Knight had a size advantage of 1 inch and 10 lb... |
If I were to travel ten light years going the speed of light, would it seem like an instant to me, but ten years for an outside observer? | You *cannot* travel *at* the speed of light, so this question becomes pseudo-scientific.
But let's say you were travelling *really* close to the speed of light. Like *really, really* close. Like 99.999...999% with a billion, billion 9s after the decimal place. Then yes, what you say is correct. To you, the journey would be nearly instantaneous. To me, standing on the Earth, the journey took you a little more than ten years (assuming you travelled 10 light-years).
But, if I could measure your clock during your journey, I would notice that your clock has come to a near standstill. You and I would both agree that, to you, the journey was nearly instantaneous. | [
"Since one might not travel faster than light, one might conclude that a human can never travel further from the Earth than 40 light-years if the traveler is active between the age of 20 and 60. A traveler would then never be able to reach more than the very few star systems which exist within the limit of 20–40 li... |
How does pilot wave theory account for quantum fluctuations? | The guided particle doesn't move through space, it moves through the space of possible positions of all particles, which instead of just 3 dimensions has 3N dimensions, where N is the number of particles. The positions of particles in a measurement device is included in this, so the question of what kinds of measurements are possible is also determined by the motions of the guided particle, which is in turn determined by the pilot wave.
The pilot wave is just the total wavefunction of all the particles and is *unaffected* by the guided particle, so all the usual aspects of quantum mechanics are already there, including the uncertainty principle. The only role of the guided particle is to bounce around like a ball in a pachinko machine, with the odds of outcomes determined by the pilot wave but only one of them realized by the path of the guided particle. So ultimately the probability of measuring a particle's position or momentum in a given place is determined by the wavefunction, and the statistics of those measurement results must obey the uncertainty principle. | [
"The pilot wave model, originally developed by Louis de Broglie and further developed by David Bohm into the hidden variable theory proposes that there is no duality, but rather a system exhibits both particle properties and wave properties simultaneously, and particles are guided, in a deterministic fashion, by th... |
AskScience AMA Series: I am Jamil Zaki, professor of psychology at Stanford University and director of the Stanford Social Neuroscience Lab. I wrote a book called The War for Kindness, which shares stories and research about how to fight for empathy even when it feels impossible to some days. AMA! | Are there empathy building exercises that have tangible impact in practical life ? Do such exercises really work or are just scoffed off by adult participants ? | [
"G2Conline is an interactive educational website that provides extensive background information on key topics in neuroscience and brain disorders. There are many video clips of interviews with scientists, including Nobel laureates James Watson and Eric Kandel.\n",
"APS publicizes psychology research in an effort ... |
Does Anybody have any information on the "Phantom Divisions" of the United States Army during World War II? (Cross Posted From r/Military) | Could they be similar in role to the [Ghost Army](_URL_0_)? | [
"This is a list of formations of the United States Army during the Second World War. Many of these formations still exist today, though many by different designations. Included are formations that were placed on rolls, but never organized, as well as \"phantom\" formations used in the Allied Operation Quicksilver d... |
why does it seem easier to get stuck in a comfort zone as an adult? | In the old days, life changed very slowly. The way the world worked when you were 5 years old was the same when you were 75 years old. So by the time you had reached adulthood you pretty much had figured out what there was to figure out. | [
"A comfort zone is a psychological state in which things feel familiar to a person and they are at ease and (perceive they are) in control of their environment, experiencing low levels of anxiety and stress. In this zone, a steady level of performance is possible.\n",
"Ambivalent attachment is characterized by a ... |
Constellations disappearing: | Stars rarely just go missing, but the constellations will change over time due to stars moving at different velocities. Here's [what some of them will look like in 50,000 years](_URL_0_). | [
"The constellation appeared in later star atlases through the 19th century but was rarely used by the end of the century; Richard Hinckley Allen noted its most recent use had been in 1878 in Father Angelo Secchi's planisphere, but stated \"it is seldom found in the maps of our day.\". The stars were later absorbed ... |
Why did Britian use the bolt action Lee-Enfield as their primary battle rifle when repeating technology (M1 Garand, Gewehr 41, etc) was already developed and working? | hey, sorry for the very late answer, i hope i don't break any rules by digging up old unanswered questions.
To answer this question you have to understand how the adoption of a self loading rifle would have worked in britain in the 1930's.
To get a new rifle adopted, someone in the board ordnance has to be persuaded to the idea of mass issuing a self loading rifle to the rank and file of the British army. Already we are fighting an uphill battle for the following reasons.
> A very limited amount of choice in rifles
halfway the 1930's there was a very limited amount of options for a self loading rifle. If we exclude all designs that aren't able to fire full power .303(the British standard munition of the time)or other full power rifle rounds we are left with weird enfield conversions and unproven prototypes(most of which they aren't even aware).
The belgian design ( the later fn49) and french design(the later mas49) were still secret and incomplete at this time too.
There is the pederson with a toggle lock, which causes problems in itself. And he zh29, familie of the zb-26(the gun the bren was designed on), but it also has problems that make it unsuited for mass adoption.
The most realistic options would be the then avs36(later svt40) and the m1 Garand.
Both those rifles would be patented so just copying them would not be an option. Lincensed production is very expensive and thus not really an option. Britain also still has a large arms production industry at this time, so they would design it themselves most likely.
> .303 british
.303 is an obsolescent round at this time, it underperformed compared to other cartridges of it's time and was expected to be replaced in the 1910's with .276 enfield, but testing showed some problems with the munition and ww1 halted this change completely.
The problem with .303 is that it is a rimmed cartridge , this causes issues when designing magazines and feed systems as there is a possibility to get the rims of the rounds caught on each other and causing so called 'rimlock'. Fully rimmed cartridges are fine for belt feds, but are very undesired for magazine fed solutions. There are ways to minimize rimlock, but no sane person would design a brand new mass issued main infantry rifle in .303(unless really desperate)
But changing to another caliber is not really an option at this time, the British empire has a massive stockpile of weapons and ammunition from ww1, and re-barreling existing vickers and enfields and producing all the new ammo is something that the british empire does not want to do in the economic depression of the 30's. They also just adopted the bren in.303 so .303 was there to stay.
> Massive stockpiles of enfields
Like is said in my last paragraph, the British empire has an absolute massive stock pile of enfields of various types in their armories. Most of them were converted to the latest patern or were in the proces of being converted. Building a new self loading rifle and spare parts, and then producing enough for the whole armed forces, takes a lot of time and money, both of which britain didn't want to spend on this.
> Doctrine and tradition
The British army had a well established infantry doctrine, and the enfield was an important part of it. Those guys loved their enfields, changing to a self loading rifle would require changing doctrine and military tradition, something generals at the time wouldn't have been keen on.
The British military command took years to remove the magazine cutoff from the enfield, a feature that was almost never used.But some people clinged to it for some odd reason, changing their mind about enfields would be even harder.
And we have to be honest here, a self loading rifle is better than a bolt-action, but the self loading rifle you would get at this point would not be a massive improvement. Add to this all the loss of experience with the platform and the gains would be fairly limited.
Additionally they would have to rewrite manuals , retrain soldiers, change the logistics as they would undoubtedly use more ammo and so on. These things all take a lot of time.
So if we take all of this together, and we place our selfs in the shoes of the British person at the board of ordnance.
We would have to do the following to adopt a selfloading rifle in the 30's :
Firstly we have to design it in Britain because there aren't any real viable designs on the market, and use another cartridge as .303. Which we do not want to do at this time, and if we designed it with .303, we would have to spend time and money preventing problems caused by the cartridge.
Then we have to pass military trials and probably refine the design, then probably do trials again(with the refined rifle).
Then we have to convince even more generals and the rest of the board of ordnance that this self loading rifle is so much better than their tried and trusted enfields, and that their budget should not be spent on other things like more bren's, vickers, tanks, ... .
After all of that we have to refine the design for mass production(not always the case but prototypes are not mass production friendly most of the time.), and tool up one or several factories, creating jigs, tools, milling machines... .
And the military command has to rewrite arms doctrine, and formulate a new manual of arms for the rifle, and so on.
After all of that we are probably in the same boat as france, russia, poland and belgium, they started development fairly early, hit some snags and before they could produce any meaningful number of rifles, ww2 had started.
Adopting a self loading rifle during the war is even worse, after dunkirk the british needed to rearm a very large part of their army. They needed to start cranking out rifles, submachine guns, bren's, tanks, ships,aircraft,..., by the millions. The massive undertaking of designing a new rifle and retooling factories at that time is all but impossible.
The USA was the only country to field a self loading rifle as their standard infantry rifle in ww2, they did not face many of the problems European nations faced for developing a new self loading rifle. And even then it took garand years to get his design right, and for production to ramp up.
As for the g41, that rifle entered the scene when the war had already started and had some major flaws in itself. Most notably using the bang system to trap gas, instead of a hole in the barrel. Therefor it was never issued in any large numbers.
| [
"The British Army looked at the M1 as a possible replacement for its bolt-action Lee–Enfield No.1 Mk III, but it was rejected when rigorous testing suggested that it was an unreliable weapon in muddy conditions. However, surplus M1 rifles were provided as foreign aid to American allies; including South Korea, West ... |
conservation of mass says matter can't be created nor destroyed. do we have any theory of how this fundamental law was originally ignored to create the big bang? | The original question not entirely accurate. Mass/energy (they are the same thing) cannot be created or destroyed, but mass *can* be turned into energy, and vice versa.
Nuclear reactions attain their vast energy outputs by converting a small (but non-trivial) amount of mass into energy. Even chemical reactions are theorized to do the same, but obviously a far smaller amount. In both cases, the total mass/energy remains the same before and after the reaction occurs. | [
"Mass and Energy Balances is a fundamental \"laws of physics\" states that mass can neither be produced nor destroyed. It is only conserved. Equally fundamental is the law of conservation of energy. Although energy can change in form, it can not be created or destroyed also. The beauty of this algorithm is the capa... |
The Norse people were shown to be capable raiders, especially in the British Isles. The Anglo-Saxons despite divided were socially and militarily organised, why did they, or others, never seek or attempt to attack Scandinavia? | I afraid that I cannot offer a single definitive answer to 'why X didn't Y' type question of OP. Instead I'll make some corrections to OP's premise below.
First of all, there was no known unified large-scale kingdom in Scandinavia before the middle of the 10th century (until the rise of the Jelling dynasty in Denmark), possibly except for the kingdom of the Godfred family in its southernmost part (Southern Denmark) in the early 9th century. Three Nordic medieval kingdoms, that is to say, Denmark, Norway and Sweden have primarily been political products since the last decades of the first millennium. In other words, it was not so likely that the majority of the Norse raiders in the middle to late 9th century were under the direct influence of one of such rulers in the unified kingdom, though some Frankish rulers might have misunderstood so that they tried to negotiate the ruler of 'the Danes' to deal with the onslaughts of the raiders mostly in vain.
Apart from the apparent problem, navigation durability of the fleet of any non-Scandinavian power at that time from their homeland to Scandinavia (that I personally have much doubt), to annihilate or to conclude a treaty with one or two polities (petty kingdoms) in Scandinavia around 900 to stop raiding would not have eliminated the threat of Norse raiders' invasion since there were probably much more polities remained than the fleet could possibly handle.
And yes, there were indeed some attempt of non-Scandinavian European powers, especially some German rulers, to invade the southernmost part of Viking Age Denmark in the 10th century, as I illustrated in [The Danes or Vikings from later Denmark would often raid the Frankish Empire and later what would become the Holy Roman Empire. How were they so successful and how did the Danes avoid being conquered by the big powers?](_URL_0_). I suppose that main force of such German invasions comprised of cavalry and infantry, not the fleet, as long as attested in narrative sources and based on the location of the battlefield (Danevirke, the palisade built by Danish rulers).
On the other hand, I should also point out the fact that not all the Norse raiders didn't probably directly came to the British Isles from Scandinavia. Many Viking war bands were active around the British Isles as well as the English Channel in the middle of the 9th century, and now researchers suppose that they kept 'stayed' in this area for more than a few years, and sometimes took shelter in one of 'their' new political centers nearby, such as Dublin in Ireland or Rouen in Normandy, or further, York in Northern England, instead of Scandinavia. Then, targeting one of these 'diaspora' polities rather than distant petty kingdoms in Scandinavia would be much more realistic and successful tactic against the Norse raiders, and some local rulers actually did so (note that the Norse ruler was once expelled from Dublin in the early 10th century (from 902 to 917)).
References:
* Brink, Stefan & Neil Price (eds.). *The Viking World*. London: Routledge, 2008.
* Garipzanow, Ildar H. 'Frontier Identities: Carolingian Frontier and the Gens Danorum'. In: *Franks, Northmen, and Slavs: Identities and State Formation in Early Medieval Europe*, ed. Id., Patrick Geary & Przemyslaw Urbancyzk, pp. 113-43. Turnhout: Brepols, 2008. | [
"Almost by definition, opponents of the Vikings were ill-prepared to fight a force that struck at will, with no warning. European countries with a weak system of government would be unable to organize a suitable response and would naturally suffer the most to Viking raiders. Viking raiders always had the option to ... |
What happened to Dutch painting in the 18th century? | Apparently during the 18th century the Dutch Republic was seen as being in a decline. Instead of commissioning new works by comtemporary artists, patrons preferred to obtain works from the Golden Age, when their country was more stable and prosperous. And in 1718, Dutch artist Arnold Houbraken published his first volume of biographies of Dutch and Flemish artists, which "initiated a retrospective assessment of the artistic production of the past century, and thereby marked its end."
Source: A Worldly Art: The Dutch Republic 1585-1718 by Mariet Westermann | [
"The enormous success of 17th-century Dutch painting overpowered the work of subsequent generations, and no Dutch painter of the 18th century—nor, arguably, a 19th-century one before Van Gogh—is well known outside the Netherlands. Already by the end of the period artists were complaining that buyers were more inter... |
how does an led change colors? | A color changing LED isn't one LED in a package but three LEDs along with a small computer to drive them. The LED is made up of red, green and blue LEDs each of which can be controlled by a microcontroller. Since the two legs on the LED that supply the power are connected to the microcontroller and not the LED elements a current limit resistor is not required.
The microcontroller is able to turn each of the colors on or off, so if the red LED is turned on then the output from the color changing LED is red. When the blue LED is turned on it is blue, if both the blue and red LEDs are turned on then the color changing LED is a shade of purple (called magenta). Similarly combining red with green gives yellow and blue & green gives cyan.
Although the color changing LED uses the six colors mentioned above, it slowly changes from one to another. This is still done using the three basic red, green & blue elements. If the red LED is combined with the blue LED, but the blue LED is only driven at 50% of its normal brightness then a color half way between red and magenta is generated.
Whilst the red LED is left turned on, if the blue LED is slowly taken from 0% brightness to 100% brightness then the color will gradually change from red to magenta.
If a standard LED is turned on and off very quickly, say 100 times every second then as far as the human eye is concerned it looks like it is constantly on. If the amount of time the LED is on for is the same as the time it is off for then it will be on for 50% of the time and 50% of its full brightness.
This same method can be done with the three LED elements inside the color changing LED. This means it is possible to combine any amount of the red, green and blue to give the desired color. Looking once again at the change from red to magenta, if the blue LED starts mainly turned off, goes to being on and off in even amounts and then to mainly being on then the the color will change as required.
[Source](_URL_0_) | [
"By selection of different semiconductor materials, single-color LEDs can be made that emit light in a narrow band of wavelengths from near-infrared through the visible spectrum and into the ultraviolet range. As the wavelengths become shorter, because of the larger band gap of these semiconductors, the operating v... |
How will it affect US economy if bill gates were to transfer all his money to some other country ? | The exact disposition of Bill Gates' personal wealth isn't information we can get our hands on, since he's a private citizen and it's none of our business. So instead let's make up a person with the same order of magnitude of wealth, imagine how he would store his wealth, and then answer the question based on that.
So here's Mr. John Smith, with a net worth of $100 billion, making him very wealthy indeed. To keep things simple, let's assume he carries *no debt at all* (which is implausible in the extreme), so his net worth comes from just the sum total of the value of all his assets.
What exactly are those assets?
Well, let's say that a *very small fraction* of that wealth is in cash. Everybody needs to deal in cash transactions on a regular basis (paying for lunch, putting gas in the car and so on), so let's say that Mr. Smith has cash holdings with a value of … oh, let's say $100,000. Just to pick a figure. That's the account he spends his money out of, to pay the electricity bill and such like that.
Where exactly is that money? If we imagine that it's sitting in *cash* — literal currency, like bills and coins — in a vault somewhere, we'll be quite wrong. Mr. Smith *could* store his cash assets that way, but he doesn't, because that's not a reasonable thing to do. Instead he keeps his cash holdings in a bank account. In that form, his cash wealth (which remember, has a value of $100,000) exists as a *liability* on the books of his bank. Basically, that means Mr. Smith goes to the First National Bank of Wherever and says "I will give you $100,000 if you promise I can come ask for it back whenever I want." The bank says sure, and takes his money, and in return gives him their promise that he can withdraw it at any time. That makes the bank *liable* to Mr. Smith for that money.
If Mr. Smith wants to move that money overseas, it's no problem at all. He simply goes to the bank and asks for whatever cash they're liable to him for. The bank provides it in whatever form Mr. Smith prefers (currency, or more likely a bank check), and Mr. Smith goes about his merry way. The bank can do this because *banking regulations require* banks to be able to give their depositors the money they're owed whenever they're asked for it. So the bank will always be able to give Mr. Smith what he asks for. If the bank ever *can't* give Mr. Smith what he asks for (as well as all their other depositors), the bank will be *insolvent,* and a regulatory organization called the FDIC will step in to conduct an orderly closure of the bank and transfer of its assets and liabilities to another institution.
So all that is a very long-winded way of saying that if Mr. Smith wants to withdraw his cash and put it in another bank overseas, he will have no problem doing so, and there will be no effect of his doing so, because banks are regulated to make sure that's true.
What about the rest of his assets? Well, Mr. Smith keeps them, as any reasonable person would, in a diversified collection of various things of value. We can broadly divide that collection into two categories: Things which are *easy* to sell, and things which are *hard* to sell. Things that are easy to sell include shares of mutual funds or stocks, for example. Those are things which a great many people want all the time, so if Mr. Smith decides to sell them, he'll have no trouble at all finding a buyer.
Let's imagine Mr. Smith owns 10,000 shares of a particular mutual fund. If he wants to, he can sell those shares at whatever the current market price is, then take the cash and deposit it in his overseas bank account. This will be very easy for Mr. Smith to do; it's just a phone call to his broker, who just has to put a sell order into his computer and then cut Mr. Smith a check for the profits. Mr. Smith then takes that money and sends it to his new overseas bank, where it gets credited to his account.
That's generally true of all of Mr. Smith's *liquid* assets — that is, assets which are very easily converted into cash. He can sell them quickly and easily for pretty much their nominal value, and then take the cash from those sales and do whatever he wants with it.
So now Mr. Smith has the $100,000 in cash he withdrew from a US bank and deposited into an overseas bank … and also some huge sum, in the billions of dollars, he had invested in securities which he liquidated and deposited in his overseas account.
But what about the rest of Mr. Smith's assets? His home, his furniture, his car, all those things? These are called *illiquid assets*, which generally means they're hard to sell. In order to sell his house, Mr. Smith needs to find somebody who wants to buy it. That's not guaranteed to be an easy thing to do! In fact, Mr. Smith might be unable to find *any* buyer for his house without lowering his price to some small fraction of what his house is nominally worth. So either he can choose to sit on those illiquid assets until he finds a buyer for them, or he can sell them at a loss to get out quickly.
Since the premise of the question is that Mr. Smith wants to "transfer all his money to some other country," we'll assume that he wants out even if it costs him money. So we'll say he sells all his illiquid assets for pennies on the dollar. The result here is pretty obvious: Mr. Smith's net worth goes down! He converted assets with a certain nominal value to cash of *less* value, so he's worth less money in total. But the good news is now he has his cash, so he can send that to his new overseas bank as well and deposit it.
Now Mr. Smith has successfully moved all his money to "some other country." What's the net result on the US economy? Essentially none. Mr. Smith's cash holdings were very small, and the bank had no problem covering their liability to him, so that doesn't have any effect. All his liquid assets — shares of stock, mutual funds, bonds and so on — were easy to sell, so other buyers snatched them up at fair market value and no significant change in wealth occurred there; assets just changed ownership. Mr. Smith sold off his *illiquid* assets at a loss, so he took a hit, but other parties got a bargain, so the net result there is pretty much nil as well.
But of course, now Mr. Smith has a problem. See, all his money (less the losses he took from liquidating his holdings) is in *cash,* and that's not good. Mr. Smith now has to turn around and use his cash to *buy more assets,* so his money can earn him an income. In so doing, he ends up investing his money *right back into the same companies he was holding before,* because they're still the right choice for him. Along the way, Mr. Smith has to cover certain fees incurred by selling and buying securities, so he loses some money, but the total overall net result on the economy is … well, absolutely none, really. Assets changed hands, and a little wealth was created and a little wealth was destroyed, but no significant effects occurred … except for Mr. Smith having to do a heck of a lot of paperwork for no real reason. | [
"In 1999, his wealth briefly surpassed US$101 billion. Despite his wealth and extensive business travel, Gates usually flew coach in commercial aircraft until 1997, when he bought a private jet. Since 2000, the nominal value of his Microsoft holdings has declined due to a fall in Microsoft's stock price after the d... |
Is there a way to conceptualise complex integration? | In complex analysis, an integral is less like the "Finding the area under a graph" integral of calc 1, and more like the line integrals of vector fields in calc 3. These path independence results are actually there in normal multi-variable calculus. In this context, integrating a differentiable complex function is similar to integrating on a conservative field, where the path doesn't matter. | [
"Integration by parts is a heuristic rather than a purely mechanical process for solving integrals; given a single function to integrate, the typical strategy is to carefully separate this single function into a product of two functions \"u\"(\"x\")\"v\"(\"x\") such that the residual integral from the integration b... |
cannabis strains classification. | It's both. There's a classification system to differentiate between plants, and from the same family of plants.
And with cannabis, naming the strains means that you can get the same product again without confusion; but you can name any strain the name you want. There's no science behind that. | [
"The scientific debate regarding taxonomy has had little effect on the terminology in widespread use among cultivators and users of drug-type \"Cannabis\". \"Cannabis\" aficionados recognize three distinct types based on such factors as morphology, native range, aroma, and subjective psychoactive characteristics. \... |
Why are siphonophorae considered "colony organisms"? What's the difference between a morphologically specialized zooid and an organ? | We consider siphonophores to be a colony organism because of how they develop and are organized compared to other cnidarians.
The cnidarians body plan generally falls into one of two categories. The medusa or the polyp. The most common example of a medusa form cnidarian is a jellyfish, and a common example of a polyp would be a sea anemone.
Many cnidarian species use both forms during their life cycles. Most jellyfish species start off life as a polyp, which often forms an asexually reproducing colony before transitioning to the free swimming adult medusa.
Other cnidarians also grow as colonies but remain that way for their whole lives. Corals for example reproduce asexually and spread just like jellyfish polyps, though they form a skeleton around themselves. We don't consider a coral colony to be a single organism even though they work together to build the skeleton and have the same DNA. But in many species connections are retained between the polyps that let them share food and resources.
Siphonophores are simply a more advanced version of this same process. They're a colony of organisms that each have specialized function, be it feeding, swimming, defense, reproduction, or what have you. The level of organization is higher than with corals, but the system is basically the same.
Some siphonophores don't reproduce directly. Instead they live as a colony that releases zooids from time to time in the form of medusa, jellyfish-like organisms that are capable of living completely independently. These medusa-zooids are known as eudoxids and they are the sexually mature form of the species. They're the ones that reproduce sexually to make new eggs that develop into siphonophore colonies again.
The amount of diversity among siphonophores is simply staggering. Some have the free swimming eudoxids like I mentioned, and in some species these eudoxids can even bud off additional zooids that will also live as medusa, but they're unable to asexually produce a new siphonophore colony.
Others keep the medusa attached to the colony and release eggs and/or sperm directly from the main colony. | [
"Siphonophores are of special scientific interest because they are composed of medusoid and polypoid zooids that are morphologically and functionally specialized. Each zooid is an individual organism, but its integration with others is so strong that the colony attains the function of a larger organism. Indeed, mos... |
Historians, how many of you speak/ have fluency in languages relevant to your areas of study? How important would knowledge of such relevant languages be to you? | I work in ancient materials, so it's reading, not speaking that's needed. Reading wise, I'm pretty solid in Hebrew and Greek, ok in Syriac. In terms of modern academic languages I can read/write/speak German pretty well. I got a relatively late start on languages and actually consider myself somewhat behind. Before completing the PhD I'll need two languages more minimum, and preferrably four. | [
"The history of foreign-language education in the 20th century and the methods of teaching (such as those related below) might appear to be a history of failure. Very few students in U.S. universities who have a foreign language as a major attain \"minimum professional proficiency\". Even the \"reading knowledge\" ... |
why airlines don't sell empty seats on flights at cheap rates | Because people who purchase tickets last minute usually *have* to travel and will pay the full price.
It's rare that a plane will be relatively empty. When that happens, it's probably just a fluke. If a route regularly has a lot of empty seats, they airlines will drop one of the flights and put it on a more profitable route. | [
"Airlines may ask for volunteers to give away their seats or refuse boarding to certain passengers in exchange for a compensation that may include an additional free ticket and/or an upgrade in a later flight. They can do this and still make more money than if they booked only to the plane's capacity and had it tak... |
Part 1: What causes a person with Tourette's to shout obscenities? Part 2: What would happen if they never learned any curse words? | I would just like to point out that not all verbal tics are curse words— [here is an article about a woman with Tourette's Syndrome who involuntarily says the word "biscuit" ~900 times an hour.](_URL_0_) The article also mentions that
> "Fewer than 10 percent of all patients [with Tourette's] swear or use socially inappropriate words." | [
"The typical clinomorphism of Tourette's is both an oversimplification and a conflation of various aspects and conditions pertaining to some persons with Tourette syndrome. Some people with Tourette syndrome do have involuntary offensive speech which is termed coprolalia and is sometimes clinomorphised into the ter... |
why can't we use the ocean to dump onto fires? | Saltwater changes the pH of soil and can really hinder the regrowth of plant communities.
If you consider an area that seldom receives rain then you have a very long time before enough freshwater (rain) has fallen to restore soil chemistry. | [
"In some cases there is sufficient heat, fuel, and oxygen to allow spontaneous combustion and underground fires to smolder for some considerable time, as has occurred at a natural reserve in Spain. Such fires can cause surface subsidence, presenting an unpredictable physical hazard as well as environmental changes ... |
Tuesday Trivia | Missing and Destroyed Documents | I deal with formerly classified documents pretty much every day. Government secrecy makes the terms "missing" and "destroyed" a little tricky to use, because they may be effectively missing and destroyed to most historians, but in reality they are often just being denied to us. Some secret documents do go missing, however, because they get misplaced or misfiled within the gargantuan government bureaucracy that at one point was trying to keep them secret, even if they no longer contain secret information in them. In fact, when it comes to secret documents, being misplaced is more common than being destroyed, because legally you cannot detroy secret documents without leaving a large paper trail — so that means that the documents are usually preserved, _if_ anyone can figure out where they are preserved.
Anyway, on my blog not too long ago I wrote a series of very long posts about my hunt for, eventually success at finding (through unorthodox archival practice), and frustrations with declassification, regarding the legendary unredacted copies of the security hearing of J. Robert Oppenheimer. [Here is the link to part I](_URL_1_), where I describe why I started looking for them and how I found them. [Here is the link to part II](_URL_0_), where I analyze the new transcripts for what they do (and don't) tell us about the Oppenheimer case.
Separately, a few years back [I wrote about a case where the US government "lost" about 4 million pages of secrets](_URL_2_) through misfiling. It happens more often than one might think, if one thought (erroneously) that the US government was very good at keeping track of large amounts of historical paperwork (it is not). | [
"Some of these documents deteriorated due to chemical treatment performed by Firkovich. Other documents which were suspected forgeries disappeared; Firkovich claimed they had been stolen. The collection was moved to the Imperial Public Library in 1863.\n",
"In 1697, an Austrian general Eugene of Savoy, raided the... |
To what extent was the Japanese government aware of the Manhattan project or similar nuclear weapons project prior to the deployment of the nuclear bombs during WWII? Was there any awareness that such a thing was possible? | Practically all physicists knew that atomic bombs were theoretically possible after the discovery of nuclear fission and the nuclear chain reaction in the early months of 1939. Most thought that they were a technology that was not going to emerge for another decade or so, and if they were interested in chain reactions, they focused on the possibility of using them to generate power, which is a much easier problem than that of a bomb. The idea of atomic bombs had been "in the air" in a general, science-fiction sense since 1914, but certainly by 1939 they were a common trope in "gee whiz" newspaper and magazine stories. When fission was discovered there was plenty of press about its possibilities, though, again, scientists had long grown skeptical about the idea of being able to release atomic energy on an industrial or military scale, because most of the discussion of it had been uninformed nonsense, and there were many technical factors that were still unknown (and, had nature differed in tiny, almost imperceptible ways, would make such weapons impossible, or at least unlikely in the near term).
The Japanese had a small nuclear project that looked into both of these possibilities. So they were aware of the theoretical potentials, though they also recognized that to develop even the power option would require creating an entirely new industry from scratch, and involve a lot of risk, and that developing a weapons option would be even more difficult.
As for specific awareness of an Allied projects, there is no evidence that anyone in Japan considered it a real issue. The Japanese scientists concluded that even the Americans would have a tough time of making a nuclear weapon. (They were right — it wasn't easy.) They seem to have made no serious effort to find out whether it was true, however. If they had, I suspect they would have quickly figured out that the United States was expending vast resources on the subject — there was a lot of evidence in plain sight, in the form of leaks and mysterious disappearances (all of the nuclear physicists stopped publishing, for example). But Japanese intelligence in the US mainland was terrible, on the whole, so I tend to just chalk up this lacunae to that fact.
I have never found any evidence that the Germans had much of an indication of the American bomb project either. [I have written on this question a bit here](_URL_0_). Basically, from what sources I have available to me (which are not complete, to be sure), it seems the Germans believed that they were far ahead of the Americans with regards to fission research. They did send information to German spies asking them to look into the question but the very questions they asked indicated that they thought it was small-scale and probably not very sophisticated. (The spies were immediately caught — the Germans also had poor intelligence in the mainland USA.)
The Soviets are a different story. They had indirect indications of an American bomb project — they noticed that the people who were working on fission right before the war suddenly vanished — and they also had volunteer spies (moles) in both the UK and US portions of the fission work. They had an extensive overview of the project as well as knowledge of many specific technical details as a result, from very early on. So it was not unexpected at all for them.
As for other countries, one of my favorite episodes is when a group of Indian physicists showed up to the United States during the war and started asking around to find out where the uranium was being enriched. The Manhattan Project security people quickly found them and asked them where they had gotten such an idea. The Indians (quite indignant about being interrogated) told them it was obvious to any competent physicist that this was something the United States must be doing. They were told to stop asking questions and released. | [
"In addition to developing the atomic bomb, the Manhattan Project was charged with gathering intelligence on the German nuclear energy project. It was believed that the Japanese nuclear weapons program was not far advanced because Japan had little access to uranium ore, but it was initially feared that Germany was ... |
What causes absorption of right- or left- circularly polarized light by chiral molecules? | The answer lies in the polarized nature of the electric and magnetic fields induced by the light. Polarized light, like all light, will induce magnetic and electric dipoles within the matter it interacts with. These induced dipoles are distortions of the electron clouds around the molecule, and can thus be seen by looking at the absorbance spectra of chiral molecules using polarized light.
So polarized light will preferentially induce a directional dipole (probably poor language) in the molecule. Because of their chiral nature, chiral molecules have unique dipole moments that lead to absorption. | [
"Simply put, since circularly polarized light itself is \"chiral\", it interacts differently with chiral molecules. That is, the two types of circularly polarized light are absorbed to different extents. In a CD experiment, equal amounts of left and right circularly polarized light of a selected wavelength are alte... |
[META] Merry (UTC) Christmas and Happy Holidays to AskHistorians! As an extra-special gift from the Asia flairs, we've completely revamped our book recommendation list! Links below! | Now we get to the comments thanking the contributors to the list. Firstly, I’d like to give special thanks to three flairs whose contributions are not (at present) immediately apparent on the list itself.
* Firstly I’d like to thank fellow Asia flairs /u/keyilan [Moderator | Historical Linguistics | Languages of Asia](#flair-moderator) and /u/NientedeNada [Late Edo Period | Meiji Restoration](#flair-asia), who were of great help during the initial planning phases in terms of deciding upon what changes to make, from broader issues like the extent of the rewrite to more minute issues of formatting.
* I’d like to again thank /u/Georgy_K_Zhukov [Moderator | Post-Napoleonic Warfare & Small Arms | Dueling](#flair-moderator) for taking the time to add affiliate links to the doc, as well as more generally for being such a great mod and such a prominent presence on this sub. Rock on, Georgy! | [
"\"A Long Vacation\" reached number two on the Weekly Oricon Album Chart and was the eighth best-selling album of the 1980s in Japan. The 20th anniversary edition reached number 13 and the 30th anniversary edition peaked at 19. Following Ohtaki's death in December 2013, the 30th anniversary edition jumped to number... |
does piracy actually hurt the profit of corporations? | If any brainy person with data can answer this well, I hope they also take into consideration the affect of franchise knock-on, which is often not discussed. And arguably makes up a larger long term profit and vertical integration, or market synergy and all that.
For example people who may pirate a show still love the show and thus buy shirts and toys and the Happy Meal. So missing out on 3 dollars for ad views is nothing compared to the $300 collected from the new Fan. | [
"In the 21st century, however, the company began to lose revenue due to the piracy of the video and album releases, with chief-executive Marie To commenting, \"Profit? We are barely making it.\" Works released by the company are also banned in Vietnam, which has the largest source of pirates.\n",
"Some countries ... |
Why does male pattern baldness follow the pattern it does? i.e. from the top of the head down, often in a perfectly straight circle around the head. | It doesn't. Sometimes the hair line recedes all the way to the back of the head, sometimes a bald spot appears on top of the head and increases in diameter over time.
Sometimes there is even a patch at the front that is missed leaving a little island of hair.
_URL_0_ | [
"The head patterning is controlled by \"orthodenticle\", a homeobox gene which demarcates the segments from the top-middle of the head to the more lateral aspects. The ocelli are in an orthodenticle-rich area, and the gene is not expressed by the time one gets as lateral as the compound eyes.\n",
"Hair on the bac... |
how did some neighborhoods in america came to be known as 'black neighborhoods'? is it mainly because of segregation? | Housing segregation enforced by redlining and blockbusting and white flight.
So, you take a neighborhood, and you line it. Red lines are where black people are able to live. Banks would (and still do) deny black people loans to live outside of the red lines, and designate the loans inside of the red lines high risk. Certain towns would also have housing contracts that said that black people weren't able to live there and that no one would sell their houses to a black family. At the same time, one white family moves out of a white neighborhood, and the house is sold to a black family. The other families then leave because black people bring down property values, thus making that neighborhood a red lined one.
There's a good article about Chicago here:
_URL_0_ | [
"The formation of black neighborhoods are closely linked to the history of segregation in the United States, either through formal laws or as a product of social norms. Despite the formal laws and segregation, black neighborhoods have played an important role in the development of African-American culture.\n",
"T... |
why were african, australian and native american civilisations so technologically inferior compared to european and east asian civilisations? | For one thing, it's cold enough in East Asia and Europe (note they're at similar latitudes) for germs to die every winter, so people live longer and technology can advance accordingly. In the case of Australia, humans inhabited the continent and killed off all the big game before they domesticated anything, so they didn't have the advantage of cows and horses. In Africa, in order to avoid diseases carried by mosquitoes, people traditionally lived in small communities far from water sources, meaning they have to put in a lot of effort to carting water. This means that they lacked the benefits of a city like job specializations, etc.
["Guns, Germs and Steel"](_URL_1_) is a really interesting read to answer this question more fully.
[There was a Cracked article](_URL_0_) that made me think we don't get the whole story about Native Americans. Supposedly they were very advanced, but a plague wiped them out and allowed Europeans to conquer them. | [
"China, India and South-East Asia were industrial powerhouse for major parts of human history. These countries and regions suffered great loss of industrial production due to colonization during 18th-20th centuries. After many decades of their independence, these countries have started reindustrializing themselves.... |
When I donate blood, I sometimes wonder: What happens if the blood recipient is allergic to something I recently ate? | Food allergies typically act on tissues the food encounters before digestion, such as the oral and esophageal mucosa, resulting in swelling or rashes of the throat leading to constricted airways. Once the food enters the stomach the allergens are broken down before entering the bloodstream, so blood to blood transmission of allergens is minimal. | [
"Allergic reactions from blood transfusion may occur from the presence of allergy-causing antigens within the donor's blood, or transfusion of antibodies from a donor who has allergies, followed by antigen exposure.\n",
"An allergic reaction will not occur on the first exposure to a substance. The first exposure ... |
what exactly does this mean (pic in post)? | In some locations, failing to upkeep a property means it can be forfeited to a new owner who does want to care for the property. The sign was posted by essentially squatters who want to prove no one cares for the property.
Its called adverse posession. | [
"A pictogram, also called a pictogramme, pictograph, or simply picto, and in computer usage an icon, is an ideogram that conveys its meaning through its pictorial resemblance to a physical object. Pictographs are often used in writing and graphic systems in which the characters are to a considerable extent pictoria... |
why does my cat insist on having me constantly feed him, even though he still has food in the bowl? | Cats are assholes? | [
"Once inside the cat searches for food in the kitchen, but comes up empty. His luck finally changes when he finds a can of cat food. He quickly opens the can and out of the can pops a mouse who is plopped down onto a dinner plate. The cat is about to dig in with a fork but the mouse puts a quick stop to that. He sa... |
swingset physics | In the absence of friction (or other energy sinks), a swingset, or indeed any simple pendulum, would simply continue to oscillate indefinitely between the two high points. At one extreme, when the pendulum is highest and its speed zero, the system has maximum gravitational potential energy, and zero kinetic energy. At the bottom / middle of the swing, the system has minimum gravitational potential energy and maximum kinetic energy - essentially trading height for velocity, and then it converts back as you come to rest at the other extreme. A swingset, of course, is not a frictionless simple pendulum in a vacuum. Energy is lost to mechanical friction, drag / friction with the surrounding air, and so forth, so to keep the swing swinging, the occupant must input energy into the system. This is done by moving the legs, which moves your centre of mass, increasing the available gravitational potential energy. On the back swing, you curl your legs behind you to raise the centre of mass, and on the front swing you extend them above you. At the bottom of the swing, you ideally want the centre of mass as low as possible to obtain the greatest difference between high and low, and hence greatest kinetic energy (velocity) at the bottom of the swing.
| [
"The poi are swung in a forwards direction in phase with each other (same time). The hands are then both moved in front of the swinger so that the poi traverse a circle in front of the spinner - the left poi spinning clockwise, the right poi counter-clockwise. Their angles are \"very\" slightly offset to prevent th... |
Which planet, if it disappeared, would affect Earth the most? | If Jupiter were to magically disappear I expect we'd quickly be exterminated by an asteroid impact.
The solar system is, to first order, the sun. Pretty much everything that goes on can be pretty thoroughly described if you just know the distance to the sun, its mass, no matter where you are in the solar system. To second order, the solar system is the sun's gravity plus Jupiter's. For example, Jupiter is about three times more massive than the other seven planets *combined.*
Because of this, Jupiter plays an important gravitational role in shepherding asteroids. Check out this [picture](_URL_0_) - white is the asteroid belt, and the colored asteroids are in Jupiter's Lagrange points or a 3:2 resonance, [which means they do 3 complete orbits of the sun for every 2 that Jupiter makes.](_URL_1_)
All of those red dots which are called the Hildas should be on unstable orbits without Jupiter and will scatter through the solar system. There's about a thousand of them.
This is made worse by the fact that Jupiter does important work clearing the inner solar system of any sort of debris that makes it in. For example, [Comet Shoemaker Levy 9 collided with Jupiter in 1994](_URL_2_), producing scars comparable to the Great Red Spot. I believe the phrase used in the popular media was "celestial vacuum cleaner." If it weren't for Jupiter taking all these hits, impacts would be far more common in the rest of the solar system, which could spell disaster for our little lifeboat in space.
Fortunately, Jupiter isn't going anywhere any time soon. I did the mass here once, and I remember that it would require a pile of nukes 4x the mass of the moon to destroy Jupiter. | [
"If Earth is not destroyed by the expanding red giant Sun in 7.6 billion years, then on a time scale of 10 (10 quintillion) years the remaining planets in the Solar System will be ejected from the system by violent relaxation. If this does not occur to the Earth, the ultimate fate of the planet will be that it coll... |
how do we know that we 'mixed' with other human species? | Scientists are able to analyze DNA and determine your ancestors. Certain areas/species have specific genes, and we have recently discovered Ozzy Osborn has traces of Neanderthal heritage: _URL_0_
That's how we "know". But evolution occurs at such a slow rate, so it's not like two subspecies of humans birthed the modern man. As evolution shows, species change over large periods of time. Millions of years. | [
"Some hybrids between similar species have been achieved by housing males of one species and females of the other together to limit the choice of mate. To create a \"natural\" macropod hybrid, young animals of one species have been transferred to the pouch of another so as to imprint into them the other species. In... |
If one clock orbits Earth moving very fast, why does it measure less time when, relative to the orbiting clock, Earth-bound clocks are moving equally fast? | See the [Wikipedia article for twin paradox](_URL_0_), specifically the resolution part. | [
"According to the theory of relativity, due to their constant movement and height relative to the Earth-centered, non-rotating approximately inertial reference frame, the clocks on the satellites are affected by their speed. Special relativity predicts that the frequency of the atomic clocks moving at GPS orbital s... |
During the Holocaust what was the difference between the death camps and the work camps? Also how was it decided who went where? | _URL_0_
u/commiespaceinvader answered a lot of my questions in this post, but I'm still unsure of how it was decided who went to what camp | [
"In 1942, Auschwitz II (Birkenau), originally intended to house slave laborers, began to be used instead as a combined labor camp and extermination camp. Prisoners were transported there by rail from all over German-occupied Europe, arriving in daily convoys. By July 1942, SS doctors were conducting \"selections\" ... |
A friend of mine tells me every culture around the world has a myth of a great flood wiping out the whole world, and that the timelines match up indicated they are talking about the same flood. How true is this likely to be? | [Mark Isaak has collection about a gazillion flood stories.](_URL_0_) That is a lot, but not every country has one. Nor is there all that much similarity across the stories. Boats are common, but you expect boats in a flood story. Some destroy the world and we go to a new one, some just destroy the local area. Nor is there any way to somehow line up any timeline.
I suspect that your friend has a confused version of the [Black Sea deluge hypothesis](_URL_1_). Roughly speaking this says that an ice dam held the Med back from the Black Sea and then it flooded. People postultulated that this event led to the various Mesopotamian flood stories (including the Noahic flood). There are several problems with that hypothesis. First, better evidence says that the Black Sea did not flood catastrophically, but rather slow enough for people to move when it was a problem. Second there is no evidence for some mass migration from the area. And finally there is nothing special about the Mesopotamian flood stories that requires a special explanation. | [
"Cultures around the world tell stories about a great flood. In many cases, the flood leaves only one survivor or group of survivors. For example, both the Babylonian \"Epic of Gilgamesh\" and the Hebrew Bible tell of a global flood that wiped out humanity and of a man who saved the Earth's species by taking them a... |
How can I learn history on my own and take steps to be a buff? | History is arguably the science of the specific. At least, that's what I argue, so I suppose it must be arguable. Which is to say, while understanding the vast sweep of history is great, it's also hard to really dive into because so much of what makes history fascinating, informative and fun is the details. Often the best thing about general history is finding new rabbit holes of specific periods and topics to become passionate about and begin researching. Which is all to say, while this thread has some good recommendations on general histories, also ask yourself specifically what most interests you based on what you do know. Follow that passion! That's often what studying history is all about, whether you are a student or a hobbyist or an academic. I (and many people) find more focused interest is a lot easier to sustain and brings very tangible rewards. Which isn't to say you shouldn't study broader histories, but that if you find your passion and your curiosity pulling you toward a particular topic, follow it and see where it leads you.
This is also important for learning how to -do- history. Because studying history is in no small part about learning to think historically - how to criticize and contextualize sources, how to use those sources to infer causality, how to develop a historical argument. And that kind of thinking is often best shown in the smaller scale of more specific topic and period studies rather than in the broadest general histories - part of making a broad narrative is concealing all the work that you've done in constructing it, while it's expected that more focused histories will show their work.
TL/DR study general histories, by all means, but don't be afraid to follow the rabbit holes of individual topics that interest you. | [
"As a teacher, Lewis believes one is better able to teach what one knows, stressing firsthand experiences particularly when it comes to history. He recreates history for his students by retracing the routes of (for example) famous nonviolent protests, often interviewing participants or relatives of original partici... |
Why were (or even how) the battle tactics of Mesoamerican peoples so different from those of the old world at the time of contact? | The idea that the "Aztecs were looking to gain captives in combat" is really quite overblown. While the taking of prisoners was important for advancement in social and military rank, the number of prisoners to gain high status was quite small -- as few as 4 captives depending on the circumstances. That the upper echelons of social/military advancement were eventually restricted only to the nobility was a further disincentive to risk life and limb to take a captive in the heat of battle. Furthermore, Postclassic military engagements were proceeded by volleys of slingstones, arrows, and atlatl darts, none of which are particularly conducive to seizing prisoners.
The focus on captive taking really conflates the actions of the elite shock troops of the noble military orders, particularly during the ritual practice of *xochiyaoyotl* (Flower War) combats, with normal combat actions. The xochiyaoyoatl were more focused on taking prisoners, but they were also arranged and limited engagements largely between the elites of two like minded groups (like the Aztecs and the Tlaxcalans) specifically for that purpose. The Aztec could, and did, engage in combats which destroyed enemy forces, stormed their cities, and resulted in massive casualties of the opposing force.
Remember that the Aztecs had spent over a century fighting near continuous wars of expansion against opponents who did not always share their zeal for seizing prisoners, and yet were rarely defeated. Moreover, in combat against the Spanish, they were really fighting a small number of Europeans accompanied by much more numerous Tlaxcalans and other native forces, including former allies of the Mexica. These indigenous forces would have been using the exact same tactics as the Aztecs they were fighting against. The idea that some sort of difference between the mentality of the Spanish and the Aztecs was a decisive part of the former's eventual victory is, in this light, simply bunk. It's not even supported by the Spanish themselves, who speak quite highly of both their native allies and opponents.
I wrote a bit more on Aztec Warfare [here](_URL_1_) and previously wrote about Mesoamerican sieges [here](_URL_0_). On the latter point, it should be noted that while the logistical constraints of siege warfare were felt more strongly in Mesoamerica, and thus more infrequently practiced, the Cortes' troops weren't exactly well-prepared in this either. Chronically running out of powder and having their cannons seized and destroyed, Diaz del Castillo recounts how they tried to build a trebuchet. It did not go well.
Those past comments reference Hassig's *Aztec Warfare* which is the seminal work on the subject. His *Mexico and the Spanish Conquest* is an excellent companion to that work. | [
"The jungle terrain of Mesoamerica made it difficult for large armies to reach their destination. The warriors who were familiar with the battle landscape could strategically retreat into familiar wilderness. Other war tactics included the siege of cities and the formation of alliances with lesser enemies to defeat... |
why flight attendants close the windows during the night? | So people can sleep. Night destination-time may not correspond to night at the longitude the plane is currently over. For example, you may be arriving in Europe early in the morning, but flying partially during daytime. | [
"At window seats there are window shields for protection from sunlight. They have to be slid up during landings and takeoffs by ICAO regulations and/or law. This rule is in place to provide visibility into and out of the aircraft during emergencies. Some airlines also require passengers to keep the window shields d... |
Does metric expansion of the universe apply to the dimension of time? If not, why not? | I'm going to try to do this without any equations. It'll make it harder, but let's see if I can pull it off.
Think for a moment about what space and time are, just to get the distinction between them clear in your head: Space is that thing that separates events that are simultaneous. Time is that thing that separates events that are colocational (which is a word I made up years ago because I don't know a better one to say "at the same place but different times"). Of course, events can be separated by both space *and* time, but for sake of clarity, let's consider for the moment only events with *either* timelike separation *or* spacelike separation and not both.
Take two events, *A* and *B.* Each event is described by a unique set of four numbers, coordinates in some arbitrarily chosen system of coordinates. We call those coordinates *t, x, y* and *z* if we're working in Cartesian coordinates, and that's just fine for this discussion, so let's call them that.
So for each event *A* and *B,* there's an ordered quadruplet of numbers that uniquely identifies that event. Using those eight numbers and something called the *metric equation* of the manifold in question, we can calculate the distance separating those two events.
For sake of argument, let's say that events *A* and *B* occur simultaneously. That is, both events have the same numerical value for their *t* coordinate. If we calculate the distance between the two events using the correct metric equation, we'll end up with a distance in space, something we can describe in terms of miles or light-years or whatever unit of length is convenient for us.
But we can also flip that assumption on its head. Instead of *A* and *B* being simultaneous, we can say they're colocated. In other words, *A* and *B* share the same numerical values for *x, y* and *z,* but have different values for *t.* We can use the same metric equation to calculate the distance between them, but this time we'll get a number that we have to describe in terms of seconds or centuries or some other unit of duration.
Now, think about what *spacelike* metric expansion means. It means that the *spacelike* distance separating *simultaneous* events is a function of *time.* In other words, the distance from event *A* to event *B* when *A* and *B* are simultaneous depends on *when* we calculate it.
Now, nothing's stopping us, mathematically, from flipping that relationship on its head. We could say that the *timelike* distance separating *colocated* events is a function of *space.* In other words we could say the distance from *A* to *B* when *A* and *B* are colocated depends on where, exactly, *A* and *B* are *on the manifold.*
When we put it in those terms, we can see that this is impossible in our universe. One of the core principles that defines our universe is the *equivalence principle,* which states that the outcome of a purely local experiment is independent of where in spacetime that experience is carried out. If this timelike expansion idea were true, then experiments conducted at different places in the universe would have different outcomes; an unstable subatomic particle *here* might decay in fifteen minutes, while the exact same particle *there* might decay only after a millisecond, because the proper time separating the particle's emission from its decay would vary depending on where the particle is.
So we must reject the idea of timelike expansion *a priori.* It contradicts something we know to be true about the universe.
Okay, well, what if we considered a different relationship? What if we said that timelike separation between colocated events is a function of *time* rather than location. But that's just saying that time is a function of time, which either reduces to triviality *("t=t")* or is nonsensical *("t≠t").* So we must reject that also, on even more basic logical grounds. (Of course, we could just postulate that the universe has two parallel timelike dimensions, *t* and *u,* and that *t* is a function of *u,* but any such theory constructed from a "metatime" postulate like that either reduces, again, to triviality, or is untestable, so that wouldn't actually get us anywhere. And imagining that *t* and *u* are perpendicular introduces all sorts of mathematical inconsistencies that I won't even bother getting into here, but the bottom line is everything falls to pieces if you try.)
So what we're left with is that the metric expansion we observe — in which spacelike separation is a function of time — is possible, while all other combinations of timelike separation being dependent on space, or timelike separation on time, or spacelike separation on space are either degenerate, contradictory or inherently logically invalid. | [
"Technically, the metric expansion of space is a feature of many solutions to the Einstein field equations of general relativity, and distance is measured using the Lorentz interval. This explains observations which indicate that galaxies that are more distant from us are receding faster than galaxies that are clos... |
why do most power plants convert heat into electricity by heating water into steam and then using it to spin a turbine? is there not a more efficient way to do it? | Steam turbines are actually quite efficient and they have the advantage in that the steam can be condensed back into water at the end of the process and reused. | [
"Power plants that use steam-driven turbines commonly use heat exchangers to boil water into steam. Heat exchangers or similar units for producing steam from water are often called boilers or steam generators.\n",
"For the sake of efficiency, it is desirable to minimise the steam content of the generator. Heat ca... |
what is the significance of having headphones in the correct ears when listening to music? | There isn't one from a music perspective, (some songs have differences in the left-right channel, but it doesn't really matter if it is reversed). The problem is with the shape of the headphones themselves. The right headphone is shaped for the right ear, so if you put it in the left ear then it will be backwards and won't be as good of a shape. | [
"Supra-aural headphones or on-ear headphones have pads that press against the ears, rather than around them. They were commonly bundled with personal stereos during the 1980s. This type of headphone generally tends to be smaller and lighter than circumaural headphones, resulting in less attenuation of outside noise... |
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