question stringlengths 37 38.8k | group_id int64 0 74.5k |
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<p>I have been looking all over and I can't find a detailed specification about the <a href="http://en.wikipedia.org/wiki/Mars_Science_Laboratory" rel="nofollow">Curiosity Rover</a>.
The length is about 10 feet but it would be cool to find out the dimensions of the wheels, clearance and so on.</p>
<p>Anybody know wher... | 3,457 |
<p>In <a href="http://astronomy.stackexchange.com/q/4/13">one of my questions</a> I asked about the career paths to become a professional astronomer. Now let's consider the next logical step. What if a person has gained his/her PhD in Astronomy and had an opportunity to do a couple of postdoc positions. The time comes ... | 3,458 |
<p>I'm writing a paper and I used them as an example, but then reconsidered . . . maybe I'm not getting it right!
thanks!</p> | 3,459 |
<p>If we set the <a href="http://en.wikipedia.org/wiki/Boltzmann_constant">Boltzmann constant</a> to $1$, then entropy would just be $\ln \Omega$, temperature would be measured in <a href="http://en.wikipedia.org/wiki/Joule">$\text{joules}$ ($\,\text{J}\,$)</a>, and average kinetic energy would be an integer times $\fr... | 852 |
<p>I just read this article at <a href="https://medium.com/the-physics-arxiv-blog/7ef5eea6fd7a">https://medium.com/the-physics-arxiv-blog/7ef5eea6fd7a</a> about the work of a physicist called Bolotin, that states that P!=NP (from computer science) implies that large quantum mechanical objects are not possible.</p>
<p>... | 3,460 |
<p>Consider a Pseudo-Riemannian Manifold with signature</p>
<p>$$ (\underbrace{+,\cdots,+}_p,\underbrace{-,\cdots,-}_q) $$</p>
<p>For any positive integers $p$ and $q$. Can this kind of manifold contain closed timelike curves (CTCs)? I know that if $p=1$, then we get a Lorentzian Manifold that can't contain CTCs, but... | 3,461 |
<p>Here is a picture of the usual vigorous Niagara Falls (in the winter).
<img src="http://i.stack.imgur.com/PgwrA.jpg" alt="enter image description here"></p>
<p>Here is the picture of Niagara Falls frozen in 1933 (in the very cold winter).
<img src="http://i.stack.imgur.com/FZB1W.jpg" alt="Niagara Falls frozen in 19... | 3,462 |
<p>Consider a triple-beam balance, like so:</p>
<p><img src="http://www.microscopesamerica.com/catalog/images/images/Large%20image%20Ohaus%20Triple%20Beam%20Balance%201610-00%20Cup%20Platform.png" alt="enter image description here"></p>
<p>An unknown mass is placed on the left pan, and the provided weights are moved ... | 3,463 |
<p>I recently read that the mass we deal with in Equation $F=Ma$ is called inertial mass and the mass we deal with in $F=Mg$ is gravitational mass. Suppose I am taking a same ball in a free fall and in accelerating it on the smooth horizontal plane the mass of ball should be mass. What is fundamental difference between... | 88 |
<p>When a clock is transported here and there into space and then brought to the same place it differs with the other clock.
When particles are accelerated with high speeds and then brought to rest their mass again gets back to its original rest mass.
Why?</p>
<p>Answer allegorically please.</p> | 3,464 |
<p>I was browsing through <em>Foundations of Space and Time,</em> a compilation of essays on various theories of quantum gravity. The following passage in the introduction intrigued me:</p>
<blockquote>
<p><em>Each compactification leads to a different vacuum state.... at least one state should describe our Universe... | 3,465 |
<p>I am an educator, and I am looking for a specific video. In the video, they ask some middle school students and some college graduates about why the moon has phases. Most of the students in both the groups get the answer wrong, saying that the phases of the moon happen because of the shadow of the Earth. I rememb... | 3,466 |
<p>After reading much online I've decided to by a 10x50 porro prism Binoculars. The one I have in mind <a href="http://www.letsbuy.com/celestron-upclose-10x50-p-34652" rel="nofollow">http://www.letsbuy.com/celestron-upclose-10x50-p-34652</a> has BK7 prisms. The one I would like to buy is this: <a href="http://www.letsb... | 3,467 |
<p>How are interplanetary trajectories that involve gravity assist maneuvers found?</p>
<p>Examples:</p>
<ul>
<li>the MESSENGER spacecraft made flybys of Earth, Venus, and Mercury before getting into orbit</li>
<li>the Juno spacecraft will flyby Earth (returning after launch) before continuing to Jupiter</li>
<li>man... | 3,468 |
<p>Assuming that a person has understanding of theory of Lie groups, Lie algebras and basic quantum mechanics, what is the simplest route to gain a basic understanding of the SM of particle physics? Are there any particular books suited for people with this background?</p> | 89 |
<p>I want to make a concave parabolic mirror that will have a focal point six inches below where I place it (on the edge of the sidewalk) so that it will melt the ice collecting in the gutter below and clear a path for the water to drain. I will probably be using shiny stainless steel for the reflector, so it won't be... | 3,469 |
<p><img src="http://i.stack.imgur.com/QoSeL.png" alt="enter image description here"></p>
<p>Sorry for the ugly picture but it makes my question more understandable.
The $\Delta V$ from $A$ to $B$ is calculated by$$\int_A^B E \, \mathrm{d}r$$ where $r$ is the distance between $A$ and $B$. The curve line is the real pat... | 3,470 |
<p>In history there was an attempt to reach (+, +, +, +) by replacing "ct" with "ict", still employed today in form of the "Wick rotation". Wick rotation supposes that time is imaginary. I wonder if there is another way without need to have recourse to imaginary numbers.</p>
<p>Minkowski spacetime is based on the sign... | 3,471 |
<ol>
<li><p>In particle mechanics where the notion of rotation does not apply, particles are said to be in static equilibrium when the sum of the external forces acting on the particle of interest in all directions equals zero.</p></li>
<li><p>In rigid body mechanics where the notion of rotation applies (or at least th... | 3,472 |
<p>I am having a very basic problem understanding the idea of detailed balance, particularly in the context of the Ising model. Most references I have found contain the following phrase:</p>
<p>"In equilibrium, each elementary process must be equilibrated by its reverse process".</p>
<p>What does it mean for one proc... | 3,473 |
<p>I am working on a textbook problem of a grounded conductor inside a uniform electric field. The textbook states that "grounded" means potential = 0. In my opinion, "grounded" should mean "same potential as infinity". But in this case we can't set potential at infinity equal zero. So my question is, what is actually... | 3,474 |
<p>Where does the energy of a light bulb come from?</p>
<p>Is it from the coil of wire, magnet in the generator, mechanical input to the generator or plug where the generator is connected to the wall?</p> | 3,475 |
<p>To better explain my question, I will need to give a brief description of the configuration used in 2D MEMS switches.</p>
<p>So, the next figure shows a configuration of a 2D MEMS switch, a light beam arrives from a fiber to the input port, travels inside the switch until it meets a mirror that is in the standing s... | 3,476 |
<p>According to Newton's law of action-reaction, there is a reaction force for the action force. He did not say when the reaction appears, whether immediately or with a delay.</p>
<p>Could you tell me the truth?</p>
<p>If the reaction appear immediately, does it disobey the relativistic principle that the changes mus... | 3,477 |
<p>Two particles $A, B$ are travelling along parallel straight paths. At some point, the velocity of $A$ exceeds that of $B$. Does this <em>necessarily</em> mean that the acceleration of $A$ is greater than the acceleration of $B$?</p>
<p>If you look at the $v - t$ graph of the two particles, the lines would intersect... | 3,478 |
<p>This is a bit of an odd question. I'm not a physicist, so bear with me if I say something wrong.</p>
<p>Lets say you have some sort of quantum event where matter is in a superposition. Standing next to you is another scientist waiting to observe the results (and, in theory, collapse the suposition). You go to get a... | 3,479 |
<p>In the <a href="http://en.wikipedia.org/wiki/Standard_Model">standard model</a> of particle physics, there are three generations of quarks (up/down, strange/charm, and top/bottom), along with three generations of leptons (electron, muon, and tau). All of these particles have been observed experimentally, and we don... | 959 |
<p>How is the following classical optics phenomenon explained in quantum electrodynamics?</p>
<ul>
<li>Color</li>
</ul>
<p>According to Schroedinger's model of the atom, only particular colors are emitted depending on the type of atom and the state of its electrons. Then, how it is possible that the same type of matt... | 3,480 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/2023/is-it-safe-to-use-any-wireless-device-during-a-lightning-storm">Is it safe to use any wireless device during a lightning storm?</a> </p>
</blockquote>
<p>We often hear the tale that a person gets st... | 90 |
<p>From <a href="http://en.wikipedia.org/wiki/Kinetic_theory" rel="nofollow">Wikipedia entry on Kinetic Theory</a></p>
<blockquote>
<p>The temperature of an ideal monatomic gas is a measure of the average kinetic energy of its atoms. </p>
</blockquote>
<p>Now if I remove all the particles from the box shown below w... | 3,481 |
<p>I have a ball attached to a spring and the spring is attached to a wall. There is no gravity for simplicity. In the rest RF the oscillating ball energy is conserved: T + U = const. In a moving RF it is not conserved. I would like to see the shortest answer to the question "Why?".</p>
<p>| <-- --><br>
... | 3,482 |
<p>Is 89MHZ station emitting photons of 89MHZ frequency? (I mean $\nu$ in $E=h\nu$).</p> | 3,483 |
<p>A photon emitted from a receding source (Doppler redshift) has less energy when detected at an observer's location. Please explain the energy loss from the perspective of energy conservation.</p> | 3,484 |
<p>Is there any explanation on a qualitative level why we can see in the observed magnitude vs. redshift z plot that the universe is expanding accelerated? See for example here:
<a href="http://hyperphysics.phy-astr.gsu.edu/hbase/astro/univacc.html" rel="nofollow">http://hyperphysics.phy-astr.gsu.edu/hbase/astro/univac... | 3,485 |
<p>A firecracker explodes at the origin of an inertial reference frame. Then, 2.0 microseconds later, a second firecracker explodes 300m away. Astronauts in a passing rocket measure the distance between the explosions to be 200m. According to the astronauts, how much time elapses between the two explosions?
Okay. My te... | 3,486 |
<p>As we know that matter-antimatter asymmetry is one of unsolved problems in physics. One possible solution to this problem is given as baryogenesis which produce asymmetry in rate of creation between matter and antimatter particles. But doesn't alternate solution like "different regions of space with different type o... | 3,487 |
<p>I am doing some research to see if there is a simple equation (or an equation that can be simplified) to estimate the volume of a drop of liquid falling due to gravity based upon the approximate flow rate, and perhaps the viscosity/surface tension of the fluid.</p>
<p>Basically this is a drip chamber fluid set for ... | 3,488 |
<p>I am reading Page 435, <em>General Relativity</em> by Wald.</p>
<p>Let $T^*\subset V^*$ be a subspace of the dual tangent space of a manifold, $W\subset V$ be the subspace of the tangent space annihilated by $T^*$, i.e. for every $\omega\in T^*$ and every $Y\in W$ we have $\omega_aY^a=0$.</p>
<p>Now the author say... | 3,489 |
<p>Visible light emitted or reflected from the objects around us provides information about the world. </p>
<p>If I sit in a dark room, and see the bright room outside, I am able to see all the objects of that bright room. In other words, it mean light emitted or reflected from those objects of the bright room are e... | 3,490 |
<p>In a discussion concerning:</p>
<p><a href="http://physics.stackexchange.com/questions/87332/physical-meaning-of-non-trivial-solutions-of-vacuum-einsteins-field-equations">Physical meaning of non-trivial solutions of vacuum Einstein's field equations</a></p>
<p>there were a number of answers claiming that the ... | 3,491 |
<p>Why we don't use <a href="http://www.ask.com/question/how-do-permanent-magnet-generators-work" rel="nofollow">this</a> in our houses to generate the electricity? Isn't the electricity generated by the magnets strong enough? Why do we have to pay for electricity if we can just create it by pushing the magnets attache... | 3,492 |
<p><a href="http://en.wikipedia.org/wiki/Principle_of_relativity" rel="nofollow">Wikipedia</a> has this quote:</p>
<blockquote>
<p><em>Special principle of relativity:</em> If a system of coordinates K is
chosen so that, in relation to it, physical laws hold good in their
simplest form, the same laws hold good i... | 3,493 |
<p>The area of a circle is $\pi r^2$ if you increase $r$ the area will increase by the square so if this area was of energy and you increase the area it is dispersed you would expect its energy to weaken by the square. Is this the intuition behind gravity weakening be the square of the distance?</p> | 91 |
<p>For a discrete symmetry: At the minimum value of the potential, $V$, in the Lagrangian density, why do we take $\phi= \langle v\rangle + \eta$? Aren't we deliberately breaking the symmetry? If we don't do this, the symmetry is intact.
On the other hand, if we replace $\phi$ by $\phi= \langle v\rangle + \eta$, even ... | 3,494 |
<p>There's a guide here on how to seal a weather balloon after filling:
<a href="http://ukhas.org.uk/guides:sealing_the_balloon" rel="nofollow">http://ukhas.org.uk/guides:sealing_the_balloon</a>
<a href="http://ukhas.org.uk/_media/guides:neck8.jpg" rel="nofollow">http://ukhas.org.uk/_media/guides:neck8.jpg</a></p>
<p>... | 3,495 |
<p>I was always told that to find whether or not a vector field is <a href="http://en.wikipedia.org/wiki/Conservative_vector_field" rel="nofollow">conservative</a>, see if the curl is zero.</p>
<p>I have now been told that just because the curl is zero does not necessarily mean it is conservative. However, if it is no... | 3,496 |
<p>So, in doing some numerical computations in QFT, I've run into the following Wigner <a href="http://mathworld.wolfram.com/Wigner6j-Symbol.html" rel="nofollow">6j-Symbol</a>: </p>
<p>$
\left\{
\begin{array}{ccc}
x & J_1 & J_2 \\
\frac{N}{2} & \frac{N}{2} & \frac{N}{2} \\
\end{array}
\right\}
$</p>
... | 3,497 |
<p>The Legendre transformation defines the helmholtz free energy (at least according to my lectures) as:</p>
<p>$F(T,V,N)=E-TS$</p>
<p>It also says to start with</p>
<p>$E(S,V,N)$ and $T=\frac{\partial{E}}{\partial{S}}$</p>
<p>My question is I have a relation for entropy (I won't give it because I want this to be m... | 3,498 |
<p>How does one solve the tensor differential equation for the relativistic motion of a partilcle of charge $e$ and mass $m$, with 4-momentum $p^a$ and electromagnetic field tensor $F_{ab}$ of a constant magetic field $\vec B$ perpendicular to the plane of motion. $$\frac{dp^a}{d\tau}=\frac{e}{m}F^a{}_bp^b$$
?
Let the... | 3,499 |
<p>We need to know two of the following three to calculate the third: redshifted color, baseline color, and velocity. The velocity is related to the difference between the redshifted color and the objects baseline color. How do we know the baseline color of distant objects to know the amount of redshifting?</p> | 3,500 |
<p>If a radio tunes to a specific frequency, where does the excess energy go? If one continues to hit the resonant frequency, shouldn't the wire begin to melt at some point from too much energy?</p> | 3,501 |
<p>Isn't a magnetic field basically an electric field originating from a line charge, but as seen in a boosted frame? I mean, that's where the relativistic explanation comes from right?</p> | 3,502 |
<p>The question is in the title.</p>
<p>If it is possible, what are some examples of gapped systems--either quantum field theories or condensed matter systems--which exhibit some kind of anomaly when coupled to a metric with curvature or placed on a spacetime with non-trivial topology?</p> | 3,503 |
<blockquote>
<p>A positive point charge $Q$ is kept eccentrically inside a neutral conducting shell. An external uniform field E is applied. Then:</p>
<p>a) Force on Q due to E is zero</p>
<p>b) Net force on Q is zero</p>
<p>c) Net force acting on Q and conducting shell considered as a system is zero</... | 3,504 |
<p>In traditional mirrors, some of the input light is absorbed by atoms in the mirrors surface and are 'lost' as heat, degrading the quality of the reflected image.</p>
<p>Could this loss be compensated by an array of "powered elements" arranged to reflect nearby photons repelling them with some sort of electo-magneti... | 3,505 |
<p>A Wick rotation is a transformation that allows to change from a Lorentzian manifold to a Riemaniann manifold. In the cases when this is possible, is the Levi-Civita connection of the Riemaniann manifold the same connection as the initial Lorentzian manifold? </p> | 3,506 |
<p><a href="http://en.wikipedia.org/wiki/Photon#Wave.E2.80.93particle_duality_and_uncertainty_principles">Wikipedia</a> claims the following:</p>
<blockquote>
<p><em>More generally, the normal concept of a Schrödinger probability wave function cannot be applied to photons. Being massless, they cannot be localized wi... | 3,507 |
<p>What is the physical interpretation of
$$ \int_{t_1}^{t_2} (T -V) dt $$
where, $T$ is Kinetic Energy and $V$ is potential energy.<br>
How does it give trajectory?</p> | 3,508 |
<p>Is there an upper limit to the angular momentum of a rotating (Kerr) black hole? </p> | 3,509 |
<p>In other words, if a photon is emitted from source, is it possible to change its course en route either by introducing a gravitational lensing or some sort to change the road it travels (spacetime) before it reaches it's source?</p> | 3,510 |
<p>When we canonically quantize the scalar field in QFT, we use a Lorentz invariant integration measure given by
$$\widetilde{dk} \equiv \frac{d^3k}{(2\pi)^3 2\omega(\textbf{k})}.$$</p>
<p>How can I show that it is Lorentz invariant?</p> | 3,511 |
<p>I am reading some articles about the ionosphere and I am a little bit confused about the terms <em>mean ionospheric height</em> and <em>effective height of the ionosphere</em>. Are these the same thing?</p>
<hr>
<p>I would refer to two texts:
<a href="http://www.ips.gov.au/IPSHosted/INAG/web-65/2004/es-heights.pdf... | 3,512 |
<p>What occurs in atomic scale that cause the photon to be reflected?<br>
In other words, what is the reason for photons to change its direction and why material can reflect certain wavelengths and absorb the rest? What are the atomic properties that causes that behaviour?</p> | 92 |
<p>While reviewing some basic field theory, I once again encountered the Bianchi identity (in the context of electromagnetism). It can be written as
$$\partial_{[\lambda}\partial_{[\mu}A_{\nu]]}=0$$
Here, $A_\nu$ is of course the electromagnetic potential. This formula is immediately reminiscent of the Jacobi identity... | 3,513 |
<p>How would you determine what initial velocity $v(r)$ of an object would have to be at some arbitrary point in the vicinity of a planet such that the object will end up on the surface of the planet with a zero velocity with respect to the point on the surface of the planet where it lands? Assume the planet is rotatin... | 3,514 |
<p>Would the effect of gravity on me change if I were to dig a very deep hole and stand in it? If so, how would it change? Am I more likely to be pulled downwards, or pulled towards the edges of the hole? If there would be no change, why not?</p> | 50 |
<p>Consider a hollow cylinder of different outer radius and inner radius and two different temperatures are maintained at the outer and inner surfaces such that inner temperature is higher. Because of this heat will flow radially outward.</p>
<p>Now I don't understand why we need to use integration to find rate of hea... | 3,515 |
<p>What is the significance of $8\pi/3$ in the first <a href="http://en.wikipedia.org/wiki/Friedmann_equations" rel="nofollow">Friedmann Equation</a>, and in the question concerning the time independence of the Hubble Constant?</p>
<p>Is it the 'same' $8\pi/3$ that appears in the total cross section formula of Thomso... | 3,516 |
<p>Part of the definition of the concept of force is that if particle $1$ exerts a force $F_1$ on particle $3$ and particle $2$ exerts a force $F_2$ on particle $3$, the total force on particle $3$ is $F_1+F_2$.</p>
<p>But, is the principle of superposition deducible from Newton's laws or is it an additional assumptio... | 3,517 |
<p>Why do photons have zero chemical potential and what is its the physical significance?</p>
<p>From what I know the chemical potential could be interpreted as the energy per unit particle that is put into a (thermodynamic) system... but surely photons also carry energy?</p> | 93 |
<p>I am quite new to thermodynamics and statistical mechanics so this might be an easy question:</p>
<p>In thermodynamics you get a bunch of thermodynamics potentials, so as for example enthalpy, internal energy, gibbs energy, helmholtz energy and so on. Now my idea was, that you use them if the natural variables rela... | 3,518 |
<p>An exercise from Goldstein (9.31-3rd Ed) asks to show that for a one-dimensional harmonic oscillator $u(q,p,t)$ is a constant of motion where
$$
u(q,p,t)=\ln(p+im\omega q)-i\omega t
$$
and $\omega=(k/m)^{1/2}$. The demonstration is easy but the physical significance of the constant of motion is not so clear to me. I... | 3,519 |
<p>I know it doesn't really make sense if looking at the photon from the wave point of view, but is there any law of physics which prohibits a photon from stopping completely? Thanks.</p> | 94 |
<p>As far as I understand it (which admittedly isn't very far), surface tension forces are made up by the tension-attractive forces of molecules at the liquid-gas/vacuum interface, such as those between hydrogen-bond-capable molecules in water.</p>
<p>But what happens when this liquid surface is in motion? I would ass... | 3,520 |
<p>When you observe or measure a process in classical physics it almost never really alters the experiment. For example, if you have an Carnot engine and measure the volume and pressure of a gas in some a cylinder while the process is running you can do it without disturbing the process, meaning that if you "ran the la... | 3,521 |
<p>Does the Hamiltonian always translate to the energy of a system? What about in QM? So by the Schrodinger equation, is it true then that $i\hbar{\partial\over\partial t}|\psi\rangle=H|\psi\rangle$ means that $i\hbar{\partial\over\partial t}$ is also an energy operator? How can we interpret this?
Thanks.</p> | 3,522 |
<p>Suppose a dynamical system of one variable $x$ with discrete time-steps. I've seen in some papers a type of graph in which $x(n+1)$ is plotted versus $x(n)$.
My questions are :
1/ Can this be considered as the phase portrait of the system ?
2/ Does this method has a specific name ?
3/ Has there been any studies with... | 3,523 |
<p>Why do water of water based liquids like sweat cool objects? The most clear example I have is the sweat on the skin. I learned that it absorbed heat because it evaporates, but this is something strange. I also read that by putting a little water on a can under the sun will cool the inside of the can, for the same re... | 95 |
<p>I've always been confused by this very VERY basic and important fact about two-dimensional CFTs. I hope I can get a satisfactory explanation here. In a classical CFT, the generators of the conformal transformation satisfy the Witt algebra
$$[ \ell_m, \ell_n ] = (m-n)\ell_{m+n}.$$
In the quantum theory, the same gen... | 3,524 |
<p>I came to this thought experiment as I was pondering good teaching examples of stable and unstable systems. It occurred to me that stable systems are really quite abundant. For a shoot-from-the-hip example, the speed of a car is stable about a given speed given a constant rate of fuel injection, since any perturba... | 3,525 |
<p>In <a href="http://www.newscientist.com/article/mg21929333.200-death-by-higgs-rids-cosmos-of-space-brain-threat.html" rel="nofollow">this article</a>, they mention that the <a href="http://en.wikipedia.org/wiki/Boltzmann_brain" rel="nofollow">Boltzmann Brain</a> paradox is supported by 'the best cosmological models.... | 3,526 |
<p>How is Base emitter junction and collector emitter junction biased? How do we determine the value of potential difference between emitter and collector required to be maintained in order to determine input characteristic of transistor? Explanations covering nitty gritty are most welcome.</p> | 3,527 |
<p>What is the reason for some writing Faraday's Induction Law as $$ \nabla \times E= -\frac{1}{c}\frac{\partial B}{\partial t} $$ versus $$ \nabla \times E= -\frac{\partial B}{\partial t} ?$$</p> | 3,528 |
<p>The first law of thermodynamics says energy cannot be created or destroyed. But we can collide photons to form electrons and positrons. Does this means that law does not apply in these microscopic scales?</p>
<p>And we can create mass from energy in the above process.but is it possible to make atoms that way? Like ... | 96 |
<p>Since mass can be given to particles via the interaction with the Higgs Field could there be a "Charger Field" that supplies particles with charge? Possibly this would require two different "charger bosons" one for + and one for -.</p> | 3,529 |
<p>Do you know where can I find simple diagram (solid, liquid, gas) for for oxygen?</p>
<p>EDIT: I made a mistake. I wanted oxygen instead of water. sorry. </p> | 3,530 |
<p>I have read several times by different supposedly knowledgeable authors that conscious observation affects quantum experiments. </p>
<p>I think these authors are confused, by which I mean they forget that "observing" is not passive. </p>
<p>To take the double slit experiment for example, observing means that the... | 3,531 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/21753/why-do-electron-and-proton-have-the-same-but-opposite-electric-charge">Why do electron and proton have the same but opposite electric charge?</a> </p>
</blockquote>
<p>Doesn't it seem very curious ... | 97 |
<p>I want to know whether decreasing the weight of the frame of a car will increase its horsepower. From what I understand horsepower is a measure of the car's ability to transport load, and decreasing the frame's weight will increase this ability. I tried to search this on internet and all I got was that it depends on... | 3,532 |
<p>I was wondering if there was something equivalent to the property of being wet with water, but with air instead. For example, if I drop water on my shirt, I'll notice by its appearance and feel that it is wet, so in a sense its properties were changed by being exposed to water.
So I'm wondering if similarly, by bein... | 3,533 |
<p>When electric charges of equal magnitude and sign are released on a regular sphere (and assume that they stick to the surface of the sphere, but they are free to move along its surface), what is the shape of the figure made by the charges as vertexes when they come to a state of equilibrium? </p>
<p>Case 1 - Only o... | 3,534 |
<p>What does the term <em>limb of the earth</em> (see <a href="http://physics.stackexchange.com/q/25038/5291">this question</a>, for example) or <em>atmospheric limb</em> mean? The phrase strikes me as very odd, since earth is nearly spherical. Do other planets with atmospheres also have a limb?</p> | 3,535 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/6068/list-of-good-classical-physics-books">List of good classical physics books</a> </p>
</blockquote>
<p>I'm having a hard time understanding force in my highschool AP physics class, i looked through yo... | 98 |
<p>In flat space-time the electric potential energy between two charges is $\frac{k Q_1 Q_2}{r_{12}}$, where $Q$'s are charges and $r_{12}$ is the distance between them. What would happen if the two charges are placed in a strongly curved space-time, which makes "distance" and "duration" measures different from place t... | 3,536 |
<p>Some Soviet space stations reportedly <a href="http://en.wikipedia.org/wiki/Almaz" rel="nofollow">had anti-aircraft cannons installed</a>. Could such a cannon hit the firing space station accidentally on a subsequent orbit? The muzzle velocity of <a href="http://en.wikipedia.org/wiki/Nudelman-Rikhter_NR-23" rel="nof... | 3,537 |
<p>Outside a narrow charged stream (say, a beam of ions or electrons) is the same as observing a current through a conducting wire - there is a circular magnetic field around it.</p>
<p>What would happen inside a charged stream (for example, inside a conducting wire or inside a solar flare)? I have a feeling that symm... | 3,538 |
<ul>
<li><p>is there any difference between these Differential $dx^2$ and $(dx)^2$!?</p></li>
<li><p>what is relation between them?</p></li>
</ul> | 3,539 |
<p>If the universe is just a Matrix- like simulation, how could we ever know? Physicist Silas Beane of the University of Bonn, Germany, thinks he has the answer!. His paper <a href="http://arxiv.org/abs/1210.1847" rel="nofollow">“Constraints on the Universe as a Numerical Simulation</a>” has been submitted to the journ... | 3,540 |
<p>The example I'm trying to understand is:</p>
<p>$ \hat{S}_{x} \begin{pmatrix}
\frac{1}{\sqrt{2}}\\
\frac{1}{\sqrt{2}}
\end{pmatrix} = 1/2 \begin{pmatrix}
\frac{1}{\sqrt{2}}\\
\frac{1}{\sqrt{2}}
\end{pmatrix} $</p>
<p>My interpretation of this is that the vector shows you the probabilities of a particle being spin ... | 3,541 |
<p><strong>Heads up</strong>: This question has never been asked (here) before the way I will ask it here, so let's shed some light on it a bit.</p>
<p><strong>Prelude and anecdote</strong>(can be skipped): The other day I was walking home, and I passed a stop sign. I looked at it and asked myself, "<strong>What kind ... | 3,542 |
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