question stringlengths 37 38.8k | group_id int64 0 74.5k |
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<p>I'm trying to understand the concepts of time dilation and spatial compression. I've been using the classic example of firing a photon of light inside a ship (spaceship, boxcar, etc.) moving at a constant velocity to the second observer. But when I do the Lorentz, I get different values depending upon the direction ... | 4,279 |
<p>We know Newton's three laws:</p>
<ol>
<li><p>A object at rest will remain at rest, and an object in motion will remain in motion unless a external force acts upon it.</p></li>
<li><p>If an unbalanced force acts on a object, the object will accelerate in the direction of the net force.</p></li>
<li><p>If an object $... | 4,280 |
<p>I'm still in high school, and while I can't complain about the quality of my teachers (all of them have done at least a bachelor, some a masters) I usually am cautious to believe what they say straight away. Since I'm interested quite a bit in physics, I know more about it than other subjects and I spot things I dis... | 4,281 |
<p>I know I have posted <a href="http://physics.stackexchange.com/q/103787/2451">this</a> question <a href="http://physics.stackexchange.com/q/101179/2451">before</a> some time ago. But no one could help so I decided to put my problem in another background.</p>
<p>The Schrödinger equation of a free scalar field is giv... | 4,282 |
<p>I don't quite understand this quote from Stephen J. Gould's <em>Ever since Darwin</em>, where he talks about the compensating physical characteristics of organisms for their size. </p>
<blockquote>
<p>Other essential features of organisms change even more rapidly
with increasing size than the ratio of surface t... | 4,283 |
<p>Consider the <a href="http://en.wikipedia.org/wiki/Metric_space#Definition" rel="nofollow">metric space</a> $(M, d \,)$ where set $M$ contains sufficiently many (at least five) distinct elements,<br>
and consider the assignment $c_f$ of coordinates to (the elements of) set $M$,</p>
<p>$c_f \, : \, M \leftrightarrow... | 4,284 |
<p>The Lagrangian for electromagnetic field has the following expression:
$$
L = -\frac{1}{c^{2}}A_{\alpha}j^{\alpha} - \frac{1}{8 \pi c}(\partial_{\alpha} A_{\beta})(\partial^{\alpha}A^{\beta})
$$</p>
<p>(I used Lorentz calibration $\partial_{\alpha} A^{\alpha} = 0 $).</p>
<p>If I add the summand $\frac{\mu^{2}}{8 \... | 4,285 |
<p>I have not been able to find a resource to tell me the standard notation for a normalized scalar value. Normalized vectors (i.e. unit vectors) are typically denoted by placing a hat over the variable, something like: </p>
<p>$${\bf \hat{e} = \dfrac{e}{||e||} }$$</p>
<p>However, does the same apply to normalizing ... | 4,286 |
<p>This question is regarding the quantum circuit in the picture below.</p>
<p>Suppose we have the set up below, where U performs the operation $U:\mid x \rangle \mid y \rangle \rightarrow \mid x \rangle\mid y \oplus f(x) \rangle$.</p>
<p>We define the function $f(x)$ on the 3-bit string $\mid x \rangle= \mid x_1 x_2... | 4,287 |
<p>In quantum mechanics can the mass and the linear momentum of a particle be measured precisely or do they commute ?</p> | 4,288 |
<p>$V=IR$</p>
<p>Right?</p>
<p>$100 (\rm{V}) = 0 (\rm{A}) \times 100 (\rm{\Omega})$</p>
<p>Lets say something has $100 \rm V$ potential But since this object is surrounded by air and current is not flowing therefore there has to be $100 \rm{\Omega}$. Right? But then the equation does not work as 100 does not equal 0... | 4,289 |
<p>Does the gravitation of Earth have a limit? when a body projected vertically with $v=11km/s$ (escape velocity) from Earth's surface does this means that it does not return back to Earth? </p> | 4,290 |
<p>As far as I know, the electromagnetic force only interacts on particles with electrical charge, but I was told that the electromagnetic force was involved in the following reaction:</p>
<p>$$\Sigma^0\rightarrow\Lambda^0+\gamma.$$</p>
<p>How can this be, when the electric charge of both the $\Sigma^0$ particle and ... | 4,291 |
<p>In my physics textbook there is an example of using capacitor switches in computer keyboard:</p>
<blockquote>
<p>Pressing the key pushes two capacitor plates closer together, increasing their capacitance. A larger capacitor can hold more charge, so a momentary current carries charge from the battery (or power sup... | 4,292 |
<p>Guys I couldn't catch a point of multiverse theory..</p>
<p>Theory: If space-time goes on forever, then it must start repeating at some point, because there are a finite number of ways particles can be arranged in space and time..</p>
<p>Question: It seems like as if multiverse theory stands on a optical argument.... | 4,293 |
<p>It is given that acceleration is constant, so can we infer that average speed and velocity are the same?? Moreover, circular motion is out of the question, as the function of x(t) where x=displacement, suggests, that for any t>=0, displacement can not be zero...</p>
<p>This is the conceptual problem I am facing in ... | 4,294 |
<p><a href="http://phys.org/news/2013-04-gravity-lingua-franca-relativity-quantum.html" rel="nofollow">Lingua Franca links relativity and quantum theories with spectral geometry</a></p>
<p>Could someone give me a short synopsis of this article in laymens terms? What implications does this have in the physics community... | 4,295 |
<p>Two very interesting new papers on arXiv last night by Lev Vaidman and friends lead me to ask about the differences between Cramer's transactional interpretation of quantum mechanics (TIQM) and the two state vector formalism (TSVF) advanced by Aharonov, Vaidman and others. At a first look, they both seem very simil... | 4,296 |
<p>In a <a href="http://arxiv.org/abs/0909.4593" rel="nofollow">paper</a> by V. Gurarie et al. , the theorem of inclusion is used to prove that there is no direct phase transition between Mott insulator and spuerfluid in presence of disorder. In Fig. 2 of that paper, why if $\Delta > \Delta_c $, there exist domains ... | 4,297 |
<p>Do atoms have any uniquely identifying characteristic besides their history?</p>
<p>For example, if we had detailed information about a specific carbon atom from one of Planck's fingerprints, and could time-travel to the cosmic event in which the atom formed, would it contain information with which we could positiv... | 4,298 |
<p>I know there is evidence that it is not predetermined and I tried reading articles on it but most of them either don't explain the intuition behind the experiment or they speak in a foreign language (That language being science). If you could explain the intuition behind the experiment and also give an analogy that ... | 4,299 |
<p>Since we know that all accelerated charges radiate energy and we also know that all matter is made up of protons and electrons which are all the while doing accelerated motion.So from this can i conclude that every piece of matter radiates energy because of jiggling motion of atoms?</p> | 132 |
<p>Okay, I know that in quantum mechanics the quantum observable is obtained from the classical observable by the prescription </p>
<p>$$ X \rightarrow x,\quad P \rightarrow -i\hbar\frac{\partial}{\partial x} $$ </p>
<p>in the position basis. Now my question is, what if $x$ or $p$ appears in the denominator in a clas... | 4,300 |
<p>How many degrees of freedom does an asymmetric top have if it is rotating about a fixed point?What are the generalised coordinates used then?</p> | 4,301 |
<p>Heisenberg famously derived his uncertainty principle by considering the disturbance that a measurement would have on a small enough system.</p>
<p>Of course in the mathematical formalism of Quantum Mechanics the relationship is derived from more basic principles.</p>
<p>How does String Theory account for it? Heur... | 4,302 |
<p>I have read some popsci articles and documentaries about the early universe and they often explain how various features of the universe came about and at what time. For example hydrogen atoms came about after hundreds of thousands of years.</p>
<p>Now, the official SI time unit, the second, is based on the caesium ... | 4,303 |
<p>I was reading "Nature of space and time" by Penrose and Hawking, pg.13, </p>
<blockquote>
<p>If $\rho=\rho_0$ at $\nu=\nu_0$, then the RNP equation</p>
<p>$\frac{d\rho}{d\nu} = \rho^2 + \sigma^{ij}\sigma_{ij} + \frac{1}{n} R_{\mu\nu} l^\mu l^\nu$
implies that the convergence $\rho$ will become infinite at ... | 4,304 |
<p>Let's say I have a hollow conductive rod, 10mm diameter (O.D.), and I place a magnet of known strength 50mm up the shaft. What is the microTesla (mT) or Gauss (G) of the magnetic field (or flux density, or whatever it would be) <strong>of the shaft</strong> 50mm away from the magnet attached to it?</p>
<p>Here's wh... | 4,305 |
<p>In the Schrödinger's cat experiment 'there is a tiny bit of radioactive substance, so small that perhaps in the course of the hour, one of the atoms decays'. The rest of the experiment magnifies this into a macroscopic superposition, but I want to know more about the claim that the radioactive decay produces a super... | 4,306 |
<p>This is for anyone with experience in optics/imaging/photography as well as anyone who likes to puzzle over tricky physics problems. </p>
<p>As the title suggests, this is about combining two (for all practical purposes) identical light beams in an optical system to one beam of twice the intensity. Mind you, I'm n... | 4,307 |
<p>I read about the quantum quench problem in condensed matter physics.
But what does really mean? Has anybody a good explanation about the origin of quantum quench problem?</p> | 4,308 |
<p>Does <a href="http://en.wikipedia.org/wiki/Newton%27s_laws_of_motion" rel="nofollow">Newton's laws</a> of <a href="http://en.wikipedia.org/wiki/Newton%27s_law_of_universal_gravitation" rel="nofollow">gravitation</a> and <a href="http://en.wikipedia.org/wiki/Kepler%27s_laws_of_planetary_motion" rel="nofollow">Kepler'... | 4,309 |
<p>I'm studying Jackiw's "Fractional Charge and Zero Modes for Planar Systems in a Magnetic Field" DOI: <a href="http://journals.aps.org/prd/abstract/10.1103/PhysRevD.29.2375" rel="nofollow">10.1103/PhysRevD.33.2500</a></p>
<p>but I have difficulties at some points. One of the problems is</p>
<p>$$\langle j^0\rangle=... | 4,310 |
<p>Is <a href="http://en.wikipedia.org/wiki/Temperature">temperature</a> of a single molecule defined?</p>
<p>This question just cropped up in my mind as I have often heard of laws being violated when it comes to the scale of a single molecule. Does this happen in case of temperature too?</p> | 133 |
<p>I have been asking around at my school and at the high school and at EWU but no one can answer this question: can a magnet or a magnetic field push gravity?</p> | 4,311 |
<p>If we get the dispersion relation from the Fourier transform of the lattice vectors then how do we get electrons information? Specifically, for the $k=0$ point of the graph, does this mean the electron has zero momentum(I am pretty sure that electrons don't have zero momentum in that case due to Heisenberg's uncerta... | 4,312 |
<p>Why Thermodynamic cycles are used to obtain work for example carnot engine rather than single isothermal process which is part of cycle and can be used to obtain more work.And why isothermal process do not violate second law even when there is no friction or any irreversibility.I know they violate second law in actu... | 4,313 |
<p>I don't know much about black holes physics and so I find the Schwarzschild equations with a few contradictions. In particular I am trying to understand this little puzzle. The Schwarzschild Newtonian gravitational field equation is expressed as follows (see <a href="http://en.wikipedia.org/wiki/Schwarzschild_radi... | 4,314 |
<p>I have obtained a series of data that is about density distribution of liquid in three dimensions, density$=f(x,y,z)$. How can I know the detail information about the way that density changes with $x$ and $y$ and $z$? And how should I do to get the positions of minimum and maximum of liquid density? </p> | 4,315 |
<p>I run into wikipedia articles about ergosphere of rotating black holes. What if some massive body passes nearby some black hole: is something like ergosphere produced, or is the event horizon distorted by the gravity of the passing body?</p> | 4,316 |
<p>When trying to calculate the lift force generated by a simple rectangular blade, I've found the following equation: $$F = \omega^2 L^2 l\rho\sin^2\phi$$ in which $\omega$ is the angular velocity, $L$ is the length of the helix, $l$ is the width of the helix (both in meters), $\rho$ is the air density at normal condi... | 4,317 |
<p>What's the difference between something being labeled a "nano-particle" or it being called a "molecule"?</p> | 4,318 |
<p>While studying alternating currents I could read and observe through an oscilloscope that there can be phase difference between emf and current. But, is a phase difference of 180 degrees possible in a series LCR circuit? </p> | 4,319 |
<p>We may choose a non-rotating earth as our reference frame and ask ourselves: how about the planetary and stellar motions. A star at a distance of 10 million light years would turn around the earth in 24h with a velocity of 10^18 m/s. </p>
<p>A friend once told me that actually articles have been published delving i... | 4,320 |
<p>The electrical field for a charge density $\varrho(r)$ is
$${\bf E}({\bf r})=\frac{1}{4\pi\varepsilon_0}\int \varrho({\bf r}')\frac{{\bf r}-{\bf r}'}{\hspace{.1cm }|{\bf r}-{\bf r}'|^3} \mathrm d^3r'.$$</p>
<p>Given a single particle of charge $q_C$ fixed in the centre of the coordinate system, a test charge $q_T$... | 4,321 |
<p>What are examples of endeavors, in the history of mankind, to understand physical phenomena with models which were proved to be incorrect later, reformed significantly, or are still under development?</p> | 4,322 |
<p>Matter-- I guess I know what it is ;) somehow, at least intuitively. So, I can feel it in terms of the weight when picking something up. It may be explained by gravity which is itself is defined by definition of the matter!</p>
<p>What is <a href="http://en.wikipedia.org/wiki/Antimatter">anti-matter</a>?</p>
<p>Ca... | 4,323 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/9165/which-mechanics-book-is-the-best-for-beginner-in-math-major">Which Mechanics book is the best for beginner in math major?</a> </p>
</blockquote>
<p>I am looking for suitable ways to learn mechanics ... | 98 |
<p>How do the Planets and Sun get their initial rotation?
Why do Venus and Mercury rotate so slowly compared to other planets and why does Venus rotate in a different direction to Mercury, Earth and Mars?</p> | 4,324 |
<p>This might be a very simple question. I just want someone to point me the right direction to understand things like this:
$$
\langle x|x'\rangle=\delta(x-x') \\
\psi(x)=\langle x|\psi\rangle \\
\tilde{\psi}(p) = \langle p|\psi\rangle \\
\langle x|p\rangle=\frac{1}{\sqrt{2\pi \hbar}}\exp(ipx/\hbar)
$$
I am using Gr... | 4,325 |
<p>This is kind of related to this,
<a href="http://physics.stackexchange.com/questions/53768/defining-a-cft-using-beta-functions">Defining a CFT using beta-functions</a></p>
<p>So what would be the right definition of a CFT even classically? </p>
<ul>
<li>Is it true that classically one will call a theory scale inva... | 4,326 |
<p>In the Lagrangian for a charged particle in an electromagnetic field </p>
<p>$$L = \frac{1}{2}mu^2 - q(\phi - \frac{\vec{A}}{c}\cdot \vec{u})$$</p>
<p>the energy of the particle is contained in the kinetic term, the rest being interaction terms of the particle with the electromagnetic field. If it's travelling at ... | 4,327 |
<p>I have always been puzzled by how do you arrive at Lagrangians? That is, how do you know that the functional you need to get Newton's equations is </p>
<p>$L$ = $T-V(x)$</p>
<p>Do you derive the Lagrangian first somehow or do you just guess the one which would satisfy the action to give equation's of motion?(becau... | 4,328 |
<p>Imagine you have two homogeneous spheres with the same diameter of $d=0.1 m$. They have the same mass $m = 1 kg$. The distance between the centers of mass is $r= 1 m$. Their electrical charge shall be disregarded. At $t=0$ the spheres do not have any relative motion to each other. Due to gravitation they will accele... | 134 |
<p>Is it ok to say $145\,{\rm k\,MPa}$ for $145\, {\rm GPa}$. We are so used to comparing stresses in ${\rm MPa}$ that I want to keep things relative to this unit. So would it be a no-no to do so. </p> | 4,329 |
<p>All of the quantum algorithms I've seen so far require a turing-complete quantum computer, at least as far as I can tell. Are there any quantum algorithms that require only a <a href="https://en.wikipedia.org/wiki/Quantum_finite_state_machine" rel="nofollow">quantum finite automaton</a>? If so, how does their asympt... | 4,330 |
<p>I'm a Mechanical Engineering student and I'm working on my senior project, so I need help. My project is about designing a solar dish having a diameter of 1.5 meters and a focal length of 60cm. so at the focal point, a circular coil (copper pipe) will be folded, in order to have a superheated steam as an output. Wha... | 175 |
<p>I believe that answer to my question is rather trivial but I can't seem to get my head around it. In context of ADM formulation of gravity (or any other differential geometry context, I guess) the covariant derivative of a normal vector to the hypersurface/foliation/slice, in any direction within the hypersurface gi... | 4,331 |
<p>This question is about the generalization of Coulomb's law to continuous bodies of charge. The basic statement of Coulomb's Law involves two discrete charges $q_1$ an $q_2$:</p>
<p>$$\vec{F}_i = \frac{1}{4 \pi \epsilon_0} \frac{q_1 q_2}{r_{12}} \hat{r}_i $$</p>
<p>Here $i$ represents the charge on which the force ... | 4,332 |
<p>The <a href="http://en.wikipedia.org/wiki/Higgs_boson" rel="nofollow">Higgs boson</a> is a hypothetical elementary particle predicted by the Standard Model (SM) of particle physics. It belongs to a class of particles known as bosons</p>
<p>What Will Happens If physicist Find the Higgs Particle that thought to be fu... | 4,333 |
<p>"Stability" is generally taken to be the justification for requiring that the spectrum of the Hamiltonian should be bounded below. The spectrum of the Hamiltonian is <em>not</em> bounded below for thermal sectors, however, but thermal states are nonetheless taken to be stable because they satisfy thermodynamic const... | 4,334 |
<p>How can triangulation be used to calculate the approximate distance to very distant celestial bodies like stars, globular clusters, etc.? And can it be used to measure the distance to a Black Hole?
(Can someone please help me with tags?)</p> | 4,335 |
<p>When using the fluctuating exchange approximation (FLEX) as a dynamical mean field theory (DMFT) solver, <a href="http://rmp.aps.org/abstract/RMP/v78/i3/p865_1" rel="nofollow">Kotliar, et al.</a> (p. 898) suggest that it is only reliable for when the interaction strength, $U$, is less than half the bandwidth. How w... | 4,336 |
<p>Inspired by physics.SE: <a href="http://physics.stackexchange.com/questions/15571/does-the-dimensionality-of-phase-space-go-up-as-the-universe-expands/15613">http://physics.stackexchange.com/questions/15571/does-the-dimensionality-of-phase-space-go-up-as-the-universe-expands/15613</a></p>
<p>It made me wonder about... | 4,337 |
<p>Excuse me, I have calculated $a^g$ a lot of times, using the relation between $:\;:$ and ${}^{{}_\circ}_{{}^\circ} \; {}^{{}_\circ}_{{}^\circ}$. But I can't get the same result with the book.
It is not too hard to get
$$
:b(z)c(z'):-{}^{{}_\circ}_{{}^\circ} b(z)c(z'){}^{{}_\circ}_{{}^\circ} =
\frac{\left(\frac{z'}{z... | 4,338 |
<p>Normally supersymmetric quantum field theories have Lagrangians which are supersymmetric only on-shell, i.e. with the field equations imposed. In many cases this can be solved by introducing auxilary fields (field which don't carry dynamical degrees of freedom, i.e. which on-shell become a function of the other fiel... | 4,339 |
<p>Fluid flows become turbulent beyond a certain velocity. The velocity is almost always with respect to a fixed boundary. However, an observer in a frame of reference travelling with the fluid will also experience turbulence when the velocity of fluid with respect to the boundary exceeds a certain value. Does this ind... | 4,340 |
<p>The following question is probably very elementary:
<strong>whether molecules of <a href="http://en.wikipedia.org/wiki/Ideal_gas" rel="nofollow">ideal gases</a> may have optic properties?</strong>
As far as I understand, when one discusses optic properties, one assumes that molecules of the material have some inner... | 4,341 |
<p>In a horizontal surface, a block (cube) is sliding due to a sudden push. When the block slides, there is frictional force which is acting on the block. </p>
<p>Frictional force will have a torque around the center of mass, so why does the block not rotate/roll around (a horizontal axis through) the center of mas... | 4,342 |
<p>Is there any way to find the energy of a particle through its decay probability?</p> | 4,343 |
<p>The singlet state of two qubits is anticorrelated in every basis. For example, in the Pauli bases, it can be expressed,</p>
<p>$\frac{1}{\sqrt{2}} ( | 01 \rangle - | 10 \rangle) = \frac{1}{\sqrt{2}} ( | +- \rangle - | -+ \rangle) = \frac{1}{\sqrt{2}} ( | \circlearrowright \circlearrowleft \rangle - | \circlearrowle... | 4,344 |
<p>I am doing some experiments on musical strings (guitar, piano, etc.). After performing a Fourier Transform on the sound recorded from those string vibrations, I find that the fundamental frequency is not absolutely the component with the largest amplitude (or energy).</p>
<p>I learnt from introductory physics cours... | 4,345 |
<p>Gauge bosons are represented by $A_{\mu}$, where $\mu = 0,1,2,3$. So in general there are 4 degrees of freedom. But in reality, a photon (gauge boson) has two degrees of freedom (two polarization states). </p>
<p>So, when someone asks about on-shell and off-shell degrees of freedom, I thought they are 2 and 4. But ... | 4,346 |
<p>Imagine we have two different differentiable functions $f(t)$ and $g(t)$ where $t$ generally represents the time, if there exists the following limit as
$$ \lim\limits_{t\rightarrow \infty } \frac{\| \dot{f}(t) \|}{\|\dot{g}(t)\|}=c$$
Then, is there any appropriate physical explanation for this limit ?
If ignore the... | 4,347 |
<p>If energy required to accelerate a particle to the speed of light is infinite then where do they get it from?</p>
<p>But first if photon's are massless, then why do they collide to some other thing and get reflected as in our daily life or get deflected after colliding to an atom in the sun and just move inside the... | 4,348 |
<p>Dopfer Momentum-EPR experiment (1998) seems to provide a interesting tweak in the EPR experiment.</p>
<p>To read more details on this experiment, see:</p>
<p><a href="http://www.hep.yorku.ca/menary/courses/phys2040/misc/foundations.pdf" rel="nofollow">http://www.hep.yorku.ca/menary/courses/phys2040/misc/foundation... | 4,349 |
<p>Long ago I learned that a <a href="http://en.wikipedia.org/wiki/Plasma_%28physics%29" rel="nofollow">plasma</a> was a distinct state of matter after solid, liquid and gas, and also that it was achieved by imparting heat to a the matter. But most references describe a plasma as an ionized gas. So I'm having trouble u... | 4,350 |
<p>I just had a confusion. Does the mass of the body actually increase when it is moving with a certain velocity? Or does it only look like the mass has increase to another observer. How can the actual mass of the body increase. Please correct me if I am wrong but I feel that it only seems to the observer that the mass... | 54 |
<p>There are videos and articles on the internet which demonstrate that water flows down a flush clockwise in Northern Hemisphere and anti-clockwise in Southern Hemisphere.</p>
<p>Here are a couple of links which claim to demonstrate this fact :
<a href="http://www.youtube.com/watch?v=Pb69HENUZs8" rel="nofollow">http... | 135 |
<p>I was near ($\approx40m$) an overhead power line and I heard a sound coming from the cables of the power line; I think the sound was made by the vibrations of the power cables due to the wind but I am not sure. The wind was very light.</p>
<p>The sound was not the "buzz" asked about <a href="http://physics.stackexc... | 4,351 |
<p>Assume I have two disks, $p_1$ and $p_2$, of radius $r$, with their own velocities (preferably in $(x,y)$ form, but $(m, \theta)$ works too) and masses (unit-less, but same unit) collide in two dimensions, how can I compute their resulting velocities?</p>
<p>I was looking around on the internet and it seems like ev... | 136 |
<p>Why can't we accelerate to the speed of light? It's just a speed and nothing else. Universe also crossed the speed of light at the time of big bang. Is this is just a interpretation or there is any fact behind it? I am asking it as I don't know much about this theory.</p> | 137 |
<p>How can I size an electromagnet? For example if I would to attract a mass of $x$ kg what are the calculations that I must do to size the ferromagnetic core and of course the solenoid? And thus, how can I compute the force of the magnetic field generated?</p>
<ul>
<li>Current: AC 230V @ 50Hz.</li>
<li>Material: Iron... | 4,352 |
<p><strong>I have a few questions related to the emission of electromagnetic radiation by black bodies. </strong>
<hr/>
Consider the following image:</p>
<p><img src="http://s22.postimg.org/77bujyudt/image.png" alt="fig.1"></p>
<p>On the above image I have drawn the rays of light that are emmited by black bodies assu... | 4,353 |
<p>A problem has been presented that goes like this:</p>
<p>Particles normally exist as several mathematical possibilities rather than one actual object. It is said that in the absence of observation, particles exist in a superposition of possibilities rather than one actual thing. But when we look they are not in suc... | 4,354 |
<p>Let's assume we have a perfect single-photon source: a device emitting exactly one photon at a time, with defined energy and direction. Let's shoot a photon: we know exactly the position of the photon (starting point and time, velocity) and it's momentum (energy and velocity). Would such a device violate uncertainty... | 4,355 |
<p>Suppose an object A is traveling at a velocity of 100 m/s, and another object B is traveling at 105 m/s. With both the objects traveling through the same direction, taking A as a reference frame, the velocity of B would be 5 m/s (Is this actually right?). But, when they're traveling in opposite directions, how would... | 4,356 |
<p>Morrison writes in "Morrison, Michael A. : Understanding quantum physics : a user's manual" </p>
<blockquote>
<p>$ |\Psi(x,t)|^2 \xrightarrow[x\rightarrow\pm \infty ]{} 0$ at all
times <em>t</em> [bound state] </p>
<p>$ |\Psi(x,t)|^2 \xrightarrow[x\rightarrow\pm \infty ]{} 0$ at any
particular time... | 4,357 |
<p>Please see the following photos. (I cannot post them...)</p>
<p><a href="http://i1163.photobucket.com/albums/q554/startanewww/CIMG4545.jpg" rel="nofollow">http://i1163.photobucket.com/albums/q554/startanewww/CIMG4545.jpg</a></p>
<p><a href="http://i1163.photobucket.com/albums/q554/startanewww/CIMG4546.jpg" rel="no... | 4,358 |
<p>I'm trying to show that $H_D = -i\boldsymbol{\alpha}.\nabla+\beta m$ is hermitian. </p>
<p>Its given that
$$
\gamma^{0\dagger}=\gamma^0
$$
$$
\boldsymbol\gamma^\dagger=-\boldsymbol\gamma
$$</p>
<p>What i've done is:
$$
H_D^\dagger = +i\boldsymbol\alpha^\dagger.\nabla+\beta^\dagger m
$$
$$
=+i(\gamma^0\boldsymbol\... | 4,359 |
<p>Please see the following photo. (I cannot post it)
<a href="http://i1163.photobucket.com/albums/q554/startanewww/CIMG4548.jpg" rel="nofollow">http://i1163.photobucket.com/albums/q554/startanewww/CIMG4548.jpg</a></p>
<p>Why is atomic bomb in a "fish-like" shape? (I don't know how to describe it) Is it specially desi... | 4,360 |
<p>This is with regards to adiabatic magnetisation. </p> | 4,361 |
<p>Having read Art Hobsons paper on Quantum field theory, he states " the field collapses into a field of atomic size" This seems to be stating that each field quanta is a different quantum field? Like 2 electrons are 2 electron fields, rather than the 2 electrons come from the same field. I thought they all emerged fr... | 554 |
<p>I've been having this confusing thought for so long now it would be amazing if someone could answer me.</p>
<p>Imagine this asterisk * . As you see, from the center point, lines go outwards, just like a sun will emit rays of light in all direction.</p>
<p>BUT, theoretically, there should be a "finite" amount of ... | 4,362 |
<p>I have been thinking about the definition of the notation $\cal N$ and its relation to the number of supercharges in <a href="http://en.wikipedia.org/wiki/Super-Poincar%C3%A9_algebra">SUSY</a>, but still feel a little confused. In dimension 2, we usually denote, for example, $\cal N = (2,2)$ supersymmetry, where we ... | 4,363 |
<p>In this question, I'm not talking about particle spin.</p>
<p>I guess, when an object rotates, its atoms also rotate. When an atom rotates, its particles must move in space. </p>
<p>I wonder that if the particles have a direction.</p>
<p>Can they rotate or do they just move position around the axis (middle) of a ... | 4,364 |
<p>I've imagined this little scenario to help me conceptualize things.</p>
<p>Let's say we have a doughnut-shaped object with a hole whose diameter is greater than that of a sphere. Let's say that the sphere is vertically aligned with the center of the doughnut and is horizontally gravitating towards it according to N... | 4,365 |
<p>If the Moon had gravity as good as Earth and a magnetic field could it have supported life? Because if the Moon had gravity, it could have retained water more than is present today on the surface. </p>
<p>If the Earth is in the habitable zone, does the Moon also lie in the habitable zone?</p> | 4,366 |
<p>I was searching the internet when I found this article <a href="http://arxiv.org/abs/0804.1764" rel="nofollow">http://arxiv.org/abs/0804.1764</a>, about achieving high voltage and power to ignite thermonuclear reaction by inertial confinement, the plan was to achieve it in a ultra vacuum and something that have to d... | 4,367 |
<p>This isn't a homework question, but it might as well be. The problem I have been pondering is:</p>
<blockquote>
<p>If a disc (or children's roundabout if you like), of radius r, mass m, is spun around it's center with an initial force F, and thereafter there is the friction force (of either the axle or air resist... | 4,368 |
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