question stringlengths 37 38.8k | group_id int64 0 74.5k |
|---|---|
<p>what are the reasons for current appearing in a wire when wire is in a changing magnetic field?</p> | 3,630 |
<p>In mean-field study of Bose-Hubbard model in an optical lattice, what parameter can be calculated to distinguish Bose glass and superfluid in a harmonic trap? </p> | 3,631 |
<p>I have a very simple question(I guess )to ask</p>
<p>$$\frac{d\mathbf{m}}{dt}= \mathbf{C} \times \mathbf{m}$$</p>
<p>where $\mathbf{m}$ and $\mathbf{C}$ are vectors. Assume that $\mathbf{C}$ is constant over a certain period of time $[0,T]$.</p>
<p>Then would someone please explain me how can we find a rotation ... | 3,632 |
<p>Stability usually favours lower potential. Yet the triangular L -points (lagrange points) L4 and L5 are stable, having higher effective potential than the other collinear L points (L1,L2,L3)</p>
<p><img src="http://i.stack.imgur.com/YMDuj.png" alt="enter image description here"></p> | 103 |
<p>For my question assume: </p>
<p>1: Big bang happened at a point (I know it happened everywhere) but after that explosion universe started to expand in all directions so it maybe considered to happened somewhere. (my imagination: water balloon popped with a pin and it start splattering away water in all directions a... | 3,633 |
<p>Let's have some theory in hamilton formalism and let's assume that it has the constraints between canonical variables $Q, \pi$. By the Dirac terminology, the set of constraints $F_{a}(Q, \pi) \approx 0$ of the first class satisfies conditions $\lbrace F_{a}, F_{b}\rbrace_{P} \approx 0$, while the set of constraints ... | 3,634 |
<p>The non-Relativistic Doppler shift equation is $f = \left( \frac{c + v_\text{r}}{c + v_\text{s}} \right) f_0 $ where c is the speed of the medium (346.4 m/s for sound at 25 C temperature). I tried calculating the Doppler shift for the case when the source was moving towards the observer, and the case where the obser... | 3,635 |
<p>I recently saw a cat fall probably 100 feet like in this video <a href="https://www.youtube.com/watch?v=OivjNVDe5gk" rel="nofollow">Cat Falls</a>. It seemed as if the cat reached terminal velocity by the time it hit. Does this mean that cats (and other small animals) could fall any distance without much harm because... | 3,636 |
<p>Until reading the Phys.SE post <a href="http://physics.stackexchange.com/q/133904/">here</a> about the neutron decay I never feel strange the fact about the antisymmetricity of this decay. But indeed why this decay is antisymmetric. The neutron is his own antiparticle, and this is without any restriction.</p>
<p>Co... | 3,637 |
<p>Lets consider this in marine seismic processsing. I am assuming you know what a first order primary reflection is, if not, I can define it. </p>
<p>Ok, so if we were to have a source $(S)$ and receiver $(R)$ lying directly on the $x$ axis seperated with a distance of $n$ meters, and a horzontial reflective surface,... | 3,638 |
<p>Which balloon will have higher relative change in volume, helium balloon immersed in liquid nitrogen or air balloon immersed in liquid nitrogen? Since volume is directly proportional to temperature does the gas in the balloon matter?</p> | 3,639 |
<p>I'm looking for an approximation for the temperature of the atmosphere at any height and pressure.</p>
<p>Both altitude and pressure are known variables,</p>
<p>I've derived this equation using maxwell's distribution:</p>
<p><img src="http://i.stack.imgur.com/Vcxk4.png" alt="Derivation"></p>
<p>Is this suitable?... | 3,640 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/2166/is-it-possible-to-go-back-in-time">Is it possible to go back in time?</a><br>
<a href="http://physics.stackexchange.com/questions/7823/is-time-travel-possible">Is time travel possible?</a> </p>
</blo... | 104 |
<p>Tyre companies boast of their wider tires for better grip on road. Also, the F1 cars have broad tires for better grip. But as far as I know Friction does not depend on the surface area of contact between the materials. Even the formula says so..
$F=\mu mg$ (where $F$ = Force of friction, $\mu$ = coefficient of fric... | 460 |
<p>Why is the center-of-mass of 2 bodies (which interact only via Newtonian gravity) located at a focus of each of the elliptical orbits?</p>
<p>I know that when there are no external forces, the center of mass moves at a constant speed, but that doesn't explain it.</p> | 3,641 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/29921/why-isnt-the-symmetric-twin-paradox-a-paradox">Why isn't the symmetric twin paradox a paradox?</a> </p>
</blockquote>
<p>Suppose there are two identical rockets, each carrying one of two identi... | 84 |
<p>i want to know the relation between voltage,current & resistance , apart from this ohm's law V=IR.Because in zener diodes,current does not increase accordingly with the voltage.At BREAKDOWN POINT, voltage remains the same as the current increases manifold.And in several other cases,even if there is a low voltage... | 3,642 |
<p>By studying quantum cosmology I was asking myself if the fact that the universe is expanding, so space is expanding and with it I would say that phase space is also expanding, so it's a non-unitary evolution, am I right? If yes, can unitarity be restored in a multiverse picture? Because I am always troubled when I h... | 3,643 |
<p>Suppose to have two capacitors in series:</p>
<p><img src="http://i.stack.imgur.com/gVAEX.png" alt="enter image description here"></p>
<p>The voltage in the middle point will be:</p>
<p>$$
V_X = V_1 \frac{C_1}{C_1+C_2}
$$</p>
<p>How can this be explained? It's been asked in <a href="http://electronics.stackexcha... | 3,644 |
<p>I am trying to measure the acceleration and deceleration of a car by using an 3 axis accelerometer which is build in an iPhone 5s. Placing the iPhone flat inside the car with the y axis to the top of the car this works pretty ok. But now I want to be able to place the iPhone basically arbitrary inside the car. (like... | 3,645 |
<p>Sorry people, very basic kinematic stuff here.</p>
<p>(1) Velocity:
$$v=\frac{d}{t}$$</p>
<p>(2) Acceleraton:
$$a=\frac{v_{f}-v_{i}}{t}$$</p>
<p>(3) Re-arrange acceleration:
$$v_{f} = v_{i}+at$$</p>
<p>(4) Ok here is my question, my lecturer produces this equation by "combining" (1) and (3):
$$d=v_{i}t+\frac{1}{... | 3,646 |
<p>I remember from an experiment about the <a href="http://en.wikipedia.org/wiki/Josephson_effect" rel="nofollow">Josephson effect</a> the state of each of the super conductors is fully described by a phase factor. From there I assume that is true for any Bose-Einstein condensate. So...</p>
<p>Let there be a huge blob... | 3,647 |
<p>The relevant question is <a href="http://physics.stackexchange.com/questions/83089/what-is-the-magnetic-effect-on-either-of-the-charges-moving-parallel">here</a>. The accepted answer may have explained my question in a descriptive manner. However, I want to see how things are related quantitatively.</p>
<p>Imagine ... | 3,648 |
<p>Suppose we try to obtain the movement equation for a particle sliding on a sphere (no friction, ideal bodies...). The only forces acting on the particle are its weight and - here's my problem - a force that keeps the particle attached to the sphere*. How I am supposed to represent mathematically this kind of forces?... | 3,649 |
<p>I'm a pure mathematician by trade, but have been teaching myself classical mechanics. I've got to the chapter on <em>Work, Energy and Power</em> and I've found an example that is causing me some problems.</p>
<p><strong>Question</strong></p>
<p>A van of mass 1250 kg is travelling along a horizontal road. The van's... | 3,650 |
<p>I'm currently a junior at San Diego State University and ever since I learned on my intro physics courses that antennas are best 1/2 wavelength. I've read wimpy explanations that it is so it can "feel" the whole wave. I don't find that convincing enough. Basically, how can you prove or show that 1/2 wavelength is... | 3,651 |
<p>I'm reading a few papers about how the optical properties of materials change when a under stress or a force acts upon them. I seem to be encountering the following three terms:</p>
<ol>
<li>Photoelastic constant </li>
<li>Photoelastic coefficient </li>
<li>Acousto-optic coefficient</li>
</ol>
<p>Is there a differ... | 3,652 |
<p>As in the title. I know she was working with radioactive atoms and she made huge progress in the field of physics. But where would you find the application of her discoveries in our world? Is it just used in theoretical physics or does it have any meaning to us mortals?</p> | 3,653 |
<p>Based on the <a href="http://en.wikipedia.org/wiki/Lambda-CDM_model" rel="nofollow">Lambda-CDM</a> cosmological model, our universe is not only expanding, but is accelerating in its expansion. However, the <a href="http://en.wikipedia.org/wiki/Equivalence_principle" rel="nofollow">Equivalence Principle</a> would sug... | 3,654 |
<p>A phase transition occurs when for example, heat is applied continuously to a liquid and after a certain time it converts into a gas.</p>
<p>How does this process work in detail? Is their a chain reaction that causes to liquid to reach a 'critical' point? Does the liquid syncronises in some specific vector, facilit... | 3,655 |
<p>Consider a 10 meter bridge that weighs 500 N supported at both ends. A person who weighs 750 N is standing 2 m from the end of the bridge. What are the forces $F_a$, $F_b$ holding the bridgeup at either end?</p>
<p>$$750 N - 2m + (500\cdot5) = F_b\cdot10 \\
1748 /10 m =F_b \\
F_b=174.8N \\
F_a=750N + 500N - 174.8... | 3,656 |
<p>The following quote is extracted from the book "The Field-The quest for the secret force": </p>
<blockquote>
<p>...There was other, quite practical, unfinished business with quantum theory. Bohr and his colleagues only got so far in their experiments and understanding. The experiments they’d conducted demonstrat... | 3,657 |
<p>I've been told my whole life that light is either a wave or a particle. When it's traveling through space, it's a wave. When it hits a wall, or a photo-sensitive chemical strip or something similar, it's a particle. </p>
<p>However, upon looking back all of the examples I've seen I can only recall instances in w... | 3,658 |
<p>This question is about taking the logarithm of the ideal gas law. In a fluids text book the author writes:</p>
<blockquote>
<p>First recall a couple of ideal gas relationships involving potential temperature, $\theta$, and entropy s...</p>
</blockquote>
<p>$$\log(\theta) = \log(T) - \dfrac{R}{c_{p}}\log(p) = \d... | 3,659 |
<p>I've just cracked open a biophysics textbook and it's all fine up until the introduction of the letter C in a wavefunction equation, and declaring C<sub>1</sub>= ±C<sub>2</sub></p>
<p>I've had lectures on eigenfunctions etc. before and no recollection of what C is, and it's not introduced earlier in the book (<em>B... | 3,660 |
<p>Let's have the S-matrix:
$$
S_{\beta \alpha} = \langle \beta | \hat{S} | \alpha\rangle .
$$
Here $|\alpha \rangle , | \beta \rangle$ are $t \to \mp \infty$ limit of the free states, $\hat {S} = \hat{T}e^{-i\int \hat{L}_{\int}d^{4}x}$, $\hat{L}_{\int}$ refers to the operator in the interaction picture. When we decide... | 3,661 |
<p>How is it possible to achieve waves which are spatially, but not temporally, coherent? Can this be done with a bandpass filter?</p>
<p>Conversely, how is it possible to achieve waves which are temporally, but not spatially, coherent? Can this always be achieved with a pinhole?</p> | 3,662 |
<p>In 1962, Josephson predicted that for a sufficiently thin insulating layer, it should be possible for Cooper pairs to tunnel between two pieces of superconductor. </p>
<p>With a potential difference $V$ across the junction, an alternating current should flow at a frequency $f$ given by:
$$
hf = 2\times e\times V.
$... | 3,663 |
<p>I'm confused by statistical entropy. It seems to me like the number of microstates for a given macrostate would increase without bound as finer partitionings of the phase space are chosen. Why is it that, as the <a href="http://en.wikipedia.org/wiki/Microcanonical_ensemble#Precise_expressions_for_the_ensemble" rel="... | 3,664 |
<p>In Gasiorowicz's <em>Quantum Physics</em>, we determined the relation: $$L_z | l,m\rangle= \hbar m | l,m \rangle$$</p>
<p>I would like to determine: $\langle l,m_1 | L_x | l,m_2 \rangle $</p>
<p>I thought about expressing $L_x$ in terms of $L_{+}$ and $L_{-}$, which gives us: </p>
<p>$$L_x= \frac12\left(L_{+}+ L... | 3,665 |
<p>A question needed for a "solid" sci-fi author: How to detect a strong magnetic monopole? (yes, I know no such thing is to be found on Earth).</p>
<p>Think of basic construction details, principles of operation and necessary components of a device capable of detecting/recognizing a macroscopic object emitting magnet... | 3,666 |
<p>I have a question regarding <a href="http://en.wikipedia.org/wiki/Coset" rel="nofollow">coset space</a> or <a href="http://en.wikipedia.org/wiki/Homogeneous_space" rel="nofollow">homogeneous space</a> $SO(n+1)/SO(n)$ which is simply $S^n$. I need some intuition regarding this result.</p>
<p>As everyone knows that f... | 3,667 |
<p>Is it another way of saying the ground state?</p> | 3,668 |
<p>The edge of Jupiter <a href="http://en.wikipedia.org/wiki/File%3aJupiter-Earth-Spot_comparison.jpg">looks very sharp</a>.</p>
<p><img src="http://i.stack.imgur.com/DH0Ay.jpg" alt="Jupiter"></p>
<p>Even more bothersome, the <a href="http://en.wikipedia.org/wiki/File:171879main_LimbFlareJan12_lg.jpg">edge of the sun... | 105 |
<p>Sorry for the long text, but I am unable to make my question more compact.</p>
<p>Any periodic function can be Fourier expanded. Usually, they say in mathematical physics books, if the function is not periodic we use Fourier transform which is more general than Fourier series expansion. </p>
<p>If Fourier transfor... | 3,669 |
<p>We consider a theory described by the Lagrangian,</p>
<p>$$\mathcal{L}=i\bar{\Psi}\gamma^\mu\partial_\mu\Psi-m\bar{\Psi}\Psi+\frac{1}{2}g(\bar{\Psi}\Psi)^2$$</p>
<p>The corresponding field equations are,
$$(i\gamma^\mu\partial_\mu-m+g\bar{\Psi}\Psi)\Psi=0$$</p>
<p>Could this model have soliton solutions? Without ... | 3,670 |
<p>I am reading a <a href="http://www.physik.uni-siegen.de/quantenoptik/forschung/publikationen/publis/epr_prl.pdf" rel="nofollow">paper</a> by Serge Haroche stating the cavity they use sustains a Gaussian mode of the e.m. field called $TEM_{900}$. I understand what Gaussian means. I found <a href="http://en.wikipedia.... | 3,671 |
<p>I'm having this lecture on QM and we are giving an introduction on Lie Groups. </p>
<p>So... this week we have been talking about central extensions of LG (such as Galilean) and related to this popped up the 2-cocycles. All I know is that they should relate somehow the phases of its projective representation and by... | 3,672 |
<p><a href="https://en.wikipedia.org/wiki/Rabi_problem" rel="nofollow">Rabi oscillations</a> are commonly known as the oscillations in time of the occupation probability of a quantum two-level system under the action of a coupling interaction between the two-levels.</p>
<p>Nevertheless, I think that Rabi oscillations ... | 3,673 |
<p>I wondered whether, under the probabilistic interpretations of QM, the <em>timing</em> of the Big Bang (or perhaps any other historical event) is <em>fundamentally</em> as uncertain as (or: like) other (e.g., future) quantum-mechanical processes. That is, looking backwards, should one—<em>if one insists on being ped... | 3,674 |
<p>In a recent Hunger Games movie, there's a scene where a certain scientist says that he invented a wire which will not melt under the current of a lightning. Is that even possible?</p> | 3,675 |
<p>What are the various approaches to fault tolerant quantum computation ? Two examples are 1. topological quantum computation which uses topological phases in quantum states (2-Dimensional for non-abelian statistics of anyons) and 2. spin-half BEC form (refer <a href="http://jqi.umd.edu/news/new-state-fifth-state" rel... | 3,676 |
<p>When we find the electric field between the plates of a parallel plate capacitor we assume that the electric field from both plates is $${\bf E}=\frac{\sigma}{2\epsilon_0}\hat{n.}$$ The factor of two in the denominator comes from the fact that there is a surface charge density on both sides of the (very thin) plates... | 3,677 |
<p>I, a newbie in physics, often read about "near determinism", which is most probably the actual state of physics, meaning: the "big world" is deterministic, but very small things (atoms and smaller) are indeterministic (e.g. quantum physics). </p>
<p>If this is true, where is the border?</p>
<p>At which size do obj... | 3,678 |
<blockquote>
<p>Consider the following situation. A certain quantity of ideal monatomic gas (say one mole) is confined in a cylinder by a piston and is maintained at constant temperature (say $T_0$) by thermal contact with a heat reservoir. Then the gas slowly expands from $V_1$ to $V_2$ while being held at the same ... | 3,679 |
<p>There is differential identity with Weyl tensor and energy-momentum tensor:
$$
D^{\lambda}C_{\lambda \alpha \sigma \beta} = 4 \pi G \left(D_{\sigma}T_{\alpha \beta} - D_{\beta}T_{\alpha \sigma} + \frac{1}{3}(g_{\alpha \sigma}D_{\beta}T - g_{\alpha \beta}D_{\sigma}T)\right). \qquad (1)
$$
One says (Carroll, "Spacetim... | 3,680 |
<p>I would like to know how good or bad behave a metallic wall in stopping the propagation of an microwave signal.</p>
<p>To be practical, let's take the example of a GSM relay antenna. If I set up the perpendicular metallic wall between me and the signal sender,
will the wall stops the signal like a plank does it in... | 3,681 |
<p>I'm doing old exam questions, and here is one that on first glance seemed rather simple to me, but I just can't get it:</p>
<p>Given are two operators $A$ and $B$, and all we know about them is that
$$[A,B] = B$$
and
$$B^\dagger B = 1 - A^2$$</p>
<p>From this, I must find the "hermiticity properties" of $A$ and ... | 3,682 |
<p>I've posed the question in this particular way to avoid the ambiguity usually found in the posing of the "<a href="http://pogue.blogs.nytimes.com/2006/12/11/the-airplane-treadmill-conundrum/" rel="nofollow">airplane on a treadmill</a>" puzzle, <a href="http://physics.stackexchange.com/questions/32269/what-will-happe... | 3,683 |
<p>I have recently come across two key concepts in quantum optics: <a href="https://www.google.com/search?q=%22shot+noise%22" rel="nofollow">shot noise</a> and <a href="https://www.google.com/search?q=%22back-action+noise%22" rel="nofollow">back-action noise</a>. This is very important for me to know: first, are shot n... | 3,684 |
<p>I almost all movies where you could see an animation about an asteroid, they move in a very distinct way.</p>
<p>I don't know how to explain better, but I think what we can see in the movies is that the asteroid is rotating around the x axis with constant speed, around the y axis with constant speed and around the ... | 3,685 |
<p>If I have a car (with a particular engine) optimized (shape & weight distribution-wise) for attaining the top speeds possible, and I put that engine into a car which is heavier (but otherwise the same shape & design), will the heavier car have the same top speed in the real world?</p>
<p>I'm guessing that t... | 3,686 |
<p>I'm reading a book about string theory, and it describes <a href="http://en.wikipedia.org/wiki/Anthropic_principle" rel="nofollow">anthropic principle</a>. Idea is clear to me, I understand this principle describes certain constants in modern physics that are so fine tuned as if to imply the existence of a creator.<... | 3,687 |
<p>I am from civil engineering, I am doing simulation and analysis (CFD and other statistical method) on flow around bluff bodies as in a wind tunnel. Different from in aerospace aerodynamics, our objects are generally very blunt and have sharp separation angles, for example flow around rectangular prisms, etc. The Re ... | 3,688 |
<p>The question and answer are on pg.8-10 of <a href="http://web.mit.edu/8.01t/www/materials/ExamPrep/final_practice_problems%20sol_f12.pdf" rel="nofollow">this PDF</a>:</p>
<p>At first, I went through it, thinking nothing of it. But then, I wondered: "What if we picked a final state in which the space junk was NOT at... | 3,689 |
<p>Consider a long semiconductor bar is doped uniformly with donor atoms so that the concentration given by $n = N_D$ and is independent of position. Radiation falls upon the end of the bar at $x=0$, this light generates electron-hole pairs at $x=0$. light keeps on falling.</p>
<p><strong>Explanation:</strong> </p>
... | 3,690 |
<p>I have a table of the characters of a set of wavefunctions for different points in reciprocal space and for different band indices (this is for a solid). For the case of a single irreducible representation, it is clear from the physical meaning of a 1D group that a character of 1 means operating with the symmetry o... | 3,691 |
<p>Why is application of probability in QM fundamentally different than
application of probability in other areas?</p>
<p><a href="http://en.wikipedia.org/wiki/Quantum_mechanics" rel="nofollow">Quantum mechanics</a> applies probability according to the same <a href="http://en.wikipedia.org/wiki/Probability_axioms" rel... | 3,692 |
<p>How can I convert </p>
<p>$$ W m^{-2} sr^{-1} nmm^{-1} $$</p>
<p>to </p>
<p>$$ W m^{-2} nm^{-1} $$</p>
<p>I have the following matlab code to illustrate the spectral energy distribution of solar radiation:</p>
<pre><code>h = 6.626e-34; % Planck's Constant = 4.135 x 10^-15 eV s
c = 3e8; % speed of li... | 3,693 |
<p>I was learning about circular motion when this question struck me:</p>
<p>In real life situations we are able to take a turn along a circular arc with our bike because friction provides us the necessary centripetal force for doing so. When we talk about cars, the road is banked which provides the centripetal force.... | 3,694 |
<p>Recently, I happened to hear about the possibility of doing <a href="http://en.wikipedia.org/wiki/Analytic_continuation" rel="nofollow">analytic continuation</a> <strong>numerically</strong>. That sounds attractive for the ubiquitous $\mathrm{i}\omega_n\rightarrow\omega+\mathrm{i}0^+$ procedure, via which we go from... | 3,695 |
<p>To state the title question perhaps more precisely:</p>
<p>What is the largest photon energy $E_{\gamma}$ and the corresponding mass number $A$ and atomic number $Z$ of a suitable nucleus ${}^A_ZX$ (presumably in a ground state) such that the hypothetical reaction</p>
<p>$$ {}^A_ZX + \gamma \rightarrow {}^{(A - a)... | 3,696 |
<p>In contrast to a "time-like" or "causal" structure connecting space-time together, Does quantum entanglement imply the existence of a "space-like" or "non-causal" structure holding space-time together as well.</p>
<p>A more general question; is there even any relevance to the <em>discussion</em> of the existence of... | 3,697 |
<p>Since by introducing <em>one</em> <a href="http://en.wikipedia.org/wiki/Higgs_boson">Higgs Boson</a> we can give a mass to the leptons and gauge bosons of the weak interaction: </p>
<p>Why should we consider more than one Higgs (doublet) once we go beyond the standard model?</p> | 3,698 |
<p>I'm interested in learning physics. I do realize that the subject is large and that it would be easier if I had a specific area of interest. However, I do not. I suppose I want to learn about the fundamentals of it all; the axioms that combine all physics fields. Or, in other words, a high school physics class. </p>... | 98 |
<p>I guess according to mathematical didactic, we first think of spacetime as a set and we reason about elements of its topology and then it's furthermore equipped with a metric. Appearently it is this Riemannian metric, which people consider to be the object, which induced the minimal symmetry requirements of spacetim... | 3,699 |
<p>I have only just finished High school physics so my understanding is still fairly simple but I'm having trouble with this question.</p>
<p>Imagine you are in space traveling at a relativistic speed with a laser/light source. When you fire the laser do you see a straight line?</p>
<p>If you do, then when the light ... | 3,700 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/25254/why-does-the-moon-sometimes-appear-giant-and-a-orange-red-color-near-the-horizon">Why does the moon sometimes appear giant and a orange red color near the horizon?</a> </p>
</blockquote>
<p>Why doe... | 106 |
<p>I am trying to study the canonical formulation of Yang-Mills theories so that I have direct access to the $n$-particle of the theory (<em>i.e.</em> the Hilbert Space). To that end, I am following Kugo and Ojima's (1978) 3-part paper.</p>
<p>At the outset, I am confused by their Lagrangian, and their two difference... | 3,701 |
<p>As temperature rise the density become lower,When temperature goes down, density is higher but in higher temperature the body become bigger so why density become lower?</p> | 3,702 |
<p>I have two atoms, both of which are either bosons or fermions, with four allowed energy states: $E_1 = 0$, $E_2 = E$, $E_3 = 2E$, with degeneracies 1, 1, 2 respectively.</p>
<p>What's the difference between the partition functions of a pair of two bosons and that of a pair of two fermions?</p> | 3,703 |
<p>How are decays related to forces, what is meant by particle X decays through the, say, strong force? </p>
<p>The way I understand forces is by how they change the acceleration of particles with the right charge (mass, electric etc), through F=ma, how does it cause one particle to turn into other? </p>
<p>How... | 3,704 |
<p>I have a theoretical question that has been bugging me and my peers for weeks now - and we have yet to settle on a concrete answer.</p>
<p>Imagine two balloons, one is filled with air, one with concrete. They are both the same size (and hence have the same air resistance). On the moon, we are taught at school that ... | 3,705 |
<p>So I am piecing together a school project on the numerous misconceptions of the universe, which I plan to "provide proof against them" with information from various sources (one of the main ones will be <em>A Brief History of Time</em> by Stephen Hawking). In coming up with the myths, I am sure that I will miss som... | 3,706 |
<p>Why the lowest order of matrices in Dirac equation (Relativistic Quantums) are 4x4 matrices (and can not be 2x2 matrices)?</p>
<p>How to prove it?</p> | 3,707 |
<p>A white light, as we all know, is composed of seven lights VIBGYOR. Each of the component lights has distinct frequency ranging from one value to another. So, when the photons have wavelength of 600 nm it becomes a yellow light and when it changes to 700 nm it becomes a red light. So, does this imply that the freque... | 3,708 |
<p>One of my professors told us this semester, that the 'infinities' that arise in QFT are partly due to the use of the $\delta$-distribution in the commutator relations which read (for fermions)</p>
<p>$\left\{\Psi(r'), \Psi^\dagger(r)\right\} = \delta(r-r')$</p>
<p>In reality we would not have such a $\delta$-distr... | 3,709 |
<p>Some people speculate that the mysterious dark matter in the universe could be tiny black holes. But on the other side, could dark matter particles attract each other by gravity and finally form a black hole? Since dark matter is even more abundant than normal matter, the dark matter black hole should not be rare.</... | 961 |
<p>A shopper pushes a 7.5-kg shopping cart up a 13 (degree)incline. Find the magnitude of the horizontal force, F, needed to give the cart an acceleration of 1.41 m/s$^2$.</p>
<p>I ask this because the solution to this problem is $7.5[1.41 + 9.81\sin(13)] = 27.1$, which describes the component of the force along the d... | 3,710 |
<p><em>Edit: I know there have been some similar questions but I don't think any had quite articulated my particular confusion.</em></p>
<p>If gauge symmetries are really just redundancies in our description accounting for nonphysical degrees of freedom, then how does one explain the deep and powerful fact that if one... | 3,711 |
<p>I am having difficulty finding a good explanation of how potential difference and deformation of a piezoelectric relate. Is there a fixed axis along which the piezoelectric crystal will respond to voltage potential / form a voltage potential when compressed? Is the action of a piezoelectric even compression/expansio... | 3,712 |
<p>I am looking at <a href="http://en.wikipedia.org/wiki/Deriving_the_Schwarzschild_solution" rel="nofollow">Wikipedia's article on deriving the Schwarzschild solution</a>. In the section "Simplifying the components", it says,</p>
<blockquote>
<p>On the hypersurfaces of constant $t$ and constant $r$, it is required ... | 3,713 |
<p>Do the apperance in the atomic nucleus of virtual matter-antimatter particle pairs play a role in the random nature of radioactive decay?</p> | 3,714 |
<p>Is it right that all units in physics can be defined in terms of only mass, length and time?</p>
<p>Why is it so? Is there some principle that explains it or is it just observational fact?</p> | 3,715 |
<p>Reaching the ground state of a large 2D classical spin model (e.g. classical Heisenberg model) might be a relatively difficult task while using conventional "flip/reject" Monte Carlo method. The system may be easily trapped in a local minima instead of the global minima, for example, the spin domains might appear w... | 3,716 |
<p>Recently i found out this <a href="http://news.stanford.edu/news/2010/august/sun-082310.html" rel="nofollow">uber strange article</a> about nuclear decay rates being somehow showing seasonal variations with a high correlation with sun activity. Two very precise questions:</p>
<p>1) <strong>has this been experimenta... | 3,717 |
<p>What kind of object is <a href="http://en.wikipedia.org/wiki/656_Beagle" rel="nofollow">656 Beagle</a> (<a href="http://comets.universetoday.com/l/3668/656-Beagle-1908-BU" rel="nofollow">1908BU</a>)?</p>
<p>I know it's a minor planet, but that includes a large array of different stuff. Specifically, I am looking at... | 3,718 |
<p>I'll keep it simple. How does inflation drive Ω close to 1?</p> | 3,719 |
<p>These questions are in reference to this beautiful review article by Minahan -
<a href="http://arxiv.org/pdf/1012.3983v2" rel="nofollow">http://arxiv.org/pdf/1012.3983v2</a></p>
<p>I gained a lot by reading some of its sections but not everything is clear to me.
I would like to ask a few questions to clarify some ... | 3,720 |
<p>Can someone compare the energy efficiency of human brain as a computer ? What is the energy in joules / flop ? may be some reasonable assumptions on the computational load of common tasks such as pattern recognition or speech synthesis can be used.</p> | 3,721 |
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