3
votes
1answer
1k views

Partial and total time derivatives of the Hamiltonian

When does the total time derivative of the Hamiltonian equal the partial time derivative of the Hamiltonian? In symbols, when does $\frac{dH}{dt} = \frac{\partial H}{\partial t}$ hold? In Thornton ...
4
votes
7answers
8k views

Can plasma turn back into gas, solid, or liquid?

I wanted to know if, since basic chemistry teaches you that states of matter can be changed, I was wondering particularly about plasma. I know that virtually all of the Sun is plasma, so I was ...
3
votes
2answers
10k views

Why is lightning considered a plasma?

I was wondering why a lightning bolt is coined as "plasma", or a "spark" from an electrical wire/device is as well, yet flares, molten lava, and burning buildings are not(flares are pyrotechnic, ...
5
votes
3answers
995 views

Are length contraction and time dilation physical?

Are length contraction and time dilation real physical phenomena, or are they just a measurement issue?
3
votes
1answer
2k views

Does time expand with space? (or contract)

Einstein's big revelation was that time and space are inseparable components of the same fabric. Physical observation tells us that distant galaxies are moving away from us at an accelerated rate, and ...
2
votes
2answers
190 views

How does energy transfer between B and E in an EM standing wave?

I'm trying to understand how an electric field induces a magnetic field and vice versa, its associated energy, as well as relating it to my understanding of waves on a string. Using a standing wave ...
-1
votes
2answers
190 views

Harmonic Motion [closed]

A light elastic string is stretched between two points, one lying vertically below the other. A particle is attached to the midpoint of the string, causing it to sink a distance h. Assuming that the ...
1
vote
1answer
278 views

Matrix operations on Quantum States in a composite quantum system

Intro (you may skip this if you're an expert, I'm including this for completeness): Say I have two bases for two systems, The first is a spin-1/2 system $|+\rangle = \left(\begin{array}{c} 1\\0 ...
1
vote
1answer
506 views

A relativistic meter stick and a thin disk

I have a question like the "pole in the barn" special relativity "paradox", but I'm not sure what to make of this: Question A meter stick lies along the $x$-axis and approaches the origin, moving ...
0
votes
1answer
745 views

Liquid nitrogen condensing oxygen out of the air

In this video, a pool of liquid nitrogen in a metal bowl can cool it enough so that oxygen from the air condenses at the bottom: ...
8
votes
1answer
969 views

Anharmonic oscillators: why is $F=-k x-k' x^3$, with no quadratic terms?

The equation of motion of a general anharmonic oscillator includes a position-dependent force that can be expanded in a Taylor series as $$m\ddot{x}+2\mu\dot{x}+k_0+k_1x+k_2x^2+k_3x^3\ldots=F.$$ I ...
1
vote
2answers
274 views

Feynman Diagrams: Mass Conservation

Can a Feynman diagram end with more matter than it began with? The answer should be no because it would break the law of conservation of mass, right? Example: I learned that two up-quarks could ...
0
votes
1answer
193 views

Help with the Heisenberg relation in Gaussian wave

In short laserpulses there is a minimal product of the frequency width and the pulselength for Gaussian pulses $\tau \cdot \Delta\omega \geq4\ln2$ this is the fourier boundary. So I know it origins ...
0
votes
1answer
18k views

Relationship between boiling point and pressure

In the bubble chamber, liquid hydrogen is kept at high pressure. When a stream of charged particles are injected into the bubble chamber, pressure on the liquid hydrogen is released and bubbles of gas ...
0
votes
2answers
2k views

How can a rapid change in the volume of a gas cause changes in its temperature?

We were learning about Boyle's law (pressure is inversely proportional to volume of a gas) and in the experiment to prove the law, we were told that we cannot change the volume of a gas too rapidly ...
8
votes
2answers
621 views

Is there an intuitive way of thinking about the extra dimensions in M-Theory?

Why are 11 dimensions needed in M-Theory? The four I know (three spatial ones plus time) have an intuitive meaning in everyday life. How can I think of the other seven? What is their nature (spatial, ...
4
votes
1answer
261 views

How does light pass through rough glass?

Light incident on a rough surface will be diffuse after passing it. Angular intensity depends on the grinding of the glass surface. I'm trying to find information about the scattering indicatrix of ...
65
votes
4answers
4k views

Is temperature a Lorentz invariant in relativity?

If an observer starts moving at relativistic speeds will he observe the temperature of objects to change as compared to their rest temperatures? Suppose the rest temperature measured is $T$ and the ...
8
votes
1answer
580 views

Charge neutrality of the Universe: evidences and theories

I've always wondered why the number of protons in the Universe exactly matches the number of electrons. They are such different particles with totally different cross sections. So, first of all, is ...
6
votes
2answers
5k views

Why would an object appear a different size when in water?

A friend of mine has a homework question and we're having some trouble figuring out what physical mechanisms come into play for this. An underwater swimmer sees a spherical air bubble that appears ...
2
votes
0answers
111 views

How do we show that photons generated by a constant electric current are distributed according to a Poisson distribution?

I saw the answer sometimes ago in a book "Quantum Electronics" or similar title. I don't remember the author since I lost the book. The book sets ( I believe so ) a constant electric current $I$ in a ...
6
votes
2answers
686 views

Normal force of ball sliding on concave surface

Imagine a ball is sliding along a surface shaped like $y=x^2$. Like , but please ignore the fact that the center of the ball is on the surface instead of the edge. When the ball is stationary, I can ...
1
vote
3answers
323 views

Does Newton's first law state something substantive, or is it merely describing a convention?

Newton's first law is often said to define what an inertial frame is - namely, a reference frame in which a body not acted on by a force will move with constant velocity. In other words, a frame where ...
0
votes
1answer
278 views

Forces on a helical screw?

The common screws which we use, are right handed helices, the simplest parametric equations of which are:- $$x(s)=\cos(s),y(s)=\sin(s),z(s)=s$$, with $z$-axis as the axis of the helix. My question ...
1
vote
1answer
260 views

Why do some capacitors leak and other capacitors hardly leak at all?

I just found out that electrolytic capacitors hardly leak whereas non-electrolytic capacitors leak and at times, leak a lot. Questions: (a) what causes capacitors to leak? (b) why do electrolytic ...
1
vote
1answer
86 views

Ghosts on Torus worldsheet

Why after the expansion, only 0-mode of bc-ghost contributes to the 4-points ghost function on a torus worldsheet? $$<c(z_1)b(z_2)\tilde{c}(\bar{z}_3)\tilde{b}(\bar{z}_4)>_{T^2} ...
3
votes
2answers
480 views

Accounting for metric tensor derivatives in Einstein-Hilbert action

I'm puzzling over the canonical derivation of GR from the Einstein-Hilbert action; getting the derivation to gel with an explicit treatment of the functional derivative isn't working out. So the ...
10
votes
1answer
635 views

Is it possible to derive Schrodinger equation in this way?

Let's have wave-function $\lvert \psi \rangle$. The full probability is equal to one: $$\langle \Psi\lvert\Psi \rangle = 1.\tag{1}$$ We need to introduce time evolution of $\Psi $; we know it in ...
8
votes
3answers
481 views

Can a planet form before the parent star ignites?

I'm unable to find an answer to my questions via my searches. This questions pertains to the timeline of a star system creation. My question: During the creation of a star system, can satellite ...
1
vote
1answer
2k views

How is light created?

I'm very curious about how light is created. I'm trying to get back to some type of real understanding about why everything on the sub-atomic level vibrates and the implications for the ...
7
votes
1answer
170 views

Do systems with level crossings have unstable eigenbases?

It's folklore dating back to von Neumann and Wigner that time-dependent Hamiltonian systems tend not to have level crossings of their energy eigenvalues. However, we can of course consider smoothly ...
2
votes
1answer
286 views

what would be the maximum depth of tunnel? [closed]

Perhaps more of an engineering question, but with the subject recently in the news about hyperspeed maglev tunnels I'll chance it here. Say you set up a network of line of sight underground tunnels ...
0
votes
2answers
376 views

Is there a fundamental difference between the statistical methods of science, comparing medicine to physics?

Is there a fundamental difference between the statistical methods of science, comparing medicine/biology with small sample sizes(n < 10^2 or 10^3) to the statistics applied in Quantum Mechanics (h: ...
-2
votes
1answer
99 views

Is information propagated across a medium in any other way than waves?

Is information propagated in any other way than waves? Please distinguish "propagation across a medium" from information "storage within stable states of matter", which might difuse or interact ...
2
votes
1answer
143 views

Ergodicity of the Drude model

The Drude model of electric conduction in solids deals with independent free electrons subject to random collisions with the crystal lattice (the direction where the electrons are scattered after a ...
1
vote
2answers
1k views

Difference resultant aerodynamics force on an airfoil and a flat plate

From basic airfoil theory the following free body diagram can be determined for a two dimensional asymmetric airfoil: Here the direction of the resultant force is governed by the geometry of the ...
3
votes
1answer
252 views

Time dilation and the speed of light in the twin paradox

Suppose we look at the twin paradox where the twin traveling at high speed relative to an observer on earth has a clock which counts time by sending photons of light across a distance within the ...
3
votes
1answer
769 views

Conserved quantity along geodesic

In my general relativity textbook (Carroll), he says that "the geodesic equation (together with metric compatibility) implies that the quantity $\epsilon ...
2
votes
0answers
83 views

What determines the probability of a pair of photons interacting, and producing a positron and an electron?

The second answer to this question describes how this process might occur, and I'm curious for more details about it: What is the probability distribution of the interaction producing ...
4
votes
0answers
265 views

Fields with SO(3) diagonal subgroup symmetry

I read about a Higgs field $\vec{\phi}=\frac{1}{2}a\hat{r}\cdot \vec{\sigma}$ (in the context of 't Hooft-Polyakov monopole) with SO(3) diagonal subgroup symmetry consisting of simultaneous and equal ...
0
votes
2answers
73 views

Problem in progresive wave

In this progressive wave we need to find out the phase difference. If we define it by $\phi$ in the x distance, we get . $$\phi = \frac{2 \pi}{\lambda}x$$ But when we write the prograsive wave ...
1
vote
1answer
810 views

Where do the photons mediating the electromagnetic force come from?

The electromagnetic field is mediated by photons (energy quanta). Its range is infinite, the interaction only weakens quadratically with distance due to the area of an expanding virtual sphere. Where ...
0
votes
2answers
232 views

What if a particle falls into the center of a central field? [closed]

Given a central field $U(r)$ satisfies $U(r) \rightarrow -\infty$ when $r \rightarrow 0$, then What if a particle falls into the center of a central field? Can you help me analysis this question in ...
15
votes
1answer
458 views

Dark matter and SO(10) grand unification

$SO(10)$ grand unified theories nicely accommodate a massive $\sim 10^{14-15}\; GeV$ sterile neutrino. Would this be a viable dark matter candidate? I haven't found any specific material regarding ...
2
votes
3answers
2k views

Explanation of homogeneity of space and time by giving examples?

while reading landau lifshitz i came across these three terms:- homogeneity of space. homogeneity of time. isotropy of time. it will be a great help for me if someone can explain it to me by ...
3
votes
3answers
441 views

Einstein equation $E=mc^2$: Does it mean an object without mass does not have energy?

Einstein equation $E=mc^2$ where $E$ is energy, $m$ mass, and $c$ the speed of light in vacuum. So does it mean objects without any mass does not posses energy for eg lights photons does not have mass ...
0
votes
1answer
260 views

How does a synchroton work?

I know that a linear accelerator (linac) works by having terminals that get longer progressively and changes polarity due to AC current. And I also know that a cyclotron works by having two ...
2
votes
3answers
524 views

How does that Boltzmann distribution interact with entropy?

In an ideal gas, the Boltzmann distribution predicts a distribution of particle energies $E_i$ proportional to $ge^{-E_i/k_bT}$. But, doesn't entropy dictate that the system will always progress ...
2
votes
1answer
146 views

Will the Hubble parameter reach zero asymptotically in the far future?

In the current accelerated expansion universe model will the Hubble parameter $H$ reach zero asymptotically in the far future?
0
votes
2answers
413 views

Is mass of a particle changed when it is charged? [closed]

If a particle of mass $M$ is given an electric charge $Q$, will its mass change?

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