# All Questions

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### Temperature of a System of molecules

Suppose I have a closed system with N molecules in it which are vibrating and all motion equations (rotation, translation and vibration) of the system are known along with any EM field equations in ...
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### For which systems is the equipartition theorem valid?

Under what conditions does a system with many degrees of freedom satisfy the equipartition theorem?
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### Why does pressure act as a source for the gravitational field?

I'm asking for a qualitative explanation if there is one. My own answer doesn't work. I would have guessed it's because when a gas has pressure the kinetic energy adds to the rest mass of a given ...
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### Explanation: Simple Harmonic Motion

I am Math Grad student with a little bit of interest in physics. Recently i looked into the wikipedia page for Simple Harmonic Motion. Guess, I am too bad at physics to understand it. Considering me ...
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### Can gravitational potential energy be released in a fire?

If one takes a bundle of wood up high to the mountains so its potential energy increases, would there be obtained more heat by burning it?
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### Why is stringless supergravity not considered by many to be a candidate theory of quantum gravity?

This paper seems to show that $d=4, N=8$ supergravity is finite. Yet the paper only has three citations in spires, and I certainly haven't heard talk of a new candidate theory of gravity. Why ...
419 views

### The source of the light we see from the Sun

Is it true that the visible light we see from the Sun comes from the electron-electron shell changes from the element iron as they absorb and emit energy in the form of photons. This energy derived ...
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### What is the quantum / Berry-Pancharatnam phase for a spin-j state with z-component m?

Quantum phase arises when a spin-j state is sent through a sequence of transitions that return it to its original position. For example with spin-1/2, a state picks up a complex phase of $\pi/4$ when ...
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### can a system with nested building blocks (atoms,cells) NOT be “fine tuned”? [closed]

Never mind whether the universe is "fine tuned" for anything in particular,just the idea that there is a nested hierarchy seems incredibly constraining on the outcome, and anything but accidental.
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### What's a good reference for this classical picture Feynman's talking about?

I have a mathematics background but am trying to educate myself a little about physics. At the beginning of Feynman's QED book (not the popular one) is the following: Suppose all of the atoms in ...
202 views

### Cooling via the quantum vacuum?

Suppose you had an isolated cloud of gas at a low temperature in a vacuum with no external sources of radiation (e.g. no CMB). The gas would clearly cool via the emission of low-energy photons. But ...
121 views

### Free electrons and energy states

Ok, background - studying for the physics part of my radiology exams, and came across a question that went something like this An electron fired through a tungsten target loses energy by: a) ...
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### Special designs to reduce the electrical resistance of a wire

The numerical simulation of this nerdy question shows that the resistance decreases with the number of nodes along longest side, and converges to a finite value when the # of nodes approaches ...
230 views

### Observing photons

Your replies to my question about being able to see a photon, from the side (answer, unanimous, “no”) have raised in me some additional questions. Would it reasonable to think that in consequence, ...
593 views

### If the size of universe doubled

My question is silly formulated, but I want to know if there is some sensible physical question buried in it: Suppose an exact copy of our universe is made, but where spatial distances and sizes are ...
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### Using delayed choice interference experiments as a computing device

I had an idea how to design a "quantum computer": How about designing interference-experiments where the design of the experiments itself represents algorithmical or mathematical problems that are ...
2k views

### What is the most efficient way to destroy the universe? [closed]

Don't worry... I won't actually do it, just would like to know how.
2k views

### Energy conservation in General Relativity

I understand that energy conservation is not a rule in general relativity, but I'd like to know under what circumstances it can still be possible. In other words, when is it possible to associate a ...
737 views

### Relativistic object impacts the earth

A familiar trope within science-fiction is that of a large relativistic object hitting a planet such as the earth. This is normally an interstellar spacecraft or a kinetic weapon with a mass in the ...
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### What would the electromagnetic field of a massless electron look like

The Standard Model gives non-zero mass to the electron via the coupling to the Higgs field. Issues of renormalizability aside, this is fundamentally unrelated to the fact that the electron couples to ...
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### How do Dirac fermions arise in graphene, and, what significance (if any) does this have for high-energy physics?

Graphene has a honeycomb lattice (in the absence of defects and impurities). By considering the low-energy limit of the half-filled Hubbard model used to model the strongly interacting electron gas we ...
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### energy field of a newly created particle

The question is: How to calculate the energy of electrostatic field of a newly created particle. The usual formula involves integration 'all over space'. According to GR I believe that 'all over ...
2k views

### gauss vs mW/cm^2: same thing?

A friend of mine is concerned about electromagnetic field negatively affecting their health and got a "DMF meter" to measure the field strength in their house in units of milliGauss. They are trying ...
602 views

### Tricky spring on a surface question

I have this relative simple-looking question that I haven't been able to solve for hours now, it's one of those questions that just drive you nuts if you don't know how to do it. This is the scenario: ...
186 views

### Non Classical mechanic answer to : length of time a thrown object spends in rest before falling down? [closed]

When an object is thrown upwards, when it eventually comes to rest and starts falling, for how long is it stationary? What about an particle in electric field having an initial velocity towards it's ...
2k views

### Visualization of proton's wavefunction

Visualizations of hydrogen's wavefunctions / electron orbitals are abound. I could not however locate a visualization of the wavefunction of a proton. The reason I was looking for one is to see ...
85 views

### Why is $\rho_m$ proportional to the deviation from critical temperature in critical phenomena?

In Peskin and Schroeder's chapter 12 about the renormalization group, it is stated that the parameter $\rho_m=m^2/M^2$, where $m$ is the mass and $M$ is the renormalization scale, is proportional to ...
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### Symmetry breaking

What is a good place to learn the details of symmetry breaking? What I am looking for is a more serious exposition than the wiki-article, which explains the details, especially the mathematical part, ...
628 views

### Thermal radiation spectrum of a blackbody

Why is it that thermal radiation of a black body usually described by a spectral distribution function rather than an intensity vs frequency curve? I have a vague explanation for this: Any measured ...
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### Reorienting a sensor axes according to particle displacement directions

Consider a sensor which is located inside the solid substance. This sensor is capable of detecting the substance oscillations along each of the three axes (usually orthogonal, but generally, any ...
183 views

### Size of our inflationary bubble

Once again, an attempt to connect popular and real science. I have read that inflation implies our universe should look flat, or really close to flat, because our observable universe is only a really ...
712 views

### does current product push or pull effect [closed]

Since i was a child i was told that current has pushing or pulling effect. However, i never got a dc shock and i don't remember ac shock (i got it very long before). The day before yesterday, an ...
3k views

### What is the statistical likelihood of getting a job as a theoretical physicist? [closed]

I'm considering taking a hobby (taking math and physics classes, reading attempting to read arXiv papers) and turning it into a career change. However, I have 3 kids and a wife who doesn't make a lot ...
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### movement of photons

In a typical photon experiment the photon is depicted as moving across the page, say from right to left. Suppose we were actually able to witness such an experiment, from the side (to position of ...
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### What would be a proper set of subjects, along with their order, for someone interested in string theory?

If one wanted to study string theory, what subjects should they learn first and what order should the study them? I would imagine that there are opionions, but I suspect there is a natural order, or ...
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### If time standard clocks and any memories about the time standard are destroyed, can we recover the time standard again?

Assume the time standard clocks and any memories about the time standard are destroyed. Can we recover the time standard again exactly? Recovering the time standard again means we can determine the ...
736 views

### Selection Rules in electron spectroscopy

How to derive the selection rules $\Delta L= \pm 1$, $\Delta S=0$ for electron spectroscopy?
281 views

### Entropy of a polymer contained in a sphere with infinitely thin chords

Imagine that I have a polymer (approximated as a freely diffusing, freely jointed chain with some number of subunits 'N'), and I place this polymer into a sphere of some volume 'V'. Next, I proceed to ...
228 views

### Predicting the ratio of translational diffusion coefficients for a sphere and a sheet

Imagine that I have a spherical particle of molecular weight $M$, volume $V$, and some experimentally observed center-of-mobility translational diffusion coefficient $D_{sphere}$ in water. I take ...
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### Poynting Vectors and Feigel Effects

There is a surprising number of papers seriously discussing the "feigel effect" This has been linked to the Abraham-Minkowski controversy also here. Although there are good discussions picking apart ...
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### Detecting coherence

Is there a way to know if a particle is acting as a wave or a particle? Alternatively, if an entangled particle was already measured? A - Yes So any experiment over an entangled particle that let ...
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### Application of mean of speed distribution

Preface The definition of average speed of an object is defined by the distance travelled over time: $$v_{avg} = \frac{x_2 - x_1}{t_2 - t1}$$ The interpretation of speed is that when you multiply ...
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### Photon absorption probability for a given molecule in gas phase

So I'm pretty sure I'm approaching this problem in the wrong way and I need some guidance (my first hint is that I think I'm thinking about a quantum mechanical problem too classically) Suppose there ...
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### Can/has string theory solved cosmological constant problem?

Can someone explain to me what the KKLT paper says, and what has and hasn't it achieved regarding the ability to construct solutions with a small positive or negative cosmological constant in string ...
686 views

### Can an insulator have magnetic poles?

Is it possible to make an insulator have two poles like a magnet? If yes, how to make it?
1k views

### Is the force carrier of the magnetism in a common household magnet a photon?

As I have understood it, the Standard Model includes particles that carry the different forces, e.g. the electromagnetic (EM) force, the gravitational (G) force. When talking about EM fields such as ...