# All Questions

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### WIMP dark matter annihilation rate equation (approximation)?

WIMP is a possible dark matter candidates, which self-annihilates. What is the WIMP annihilation rate, as a function of density? Most sources state this scales as $\rho^2$, (density squared), but ...
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I am interested in Lagrangian Mechanics and I want to know why higher derivative theories are inconsistent with the nature. I heard that there is something called Ostrogradsky instability for higher ...
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### Quantum Mechanics, Free Particle with Gaussian Distribution [on hold]

Assume a free particle of mass $m$ is initially at rest, $v = 0$, which has a time dependent Gaussian distribution $V= \text{expected value of }v$. Write down the expression for the wave function: Is ...
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### Electron double slit, different probabilities of going through each slit [on hold]

The Problem: Consider a two slit experiment where the slits are not the same. Specifically, consider the case where the probability of an electron passing through one slit is different from that of ...
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### Solving Poisson's Equation in 1-D for a point charge? [migrated]

Ok so I was trying to solve the Poisson's equation for a point charge with a Fourier transform to get the familiar equation. This is what I did so far: So ultimately I am trying to solve this in 3 ...
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### What is the atomic composition of the human body, by volume?

According to Wikipedia, the composition (by atomic percent) of the human body is: 62% hydrogen 24% oxygen 12% carbon 1% nitrogen etc. Question: What is our volumetric composition*? *I get this is ...
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### Are known (“old”) elements being made synthetically using fusion?

Are known ("old") elements being made synthetically using fusion? I hear about research about making new heavy elements, but type "making known elements" on Google and nothing comes up. Are any known ...
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### Is there a difference between 0.18 and 0.180 seconds? [on hold]

Q. Is there a difference between 0.18 and 0.180 seconds ? In our databases we are collecting timestamps and there are 2 time instants which are the same for the hour, minute and seconds but the ...
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### Charge distribution on a Gaussian surface

In the text, it is said that the skewed distribution of positive charge on the inner wall cannot produce an eletric field in the shell to affect the distribution of charge on the outer wall. Why? ...
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### How can the orbit of a planet having a 3600 year period and a perigee between Uranus and Neptune be computed [on hold]

There is a significant difference between the distance that gravity would move a planet with no velocity and the distance that gravity curves space time for a moving object. The 'fictitious' ...
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### Literature on interferometry

I am looking for a good book/notes etc. about interferometry. I need detailed information about optical as well as atom interferometers with strong emphasize on quantum version for high precision ...
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### What's the physical meaning of a “sphere”, and a pair (or even a series) of “concentric spheres”, in a region with Schwarzschild geometry?

This accepted answer to the question "What is the physical meaning of the Eddington-Finkelstein coordinates?" (PSE/q/91724) prescribes to 1. Enclos[e] the origin of our Schwarzschild spacetime in ...
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### Reaction force explanation? [on hold]

I heard that reaction force is the total force applied back due to electromagnetic repulsion between the atoms of the thing that exerted the force and the thing that the force was exerted on, so can ...
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### Observers in a Double Slit Experiment

Does it matter what the observer is in the double slit experiment? Could it be anything from an ant to a dog? Has it ever been tried with a non-human observer?
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### Why does a cloud form around ice cream?

Everyone have probably seen the phenomenon as one opens a cool ice cream from its pack, a white cloud begins to flow around the ice cream surface, and it constantly spreads out until the ice cream ...
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### Is radiative decay the same the electromagnetic decay?

Question could be a duplicated of this one "Radiative" particle decay? An electromagnetic decay should be clearly one that involves at least a photon, either directly or producing a pair ...