0
votes
2answers
28 views

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 ...
1
vote
0answers
19 views

Ostrogradsky instability [duplicate]

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 ...
0
votes
0answers
44 views

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 ...
0
votes
0answers
41 views

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 ...
0
votes
0answers
23 views

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 ...
1
vote
1answer
36 views

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 ...
0
votes
1answer
28 views

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 ...
-1
votes
1answer
68 views

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 ...
0
votes
1answer
31 views

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? ...
-4
votes
0answers
34 views

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' ...
0
votes
1answer
19 views

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 ...
0
votes
1answer
36 views

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 ...
2
votes
1answer
28 views

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 ...
0
votes
1answer
24 views

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?
0
votes
1answer
58 views

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 ...
0
votes
1answer
50 views

Possible values for $L_x$

I've a physical system with $l=1$ and I have to calculate the values I can obtain if I measure $L_x$ and their probability. I know that: the values I can obtain are $\ m=0, \pm 1$ $\displaystyle ...
1
vote
0answers
23 views

Upsilon full decay width? (and reference request)

The decays of 1S, 2S, 3S states of the $\Upsilon$ meson are according the particle data group surprisingly stable, but not as stable as a typical weak-only decay. Some electromagnetic decays, such as ...
0
votes
3answers
40 views

Kayaking against the wind is faster than with wind in my back? [on hold]

Today I was kayaking on a lake. I noticed that there is not very strong, but noticeable wind. There were also currents, all going in one direction, probably caused by wind. One more thing I realized ...
3
votes
2answers
84 views

What all has intrinsic spin?

What does and does not have intrinsic spin? Wikipedia Spin (Physics) https://en.wikipedia.org/wiki/Spin_(physics) says: “In quantum mechanics and particle physics, spin is an intrinsic form of ...
2
votes
1answer
47 views

If a fizzy drink was poured in zero gravity what will happen?

What will happen if I pour some soda in zero gravity ?
1
vote
2answers
74 views

(Local) Conservation of Energy in Quantum Mechanics

Generally, we say that conservation of energy is a local law; the change in energy in some small region of space is equal to the energy flux out of that region. However, in quantum mechanics, we can ...
0
votes
1answer
53 views

Best twin paradox trajectory for constant acceleration rocket?

Let's say I have a rocket that can provide constant (proper) acceleration (let's say of 1 gee) for an infinte amount of time. Let's say I want to use this rocket as a means of "suspended animation," ...
-1
votes
2answers
50 views

Period of a T-shaped pendulum [on hold]

I'm trying to calculate the period of a pendulum that has a T-shape. For a normal pendulum it's $T = 2 \pi \sqrt{\frac{L}{g}}$ so with $L = 1m$ and $g = 9.8\frac{m}{s^2}$ it's about 2 seconds. I've ...
0
votes
1answer
38 views

Fleming's right hand and left hand rule

Why are there two rules: Fleming's left hand and right hand rules? What is the difference between the two and why can't we use just one rule? Suppose the magnetic field is from right to left and ...
1
vote
2answers
48 views

Photons have a property from the matter they interact with?

When a photon leaves its source and hits our eye, our brain sees the source of the photon (Like a lightbulb or a star). When a photon is ejected from its source and bounces off of an object we see the ...
0
votes
0answers
33 views

What is the degrees of freedom of metric tensor?

As $g_{\mu\nu}$ can be taken to be symmetric, it contains 10 functions of spacetime in 4 dimensions. But, why we call these 10 functions as the degrees of freedom of the metric while they are the ...
4
votes
1answer
99 views

Why can gold be drawn out finer than light?

The metal gold is extremely malleable. Gold is also ductile and one ounce can be drawn into 80 km (50 miles) of thin gold wire (5 microns diameter) to make electrical contacts and bonding wire. I ...
1
vote
1answer
80 views

Height of Water 'Splashing'

Suppose from a height $H$, I throw a ball of mass $M$ and radius $R$ with initial velocity $u$ into a pool of depth $x$ having a liquid with density $\rho$ and coefficient of viscosity $\eta$. ...
2
votes
0answers
31 views

Classical probability of harmonic oscillator

I am trying to derive the classical probability density function to find the harmonic oscillator at position $x$. I am confused between the random variables involved here $x, t$ and not able to ...
-3
votes
0answers
19 views

Can we say stuff about smog by taking on the lines of Brownian motion? [on hold]

I have a talk on smog in few days. So I want to include Brownian motion in it. I know that smog is a suspension so its particles will follow Brownian motion. What else can we say about smog?
0
votes
1answer
34 views

Melamine dish cools beyond ambient temperature

I have observed a phenomenon that I find hard to understand. A plastic, melamine like dish is filled with food (spaghetti, chile, soup, etc.) The dish and food is heated in a normal microwave oven ...
1
vote
1answer
51 views

Speed distribution of objects in the universe

If we pick a reference frame where, for example, our planet is standing still (although it should be irrelevant), what would the speed distribution of all objects in the universe look like? For the ...
0
votes
0answers
7 views

Electron avalanche causes dielectric material conductive? [on hold]

What's the relationship between electron avalanche and dielectric material becoming conductive?
1
vote
0answers
11 views

Relaxation Times in Quantum Optics

I am studying laser physics and in in the lecture we defined the transversal and longitudinal relaxation times as the relaxation times of the coherent/ population states of the density matrix. The ...
-6
votes
0answers
12 views

Relationships in among different terminologies in rotation motion [on hold]

What is the relation between moment of inertia and distance from the centre of mass?
2
votes
1answer
44 views

Why is the Mixed Faraday Tensor a matrix in the algebra so(1,3)?

The mixed Faraday tensor $F^\mu{}_\nu$ explicitly in natural units is: ...
0
votes
0answers
27 views

First integrals for a particle in a central-force field

Consider an arbitrary dimension $n>3$. What are the independent first integrals for a particle? The Hamiltonian is $$ H = \frac{p^2}{2m} +V (|r|) . $$
-1
votes
0answers
25 views

Will water vapour rise in vacuum?

If I put water vapour in vacuum, will it behave normally like a gas? Will it rise up in the vacuum?
-1
votes
0answers
34 views

Verification of Lenz's law in magnetic induction

So the device is a Galvanometer. According to the Lenz's Law, when we take the magnet towards the coil, the pole at the right end, should be north pole and when we take it away, the pole should be ...
2
votes
2answers
78 views

Superposition in Quantum Mechanics

First of all, let $V$ be a vector space over the field $\mathbb{F}$. It is possible then to show, by Zorn's Lemma that there is a basis for $V$. The main point is that although basis are quite ...
0
votes
0answers
15 views

How did each Base Quantity get it's name? [on hold]

I've tried searching everywhere, but I can't seem to find anything related to how the quantities got named! Base Quantities: 1.Mass 2.Distance 3.Time 4.Temperature 5.Electric Current 6. Quantity of a ...
1
vote
0answers
32 views

What is the minimal size of the spec of dust I can see with naked eye?

When sun directly shines thru the window - I can see small specs of dusts in the air. All specs have different sizes. Assuming direct sun luminosity is 100kLux, spec is a perfect sphere, reflection ...
0
votes
0answers
21 views

Net force when deriving relation between torque and angular acceleration

When deriving the equation $\tau = I\alpha$, it is assumed that $$F_{tangential}=ma_{tangential}$$$$a_{tangential}=\alpha r$$$$\tau=rF_{tangential}$$$$\tau=mr^2\alpha=I\alpha$$ However, doesn’t ...
-1
votes
0answers
44 views

Need help with Weinberg II (19.5.42)

In "The Quantum Theory of Fields", Volume II, p. 202, I can't see how eq. (19.5.42) leads to the next equation. The transformation seems to go the wrong way; for example, in order to get $\sigma$ ...
-3
votes
0answers
19 views

Best thermal (heat) radiation barrier (insulator)? [on hold]

Which material provides best insulation from thermal (heat) radiations? In other words, which material blocks most of heat radiation from escaping?
0
votes
0answers
27 views

Boundary conditions for a radiative heat transfer problem

Consider the heat equation $$ \frac{\partial T}{\partial t} - a\Delta T + \mathbf v \cdot \nabla T = S $$ where $S$ is a source term dependent of the radiation intensity $I$ and the temperature $T$. ...
0
votes
1answer
25 views

What is the recommended symbol for Volumetric flow rate? [on hold]

I'm currently working on a paper with a mathematician. He always writes $\dot Q$ as well as $\dot V$ for volumetric flow rate and claims both are standard notations. Till now I always used $Q$ ...
0
votes
1answer
30 views

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 ...
0
votes
1answer
35 views

Density Matrix in Quantum Optics

I am studying laser physics and didn't get the whole idea of the density matrix (in this case for two-level systems). I know this is really basic so bear with me! I understand that the diagonal ...
0
votes
0answers
6 views

To approximate the uncertainty of viewing angle in Telecentric optics?

I am thinking how to approximate the uncertainty of the viewing angle in the telecentric optics when the viewing angle is less than 5 degrees. I have a Cadcam called ArtCam from a Japanese ...

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