1
vote
0answers
15 views

Observationally distinguishing a galaxy of antimatter from a galaxy of matter [duplicate]

I was just wondering how, observationally, we would distinguish a distant galaxy of "normal" matter from one of antimatter. Maybe there is a simple answer but I don't see it. Once I started thinking ...
-2
votes
0answers
16 views

Physics and baseball

In the following scenario lets just use approximate values. Johnny is a pitcher and he throws 50mph. Johnny climbs on the roof of a car who is traveling 50mph. Johnny throws his normal pitch to his ...
0
votes
0answers
25 views

Momentum operator on 1D Schrodinger equation

I am looking to grasping the concepts of the wave function by asking for help with the simplest Schrodinger equation on a 1D square well between x = -L/2 and x = L/2 with zero potential. $$ i \hbar ...
0
votes
0answers
17 views

The viewing angle of the horizon from low Earth orbit

I had heard a "flat earth" sympathizer claim that proof earth was flat, was that the horizon appeared perfectly 90 degrees to the chord connecting the center of the earth to the International space ...
-1
votes
0answers
13 views

Improved gap estimates for quantum adiabatic evolution

In his PhD thesis, Daniel Nagaj mentioned that Deift† et al has tightened the relationship between the adiabatic evolution time $T$ and the energy gap between the ground state and first excited state, ...
0
votes
0answers
32 views

Why does the method below work?

Please explain why this method works. I get this idea when try to solve adiabatic gas expansion by using numerical method. The analytic/exact solution for the expansion will be $PV^\gamma$=constant. ...
-1
votes
0answers
27 views

Thought experiment in Quantum Gravity

Recent results show mean field games behaves as a quantum mechanical system. If we consider stellar systems like galaxies as a game with gravity between stars. nash equilibria will correspond to ...
0
votes
1answer
16 views

Worldsheet metric & event horizon

Given a certain metric $g_{\alpha \beta}$ (not necessarily diagonal) in which $g_{\tau \tau}=0$ for a certain function, is there any way of determining if there is a singularity in that point, or if ...
0
votes
2answers
41 views

How are laws proven in general?

This may be a bad question, but what are the ways that laws are proven? I would expect that some ways would include by proving them mathematically or through experimentation. My biggest question ...
2
votes
2answers
41 views

What happens when we manipulate the observer in the double slit experiment?

Consider the following alterations to the double slit experiment: turn the observer on and off rapidly move the observer further and further away, until the point at which it can no longer ...
0
votes
1answer
20 views

How to memorize the second quantization form of the two-body interaction term?

Suppose the two-body interaction potential is $V (x , y )$. The second-quantization form of the interaction hamiltonian is $$ H_{int} = \frac{1}{2}\iint dx dy \psi^\dagger(x) \psi^\dagger(y) \psi(y) ...
0
votes
0answers
17 views

Is it possible that cosmic ray particles and neutrinos account for a significant portion of dark matter?

Sounds a bit naive but I read somewhere that neutrinos were thought to account for dark matter to an extent and I think Zwicki came up with the idea before cosmic rays were announced (not sure ...
3
votes
2answers
47 views

Combining two data points with different uncertainties

I have two separate algorithms (call them "A1" and "A2") which reconstruct the $(x, y)$-position of an event in a particle detector. I can test both of these algorithms on simulated events from a very ...
0
votes
0answers
16 views

Can someone explain what the wave function is? [duplicate]

I've been doing she research I don't really understand what a wave function is. I used to think it was the de Broglie's wavelength but I've soon found otherwise. Just a simple and clear explanation ...
0
votes
0answers
44 views

Rigorous derivation of general relativity from first principles

What is the minimal set of axioms required to derive the mathematical formulation of General Relativity from first principles? What are these first principles? What are good references that detail ...
0
votes
0answers
30 views

What REALLY happens when matter and antimatter colide? [duplicate]

I've read on numerous websites that when 1 kg of matter collides with 1 kg of antimatter all the mass gets anhilated and converted into energy according to E = mc^2. I know this is the right ...
0
votes
1answer
12 views

What is the effect of volume on liquid temperature during evaporative cooling?

Imagine two evaporative cooling experiments: In the first, a beaker contains a known volume of liquid. The liquid starts at ambient temperature. The temperatue of the body of liquid remaining in the ...
0
votes
2answers
28 views

why cannot longitudinal waves travel through space (vacuum)

'The reason sound can't travel through a vacuum is that sound needs a medium (solid, liquid or gas with real vibrating molecules) and not because it is a longitudinal wave' How does this make sense as ...
0
votes
0answers
12 views

Photoelectric effect and evanescent fields

We all know that if light impinges upon a metal and if it's the energy of the photon (hv) is greater than the work function of the metal then an electron will become unbound from the metal and be ...
0
votes
0answers
19 views

Variation with respect to the metric and other tensors

When varying an action with respect to tensors and the metric, I'm afraid I get confused as how to one organizes the Lagrangian and then performs the variation. Take for example, the following example ...
1
vote
0answers
25 views

What is the significance of the possible new 17-MeV “protophobic X boson?”

Krasznahorkay et al ...Possible Signature of a Light, Neutral Boson published results in 2015 of a possible new particle at 16.7 MeV+/-0.35. The researchers suggest "such a boson might be a good ...
2
votes
2answers
172 views

Universal Gravitation Vector Notation

I'm learning about astrodynamics on my own and I was wondering why the $r_{ij}$ is cubed in the vector notation for of Newton's Law of Universal Gravitation: $$F_g=(Gm_1m_2/(r_{ij})^3)r_{ij}$$ Here ...
2
votes
1answer
33 views

Fastest Speed of Sound

Obviously, sound (like every other causal phenomena) may not travel faster than the speed of light. I know that materials with a high bulk modulus and low density will typically have faster speeds of ...
0
votes
1answer
42 views

Need help with Schwartz's QFT: Problem 3.9 in Page 44

This is the problem: I have worked about questions (a), (b) and (c). I do not quite understand question (d), and therefore (e) (in the next page). What does "instantaneous" mean in this case? In ...
-1
votes
0answers
20 views

How to convert detection (of say metal/movement) to electricity?

Is there a way (using (magnetic?) sensors to detect?) , converting movement/speed of for example cars into electricity or other form of energy?
0
votes
1answer
12 views

Would a celestial body in a horseshoe orbit be tidally locked to the planet?

A smaller celestial body like a moon or an asteroid can be in a horseshoe orbit around a planet. Since it might go inside the tidal lock radius (but does not stay inside it all the time), during the ...
0
votes
0answers
9 views

Measurement of Quantum Hall Effect

I'm somewhat confused about the original measurement of the QHE in a Si-MOSFET, which might stem from my not understanding MOSFETs very well. In their measurement, von Klitzing et al. measure the ...
0
votes
0answers
31 views

Wave as a source of electricity?

I was studying a high-school physics textbook and I came across a rather interesting and confusing example. I've been reading about rectification, and it all made sense until it came to the part where ...
0
votes
1answer
38 views

Poincare Group (Wald, Chapter 4 Page 59)

In Wald's text on general relativity, he mentions that in special relativity, many different global inertial coordinate systems are possible and can be put into one-to-one correspondence with elements ...
1
vote
1answer
49 views

“Measure of time in general relativity”

Suppose to be in an arbitrary gravitational field and you are moving in it arbitrarily with a clock in your hand. In this general situation I ask: if I read the positions of the hands of the clock, ...
0
votes
0answers
22 views

How do I load a CIF file in Maud on OSX? [on hold]

I am trying to load a CIF file in Maud, but when I go to edit->load object from CIF and then select my file, nothing shows up but the name. No graph appears. In the edit selected object on the ...
2
votes
1answer
25 views

How many orientifold planes does one need?

According to the book ''String Theory in a Nutshell'' by Elias Kiritsis (page 204, linked here), the tension of an $Op$-plane is $$T_{Op} = -2^{p-4}T_{Dp}$$ With this picture, one gets -- for type ...
0
votes
2answers
44 views

Conservation of electromagnetic energy-momentum tensor

I'm trying to show that $\partial_\mu T^{\mu \nu}=0$ for $$T^{\mu \nu}=F^{\mu \lambda}F^\nu_{\; \lambda} - \frac{1}{4} \eta^{\mu \nu} F^{\lambda \sigma}F_{\lambda \sigma},$$ with the help of the ...
0
votes
1answer
19 views

How to estimate a drag of flow reversing cylinder?

I am assuming a turbulent flow and a full reversal of the flow (in the picture the arrows are at non-straight angle but please consider the skew as negligible). Assuming we are talking about ...
0
votes
0answers
18 views

Determine the angle the mass leaves a smooth semi cylinder

A small body of mass m rests at the top of a smooth hemisphere with radius r. It is released from rest. At the moment it is released $\theta=0$ with zero initial velocity. There is no friction between ...
2
votes
1answer
20 views

How do flames neutralize a static charge?

I was working with a demonstration galvanometer recently when it accidentally picked up a static charge from me lightly rubbing my hand across it. The case was made of a clear plastic. My attempts ...
0
votes
2answers
31 views

Why doesn't the gravitational force have a permittivity in its formula? [duplicate]

We know that the electrostatic force between two charges depends on the medium between the charges and its permittivity. Why, then, doesn't the gravitational force depend on the medium?
1
vote
0answers
24 views

Amplifying an electromagnet's generated field

Given an electromagnet like this: which is essentially an iron casing with coils inside: Is it right that the centre disc would have one polarity whilst the outer housing another? To boost the ...
0
votes
1answer
25 views

What is the difference between reflection and total internal reflection (TIR)?

I look at what TIR is and then what reflection is - when the angle of incidence and the angle of election are the same. And TIR is when the angle of incidence is greater than the critical angle. TIR ...
-1
votes
0answers
13 views

compressed air thrust calculation [on hold]

I am working on a project in which there is an article of 100 kg hanging on a wire rope supported by wheels at a height of 12 m from ground at one end and 25 m at the other end. The article needs to ...
0
votes
2answers
75 views

Can quarks have anti-colors?

I get the basics of QCD (or I think I do). What I was wondering is whether up and down quarks, and their heavier cousins, absolute HAVE to carry color charges, or if they can have anti-color charges ...
0
votes
1answer
28 views

How does radiative cooling between the earth and space work?

On a chilly (but above freezing) temperatures on a clear night, you can freeze water outside because of radiative cooling. By what mechanism do warm bodies on earth actually lose heat to space? ...
0
votes
0answers
27 views

Expectation value in second quantization

I am stuck calculating a simple expectation value for an operator, which is expressed in second quantization. I know the result, but I fail to proof it. Lets say I have one-particle wave function ...
-1
votes
0answers
16 views

Find voltage at a point on infinite ladder of resistances [duplicate]

Find voltage at point C. What I have tried. Find the effective ladder of resistances. Which comes out to be R(sqrt.3 - 1) Then find the current. 48/Reff Then split the current and find current ...
0
votes
0answers
10 views

Energy Transformation BLDC Motor

I would like to know what kind of Energy Transformation happens in a BLDC Motor. I googled it and read that the electric energy is transformed to magnetic energy, and then from magnetic energy to ...
-1
votes
2answers
40 views

Selection rules and type of photon?

Let us consider the following matrix element: $$\langle n',m',l'|x| n, m, l \rangle$$ For the corresponding radiative transition we have the selection rule that $\Delta m=\pm 1$. But will the photon ...
-3
votes
1answer
63 views

What is y(x,t) = Acos(kx - wt)? [on hold]

Im very new to wave mechanics and I've come across the following wave equation. I know this is asking too much,but I wanted to know what is the significance of this equation? what does it tell us / ...
2
votes
1answer
27 views

Do satellite galaxies have the same proportion of dark matter as “ordinary” galaxies

My question is relatively straightforward: Do we know if satellite/ dwarf galaxies contain the same proportion of dark matter to ordinary matter as "regular" sized galaxies? The Milky Way, for ...
0
votes
0answers
37 views

Gauss-Weingarten equation

In E Poisson "A relativist tool kit" p.75 it says that the Gauss-Weingarten relation is: $$e^{\alpha}_{a;\beta}e^{\beta}_{b}=\Gamma^{c}_{ab}e^{\alpha}_{c}-\epsilon K_{ab}n^{\alpha}$$ We have the ...
1
vote
1answer
27 views

Difference between the CKM and the PMNS matrix

My question is very simple: is there a fundametal difference between the CKM (responsible for quark mixing) and the PMNS matrix (responsible for lepton mixing)? The CKM matrix allows (in charged ...

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