9
votes
3answers
6k views

Bell's theorem for dummies, how does it work?

I've been reading up on theoretical physics for a few years now and I feel like I am starting to get an understanding of particle physics, at least as much as you can from Wikipedia pages. One thing ...
3
votes
3answers
226 views

Does one square centimenter of the sun core really radiate this amount of energy?

I have been thinking that since the core of the sun maintains its temperature at 15 million degrees Kelvin, then every cubic centimeter of this core is receiving a certain amount of energy to keep it ...
2
votes
2answers
116 views

Field interaction betweeen two point charges?

[SOLVED] Consider two particles A and B having equal charges and placed at some distance. The particle A is slightly displaced towards B.So, Does the EM force on B increase(+/-) as soon as the ...
4
votes
3answers
162 views

Linear independence of the Covariant Derivative

What's the easiest way to show that the covariant derivative $\nabla U^{\mu}$ is linearly independent to $U^{\mu}$, which is a vector? I mean I'm assuming they are since I'm proving the second ...
14
votes
3answers
969 views

Alternatives to electromagnetism for communication?

It seems, from my (weak) understanding of the standard model that the only field suitable for long range communication is the one we actually use, electromagnetism. (Gravity waves could be used as ...
2
votes
3answers
380 views

Why don't we define absolute coordinates?

Why don't we chose a random point in the void present between galaxy clusters and define it as the absolute origin? I know that rest is not absolute and that space expands, but we can easily keep ...
1
vote
2answers
573 views

Help with a solid sphere sliding and then rolling

Initially at time $t=0$, a solid sphere slides with velocity $v$ along a horizontal surface. The coefficient of friction is u. Find the required time for the sphere to stop sliding (the sphere will ...
1
vote
1answer
227 views

Why is speed/position relative but acceleration not? [duplicate]

I think i understand it now, if found this: link I know that position and speed are relative. There is no such thing as universal coordinates. Then why is acceleration absolute? Is the 3th and 4th ...
1
vote
2answers
595 views

Electric potential of spherical water droplet [closed]

I'm trying to answer the following: 1000 spherical water droplets, each of radius $r$ and each carrying a charge $q$, coalesce to form a single bigger spherical drop. If $v$ is the electric ...
3
votes
1answer
361 views

How does the Gordon Decomposition of Dirac Current give rise to spin angular momentum?

How does the Gordon Decomposition of Dirac Current give rise to spin angular momentum? I used the Gordon Decomposition to split the Probability Current of the Dirac Field into its orbital current and ...
1
vote
3answers
174 views

Solar neutrino problem in 1968 and experimental verification of neutrino oscillation in 2001. Why the huge delay?

Solar neutrino deficit was first observed in the late 1960's. And theory of neutrino oscillation was developed in 1967. But,in 2001, the first convincing evidence of solar neutrino oscillation came in ...
1
vote
2answers
174 views

Road to String Theory [duplicate]

I have a question for our theoretic SuperUsers. How much knowledge and which fields of physics you have to know to start studying string theory? I am now on QFT, after I think I'll start study ...
0
votes
1answer
114 views

Square-Cube Law?

I've heard about something called the square-cube law. What is it? All I know of it is that it has something to do with mass of large objects and their gravitational influence.
0
votes
3answers
289 views

Latent heat of condensation

Regarding atmospheric processes, I understand that energy is required to evaporate water by moving molecules further apart i.e. a phase change from liquid to gas. The air then ascends into the ...
1
vote
0answers
100 views

What is the first excited state of the honeycomb Kitaev model in its gapped phase?

As we know, there are both gapless and gapped phases of the Kitaev model, and let's fix the couplings $J_x,J_y,J_z$ such that the model being in the gapped phase. My question is, what is the first ...
2
votes
1answer
184 views

Which air will give more effective cooling ? Dry or Moist?

Yesterday, I had an innovative idea. I live in India, and in summer season, the temperature can reach up to 45 degree Celsius. We use Split 1.5 Ton AC in our small office. The idea is to put an ...
1
vote
0answers
33 views

Audio anomaly identification

I left an audio recorder in the forest in many different locations for fauna identification. I am collecting subjects on my audio recorder that are clearly not in the frequency range of any animal ...
1
vote
1answer
260 views

Fourier Coefficents in general solution to Klein-Gordon Dirac-equation?

The most general solution to the Klein-Gordon equation is written as \begin{equation} \Phi(x)= \int \mathrm{d }k^3 \frac{1}{(2\pi)^3 2\omega_k} \left( a(k){\mathrm{e }}^{ -i(k x)} + a^\dagger(k) {...
1
vote
1answer
141 views

Question about De Broglie Wavelength

I read that: The smallest wave packet we can build has a size on the order of the de Broglie wavelength $\lambda$ of a free particle moving with the same speed $v$. I haven't been able to find a ...
0
votes
5answers
151 views

Would my fridge magnet drop off on a non-magnetic planet?

As far as I understand, the magnetic power of an ordinary permanent ferromagnet comes from and is maintained by the motion of molten iron in the Earth's core. So a fridge magnet would eventually come ...
48
votes
9answers
3k views

Is the uncertainty principle a property of elementary particles or a result of our measurement tools?

In many physics divulgation books I've read, this seems to be a commonly accepted point of view (I'm making this quote up, as I don't remember the exact words, but this should give you an idea): ...
1
vote
2answers
55 views

Forces acting on particles

What is the difference between air resistance/friction force and up thrust force? I always think that air friction is the same as up thrust but it does not seem that way.
1
vote
0answers
69 views

Scattering of two particles - phase factor

I did see some posts on stackexchange on this matter, but I find them to be beyond my scope or not directly related to what I am looking for. I am reading Feynman Lectures III, chapter 4. It talks ...
2
votes
3answers
640 views

Problems Understanding Mass Energy Equivalence

So I've had a problem for a long time now understanding energy-mass equivalence, in particular I've had a lot of trouble understanding how something like interatomic potentials can be seen as mass. I'...
7
votes
2answers
13k views

How hot can plasma get?

I remember reading about an experiment where fine rods of tungsten were super-heated with millions of amps of electricity, melting them into ionised gas and were then compressed (by magnetic fields?) ...
-2
votes
2answers
104 views

Are black holes trapdoors to the center of the universe? [closed]

Correct me if i'm wrong here, but if you consider the analogy of inflating balloon when explaining the universe expansion, then the center of the universe lies within the center of the inflating ...
3
votes
2answers
356 views

Conservation of energy (or lack thereof) in Doppler cooling [duplicate]

I did not find my question answered elsewhere, so here it is. I'm doing a project in my first optics course, and we are reading a bit about Doppler cooling. I understand that a laser is tuned to a ...
3
votes
0answers
64 views

Does a local symmetry transformation cause a change in kinetic energy?

Consider a local transformation $$ \varphi_i^{\prime}= \varphi_i + \alpha(x) \delta\varphi $$ If this is a symmetry of the action, the Lagrangian is given by $$ \mathcal{L}^{\prime}=\mathcal{L}+ j^{...
0
votes
0answers
597 views

Two-Dimensional Tight-Binding Dispersion Relation

As in my last post, I am doing out a calculation in Giamarchi's Many-Body text: http://dpmc.unige.ch/gr_giamarchi/Solides/Files/many-body.pdf. This time, I am going through the derivation of the ...
4
votes
1answer
193 views

What are phase conventions in angular momentum and rotation calculations?

I work with complicated angular momentum calculations related to atomic physics; nevertheless, I never need to use anything related to a phase convention (apparently because it's taken care of in a ...
2
votes
1answer
369 views

How does tempered glass work?

I've read that tempered glass work by heating and then rapidly cooling the glass so that the outer layer 'freezes' (stops expanding/contracting) but the core contracts further as it cools. I'm told ...
2
votes
1answer
475 views

How can a vacuum have a breakdown voltage?

This question (What is the capacitance between the Earth and Moon?) on EESE makes me wonder: How can a vacuum have a breakdown voltage? If electrons can find the shortest path through a vacuum, ...
1
vote
0answers
63 views

Logistic map and attractors

Does the logistic map have a strange attractor for some "chaotic" values of the parameter?
2
votes
0answers
39 views

What is the effective physical difference between a massive region of a polarized vacuum and a region of curved space-time?

What is the effective physical difference between a large region of curved space-time and an equally large region of a polarized vacuum? Consider the fact that vacuum polarization amounts to an ...
0
votes
2answers
67 views

Current and magnetism [closed]

When the current in 2 parallel wires flows in same direction they attract each other.Shouldn't the electrons travelling in opposite direction should also repel ?
0
votes
1answer
87 views

Monopoles in non-abelian semi-simple gauge groups

Relative to the following Indeed, the modern point of view is that the operator of electric charge is the generator of a U(1) group. The charge quantization condition arises in models of ...
4
votes
2answers
300 views

Non-local structure of field theory

Can someone explain what is non-local structure of field theory? I know you cannot have $\phi(x) \phi(y)$ term in Lagrangian which indicates the non-locality. However, why I cannot have the non-local ...
3
votes
1answer
2k views

Are there reasons for the discrepancies in absolute temp units - Kelvin vs. kelvins vs. degrees Kelvin?

Before 1968, the units for absolute temperature were described as "degrees Kelvin" or "degrees absolute." After that, the SI system got rid of the idea of "degree" for absolute temperature, so the ...
4
votes
1answer
59 views

What technological advance would allow LEP3 to surpass LEP2?

I learned that for electron accelerators synchrotron radiation and acceleration are the limiting factors. This article, that I found in one answer to this question mentions that one would not use the ...
3
votes
3answers
196 views

What does “an average over noise” mean in Zwanzig's book

This is a very specific question about Robert Zwanzig's book Nonequilibrium Statistical Mechanics. Specifically, what is he talking about in equation 1.25 on page 10 that he calls "an average over ...
2
votes
1answer
113 views

Pulse Reflection

I wanted to ask why a pulse that reaches to a free end will reflect off and return with the same direction of displacement that it had before reflection. I am looking for explanation with forces.
7
votes
3answers
683 views

Can one assign an equivalence principle of some kind to the EM field?

Introduction: Consider the EM field. There was a time when the field was defined in a similar manner to that of the gravitational field. This changed when the view on gravitation evolved to this ...
0
votes
1answer
102 views

Is the universe expanding faster than we could catch up with it? [closed]

Like the title says, could we ever catch up with the expanding universe?
4
votes
1answer
280 views

Why is a dipole moment called a dipole moment?

The General Formula for a moment is the following one: $$ \vec{M} = \vec{r} \times \vec{F}. $$ However the formula for a dipole moment is this one: $$ \vec{p} = Q \vec{d}. $$ How comes this is still ...
0
votes
1answer
89 views

Initial velocities of a collision [closed]

This is the question: A car of mass 900 kg and a van of mass 1300 kg collide at a crossroads. Investigation into the collision discloses that the car was travelling south east and that the van was ...
0
votes
1answer
40 views

Can the thermal energy in an object be aligned, creating a thermal jerk?

Thermal energy is related to the speed at which atoms vibrate, therefor thermal energy is a form of motion. In a stationary object, all of these vibrating atoms 'impact' each other in such a way that ...
4
votes
1answer
717 views

Rotational Friction

This is the question- Consider a cylinder of mass $M$ resting on a rough horizontal rug that is pulled out from under it with acceleration $a$ perpendicular to the axis of the cylinder. What is $F$ (...
2
votes
2answers
94 views

What were the maximal collision energy of the LHC if it were rewired to $e^{-}-e^{+}$ collisions?

Yes, I know, that it weren't a large hadron collider then. No, I don't think, that the creators of the LHC didn't know what they do. I am just curious. How could it be calculated? A such rewiring ...
5
votes
2answers
106 views

Possible mechanics based on the known symmetries in the nature (investigating rumor)

Somewhere I've heard about a relative new mathematical result regarding mechanics. Specifically, there is a list of the known symmetries of mechanics (both Newtonian and relativistic), i.e. different ...
15
votes
1answer
1k views

How intense a magnetic field would it take to keep an hypothetical iron-made moon orbiting around it?

The intention of the question is to provide an example of the weakness of gravity. I imagine a horseshoe magnet located at the Earth's centre (remove the Earth), and a ferromagnetic moon. How ...

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