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1500 questions
36
votes
2 answers
Can we get complete non-perturbative information of the interacting system by computing perturbation to all orders?
As we know, the perturbative expansion of interacting QFT or QM is not a convergent series but an asymptotic series that is generally divergent. So we can't get arbitrary precision of an interacting theory by computing higher enough order and adding…
maplemaple
- 2,217
36
votes
3 answers
Would a spin-2 particle necessarily have to be a graviton?
I'm reading often that a possible reason to explain why the Nobel committee is copping out from making the physics Nobel related to the Higgs could be, among other things, the fact that the spin of the new particle has not yet been definitively…
Dilaton
- 9,771
36
votes
4 answers
What really is a fluid?
My question may be pretty basic, but I feel it is important to ask this as I've gone through several texts and none offer me the clarity I seek.
The question is: What is a fluid? What is flow? If we say that a fluid is something that flows, the next…
stoic-santiago
- 1,961
36
votes
4 answers
What was the 'quantum mechanics' before quantum mechanics?
Quantum mechanics is near-universally considered one of the most difficult concepts to grasp, but what were the persistently unintuitive, conceptually challenging fields physicists had to grasp before the emergence of quantum mechanics?
The aim of…
dTdt
- 723
36
votes
2 answers
Why does the Earth even have a magnetic field?
From my knowledge of magnetism, if a magnet is heated to a certain temperature, it loses its ability to generate a magnetic field. If this is indeed the case, then why does the Earth's core, which is at a whopping 6000 °C — as hot as the sun's…
Rumplespaceking
- 488
36
votes
1 answer
What's the relation between Wilson Renormalization Group (RG) in Statistical Mechanics and QFT RG?
What's the relation between Wilson Renormalization Group(RG) in Statistical Mechanics and QFT RG? For easier to compare, I choose scalar $\phi^4$ in both cases.
Wilson RG:
Given $\phi^4$ model,
$$Z=\int\mathcal{D}\phi(x)\exp[-\beta…
maplemaple
- 2,217
36
votes
3 answers
Why does snow stay after a snowfall?
I have just experienced a snowfall and I am not so clear on how it works.
Three days after a short day of snowfall, and having 2 min | 17 max degrees Celsius, full sunny scarcely cloudy each day, there is still some snow persisting in shadow and…
Brethlosze
- 723
36
votes
7 answers
Deriving Lagrangian density for electromagnetic field
In considering the (special) relativistic EM field, I understand that assuming a Lagrangian density of the form
$$\mathcal{L} =-\frac{\epsilon_0}{4}F_{\mu\nu}F^{\mu\nu} + \frac{1}{c}j_\mu A^\mu$$
and following the Euler-Lagrange equations recovers…
mcamac
- 463
36
votes
3 answers
Why does the Earth cool at night time?
I do understand that open water and open ground cools by the means of convection — lower air takes the heat and goes up, where it cools.
But why does the Earth lose energy and where does it go? Does it emit heat radiation to space? Does the heat go…
Denis Kulagin
- 481
36
votes
2 answers
Can a neutron star become a black hole via cooling?
How much does thermal expansion affect neutron stars? Would the loss of temperature cause a neutron star to be more densely packed and thus collapse into a black hole?
user289661
- 916
36
votes
3 answers
Might a planet perform figure-8 orbits around two stars?
Might a planet perform figure-8 orbits around two stars?
I'm thinking that if the two stars were equal mass (and not orbiting each other) then a planet that were to go right between them would continue in a straight line, with no preference for…
dotancohen
- 4,543
36
votes
3 answers
What do the poles of a Green function mean, physically?
Is there a physical interpretation of the existence of poles for a Green function? In particular how can we interpret the fact that a pole is purely real or purely imaginary? It's a general question but I would be interested in the interpretation in…
PanAkry
- 1,001
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- 18
36
votes
2 answers
How well can a laser be focused over interstellar range?
I try to read up on diffraction limiting and gaussian beams, but it always gives a result saying it’s characterized by an angle which is the edges of a cross section of a cone. Which says nothing on the physical limits of how I choose that angle. …
JDługosz
- 5,357
36
votes
5 answers
Regularization of the Casimir effect
For starters, let me say that although the Casimir effect is standard textbook stuff, the only QFT textbook I have in reach is Weinberg and he doesn't discuss it. So the only source I currently have on the subject is Wikipedia. Nevertheless I…
Squark
36
votes
1 answer
Why was the first discovered neutrino an anti-neutrino?
In the search for neutrinos, Cowan and Reines discovered the electron anti-neutrino and named it as such. Why is the particle they discovered the anti-variety?
The reason we call electrons 'electrons' and not 'anti-electrons' is because the…
Joshua
- 1,373