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1500 questions
39
votes
4 answers
Can virtual particles be thought of as off-shell Fourier components of a field?
I just found this blog post, which gives an interpretation of virtual particles I haven't seen before.
Consider a 1D system of springs and masses, where the springs are slightly nonlinear. A "real particle" is a regular $\cos(kx-\omega t)$…
knzhou
- 107,105
39
votes
2 answers
How does string theory reduce to the standard model?
It is said that string theory is a unification of particle physics and gravitation.
Is there a reasonably simple explanation for how the standard model arises as a limit of string theory?
How does string theory account for the observed particle…
Arnold Neumaier
- 46,304
39
votes
3 answers
The exchange of photons gives rise to the electromagnetic force
Pardon me for my stubborn classical/semiclassical brain. But I bet I am not the only one finding such description confusing.
If EM force is caused by the exchange of photons, does that mean only when there are photons exchanged shall there be a…
skywaddler
- 1,515
39
votes
4 answers
Why does a moving fan seem transparent?
We all know when fan starts moving faster, we cannot see its blades. Why is this?
First I assumed persistence of vision may be the reason. But that can happen with blade also right? Image of blade can remain in our memory and moving fan can appears…
tollin jose
- 1,293
39
votes
8 answers
Does the scientific community consider the Loschmidt paradox resolved? If so what is the resolution?
Does the scientific community consider the Loschmidt paradox resolved? If so what is the resolution?
I have never seen dissipation explained, although what I have seen a lot is descriptions of dissipation (i.e. more detailed pathways/mechanisms for…
propaganda
- 948
39
votes
2 answers
How does the Higgs mechanism work?
I'm not a particle physicist, but I did manage to get through the Feynman lectures without getting too lost.
Is there a way to explain how the Higgs field works, in a way that people like me might have a hope of understanding?
Mike Dunlavey
- 17,328
39
votes
1 answer
How can dark matter collapse without collisions or radiation?
I understand that dark matter does not collapse into dense objects like stars apparently because it is non-interacting or radiating and thus cannot lose energy as it collapses. However why then does it form galactic halos? Isn't that also an example…
Astrobuf
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39
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5 answers
If the Earth is a good conductor of electricity, why don't people get electrocuted every time they touch the Earth?
Since the Earth is a good conductor of electricity, is it safe to assume that any charge that flows down to the Earth must be redistributed into the Earth in and along all directions?
Does this also mean that if I release a million amperes of…
Swami
- 1,917
39
votes
8 answers
Will we ever be able to view the past?
By analogy with the sun, whose light is apparently reaching us in 8 minutes, it means that we are only viewing the sun 8 minutes ago when we look up at it. However, what if we were eventually able to build powerful machines that could view light…
user45220
- 1,271
39
votes
2 answers
The impossibility (or possibility) of solving $N$-Body problem
One can obtain the solution to a $2$-Body problem analytically. However, I understand that obtaining a general solution to a $N$-body problem is impossible.
Is there a proof somewhere that shows this possibility/impossibility?
Edit: I am looking to…
Graviton
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39
votes
1 answer
What are the alternative theories of dark energy? ($w \neq -1$)
There has been a lot of related questions about dark energy around here but these are usually 2-4 years old and the closest question to mine hasn't really been answered, so I am going to proceed. Experts may skip to the last paragraph, but I am…
Void
- 21,331
39
votes
2 answers
Difference between regularization and renormalization?
In quantum field theory we have the concepts of regularization and renormalization. I'm a little confused about these two. In my understanding regularization is a way to make divergent integrals convergent and in renormalization you add terms to the…
Apogee
- 1,356
39
votes
3 answers
What's the relationship between $SL(2,\mathbb{C})$, $SU(2)\times SU(2)$ and $SO(1,3)$?
I'm a beginner of QFT. Ref. 1 states that
[...] The Lorentz group $SO(1,3)$ is then essentially $SU(2)\times SU(2)$.
But how is it possible, because $SU(2)\times SU(2)$ is a compact Lie group while $SO(1,3)$ is non-compact?
And after some…
346699
- 6,211
39
votes
2 answers
Mathematically, what is color charge?
A similar question was asked here, but the answer didn't address the following, at least not in a way that I could understand.
Electric charge is simple - it's just a real scalar quantity. Ignoring units and possible quantization, you could write $q…
Hugh Allen
- 1,635
39
votes
3 answers
Are the Hamiltonian and Lagrangian always convex functions?
The Hamiltonian and Lagrangian are related by a Legendre transform:
$$
H(\mathbf{q}, \mathbf{p}, t) = \sum_i \dot q_i p_i - \mathcal{L}(\mathbf{q}, \mathbf{\dot q}, t).
$$
For this to be a Legendre transform, $H$ must be convex in each $p_i$ and…
N. Virgo
- 35,274