Most Popular
1500 questions
36
votes
13 answers
Why don't we use rapidity instead of velocity?
In school we learn that we can add velocities together, and then later on we learn that it's not correct and that there is a speed limit. Why create all this confusion when we could just use rapidity to begin with?
Rapidity is defined as $w =…
Fax
- 511
36
votes
4 answers
Why do photons follow specific path after reflection from a mirror surface if they can be emitted in any direction by electrons of mirror surface?
The electron absorbs the energy of photon(with specific frequency)and re-emits the photon.The photon can be emitted in any direction. So why do they get re-emitted in a specific direction after reflection? On hitting normal to surface the photons…
Karan Bhatia
- 501
- 4
- 7
36
votes
3 answers
Can a wormhole be created if it has not always existed?
I know there are solutions to Einstein's field equations that give a wormhole geometry. But they are time independent. They are static. Is there a process where empty flat spacetime can evolve into a wormhole by an appropriate flow of matter and…
JeffK
- 697
36
votes
6 answers
Why doesn't the nucleus have "nucleus-probability cloud"?
While deriving the wave function why don't we take into the account of the probability density of the nucleus? My intuition says that the nucleus is also composed of subatomic particles so it will also have probability cloud like electrons have. Do…
Tim Crosby
- 1,323
- 11
- 18
36
votes
5 answers
How do we know neutrons have no charge?
We observe that protons are positively charged, and that neutrons are strongly attracted to them, much as we would expect of oppositely charged particles. We then describe that attraction as non-electromagnetic "strong force" attraction. Why posit…
MacThule
- 421
36
votes
8 answers
How large would the steam explosion at Chernobyl have been?
So the second episode of the HBO series began to cover the risk of a steam explosion that led to them sending three divers into the water below the reactor to drain the tanks.
This occurred after the initial explosion that destroyed the reactor, and…
Nick S
- 465
36
votes
4 answers
Entropy and the principle of least action
Is there any link between the law of maximum entropy and the principle of least action. Is it possible to derive one from the other ?
Anarchasis
- 1,343
36
votes
1 answer
What's the basic ontology of QFT?
I've been studying QFT for almost a year now but am still fairly unclear on the basic ontology of the theory. Here's what I'd consider the "basic ontology" of non-relativistic quantum mechanics:
A particle is represented by a wavefunction…
WillG
- 3,315
36
votes
6 answers
To which extent is general relativity a gauge theory?
In quantum mechanics, we know that a change of frame -- a gauge transform -- leaves the probability of an outcome measurement invariant (well, the square modulus of the wave-function, i.e. the probability), because it is just a multiplication by a…
FraSchelle
- 10,493
36
votes
2 answers
Can light be compressed?
What if we take a cylindrical vessel with an inside surface completely reflecting and attach a piston such that it is also reflecting. What will happen to light if we compress it like this?
user204283
- 477
36
votes
2 answers
In nuclear bomb explosions, witness describe their hands becoming transparent. How does that happen?
Witnesses of nuclear explosions have described their hands becoming transparent, and that they could see the bones. For example, see here. How does that happen?
radon
- 385
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
- 2,127
36
votes
6 answers
What are holonomic and non-holonomic constraints?
I was reading Herbert Goldstein's Classical Mechanics. Its first chapter explains holonomic and non-holonomic constraints, but I still don’t understand the underlying concept. Can anyone explain it to me in detail and in simple language?
Akash Shandilya
- 371
36
votes
3 answers
What does an integral symbol with a circle mean?
I have frequently seen this symbol used in advanced books in physics:
$$\oint$$
What does the circle over the integral symbol mean? What kind of integral does it denote?
user11543
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