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seen Aug 29 at 21:31

Aug
15
comment What is the physical meaning of commutators in quantum mechanics?
@MarkMitchison: The reason why I made my original comment was to put the answer in a short reader-friendly form. Your answer has been a very nice reading - lots of thanks for it!
Aug
14
comment What is the physical meaning of commutators in quantum mechanics?
@MarkMitchison: Commutator is zero - you measure A, Heisenberg inequeality does not restrict measurement of B. Commutator has a large norm, you measure A, the outcome of B is constrained. Similar reasoning for symmetry transformations.
Aug
14
comment What is the physical meaning of commutators in quantum mechanics?
@MarkMitchison: Ah, I see! But I never said that.
Aug
14
comment What is the physical meaning of commutators in quantum mechanics?
@MarkMitchison: I assume you mean that measuring B does not imply measuring A? Definitely true, it can be put even more precisely, but the idea is really just about independence of A and B.
Aug
14
comment What is the physical meaning of commutators in quantum mechanics?
Your answer put simply: $[A,B]$ tells us, how well can we know $A$ right after measuring $B$.
Jun
4
comment Speed of gravity
For weak gravitational fields you can also introduce the concept of field energy, which indeed does differ in both cases.
Jun
4
comment If a 1kg mass was accelerated close to the speed of light would it turn into a black hole?
@voix, if you rotate a mass, then you have to provide a lot of energy and pressure to keep it rotating (centrifugal forces). Those in turn will gravitate on theire own, and it will mess up the problem a little bit.
Jun
4
comment If a 1kg mass was accelerated close to the speed of light would it turn into a black hole?
@TedBunn: And yet, light bending will become very peculiar for a very fast mass. Special relativistic aberration will come into play in ultrarelativistic regime which will enhance the otherwise weak lensing. Also, the fast body will feel strongly enhanced tidal forces in its frame, and there will be quite a lot of other interesting things happening.
Jun
4
comment Does a charged particle accelerating in a gravitational field radiate?
@JerrySchirmer, by the way, even non-charged point masses may have self-force in GR, similarly to Abraham-Lorenz force.
Jun
4
comment Does a charged particle accelerating in a gravitational field radiate?
@JerrySchirmer: I would say, the answer is also qualitative, it just asks why does the paradox appear. The paradox is resolved by two statements: 1) The charge in its own frame does not radiate only locally, 2) Additionally, static fields may turn into radiation when the frames are switched. So I just didn't go into calculations. And as you show in your answer, it takes an article size derivation to get the field estimates.
Jun
4
comment Does a charged particle accelerating in a gravitational field radiate?
By the way, correct answer, but doesn't expicitly address the question. Indeed, the word 'locally' is the resolution of the paradox. The charge does not emit radiation locally in its comoving frame. And yet does so generally for accelerated or non-comoving observers.
Jun
4
comment Does a charged particle accelerating in a gravitational field radiate?
@JerrySchirmer, and yet, could you please kindly be specific in your statements? Is there any particular argument that you find wrong in my answer? Do you think some aspect of the question was not touched upon? Or in which way could in general the answer be better in your opinion?
Jun
4
comment Does a charged particle accelerating in a gravitational field radiate?
Dear @JerrySchirmer, many thanks for pointing this out!
Mar
9
awarded  Nice Question
Jan
10
comment Does a charged particle accelerating in a gravitational field radiate?
@JánLalinský: It is beacuase when you switch to an accelerated frame as an observer, metric will be constant with your proper time. If you write down Einstein-Maxwell equations, you will have equations for electric and magnetic fields, which do not depend on time. There may possibly be some flux components, though, I don't have a proof at hand.
Jan
4
awarded  Yearling
Dec
14
awarded  Necromancer
Dec
14
comment Binary star system - Revolution around Primary vs Companion
Your 'likely' depends on initial configuration or scenario in consideration. Do you mean real populations of newly formed stars?
Dec
14
comment How is the universe is experienced at light speed?
Proper time is surely not defined for photons, however, it is still meaningfull to talk of what does it see as a function of its position, or (some agreed) canonical parameter, if you like. Another thing is that (extrapolating the know effect for observers) due to relativistic beaming all the 'perceived' rays will seem to lie on one single line, so effectively photon 'sees' in 1d.
Nov
11
accepted Proper name for a thermodynamic process with constant internal energy $U$