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How quickily does a photon reach c?

by Neghentropia
Tags: photon, quickily, reach
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derek101
#19
Nov28-12, 11:31 AM
P: 22
Question.So does the model I described work ok for gas and liquids?

A photon entering a solid is no longer a particle until it is re-emitted/re-created.
mfb
#20
Nov28-12, 11:32 AM
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Liquids are very similar to solids, and gases can behave similar, too (if the wavelength is long compared to the typical distances between atoms).
Neghentropia
#21
Nov28-12, 12:16 PM
P: 18
Quote Quote by derek101 View Post
Question.So does the model I described work ok for gas and liquids?

A photon entering a solid is no longer a particle until it is re-emitted/re-created.

I would imagine it is like you describe. Although I can't quite grasp the meaning of a photon being absorbed by a phonon, given the latter is a quasiparticle.

anyway, from this topic as a whole, I think I got that photons, no matter the medium they are travellig through are always going to speed = c. Aristotele would say it's their natural state :)


at this point I'm wondering: what happens to those photons that enter a black hole??
I'm tempted to believe a black hole core (where the photons are dragged by gravity) has no vibrational state, so there are no phonons to absorb the photons.
Maybe I'm asking something beyond our current knowledge?
ontheroad
#22
Nov28-12, 12:54 PM
P: 1
i would like to discuss this question from the wave hypothesis of light.
an analogy. if a photon is a wave like a sound wave, then think of the
creation of a photon as the plucking of a string. as the string is plucked
a train of waves, sound waves are created. and then the question becomes
how quickly do the sound waves build up? anybody familiar with music
will recognize this as the attack time.
so now the acceleration question becomes a question about how quickly
the wave of a photon builds up. and i think that this may have real
significance,
ZapperZ
#23
Nov28-12, 02:10 PM
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Quote Quote by ontheroad View Post
i would like to discuss this question from the wave hypothesis of light.
an analogy. if a photon is a wave like a sound wave, then think of the
creation of a photon as the plucking of a string. as the string is plucked
a train of waves, sound waves are created. and then the question becomes
how quickly do the sound waves build up? anybody familiar with music
will recognize this as the attack time.
so now the acceleration question becomes a question about how quickly
the wave of a photon builds up. and i think that this may have real
significance,
But is this really a valid analogy for light?

For sound, you require that string to be there. Light requires no such medium.

Secondly, there is "build up" required to generate photons. After all, we have ample single-photon sources here. Are there "single photon" sources for sound? Have you ever heard of single-phonon sources for vibrational modes?

The wave picture breaks down rather easily here, and such analogy doesn't help.

Zz.
mfb
#24
Nov28-12, 03:00 PM
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Quote Quote by Neghentropia View Post
at this point I'm wondering: what happens to those photons that enter a black hole??
I'm tempted to believe a black hole core (where the photons are dragged by gravity) has no vibrational state, so there are no phonons to absorb the photons.
Maybe I'm asking something beyond our current knowledge?
I think this will need a theory of quantum gravity.
Photons do not need phonons to get absorbed in a medium, but the central singularity (if it is one) cannot be described with current physics.
Kazz
#25
Nov29-12, 07:02 PM
P: 14
Although I very much doubt it... It could be C(m/s)/Planck Time(seconds)=5.5609185948589E+51 M/S^2
But, like I said. I doubt it.
davenn
#26
Nov29-12, 08:10 PM
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Quote Quote by dkotschessaa View Post
..............I think this is probably important to understand. C isn't just the "speed of light," but it is the maximum speed of other things as well, like the electrons that are running through the light bulb.

Do I have this about right?

-Dave K
careful there ;) electron drift through a conductor is actually very slow

there's been quite a bit of duiscussion on that in the past on this forum
do a search on electron drift

Dave
liometopum
#27
Nov29-12, 11:33 PM
P: 53
That is a great question. My thought...Compare the situation to water or sound waves. Both emerge from the disturbance at the velocities allowed by the medium. So maybe the answer is the time from the start of the disturbance to the time the wave starts to depart.
w4k4b4lool4
#28
Dec1-12, 04:58 AM
P: 49
Quote Quote by dkotschessaa View Post
Sorry to sound redundant, and I know you probably want a discussion - but the link I posted above pretty much answers all these questions.

(to repeat, it's here: http://van.physics.illinois.edu/qa/listing.php?id=2026)

-Dave K
Quote Quote by Neghentropia View Post
Hi,
I have a very dumb question in my head: when a photon gets emitted by a source, how long does it take to reach c?
the fact it has no mass makes me thinking the acceleration is instantaneous (t=0) but this is from a classical physics point of view (and I also know that around speed of light few things go as it would be intuitive to think them going)

thanks :)
You know that's not a dumb question..
Anyway, the relation E= hck is only true after an amount of time h/E (due to the Heisenberg uncertainty relation, DE DT > h), and so that's the amount of time it takes to reach c


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