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KoreUptd
2014-Mar-26, 05:36 PM
I have wondered about this for a long time, and perhaps it is quite easily answerable. This is a theoretical question...so here it goes:

Say you have a sphere that is coated with 100% light reflective material inside, and somehow you were able to capture light within, would the light just bounce around in there forever? Would it be a perpetual glow?
...or, what if it were a laser beam instead? Would it continue indefinitely?

also related to this inquiry is my question: if light continues through the vacuum of space unimpeded, will it continue moving through space-time infinitely? Or does light lose energy and eventually "die"?

I'm no physicist (obviously) but very curious about this :)
Thanks everyone!

antoniseb
2014-Mar-26, 06:13 PM
Each photon will continue until it is absorbed, never getting tired, or losing energy, and if it is never absorbed it will continue this way forever.

In terms of your question about the ball with the perfectly reflective interior surface, there are no such surfaces, but if there were, the light would continue bouncing more-or-less forever, but I don't know what you mean by perpetual glow. If something is detecting the light, then the light is being absorbed.

NEOWatcher
2014-Mar-26, 06:16 PM
Deja vu, toseeked (http://cosmoquest.org/forum/showthread.php?150002-question-about-lasers-and-mirrors), etc.
I wondered what sparked this idea.

Noclevername
2014-Mar-26, 06:25 PM
Since it moves at lightspeed, a photon has maximal time dilation. So effectively (a understand it), no subjective time passes and it has all the effects of its trip happen at once.

mkline55
2014-Mar-26, 07:19 PM
I have wondered about this for a long time, and perhaps it is quite easily answerable. This is a theoretical question...so here it goes:

Say you have a sphere that is coated with 100% light reflective material inside, and somehow you were able to capture light within, would the light just bounce around in there forever? Would it be a perpetual glow?
...or, what if it were a laser beam instead? Would it continue indefinitely?

also related to this inquiry is my question: if light continues through the vacuum of space unimpeded, will it continue moving through space-time infinitely? Or does light lose energy and eventually "die"?
As I understand the theory, the photon traveling through space would gradually lose energy relative to the locality it is in due to the continued expansion of space. However, the photons in the sphere would not lose energy. Or, perhaps, I misunderstand the theory. :)

EigenState
2014-Mar-26, 09:01 PM
Greetings,


Each photon will continue until it is absorbed, never getting tired, or losing energy, and if it is never absorbed it will continue this way forever.

Absorbed or undergoes inelastic scattering.

Best regards,
ES

Shaula
2014-Mar-26, 09:18 PM
Since it moves at lightspeed, a photon has maximal time dilation. So effectively (a understand it), no subjective time passes and it has all the effects of its trip happen at once.
The photon frame is not a valid inertial frame, so you cannot really say this.

Noclevername
2014-Mar-26, 09:21 PM
The photon frame is not a valid inertial frame, so you cannot really say this.

Awww. :(

Shaula
2014-Mar-26, 09:28 PM
Awww. :(
Sorry, but after the mild trauma I suffered having to endlessly argue that in two ATM threads... RSI of the soul is not fun.

EigenState
2014-Mar-26, 09:52 PM
Sorry, but after the mild trauma I suffered having to endlessly argue that in two ATM threads...

:)

Ken G
2014-Mar-26, 11:59 PM
As I understand the theory, the photon traveling through space would gradually lose energy relative to the locality it is in due to the continued expansion of space.Yes, if the photon was detected by "comoving" detectors (detectors that move with the local matter distribution), it would be measured as having a dropping energy. Whether or not the photon is itself "losing energy" is a matter of reference frame, but the photon still won't "die" or disappear, it will just continue on forever even if the detectors can't see it any more.
However, the photons in the sphere would not lose energy. Yes, that is true also. Of course, we don't really know, this is just what our current best theories about photons say. As long as "dark energy" is kicking around in its current unexplained status, I'd say we cannot assert too much with great certainty.

Elukka
2014-Mar-27, 12:12 AM
Say you have a sphere that is coated with 100% light reflective material inside, and somehow you were able to capture light within, would the light just bounce around in there forever? Would it be a perpetual glow?
The things you see are photons hitting your eyes. If photons don't leave the sphere then they'll never get to your eye and thus there's no way it could glow.

WayneFrancis
2014-Mar-27, 01:08 AM
I have wondered about this for a long time, and perhaps it is quite easily answerable. This is a theoretical question...so here it goes:

Say you have a sphere that is coated with 100% light reflective material inside, and somehow you were able to capture light within, would the light just bounce around in there forever? Would it be a perpetual glow?
...or, what if it were a laser beam instead? Would it continue indefinitely?

also related to this inquiry is my question: if light continues through the vacuum of space unimpeded, will it continue moving through space-time infinitely? Or does light lose energy and eventually "die"?

I'm no physicist (obviously) but very curious about this :)
Thanks everyone!

If you could get a 100% reflective surface then no it would not glow because the light on the inside would stay on the inside thus no "glow"
Light by itself doesn't loose energy. Because of cosmic expansion we end up having a change of frame of reference that continuously stretches the light from the point of view of the observer compared to the point of the emission. If you had a completely empty flat static universe then light would continue on forever never loosing energy. There is no "decay" process for a photon.

In reality what would happen is that the object would slowly heat up as each reflection imparted some of the photons energy into the object. At some point the photon would also just pass right through the material as there is no material that can reflect all wave lengths of light/radiation. If the photon wasn't absorbed by one of the atoms it would essentially pass right through it, IE the object would be transparent to that wave length of light. Even if it got absorbed then the photon should start a random walk were it will either emerge from the object or perhaps even be emitted back into the centre to travel to wall at some other point and be reabsorbed and face another random walk. Statistically speaking it will eventually get out.