light

[GEddie]

Interesting question indeed. What has happened to all the photons emitted by the sun in its entire history? Do they reflect off the boundaries of the universe? Do we see them again?

By far most of them have gone off into deep space, and in decagigayears, will come back around, if the universe has a closed shape.

A small number reflect off the planets, the Earth, the clouds etc, and on into deep space.

A smaller number are absorbed by matter and convert to heat.
And a very few are absorbed by human eyes and trigger images in the mind.

ICXC NIKA

 

[DaveBj]

We may be arguing over definitions. Yes, light is attenuated as it spreads from
the source in concentric spheres, but it does not dissipate in the sense of losing energy, as sound waves or moving objects do. A photon will have the same energy reaching your optic nerve as it had at the source, but if the source is too far away, there will not be enough photons to trigger the optic nerve.

ICXC NIKA

I find us to be in exact agreement

 

[DaveBj]

**By far most of them have gone off into deep space, and in decagigayears, will come back around, if the universe has a closed shape. **

A small number reflect off the planets, the Earth, the clouds etc, and on into deep space.

A smaller number are absorbed by matter and convert to heat.
And a very few are absorbed by human eyes and trigger images in the mind.

ICXC NIKA

One astronomer (I don’t remember who) said something to the effect that if a big enough telescope could be made, it wouldn’t surprise him to find that he was looking at his own butt.

 

[Jim_Baur]

Aelred Minor

Thanks!

And to all who are so kind and patient, thanks!

 

[Jim_Baur]

Any further help?

 

[Ladervijd]

How long does it take for light to dissipate?
It seems almost impossible that light from 15 billion years ago has not dissipated.

Quick search found:
physicsforums.com/showthread.php?t=474626

Also, roughly estimated, considering that universe is expanding at a speed faster than c, what is the (changing) ratio of volume-space with light and of volume-space without light?
If we put the viewing point on, respectivly near (as in at least one “pixel”), the “edge” of an expanding universe, inside looking inwards, it would probably appear with no light at all, unless the “shell” is constantly emitting light inwards which would be possibly visible to a living human eye in body looking inwards (having contrast noticing light by shadow unless face is emitting light at the same rate as the background) albeit not so if the rate of light emission is too low for such (and e.g. the from-inner-shell-emission of light being such that particles of light in a line have noticable distance inbetween them).
Regarding “Big Bang”, would it be reasonable to assume that there is light travelling on the outer shell (as in “dots of light” perhaps even in perfect symmetry or complete area of light, both of which possibly either on the outer shell and/or in a 3d-layer/sphere moving behind the shell)?
If the universe would be contracting, what would happen to the light the “shell” would meet “on its way back”?
There is more to it of course, and e.g. we could assume that all light, or all light except for the first light, was taken (back) by galactical centres, kind of as the solar wind on the edge of the solar system.

I know that the speed of light is a constant, but could it slow down?

Apparently, the speed of light is slower in transparent/translucent materials, e.g. air or glass (visible light at about 2/3 of c), than speed of light in vacuum (c), and light is by opaque materials/matter absorbed, reflected or transmitted.