Follow up question: Does light have a maximum distance it can travel?

Question

The majority answered in a perfect vacuum light should go on forever. That the photons would need not worry about fait. So then, what about in outer-space vacuum where particles do exist. Do you think it is possible that light beams can only reach a distance of about 15 billion light years? (by the way for those of you, only the visible universe is estimated to be about 15 billion years old. the universe could easily be much older than that and if light is limited in its space travels because of random space particles then who knows...)

Answer 1

Good question, this'll take some thought...

But assuming an infinite traversal of space the effects of Doppler shift would eventually cause the entropy of light energy.

As the light waves travel they are impacted by the gravity of neighboring bodies. The effect of which is a decrease in wave length for any one given point of light. Again assuming infinite traversal, eventually these light waves will have a nullified wavelength of zero and therefore be nothing but a stream of photons. And assuming the continued entropy caused (aided) by gravity the photons themselves may dephase and disperse randomly thus finding the maximum distance light might travel.

As for an accurate measure, how about you do all the math and just give me a by line when you publish... ;-)

Answer 2

You mentioned particles in space. These then would tend to diffuse the light until scattered all over the place as random photons until their energy is asorbed at some point. But, to keep on with the discussion, lets assume that some coherent light remains to continue to the end of the universe.

Lets go with your 15 billion year old universe, just to have a number. The universe's rate of expansion is probably not the speed of light. Why? Dunno, just a gut feeling. But let's say it does expand at C. So, with this number, the universe is something less than something like 30 billion light years wide. (in 15 billion years it expanded equally in all directions)

A beam of light originating from one end of the universe could travel no more than 30 billion light years. Time/space continuum ends at the end of the universe, so, beyond that, the light would cease to exist. The energy, however must still be retained by the universe, so, I guess it all heats up by the light's energy equivilant.

Does this work, or am I missing something?

Oh, yes, I am missing something! During the time the light traverses the 30 billion light years, the universe continues to expand (at the speed of light) AND, it expands in all directions, equally so, 1. it will never reach the far end, and 2. the ENTIRE universe expands, not just the edges, so the source, and the light expands forwards and backwards.

The light not only never reaches the far end, THE LIGHT NEVER TRAVELS AT ALL!

What have I done? Have I destroyed us all?

Answer 3

Your concern will always be if a. the light becomes so diffuse you can never see it, or b. if the light hits something along the way. So while a. is definetely a factor (we can detect some light from the early universe but astrophysicists keep trying to get fainter), as far as the physics goes your only real issue would be with b. As space isn't a perfect vacuum (there is one atom per cubic meter between galaxies, give or take), eventually your photon will hit one of these atoms and interact with it. I suppose you could work out how much a photon must travel to definetely hit something, but it's definetely more than 15 billion light years!
There is one final peril for a photon in outer space: if it gets too close to another object, it will be gravitationally lensed off its original course. So I guess the photon would survive, but it wouldn't end up a straight line away from its original starting point as it would have been bent.

Answer 4

In a vacuum, light should propagate until it is absorbed by something. The problem with seeing something 15 billion light years away is brightness. Light intensity is inversely proportional with the square of the distance between the source and the observer.

For example, if you double the distance, the perceived brightness is 1/4th the actual brightness. By the time you get 15 billion light years away, the object you're looking at had better be really bright (quasars and so on), or you need a really huge telescope to collect enough photons to actually see anything.

Answer 5

Well, you almost answered your own question. Only in a perfect vacum can light travel forever. In any system where there's something else, the light will strike it. Of course, the energy will remain.

As to "How far can light travel with stuff in the way?", I have no idea. It really depends on what gets in the way. It would be possible for a photon to travel from one side of the universe to the other {assuming the universe has sides}. The random molecules in the way {and huge gravity fields which can bend photon paths} will stop them, but I doubt we could more than guess at how far they can go.

Answer 6

Theoretically, light could go on forever. It's just it takes so much time for it to travel something like 15 billion light years that if you did see any light, it would be light from 15 billion light years ago. To even go that far you would have to use a telescope that did not depend on light to see. This is also one way scientists are trying to prove the big bang (which they have not been successful at because of course, we were created by God).

Answer 7

Light particles can go on forever until they are absorbed as heat by another object. Some estimates about universe expansion claim that it is expanding faster than the speed of light, so a light particle can keep flying until it catches up with expansion.

Answer 8

2000 miles is what i would say

Answer 9

yea