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Is there any limit to how far photons travel/propagate through space? In other words, would they eventually come to a place where they are no longer able to travel/propagate at the edge of "space". My intuition says there is no limit, but my intuition is usually wrong when it comes to this stuff.
nothing travels faster than light........... so there should come a time when photon reaches the edge of he universe.....
Quote from: sherya on 18/09/2010 09:16:55nothing travels faster than light........... so there should come a time when photon reaches the edge of he universe.....The speed of light is the slowest that the universe has ever expanded. At one point in the fairly early stages of the Big Bang it's widely accepted (but still open to debate) that the universe expanded faster than the speed of light.It needs to be remembered too, that although we may tend to think of photons as being the most fundamental expression of energy, it is significant that the Standard Model predicts that the very early universe was opaque to light.During this period then, the universe appears to have expanded faster than the speed of light, but at the same time, the universe was nearly uniform and once photons started to appear as discrete particles, and existed as such for a significant amount of time before interacting, the did so pretty much uniformally throughout the universe.The 'boundary' of the universe then, that's expanding, will have emitted photons in the direction of expansion, as well as photons in every other direction as well, and those that reach us are what we call the Cosmic Microwave Background Radiation (CMBR). So just as some of the light from the BB has reached us, some of it is still travelling outwards, right at the forefront of the expanding universe.Arguably, it is the presence of those photons, moving outwards at the speed of light, that are creating the expanding universe.
Not that I know much about any of this stuff, but that seems about right. After all, if a photon sort of "ran out of" space, what would it do? Unless the energy went down some sort of ethereal plughole, it would have to reflect off the edge. But that seems highly unlikely (to me anyway).
People are pretty sure nowadays that the universe is "flat" like the bottom illustration. If you jet off in one direction, you don't end up coming back from the opposite direction.
I'm a bit confused by the hypersphere picture. Since its space-time, does that mean that if you jet off in one direction, you'll eventually come back to the same coordinates in space-time? That would mean you'd traveled back in time to the point from which you left...