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gordiebrooks
2010-Feb-25, 06:10 AM
Will light from the universe ever catch the boundary of the expanding universe? Or do the two eventually travel at the same speed?

01101001
2010-Feb-25, 07:01 AM
Welcome to BAUT Forum.


Will light from the universe ever catch the boundary of the expanding universe?

Which boundary? Where?

Sean Carroll Cosmology Primer FAQ :: What is the universe expanding into? (http://preposterousuniverse.com/writings/cosmologyprimer/faq.html#into)


As far as we know, the universe isn't expanding "into" anything. When we say the universe is expanding, we have a very precise operational concept in mind: the amount of space in between distant galaxies is growing. (Individual galaxies are not growing, as they are bound together by gravity.) But the universe is all there is (again, as far as we know), so there's nothing outside into which it could be expanding. This is hard to visualize, since we are used to thinking of objects as being located somewhere in space; but the universe includes all of space.

astromark
2010-Feb-25, 07:41 AM
Will light from the universe ever catch the boundary of the expanding universe? Or do the two eventually travel at the same speed?

No. It will not. and yes they do both travel at c. but as the space between is expanding and eccelorating as it does so.. So no the light emitted from the universe may never catch or reach what you perceive to be an edge.
Is this right; Perception of movement = Velocity. Change of velocity = acceleration. Changes of acceleration are, what ?

pzkpfw
2010-Feb-25, 07:58 AM
Will light from the universe ever catch the boundary of the expanding universe? Or do the two eventually travel at the same speed?

Kind of the reverse...

The one "boundary" that makes sense is the "visible Universe" - the limit of what we can see. (The Universe is expected to be bigger than what we can see. We are at the centre of our visible Universe, but there is no centre of the Universe itself.)

The visible Universe is limited due to the expansion of the Universe (and the finite age of the Universe). The stuff that is further away than what we can see, has made light - but that light hasn't yet had time to reach us.

Due to the continuing expansion of the Universe, there is light being made that will never reach us. Galaxies that we'll never see. In fact, stuff that is now visible eventually won't be visible any more (a long time in the future).

What is visible in the Universe will get less and less. Fewer and fewer things out there will be making light that can reach us.

We'll end up very lonely.

forrest noble
2010-Feb-26, 02:46 AM
gordiebrooks,


Will light from the universe ever catch the boundary of the expanding universe? Or do the two eventually travel at the same speed?


According to Einstein's cosmological equations based upon General Relativity the universe curves in a physical fourth dimension so that there is no perimeter or center to it. If you start in a straight line, accordingly you would eventually end up where you started. So in this model, the standard cosmology model, there is no perimeter so your question cannot be answered.

In Minkowsky flat-space models of a finite universe, there would be a perimeter to the universe but the answer to your question would probably be dependent on the particular model.