Universe

[nucleardream]

At what speed does it expand and contract?

[wendilla]

The Newtonian view assumes instant communication of the gravitational field. In such a case, one could pose that the kinetic energy of all the matter in the universe speeding off in all directions is equally balanced by gravitational potential energy that would bind all matter together. I suppose this works when the universe was very close to the size of a singularity. However, the force of gravity travels at the limited speed of light by force cariers called gravitons. So by the time a graviton travels from one side of the universe to the particles on the other side, the particles on the other side have travelled even further away. I suppose this would make the gravitational force of a particle felt by particles on the other side of the universe seem weaker than in the pure Newtonian scheme. This is like slowly reducing the force of gravity as the universe expands. Wouldn't this have the tendency to make the particles fly apart more rapidly since you are slowly eliminating the opposition of gravity? Or at least it would insure that the universe expands forever. Right?

If we throw in a particle horizon where some particles have not yet even felt the gravitational force of other particles very distant from us, this would contribute to expansion, maybe even acceleration.

And if we also have an event horizon where more and more distant objects are accelerated to the speed where we will never again feel their gravitational force, then that would only contribute to even faster acceleration, right?

The question is: can we explain the expansion of the universe without supposing that space itself is expanding, where instead expansion and acceleration can be explained in terms of gravitational forces that are delayed or removed from consideration? Thanks.

--------------------------------------------------------------------------------

[wendilla]

also type in (at what speed does the universe expand)into "google" and you will get more imfo there. hope this helps

[jake-the-peg]

I don't know if this is what you are getting at but the Universe is expanding faster than the speed of light - or at least has in the past.

This might appear to contradict what we know about the speed of light being constant but that applies to things moving in the Universe not necessarily the Universe itself.

You can read more about this here:
http://curious.astro.cornell.edu/question.php? number=575

[nucleardream]

Thanks for the feedback Wendilla. Your post shows that some questions often times lead to larger, more complex ones. That's scientific inquiry though, right?

You got me Jake... that was one element I was alluding to in the question. I know that the speed at which the universe expanded in the first fraction of a second of its existence was something of an unbelievable magnitude, but if it is true that it is also accelerating in its expansion rate, then wouldn't logic dictate it continues to pick up speed from the start? If this is not true - if the universe is expanding at an accelerating rate, but not as fast as the first moment of its existence, then at one point it's speed actually decreased, then increased, and will one day reverse it's rate of expansion into contracting into the single element from which it arose. Maybe I should read the link you provided first...