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View Full Version : Causality of particles prior to expansion



alainprice
2008-Oct-30, 07:51 PM
I often hear people saying that parts of the universe that are not causaully connected prior to inflation would not be homogenous with our observable universe.

What is the proof that leads to the statement?

I just don't understand why something requires 'close proximity' at some point to be homogenous overall.

Cougar
2008-Oct-30, 11:15 PM
Well, it's just too much of a coincidence that radiation coming from areas that appear to be non-causally connected would be exactly the same temperature....

speedfreek
2008-Oct-30, 11:17 PM
I think it all comes down to the uncertainty principle which would imply that there is no way the universe would have formed with an even temperature throughout. With metric expansion, the edges of the observable universe were receding from each other faster than light and so any differences in temperature would not have had time to even out between them, and the universe today should have far larger differences in the background temperature of different regions than the almost perfectly even background temperature we measure.

trinitree88
2008-Oct-30, 11:27 PM
I think it all comes down to the uncertainty principle which would imply that there is no way the universe would have formed with an even temperature throughout. With metric expansion, the edges of the observable universe were receding from each other faster than light and so any differences in temperature would not have had time to even out between them, and the universe today should have far larger differences in the background temperature of different regions than the almost perfectly even background temperature we measure.

speedfreek. What reason is given for the suspension of the inviolate rules of Special Relativity during the era that the universe expanded faster than light?

grant hutchison
2008-Oct-30, 11:52 PM
What reason is given for the suspension of the inviolate rules of Special Relativity during the era that the universe expanded faster than light?We are still in that era. A large part of the visible Universe (everything with a cosmological redshift greater than about 1.46) is expanding away from us faster than light.

Grant Hutchison

alainprice
2008-Oct-31, 12:10 AM
I think it all comes down to the uncertainty principle which would imply that there is no way the universe would have formed with an even temperature throughout. With metric expansion, the edges of the observable universe were receding from each other faster than light and so any differences in temperature would not have had time to even out between them, and the universe today should have far larger differences in the background temperature of different regions than the almost perfectly even background temperature we measure.

What about entropy? Wouldn't entropy say the temperature should 'normalize' with time.

The uncertainty principle applies to a lot of things, but usually we are examining single particles. Even if a single particle manages to acquire a lot of kinetic energy from its neighbors, why would this difference 'grow' with expansion. It's not like the particle gets bigger allowing it's excess kinetic energy to spread to a bigger area.

I still don't get it.

grant hutchison
2008-Oct-31, 10:51 AM
What about entropy? Wouldn't entropy say the temperature should 'normalize' with time.How does the Universe reach a consensus about what is "normal", if parts of it have never been in contact with each other? And yet it has chosen the same "normal" everywhere, to better than one part in 100,000.

When I go to West Africa and find a bunch of African folk speaking French, I feel justified in assuming that there has been some contact between France and West Africa; whereas I find it completely implausible to assume that the languages of France and West Africa have simply "normalized" in a near-identical way.

Grant Hutchison