On Mon, 6 Jun 2005, Jesse Mazer wrote:

Norman Samish wrote:

    If the universe started contracting, its entropy would get smaller,
which nature doesn't allow in large-scale systems.  This seems to me an
argument in support of perpetual expansion.

From what I've read, if the universe began contracting this would not
necessarily cause entropy to decrease, in fact most physicists would consider that scenario (which would mean the 'arrow of time' would reverse during the contraction) pretty unlikely, although since we don't know exactly why the Big Bang started out in a low-entropy state we can't completely rule out a low-entropy boundary condition on the Big Crunch.

This is quite correct. The idea that there are future as well as past boundary conditions is an extreme minority one.


    And where did this mysterious Big Bang come from?  A "quantum
fluctuation of virtual particles" I'm told.

Whoever told you that was passing off speculation as fact--in fact there is no agreed-upon answer to the question of what, if anything, came before the Big Bang or "caused" it.

Jesse


Maybe Norman is confusing the rather more legit idea that the *fluctuations* in the Big Bang, that explain why the universe is not completely uniform, come from quantum fluctuations amplified by inflation. This is currently the leading theory for the origin of structure, in that it has quite a lot of successful predictions to its credit.

Paddy Leahy

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