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Sent: Wednesday, January 23, 2002 10:49 AM
To: brian@holtz.org
Subject: Re: Can time go infinitely backward?

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From: brian@holtz.org (Brian Holtz)
Newsgroups: alt.atheism.moderated
Subject: Re: Can time go infinitely backward?
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"India" <spamtrap@rationalchristianity.net> wrote 

> Atheist: Why does the uncaused cause have to be God?  Maybe the
> universe always existed, and is itself an uncaused cause.
> 
> T: But you can't have time going infinitely back, any more than an
> infinite series of causes, so the universe can't have always existed. 
> (God, on the other hand, is outside time and space, so he could exist
> before the universe and time existed).
> 
> I'm sure y'all have rebuttals to this

Yes: if God could always have existed, then so could the universe.
If God could have been outside time and space, then so could have
been the Big Bang singularity.

> so my question is, can time
> really go infinitely backwards, and if so, how?

Here are some possible answers:

1. The same way time can go infinitely forwards. (Also, see 3.)

2. From my book:
  Eternity is an entire linear continuum of instants. Thus by 
  definition there is between any two instants another instant.  
  However, it is not necessary that between any two events there 
  is another event.  Nor is it necessary that there be a first 
  event, even if the past is of finite duration.  Just as there 
  is no smallest positive real number, there might be no first 
  event, because there might be no event associated with a first 
  instant (t=0).  Instants are mathematical constructs that do 
  not always have an associated actual event.

3. From "The Other Side of Time" by Victor Stenger at
http://www.infidels.org/library/modern/vic_stenger/otherside.html:

  We can label as t = 0 the time at which the initial quantum 
  fluctuation takes place. The expansion then proceeds on the 
  positive side of the t-axis, as defined by the increasing 
  entropy on that side. [..]

  Now, what about the negative side of the t-axis, the 
  other half dimension? If we look at Einstein's equations, 
  nothing forbids an expansion in that direction as well. [..]

  This implies the existence of another part of our universe, 
  separated from our present part along the time axis. From our 
  point of view, that part is in our deep past [...] However, 
  from the point of view of an observer in the universe at that 
  time, their future is into our past--the direction of increasing 
  entropy on that side of the axis. They would experience a universe
  expanding into their future, just as we experience one expanding 
  into our future.

  Would these different parts of the universe be identical, kind 
  of mirror images of each other? Not unless physics is completely 
  deterministic, which we do not believe to be the case.

This idea of dealing with an infinite regress by a sort of "rebound"
is vaguely similar to the idea in string theory that when you try
to get below the Planck scale you can't help but come back up again.
-- 
brian@holtz.org
http://humanknowledge.net