Re: Creation (long)

[DSCHROEDER@cc.weber.edu]

> Also it is *not* thought to be the case that "the stuff of this Universe is
> expanding into this expanding space".  The stuff of the universe is thought
> to completely fill out the whole universe at *all* times.

> The Big Bang happened everywhere.  This singularity is *not* a point *in*
> space.  Rather, it is the confluence of all of space to an infinitely
> compressed state at a finite point *in time* in the past.  I would not want
> to speculate about the dynamical behavior of the spacetime of 'other
> universes', but if they exist, then their spacetime manifolds are
> disconnected (by definition of *other* spacetime) from the spacetime of our
> universe and the concept of 'where' or 'when' they are makes no sense
> within our our own spacetime.

In the simplest (homogeneous) cosmological models, yes, the big bang
happens everywhere.  But from an observational standpoint, I don't see
how you can be sure of this.  We can observe only a limited amount
of the universe, after all.  Who's to say what conditions are like
a billion billion light-years away from us, or what the history of
such distant places was?

> Actually, if the universe is 10 billion years old we *can* see farther
> than 10 billion light years because of the expansion of the universe.  If
> a photon has been travelling for 10 billion years from when it was emitted
> until it was absorbed, the proper distance between the emission point and
> the absorption point is significantly *greater* than 10 billion light years
> at the moment of absorption, and is *much* less than 10 billion light years
> at the moment of emission.  The space between the emission point and the
> absorption point is stretching while the photon is propagating.  If the
> universe is 10 billion years old, and if the universe is the asymptotically
> spatially flat borderline case between openness and closedness
> (as predicted by inflationary senarios, and if the cosmological constant is
> really close to zero) then the current proper distance to the observational
> horizon is just under *30* billion light years because for such a spacetime
> the proper spatial separation between the emission point and the absorption
> point at the moment of absorption (given that the emission time was
> immediately after the Big Bang) is *3 times* the light travel distance that
> a photon propagating for the same amount of time on a static spacetime
> would have.

I stand corrected.  Thanks for the clarification.

-dan