On 1/18/2020 7:54 PM, Alan Grayson wrote:
On Saturday, January 18, 2020 at 6:40:49 PM UTC-7, Brent wrote:
On 1/18/2020 4:04 PM, Alan Grayson wrote
On Saturday, January 18, 2020 at 2:55:16 PM UTC-7, Brent wrote:
On 1/18/2020 1:29 AM, Alan Grayson wrote:
*the infinite spatial extent must have occurred
instantaneously, at the BB.*
It doesn't have to "occur". If the universe is infinite then
it didn't become infinite, it was always (in some timeless
way) infinite. The equations of cosmology are just for a
scale factor. We estimate the parameters from observation and
project back to a beginning. So there's really no sense in
projecting back to zero scale factor...there the size of a
flat universe according the equations is infinity*zero.
Hopefully a quantum theory of gravity will replace that oo*0
with something more sensible.
Brent
What do "infinity*zero" and "oo*0" mean? I see your point. My
problem is that we seem to have a universe with a BEGINNING,
called the BB,
That's not true and whether the universe had a beginning is a
independent of their having been a Big Bang. The “Big Bang” is
used to designate the sudden expansion of the universe which is
the current best theory of the universes evolution.
*IMO, the BB is more than that. In say, eternal inflation, it's the
moment of emergence from the Multiverse. A few Planck durations later,
the sudden expansion began. AG*
It doesn’t actually refer to some beginning from nothing.
*My "nothing" doesn't imply no Multiverse. "Nothing" is what our
universe was before it emerged. It's a reasonable inference, not just
philosophical bias or garbage. Even with eternal inflation, it's
postulated that something that previously wasn't, emerged from
something we call, for lack of a better word, the Multiverse. AG*
There are theories, like Hartle and Hawking’s in which there is a
t=0 starting point, although physical time starts at t>0.
*This is what I've been assuming, a starting point! **So at t=0 there
might have been infinite spatial extent? But you say not to take
"infinity" seriously. I have a more reasonable theory; that the
emergent bubble started out with zero volume (a real number btw), and
has always been finite and closed. If you can't show that the
equations demonstrate an infinite universe at time of emergence --
which they can't since infinity is not a number -- ISTM you're adding
an unwarranted ad hoc hypothesis. AG*
And there are theories like eternal inflation in which our
universe condenses like a bubble out of an eternal background
multiverse, and some other theories besides. Almost all of them
include a Big Bang phase because the Big Bang is implicit in just
projecting current motions back in time. Whether there is a zero
time depends on the model, but it will have to be a model that
does something different near the beginning than simply
extrapolating GR equations back because those extrapolate back to
infinity*zero which as your algebra teacher no doubt told you is
indeterminate.
* Since infinity isn't a number, one can't use it for arithmetic
operations. (I didn't realize that the " * " meant multiplication.) AG*
and I find it virtually impossible to imagine it starting with an
infinite spatial extent.
So it's a failure of your imagination. Work on that.
*Your condescension adds nothing. You say not to take infinity in a
theory seriously, yet you assume it at t=0. AG*
How could "nothing" become
You keep sticking "become" and "emerge" into the story. It
equations say it STARTS OUT INFINITE!
*All the equations tell us is that matter density decreases as time
increases, *
No. They also tell us that closed spacetime goes with positive
curvature; infinite spacetime goes with flat space.
*and that it increases as time decreases; that is, expansion and
contraction of the physical universe. I don't believe you can show
where the equations say the universe starts out infinite? *
But I can point to evidence, empirically, that space is flat.
*TIA, AG*
And you can't say where it becomes infinite. Yet you insist that it
both must have become infinite AND it cannot have become infinite.
You seem stuck with that meta-physical prejudice that nothing is a
natural state and can be assumed with no justification.
*No. I am just assuming that OUR universe, or bubble, didn't exist
before it emerged from, say, the Multiverse. So there was "something"
before our universe emerged. I even went so far to assert that this
something might be flat with an infinite past. AG*
Remember Norm Levitt used to say, "What is there? Everything! So
what isn't there? Nothing!"
infinite in any parameter, suddenly, or due to finite processes?
What I can imagine is it emerging from something flat and
eternal, having an infinite past. AG
Any physics with "infinite" or "infinitesimal" in it should be
taken with a big grain of salt.
*Isn't this precisely what you're doing when you claim flat space, and
therefore spatial extent to, perish the word, infinity? AG
*
I don't claim anything except that GR has solutions for a cosmos in
which space is flat and, in that solution, space is infinite and
empirically it appears that space is flat.
*
*
It just shows the mathematics has run the problem over the horizon
of our knowledge.
Brent
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