On 1/18/2020 4:04 PM, Alan Grayson wrote:
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. It doesn’t actually refer to some beginning from nothing. There are theories, like Hartle and Hawking’s in which there is a t=0 starting point, although physical time starts at t>0. 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.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. BrentWhat 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,
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.
How could "nothing" become
You keep sticking "become" and "emerge" into the story. It equations say it STARTS OUT INFINITE! You seem stuck with that meta-physical prejudice that nothing is a natural state and can be assumed with no justification. 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. It just shows the mathematics has run the problem over the horizon of our knowledge.
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