On Wednesday, February 26, 2025 at 4:29:13 AM UTC-7 Quentin Anciaux wrote:
AG, the key point is that the observable universe is just a finite portion
of an infinite whole. As we go back in time, the observable region
contracts because the horizon of what we can see shrinks, but the entire
universe remains infinite.
Why does the unobservable part remain infinite? Because spatial infinity
doesn’t depend on what we can observe. If the universe was infinite at one
moment, it stays infinite—shrinking only applies to what is within our
causal past, not the entire space.
The density increases everywhere, meaning in any finite region—including
our observable universe—matter gets packed into a smaller space. But an
infinite universe still has no overall “volume”, so it never “shrinks,”
only becomes denser.
The dichotomy isn’t a contradiction, it’s a consequence of causal
horizons—our observable universe is just a window into an infinite cosmos.
And you know that how? How did you conclude it's infinite, other than
having an opinion? AG
Quentin
Le mer. 26 févr. 2025, 11:08, Alan Grayson <agrays...@gmail.com> a écrit :
On Wednesday, February 26, 2025 at 3:51:50 AM UTC-7 Quentin Anciaux wrote:
AG, your statement "density can't diverge unless volume goes to zero"
assumes a finite volume, which doesn’t apply in an infinite universe. In an
infinite universe, density can increase indefinitely everywhere without
requiring a total volume to shrink.
I was explicit, that the observable universe shrinks, but according to you
and Brent the unobservable part remains infinite. I can't imagine such a
dichotomy. AG
Brent is correct that the observable universe (the region we can see)
shrinks as we go back in time, but that doesn’t mean the entire universe
(including the unobservable part) does the same.
Why not? Is that just your opinion, or something demonstrable? AG
The observable universe is just a region within an infinite space, and as
we go back in time, the light cone that defines what we can observe gets
smaller.
If the entire universe is infinite, its total volume remains infinite at
all times
OK. AG
—but its density can still increase without bound.
Density of what region? AG
There’s no contradiction.
The contradiction is the dichotomy between the behavior of the two regions.
AG
Quentin
Le mer. 26 févr. 2025, 10:47, Alan Grayson <agrays...@gmail.com> a écrit :
On Wednesday, February 26, 2025 at 3:33:55 AM UTC-7 Quentin Anciaux wrote:
Le mer. 26 févr. 2025, 10:24, Alan Grayson <agrays...@gmail.com> a écrit :
On Wednesday, February 26, 2025 at 1:22:21 AM UTC-7 Alan Grayson wrote:
On Tuesday, February 25, 2025 at 10:07:41 PM UTC-7 Brent Meeker wrote:
On 2/25/2025 7:59 PM, Alan Grayson wrote:
On Tuesday, February 25, 2025 at 6:40:35 PM UTC-7 Brent Meeker wrote:
On 2/25/2025 3:48 PM, Alan Grayson wrote:
On Tuesday, February 25, 2025 at 12:46:46 PM UTC-7 Brent Meeker wrote:
I think all cosmologist, like Hartle, recognize that *the observable
universe* was much smaller in the past. Which is perfectly compatible with
*the
universe* be spacially flat and infinite.
Brent
I fully anticipated that response. But why would the observable universe
behave radically different from the entire principle, particularly in light
of the Cosmological Principle? AG
It's not radically different. It's different in exactly the way that
finite subsets of infinite sets behave.
Brent
But if the observable universe contracts to zero volume, the entire
universe has a singularity, which is inherently contradictory. So, the
model is, to say the least, inconsistent. AG
It's not contradictory or inconsistent, it's unphysical, i.e. it can't be
physically realized; which just means the theory of general relativity
doesn't work there. This is not a surprise since GR is not a quantum
theory and if you're concerned with a subatomic scale region you'll
probably need a quantum theory.
Brent
My conjecture is that there's a fifth force, repulsive in Nature, that
prevents the mass of a high mass collapsing star to reach zero volume. AG
I don't imagine a quantum theory. More important, I can't grasp the idea of
the observable universe contracting to zero or near zero volume as we go
backward in time, while the unobservable universe remains infinite in
spatial extent. Can you grasp it? Can you explain it? AG
As I've explained already, it's not that the volume goes to zero, but
density that goes to infinity, everywhere, there is no valid notion of
volume in an infinite universe.
Quentin
Density can't diverge unless volume goes to zero. FWIW, Brent thinks the
observable universe shrinks to zero or near zero as we go backward in time,
while the unobservable part remains infinite. AG
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