Re: Clark on the singularity at T=0

[John Clark]

On Sat, Feb 8, 2025 at 3:47 AM Alan Grayson <agrays...@gmail.com> wrote:

> I can't recall on which thread I made the argument, and Clark agreed, that if the universe has a finite age, it cannot be infinite in spatial extent.

That's not quite what I agreed to. If it has a finite age then the observable universe can't be infinite in spatial extent, but no cosmologist believes that the observable universe is the entire universe, despite the fact that it's impossible even in principle to ever see it.

 

 > Isn't there a theorem, which might have been proven by Penrose, that the contracting universe must converge to a point or zero volume containing all matter and energy? What is the name of that theorem, assuming it exists?  AG

Some call it the Penrose Singularity Theorem, in 1965 Penrose used topology to prove that any sufficiently dense object must form a Black Hole, he won the Nobel prize because of it. It was the first time anyone had found a use for topology in physics.  

  John K Clark    See what's on my new list at  Extropolis

tiu

 

[Alan Grayson]

On Saturday, February 8, 2025 at 5:31:25 AM UTC-7 John Clark wrote:

On Sat, Feb 8, 2025 at 3:47 AM Alan Grayson <agrays...@gmail.com> wrote:

> I can't recall on which thread I made the argument, and Clark agreed, that if the universe has a finite age, it cannot be infinite in spatial extent.

That's not quite what I agreed to. If it has a finite age then the observable universe can't be infinite in spatial extent, but no cosmologist believes that the observable universe is the entire universe, despite the fact that it's impossible even in principle to ever see it.

I deleted, and then rewrote this post because I realized you didn't "quite" agree to my conjecture. What is true is that the universe, the entire universe, cannot be infinite in spatial extend unless it started that way. This is what you agreed to. AG 

 

 > Isn't there a theorem, which might have been proven by Penrose, that the contracting universe must converge to a point or zero volume containing all matter and energy? What is the name of that theorem, assuming it exists?  AG

Some call it the Penrose Singularity Theorem, in 1965 Penrose used topology to prove that any sufficiently dense object must form a Black Hole, he won the Nobel prize because of it. It was the first time anyone had found a use for topology in physics.  

If we run the clock backward in time, the universe becomes progressively denser as the average distance between galaxies decreases. So if it becomes a BH, it seems highly unlikely it started out infinite in spatial extent, which is what you and Brent conjectured. AG 

[John Clark]

On Sat, Feb 8, 2025 at 9:23 AM Alan Grayson <agrays...@gmail.com> wrote:

> If we run the clock backward in time, the universe becomes progressively denser as the average distance between galaxies decreases. So if it becomes a BH, it seems highly unlikely it started out infinite in spatial extent, which is what you and Brent conjectured.

It doesn't become a black hole of the universe is infinite. Equations for the formation of a black hole assume that there is no significant amount of matter outside the event horizon.  

  John K Clark    See what's on my new list at  Extropolis

eyw

[Alan Grayson]

You agreed that since the universe has a finite age, if it's infinite in spatial extent, that would necessarily have occurred at its origin. But although Penrose's theorem suggests it started as a BH, we can be relieved of that illusion based on our extensive knowledge of the interior and behavior of BH's. AG 

eyw

[John Clark]

As I said, before, Penrose Theorem assumes that there is no significance  Outside of the event, Horizon and that would not be true if the universe was infinite So the theorem Does not apply.

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[Alan Grayson]

On Saturday, February 8, 2025 at 2:25:00 PM UTC-7 John Clark wrote:

As I said, before, Penrose Theorem assumes that there is no significance  

What do you mean by no significance? As for my speculation at T=0, it's hard to imagine galaxies becoming progressively less distant from each other as we go back in time, and then suddenly at T=0, spreading out in spatially infinite directions. That's what must happen in a universe of finite age which become spatially infinite at T=0. OTOH, if all mass and energy converges to zero volume at T=0, it's conceivable, via the Singularity Theorem, for a BH to form. AG

 

Outside of the event, Horizon and that would not be true if the universe was infinite So the theorem Does not apply.

On Sat, Feb 8, 2025 at 2:56 PM Alan Grayson <agrays...@gmail.com> wrote:

On Saturday, February 8, 2025 at 12:08:24 PM UTC-7 John Clark wrote:

On Sat, Feb 8, 2025 at 9:23 AM Alan Grayson <agrays...@gmail.com> wrote:

> If we run the clock backward in time, the universe becomes progressively denser as the average distance between galaxies decreases. So if it becomes a BH, it seems highly unlikely it started out infinite in spatial extent, which is what you and Brent conjectured.

It doesn't become a black hole of the universe is infinite. Equations for the formation of a black hole assume that there is no significant amount of matter outside the event horizon.  

That's an assumption. Never forget what's assumed! AG 

[Brent Meeker]

I never conjectured it was originally a black hole.  Models of the origin of the universe, like FLRW, have the nascent universe at extremely high temperature, uniform, and expanding very rapidly,

Brent

[Alan Grayson]

On Saturday, February 8, 2025 at 4:19:30 PM UTC-7 Brent Meeker wrote:

I never conjectured it was originally a black hole. 

And neither did I claim you conjectured as such. Rather, you asserted that the universe could have begun as spatially infinite (if, as I claimed, it couldn't have become spatially infinite if it has a finite age). AG

 

Models of the origin of the universe, like FLRW, have the nascent universe at extremely high temperature, uniform, and expanding very rapidly,

So it must have begun as spatially very small, or perhaps having zero volume? AG 

[Alan Grayson]

On Saturday, February 8, 2025 at 5:05:05 PM UTC-7 Alan Grayson wrote:

On Saturday, February 8, 2025 at 4:19:30 PM UTC-7 Brent Meeker wrote:

I never conjectured it was originally a black hole. 

And neither did I claim you conjectured as such. Rather, you asserted that the universe could have begun as spatially infinite (if, as I claimed, it couldn't have become spatially infinite if it has a finite age). AG

 

Models of the origin of the universe, like FLRW, have the nascent universe at extremely high temperature, uniform, and expanding very rapidly,

So it must have begun as spatially very small, or perhaps having zero volume? AG 

Brent

I think I am on fairly sound ground to claim the universe began as a BH, referencing the Penrose-Hawking Singularity theorem. 

"The Hawking singularity theorem is based on the Penrose theorem and it is interpreted as a gravitational singularity in the Big Bang situation."

https://en.wikipedia.org/wiki/Penrose%E2%80%93Hawking_singularity_theorems 

AG

[Cosmin Visan]

Universe doesn't exist. "Universe" is just an idea in consciousness.