Clark, on the claim that everything that's possible, MUST happen

[Alan Grayson]

IIUC, it's based on the assumption that the universe is infinite in spatial and temporal extent, but this is mistaken. Our universe, by which I mean our bubble, is finite. We know that by applying basic logic. First, since nothing can become infinite via a finite process, which is implied by the finite age of the universe. So if the universe is spatially infinite, that must be its initial condition when it came into being with the Big Bang. But that would require adding a singularity of sorts to the usual concept of the BB; namely, that at its inception, it became infinite in spatial extent instantaneously. This hypothesis must be rejected for the same reason we regard theories with infinities as incorrect when they make such predictions. AG

[John Clark]

On Sat, Jan 25, 2025 at 5:11 AM Alan Grayson <agrays...@gmail.com> wrote:

> IIUC,

According to Google, that means the "International Islamic University Chittagong", but it must not understand correctly.

 

> it's based on the assumption that the universe is infinite in spatial and temporal extent, but this is mistaken.

You're right, that is mistaken, so it's fortunate that Hugh Everett did not make that mistake. By the way, I don't feed trolls so if I hear any of that "Trump physics" crap this conversation is over.

> Our universe, by which I mean our bubble, is finite.

In Hugh Everett's Many Worlds theory the word "bubble" has no meaning although that word does have meaning in "Eternal Inflation" and in the "String Theory landscape", but as far as Everett's Many Worlds is concerned they are irrelevant, they may or may not be true.

Max Tegmark has proposed 4 different types of "Many Worlds"

1) A spatial extension of our observable universe, perhaps by an infinite number of light years or perhaps by just an astronomical number of light years. 

2) The same as #1 but the more distance you travel the more the fundamental "constants" of nature change.

3) Hugh Everett's Many Worlds.

4) Ultimate Ensemble Theory, everything that is not logically self-contradictory exists, not just everything that Quantum Physics allows. 

I believe in #1 as does every astronomer and physicist on the planet, I am an agnostic concerning #2, and I am close to being an atheist concerning #4. Tegmark is comfortable with #3 as am I, but he is willing to go much further than I am.

 

> nothing can become infinite via a finite process, which is implied by the finite age of the universe.

But something can remain being infinite after a finite amount of time if it started out being infinite, and that may or may not be the case with our universe,  Everett's Many Worlds has nothing to say about that issue.

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

t6z

[Alan Grayson]

On Saturday, January 25, 2025 at 6:57:27 AM UTC-7 John Clark wrote:

On Sat, Jan 25, 2025 at 5:11 AM Alan Grayson <agrays...@gmail.com> wrote:

> IIUC,

According to Google, that means the "International Islamic University Chittagong", but it must not understand correctly.

 

> it's based on the assumption that the universe is infinite in spatial and temporal extent, but this is mistaken.

You're right, that is mistaken, so it's fortunate that Hugh Everett did not make that mistake. By the way, I don't feed trolls so if I hear any of that "Trump physics" crap this conversation is over.

> Our universe, by which I mean our bubble, is finite.

In Hugh Everett's Many Worlds theory the word "bubble" has no meaning although that word does have meaning in "Eternal Inflation" and in the "String Theory landscape", but as far as Everett's Many Worlds is concerned they are irrelevant, they may or may not be true.

i call it a Bubble to suggest an approximately spherical shape, which is implied by the Cosmological Red Shift, which has approximately the same value in every direction. So its shape is like a somewhat distorted sphere. AG 

Max Tegmark has proposed 4 different types of "Many Worlds"

1) A spatial extension of our observable universe, perhaps by an infinite number of light years or perhaps by just an astronomical number of light years. 

Falsified by the data, the age estimate of the universe. AG 

2) The same as #1 but the more distance you travel the more the fundamental "constants" of nature change.

Ditto, or irrelevant to my argument. AG 

3) Hugh Everett's Many Worlds.

4) Ultimate Ensemble Theory, everything that is not logically self-contradictory exists, not just everything that Quantum Physics allows. 

I believe in #1 as does every astronomer and physicist on the planet,

Not true; not even close to true. They mostly, or perhaps entirely believe in the age estimate of the universe. AG

 

I am an agnostic concerning #2, and I am close to being an atheist concerning #4. Tegmark is comfortable with #3 as am I, but he is willing to go much further than I am.

#3 depends on an infinite universe, which I have falsified. AG

 

> nothing can become infinite via a finite process, which is implied by the finite age of the universe.

But something can remain being infinite after a finite amount of time if it started out being infinite, and that may or may not be the case with our universe,

Almost certainly false, as I argued. Did you read it? Same reason GR doesn't apply at the moment the BB occurred. AG

 

 Everett's Many Worlds has nothing to say about that issue.

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

IIUC = If I Understand Correctly. IIUC your reply hasn't come remotely close to a genuine reply to my argument.  AG 

t6z

[Jesse Mazer]

On Sat, Jan 25, 2025 at 1:57 PM Alan Grayson <agrays...@gmail.com> wrote:

On Saturday, January 25, 2025 at 6:57:27 AM UTC-7 John Clark wrote:

On Sat, Jan 25, 2025 at 5:11 AM Alan Grayson <agrays...@gmail.com> wrote:

> IIUC,

According to Google, that means the "International Islamic University Chittagong", but it must not understand correctly.

 

> it's based on the assumption that the universe is infinite in spatial and temporal extent, but this is mistaken.

You're right, that is mistaken, so it's fortunate that Hugh Everett did not make that mistake. By the way, I don't feed trolls so if I hear any of that "Trump physics" crap this conversation is over.

> Our universe, by which I mean our bubble, is finite.

In Hugh Everett's Many Worlds theory the word "bubble" has no meaning although that word does have meaning in "Eternal Inflation" and in the "String Theory landscape", but as far as Everett's Many Worlds is concerned they are irrelevant, they may or may not be true.

i call it a Bubble to suggest an approximately spherical shape, which is implied by the Cosmological Red Shift, which has approximately the same value in every direction. So its shape is like a somewhat distorted sphere. AG 

Max Tegmark has proposed 4 different types of "Many Worlds"

1) A spatial extension of our observable universe, perhaps by an infinite number of light years or perhaps by just an astronomical number of light years. 

Falsified by the data, the age estimate of the universe. AG 

If the universe *were* infinite spatially (or at least much larger than the observable region), but still began in a Big Bang a finite time in the past (or at least we could not receive light signals from before then, even if there was something before as in 'eternal inflation' theories), do you think the observational data would be any different? Assuming a finite speed of light, the observable region would still be a finite size in this scenario, no?

Jesse

[John Clark]

On Sat, Jan 25, 2025 at 1:57 PM Alan Grayson <agrays...@gmail.com> wrote:

 

>> I believe in #1 as does every astronomer and physicist on the planet,

> Not true; not even close to true. They mostly, or perhaps entirely believe in the age estimate of the universe. AG

We know that to the limits of experimental accuracy on the largest scale space is flat, and no physicist or astronomer alive believes the Earth is the center of the universe; put those two facts together and there is only one logical conclusion, every physicist or astronomer alive believes that the observable universe can NOT be the entire universe, it might be an infinite number of light years across or it might be only an astronomical number of light years across, but either way it must be much much bigger than what we can see.  

> #3 depends on an infinite universe, which I have falsified. AG

Like hell you have!! You have not even falsified #1 or #2, much less #3. And if Hugh Everett's theory is correct then the Multiverse is infinitely old. 

> IIUC = If I Understand Correctly. IIUC your reply hasn't come remotely close to a genuine reply to my argument.  AG 

Therefore I must conclude that you have not understood Quantum Mechanicscorrectly, just as you are unable to understand Special Relativity correctly. 

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

z00

[Alan Grayson]

On Saturday, January 25, 2025 at 12:54:06 PM UTC-7 John Clark wrote:

On Sat, Jan 25, 2025 at 1:57 PM Alan Grayson <agrays...@gmail.com> wrote:

 

>> I believe in #1 as does every astronomer and physicist on the planet,

> Not true; not even close to true. They mostly, or perhaps entirely believe in the age estimate of the universe. AG

We know that to the limits of experimental accuracy on the largest scale space is flat, and no physicist or astronomer alive believes the Earth is the center of the universe; put those two facts together and there is only one logical conclusion, every physicist or astronomer alive believes that the observable universe can NOT be the entire universe,

What the F are you talking about??? I never claimed what you suggest! Apparently you didn't read what I wrote, or minImally not carefully. AG

 

it might be an infinite number of light years across or it might be only an astronomical number of light years across, but either way it must be much much bigger than what we can see.  

Sure, it MIGHT be, but it isn't for the same reason GR fails at the time of the BB. AG 

> #3 depends on an infinite universe, which I have falsified. AG

Like hell you have!! You have not even falsified #1 or #2, much less #3. And if Hugh Everett's theory is correct then the Multiverse is infinitely old. 

Don't you grasp what a finite age of the universe implies? Everett depends on an infinite universe, or on offshoot of what Tegmark claims. Obviously, you haven't read my claim, but prefer to shoot from the hip, as it were, to defend the cult. I am discussing our Bubble, not the Multiverse based on Eternal Inflation. AG 

> IIUC = If I Understand Correctly. IIUC your reply hasn't come remotely close to a genuine reply to my argument.  AG 

Therefore I must conclude that you have not understood Quantum Mechanics correctly, just as you are unable to understand Special Relativity correctly. 

I assume you mean S's equation. It doesn't imply the MWI. That's your unshakeable obsession. Do you think S interpreted slit experiments are implying hugely Many Worlds are created for EACH particle going through the slit after being detected as a single outcome? As for SR, I find it hard to understand Brent's diagrams because he doesn't clearly describe all his assumptions, and I am still unsure it solves the Parking Paradox. Pardon me for being thorough. AG

[John Clark]

On Sat, Jan 25, 2025 at 5:43 PM Alan Grayson <agrays...@gmail.com> wrote:

 

> prefer to shoot from the hip, as it were, to defend the cult.

Goodbye.  

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

ez9

z0

[Alan Grayson]

On Saturday, January 25, 2025 at 5:25:47 PM UTC-7 John Clark wrote:

On Sat, Jan 25, 2025 at 5:43 PM Alan Grayson <agrays...@gmail.com> wrote:

 

> prefer to shoot from the hip, as it were, to defend the cult.

Goodbye.  

Yes, it's a cult, and you're its prime defender. AG

[Alan Grayson]

You pose a compound question, so hard to answer. I am just dealing with our Bubble, nothing to do with Eternal Inflation. And within our Bubble, or any Bubble, I think the observable universe will be finite since the SoL is finite. Also, the unobservable part is estimated to be hugely larger, some estimates are 200 times larger but I'm not sure if that refers to its volume or radius. But with a finite age, it cannot evolve to infinity in spacial extent, no matter how fast it expands. That condition could only exist IMO if that was its initial condition. But as I wrote, that would be imposing another infinity on the BB (aside from infinite density at T=0), which again, IMO, is highly dubious. I'm not sure I answered your question, so you might have to rephrase it. AG

[Jesse Mazer]

In the math of general relativity the universe could have been spatially infinite at every finite time after the Big Bang, and the Big Bang itself is treated as a singularity so it need not have a well-defined size. But anyway, the argument you are making above about why you think the universe must be finite seems to be a theoretical one, but before that in the post I was responding to, you seemed to be saying an infinite universe was falsified by *empirical* data, not just theoretical arguments--is that right? If you were making that claim, you should be ready to defend it even in the case where you grant for the sake of argument that there is no theoretical problem with the GR model of a universe that's infinite in size but began a finite time in the past (or at least agree to put aside all theoretical objections for the time being). Are you saying that even if you do put theoretical objections aside, you still think the empirical data is in conflict with the idea of an infinite universe that began a finite time in the past?

Jesse

[Alan Grayson]

On Saturday, January 25, 2025 at 6:57:31 PM UTC-7 Jesse Mazer wrote:

On Sat, Jan 25, 2025 at 8:29 PM Alan Grayson <agrays...@gmail.com> wrote:

On Saturday, January 25, 2025 at 12:11:15 PM UTC-7 Jesse Mazer wrote:

On Sat, Jan 25, 2025 at 1:57 PM Alan Grayson <agrays...@gmail.com> wrote:

On Saturday, January 25, 2025 at 6:57:27 AM UTC-7 John Clark wrote:

On Sat, Jan 25, 2025 at 5:11 AM Alan Grayson <agrays...@gmail.com> wrote:

> IIUC,

According to Google, that means the "International Islamic University Chittagong", but it must not understand correctly.

 

> it's based on the assumption that the universe is infinite in spatial and temporal extent, but this is mistaken.

You're right, that is mistaken, so it's fortunate that Hugh Everett did not make that mistake. By the way, I don't feed trolls so if I hear any of that "Trump physics" crap this conversation is over.

> Our universe, by which I mean our bubble, is finite.

In Hugh Everett's Many Worlds theory the word "bubble" has no meaning although that word does have meaning in "Eternal Inflation" and in the "String Theory landscape", but as far as Everett's Many Worlds is concerned they are irrelevant, they may or may not be true.

i call it a Bubble to suggest an approximately spherical shape, which is implied by the Cosmological Red Shift, which has approximately the same value in every direction. So its shape is like a somewhat distorted sphere. AG 

Max Tegmark has proposed 4 different types of "Many Worlds"

1) A spatial extension of our observable universe, perhaps by an infinite number of light years or perhaps by just an astronomical number of light years. 

Falsified by the data, the age estimate of the universe. AG 

If the universe *were* infinite spatially (or at least much larger than the observable region), but still began in a Big Bang a finite time in the past (or at least we could not receive light signals from before then, even if there was something before as in 'eternal inflation' theories), do you think the observational data would be any different? Assuming a finite speed of light, the observable region would still be a finite size in this scenario, no?

Jesse

You pose a compound question, so hard to answer. I am just dealing with our Bubble, nothing to do with Eternal Inflation. And within our Bubble, or any Bubble, I think the observable universe will be finite since the SoL is finite. Also, the unobservable part is estimated to be hugely larger, some estimates are 200 times larger but I'm not sure if that refers to its volume or radius. But with a finite age, it cannot evolve to infinity in spacial extent, no matter how fast it expands. That condition could only exist IMO if that was its initial condition. But as I wrote, that would be imposing another infinity on the BB (aside from infinite density at T=0), which again, IMO, is highly dubious. I'm not sure I answered your question, so you might have to rephrase it. AG

In the math of general relativity the universe could have been spatially infinite at every finite time after the Big Bang, and the Big Bang itself is treated as a singularity so it need not have a well-defined size. But anyway, the argument you are making above about why you think the universe must be finite seems to be a theoretical one, but before that in the post I was responding to, you seemed to be saying an infinite universe was falsified by *empirical* data, not just theoretical arguments--is that right?

Yes. The finite age is empirical evidence that our universe cannot be infinite in spatial extent UNLESS that's its initial condition, which I reject as a type of a singularity. AG

 

If you were making that claim, you should be ready to defend it even in the case where you grant for the sake of argument that there is no theoretical problem with the GR model of a universe that's infinite in size but began a finite time in the past (or at least agree to put aside all theoretical objections for the time being). Are you saying that even if you do put theoretical objections aside, you still think the empirical data is in conflict with the idea of an infinite universe that began a finite time in the past?

Yes. I don't think I ever made a theoretical argument; just an empirical one that the universe was never spatially infinite, now or in the past. Cosmologists agree that the universe gets smaller as we go backward in time. How could it get smaller as it returns to the BB, and yet still be infinite in spatial extent? Much more plausible is that it was never infinite in spatial extent. If GR assumes an infinite universe at T=0, on what principle was that assumed? Off hand it seems gratuitous. AG 

Jesse

[Brent Meeker]

On 1/25/2025 6:56 PM, Alan Grayson wrote:

Yes. I don't think I ever made a theoretical argument; just an empirical one that the universe was never spatially infinite, now or in the past.

There's no empirical argument for that because the universe looks flat, which is empirically consistent with it being spatially infinite.  Now you may object to that on some philosophical or metaphysical grounds and just say it is very, very big compared to the part we can see and hence looks flat (as the Earth looks flat locally).

Cosmologists agree that the universe gets smaller as we go backward in time. How could it get smaller as it returns to the BB, and yet still be infinite in spatial extent?

It could have been always spacially infinite.

Brent

[Jesse Mazer]

OK, but what are the specific empirical observations that you think conflict with the theory that it's infinite? If hypothetically it *was* infinite, but the speed of light was finite and it began a finite time in the past, would you expect in that case there WOULD be an upper limit to the distance we could observe (i.e. the observable universe would be finite, even it the unobserved part beyond that went forever), or that there WOULD NOT be any upper limit? (I would say the answer is obviously that there WOULD still be an upper limit because light can only travel a finite distance in a finite time, but I'm curious if you disagree)

 

Cosmologists agree that the universe gets smaller as we go backward in time.

They agree the observable universe gets smaller, and the distance between any pair of landmarks at rest relative to the cosmic background radiation (say, a pair of galaxies) gets smaller. But they do not make any claims about whether the *whole* universe gets smaller, since both of those things could be true even if the universe was infinite in size at all times.

Jesse

[Alan Grayson]

On Saturday, January 25, 2025 at 9:27:58 PM UTC-7 Brent Meeker wrote:

On 1/25/2025 6:56 PM, Alan Grayson wrote:

Yes. I don't think I ever made a theoretical argument; just an empirical one that the universe was never spatially infinite, now or in the past.

There's no empirical argument for that because the universe looks flat, which is empirically consistent with it being spatially infinite.  Now you may object to that on some philosophical or metaphysical grounds and just say it is very, very big compared to the part we can see and hence looks flat (as the Earth looks flat locally).

Cosmologists agree that the universe gets smaller as we go backward in time. How could it get smaller as it returns to the BB, and yet still be infinite in spatial extent?

It could have been always spacially infinite.

Sure, but I'm arguing that it couldn't BECOME spatially infinite in finite time, regardless of its rate of expansion. So if it is now spatially infinite, that must have been its initial condition. But I reject that conjecture on the grounds that it's a type of singularity, and we strrongly tend to reject theories which posits a singularity.  AG

[Alan Grayson]

All measurements which support the conclusion that the age of the universe is finite, contradict the conclusion that the universe is infinite in spatial extent. AG

 

If hypothetically it *was* infinite, but the speed of light was finite and it began a finite time in the past, would you expect in that case there WOULD be an upper limit to the distance we could observe (i.e. the observable universe would be finite, even it the unobserved part beyond that went forever), or that there WOULD NOT be any upper limit? (I would say the answer is obviously that there WOULD still be an upper limit because light can only travel a finite distance in a finite time, but I'm curious if you disagree)

The relavant question IMO is whether or not the universe can BECOME spatially infinite in finite time, and the answer is definitely negative, and assuming this is correct, the unobservable region must have an upper bound. OTOH, if it is now spatially infinite, meaning no upper bound on the unobservable region, that means it was an initial condition which I reject as positing a singularity at T=0. AG

 

Cosmologists agree that the universe gets smaller as we go backward in time.

They agree the observable universe gets smaller, and the distance between any pair of landmarks at rest relative to the cosmic background radiation (say, a pair of galaxies) gets smaller. But they do not make any claims about whether the *whole* universe gets smaller, since both of those things could be true even if the universe was infinite in size at all times.

I generally agree. But it's hard to imagine a universe which is spatially infinite and yet expanding, which would mean the average distance between galaxies is increasing. AG 

Jesse

[Alan Grayson]

On Saturday, January 25, 2025 at 10:27:55 PM UTC-7 Alan Grayson wrote:

On Saturday, January 25, 2025 at 9:27:58 PM UTC-7 Brent Meeker wrote:

On 1/25/2025 6:56 PM, Alan Grayson wrote:

Yes. I don't think I ever made a theoretical argument; just an empirical one that the universe was never spatially infinite, now or in the past.

There's no empirical argument for that because the universe looks flat, which is empirically consistent with it being spatially infinite.  Now you may object to that on some philosophical or metaphysical grounds and just say it is very, very big compared to the part we can see and hence looks flat (as the Earth looks flat locally).

I forgot to mention that despite what the Planck data suggests, namely flatness, I think the universe is so large, that we can't distinguish flat, from negative or positive curvature. But since the Cosmological Red Shift is approximately uniform in all directions, this implies a spherical shape with some distortion on its closed boundary. AG

[Alan Grayson]

The relevant question IMO is whether or not the universe can BECOME spatially infinite in finite time, and the answer is definitely negative, and assuming this is correct, the unobservable region must have an upper bound. OTOH, if it is now spatially infinite, meaning no upper bound on the unobservable region, that means it was an initial condition which I reject as positing a singularity at T=0. AG

 

Cosmologists agree that the universe gets smaller as we go backward in time.

They agree the observable universe gets smaller, and the distance between any pair of landmarks at rest relative to the cosmic background radiation (say, a pair of galaxies) gets smaller. But they do not make any claims about whether the *whole* universe gets smaller, since both of those things could be true even if the universe was infinite in size at all times.

I generally agree. But it's hard to imagine a universe which is spatially infinite and yet expanding, which would mean the average distance between galaxies is increasing. AG 

Consider this; If cosmologists thought the universe is now spatially infinite, why, when they reversed its clock to T=0, would they think of a singularity with infinite density? IMO, when they think of it getting smaller in earlier times, they really do mean smaller. AG 

Jesse

[John Clark]

On Sat, Jan 25, 2025 at 8:57 PM Jesse Mazer <laser...@gmail.com> wrote:

> In the math of general relativity the universe could have been spatially infinite at every finite time after the Big Bang,

Yes.

 

> and the Big Bang itself is treated as a singularity so it need not have a well-defined size.

True, but I would go even further and say the very idea of the "size" of the singularity has no meaning because to measure size you need a metric and at the singularity all our equations break down. So it doesn't make sense to talk about the "size" of the singularity, but it does make sense to talk about size at the first instant AFTER the Big Bang singularity. So if the universe started out infinite then it's still infinite, and if it started out finite then it's still finite.

In fact I would argue that an infinite universe has simpler initial conditions than a finite one because it doesn't have to specify edges or boundaries. That's true even in classical physics, it's easy to calculate the exact electrical field around an infinitely long electrically charged rod, I learned how to do that in high school, but calculating the same thing around the rod that was only finitely long was far more difficult, I only learned how to do that in my second college physics course. And Fred Tipler used General Relativity to show that an infinitely long extremely dense rod that was rotating at close to the speed of light would produce a closed timelike curve (a.k.a. a time machine) but nobody has been able to figure out if General Relativity says the same thing would happen if the rod was only finitely long because the mathematics becomes too difficult.  

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

ctb

[Alan Grayson]

Since a singularity is undefined, no one except Jesse refers explicitly to its size. Plots by cosmologists describing the evolution of the universe always show it getting smaller as T approaches zero, the singularity. So that's what they believe, not having any positive size at the time of the BB. BTW, FWIW, Tegmark believes that a universe which is infinte in space and time, can create multiple, maybe infinite copies of everything, so it is consistent with, and indirectly supports the MWI. AG by

[Jesse Mazer]

Because that's what's predicted in GR models of an expanding universe (the FLRW metric at https://en.wikipedia.org/wiki/Friedmann–Lemaître–Robertson–Walker_metric ), which include "closed" universes of finite size and "open" universes of infinite size (which can have either 'flat' or 'hyperbolic' spatial geometry). In both cases, the distance between any two particles of the matter filling space in the model would approach 0 as time approaches T=0.

Jesse

 

[Alan Grayson]

So a closed finite universe is one of the possible solutions of the FLRW metric, which doesn't contradict GR, and is consistent with a universe that is actually getting smaller in volume as we go backward in time. This is my prediction, as well as the graphical models used by cosmologists, which must mean what think is the physical reality of the universe. It gets smaller AND the average distance between galaxies goes to zero while the density diverges to infinity. AG 

 

[Jesse Mazer]

The curvature of space in the real universe is measurable, so far it seems to be indistinguishable from flat, and the flat FLRW model is infinite, though given error bars on the measurement that means a very small positive curvature is possible, which would give a closed universe (but one much larger than the observable universe); there is no empirical/observational evidence I know of that is exclusively compatible with positive curvature as opposed to flat or negative curvature. And what specific "graphical models used by cosmologists" are you talking about? In a book or article written by cosmologists you will typically find graphical illustrations of multiple possible curvatures, as on p. 3 of Ned Wright's cosmology tutorial at https://www.astro.ucla.edu/~wright/cosmo_03.htm

Jesse

[Alan Grayson]

I agree; measurements by the Planck spacecraft strongly suggest a flat universe, but don't rule out positive or negatively curved universes. If I can find the type of graph I earlier referred to, I will post it. It's like a wide cylinder, converging to a point at the time of the BB. It's quite common and you'll recognize it when you see it. AG 

[Alan Grayson]

OTOH, the approximate uniformity of the Cosmological Red Shift suggests a spherical shaped universe. AG

[Alan Grayson]

If you scroll down on this link, you'll see the plot I have been referring to.  https://bigthink.com/starts-with-a-bang/time-run-backwards/  AG

[Jesse Mazer]

Those kinds of plots can be used to represent both open and closed universes, see the attached images showing illustrations from the physicist Roger Penrose's book The Emperor's New Mind, where he presents plots for positive curvature, flat curvature, and negative curvature (in the case of negative curvature the circular cross-sections are supposed to be a special kind of diagram which compresses an infinite hyperbolic geometry onto a disc where the size of all the shapes gets more and more compressed closer to the edge, see https://www.reed.edu/math-stats/wieting/essays/CapturingInfinity.pdf for more on this; in the case of flat curvature, the cross sections are just meant to be finite pieces of an infinite plane)

 

[Alan Grayson]

 They all seem to show the BB as a point. Anyway, you wanted to see what I was referring to, so I delivered. AG

[Cosmin Visan]

Universe doesn't exist. "Universe" is just an idea in consciousness. Ideas are possible only if their proper context is met. For example, to learn 12th grade calculus, you need to know 1st grade aritmetics.

On Saturday, 25 January 2025 at 12:11:29 UTC+2 Alan Grayson wrote:

IIUC, it's based on the assumption that the universe is infinite in spatial and temporal extent, but this is mistaken. Our universe, by which I mean our bubble, is finite. We know that by applying basic logic. First, since nothing can become infinite via a finite process, which is implied by the finite age of the universe. So if the universe is spatially infinite, that must be its initial condition when it came into being with the Big Bang. But that would require adding a singularity of sorts to the usual concept of the BB; namely, that at its inception, it became infinite in spatial extent instantaneously. This hypothesis must be rejected for the same reason we regard theories with infinities as incorrect when they make such predictions. AG

[John Clark]

On Sun, Jan 26, 2025 at 5:52 PM Jesse Mazer <laser...@gmail.com> wrote:

> Those kinds of plots can be used to represent both open and closed universes, see the attached images showing illustrations from the physicist Roger Penrose's book The Emperor's New Mind, where he presents plots for positive curvature, flat curvature, and negative curvature (in the case of negative curvature the circular cross-sections are supposed to be a special kind of diagram which compresses an infinite hyperbolic geometry onto a disc where the size of all the shapes gets more and more compressed closer to the edge,

True. Penrose diagrams are able to depict infinity because they use hyperbolic geometry in such a way that angles are preserved, at least locally, but not distance. They are very useful but they can give the misleading impression that the spot labeled "Big Bang" is a mathematical point when it is not; instead it indicates a place where our understanding of distance, and therefore of size, breaks down. 

Also, because it needs to be printed on a 2-D piece of paper or computer screen and time needs to be one of those dimensions, only one dimension of space can be depicted, not three.  

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

  rwe

[Alan Grayson]

But all the plots show the universe getting progressively smaller as T approaches zero, so IMO that implies something about its size at the singularity. AG 

  rwe