Is the Universe infinite?

[Carrock]

11 hours ago, Mordred said:

 

I'm really not sure I understand your argument here.

What is wrong with the possibility of an infinite number of finite "Observable portions". You can have an infinite universe where each observer has its own Observable finite portion. Quite frankly in an infinite universe this statement must be true lol. Seeing as how observable is simply  the radius of shared causality

 

A problem with Prof. Wright's claim

Quote

The Universe was not concentrated into a point at the time of the Big Bang. But the observable Universe was concentrated into a point.

is that he doesn't mention what assumptions he's using.

But it certainly seems he assumes a point source for each observable universe and that each point expands into a finite observable universe currently around 10^21 light years in volume - rather large for each observer. You don't get significant overlap as each point expands a similar amount.

A strongly implied claim is that at the time of the Big Bang sufficient space existed to contain two or more points.

A volume large enough to contain two points is also large enough to contain an uncountable infinity of points.

The problem is that if each point expands to a finite volume, you have an uncountable infinity of finite volumes. As I've said before in this thread, that would require every zero volume point in the (spatially finite or infinite) universe to enclose a finite volume of space.

Most physicists regard this prediction as not valid, which is why they describe the universe as originating from a singularity.

 

4 hours ago, Dan B. said:

Please look at the following:

http://www.astro.ucla.edu/~wright/infpoint.html

 

As there are galaxies all over the Universe, can we assume that there was many (or infinite) spots (at the size of our milky way)  which represents other early observable universes?

Strange has addressed this.

 

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But the observable Universe was concentrated into a point.

in http://www.astro.ucla.edu/~wright/infpoint.html is rubbish,. That is presumably where you got the above strange idea. I suggest you try to forget anything you think you learned there.

[Mordred]

So let me get this straight. You don't agree that each sphere of causality under speed of information exchange via GR leads to each "Observable portion"(which is a sphere of causality) would concentrate to a finite pointlike portion under the FLRW metric, which is a simplification of GR when you run the time/expansion backwards?

ie turning back the clock and having the universe contract. In reverse to its expansion history.

Edited September 9, 2017 by Mordred

[Carrock]

11 minutes ago, Mordred said:

So let me get this straight. You don't agree that each sphere of causality under speed of information exchange via GR leads to each "Observable portion"(which is a sphere of causality) would concentrate to a finite pointlike portion under the FLRW metric, which is a simplification of GR when you run the time/expansion backwards?

ie turning back the clock and having the universe contract. In reverse to its expansion history.

You'd have to define 'a finite pointlike portion' before I could answer that.

[Mordred]

Compton wavelength is typically the descriptive that applies to pointlike field excitations. Which corresponds to the Planck length as being the minimal measurable volume via the QFT treatments of Observable action. In effect an IR cutoff by analogy to Feyman path integrals. (by analogy which conforms to the Wheeler-Dewitt treatments) just a side note there

 

Edited September 9, 2017 by Mordred

[beecee]

2 hours ago, Carrock said:

A problem with Prof. Wright's claim

is that he doesn't mention what assumptions he's using.

I fail to see any problem with the good professor's claim. But certainly, if you believe there is, then why not E-mail him and show him the error of his ways?

Quote

 

 You don't get significant overlap as each point expands a similar amount.

A strongly implied claim is that at the time of the Big Bang sufficient space existed to contain two or more points.

A volume large enough to contain two points is also large enough to contain an uncountable infinity of points.

 

I have understood for a long while that most physicists do not believe any physical singularity exists: at least those pertaining to BHs and I don't see why there would be any different opinion with the BB singularity. In essence singularities need not be infinite, but may lead to infinite quantities. And of course in the instances that I mention, singularities are simply where our models break down or do not apply.

Again, as I have mentioned before, I see the problem existing with trying to picture or assign properties to infinity...But then again, I'm only a poor old amateur at this game.  

Edited September 9, 2017 by beecee

[Mordred]

This is the lightcone diagram for the FLRW ds^2 worldlines. The image is from Lineweaver and Davies. http://arxiv.org/pdf/astro-ph/0402278v1.pdf[/url

This defines your causality to Observer worldlines. This is the basis behind Wrights website. Though under different parameters etc.

The paper is a highly recommended read for numerous BB misconceptions. The calculator in my signature conforms to the lightcones produced via the above paper as its basis to programming. It uses the stretch value described in the above article

 

Edited September 9, 2017 by Mordred

[beecee]

30 minutes ago, Mordred said:

This is the lightcone diagram for the FLRW ds^2 worldlines. The image is from Lineweaver and Davies. http://arxiv.org/pdf/astro-ph/0402278v1.pdf[/url

As an aside, the UNSW was the one my Son attended doing IT, and just a hop, skip and a jump from where I live in Maroubra. I have also briefly met Tamara, (although I doubt that she would remember ) along with an Astronomer named  Geraint Lewis who Professor Tamara mentions in her paper. It was during a Lunar eclipse and a Lunar eclipse party the ABC (Australian Broadcasting Commision) and their science department put on at that time.

Edited September 9, 2017 by beecee

[Carrock]

12 hours ago, beecee said:

I fail to see any problem with the good professor's claim. But certainly, if you believe there is, then why not E-mail him and show him the error of his ways?

I was planning to email him. Then I noticed the age of the paper. It's not believable that no one has raised this issue with him in nineteen years. One more email won't make any difference.

[beecee]

9 hours ago, Carrock said:

I was planning to email him. Then I noticed the age of the paper. It's not believable that no one has raised this issue with him in nineteen years. One more email won't make any difference.

Unless of course the problem you envisage does not exist.  

[Dan B.]

On 9.9.2017 at 5:43 AM, Mordred said:

 

I'm really not sure I understand your argument here.

What is wrong with the possibility of an infinite number of finite "Observable portions". You can have an infinite universe where each observer has its own Observable finite portion. Quite frankly in an infinite universe this statement must be true lol. Seeing as how observable is simply  the radius of shared causality

 

After all of this discussion, it is clear that our universe is bigger than our observable Universe, but how big?

Is it Infinite Universe or Infinite number of finite observable Universes?

What kind of data is needed in order to get a final confirmation for the above question?

How can we explain the creation of each kind of Universe? 

Edited September 18, 2017 by Dan B.

[beecee]

2 hours ago, Dan B. said:

After all of this discussion, it is clear that our universe is bigger than our observable Universe, but how big?

Data from the WMAP probe showed the universe to be flat within very small error bars. That means the universe is infinite (ignoring non standard geometries such as torus shape)   Though small though, those error bars still exist, and as such perhaps the universe maybe closed with those small error bars actually being the arc of a much larger curvature. At this time the finite or infinite nature of the universe is not really known.

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Is it Infinite Universe or Infinite number of finite observable Universes?

If the universe is infinite, then there are an infinite number of observable universes. Please correct me if I'm mistaken, but your following question  

Quote

How can we explain the creation of each kind of Universe? 

seems to suggest you are in error re what you believe an "observable" universe is. The observable universe is simply that spherical region, that exists around an observer, and governed by the light that has had time to reach the observer. So in effect an observer situated near the horizon of our observable universe, would see us in one direction, and a region of equal distant in the other direction, that is not part of our observable universe. But obviously still a part of the universe as a whole.

 

Quote

 

What kind of data is needed in order to get a final confirmation for the above question?

How can we explain the creation of each kind of Universe? 

 

Perhaps research into the relatively newly discovered gravitational waves? I might add that in general, when cosmologists speak of the universe, they generally mean the observable universe, although the observable universe does in no way mean or suggest that the boundary of the observable universe is a boundary of the whole universe.

Edited September 18, 2017 by beecee

[Strange]

2 hours ago, Dan B. said:

After all of this discussion, it is clear that our universe is bigger than our observable Universe, but how big?

We don't know.

Quote

Is it Infinite Universe or Infinite number of finite observable Universes?

This is a false dichotomy. Even if the universe is finite, there could be an infinite number of observable universes (as long as space isn't quantised). 

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What kind of data is needed in order to get a final confirmation for the above question?

As the universe beyond our universe is not observable, I'm not sure the the question can ever be answered.

Quote

How can we explain the creation of each kind of Universe? 

Maybe there was no "creation". Maybe the universe has always existed.

[Dan B.]

6 hours ago, beecee said:

Data from the WMAP probe showed the universe to be flat within very small error bars. That means the universe is infinite (ignoring non standard geometries such as torus shape)

If the WMAP data means (within very small error bars) that the Universe is Infinite - 

Why do we still claim that we don't know the size of the Universe?

6 hours ago, Strange said:

Even if the universe is finite, there could be an infinite number of observable universes (as long as space isn't quantised). 

Even if the Universe is finite - do we have any idea what is it's minimal size?

What do you mean by "(space isn't quantised)".

How this data could affect the size of the Universe?

[beecee]

2 minutes ago, Dan B. said:

If the WMAP data means (within very small error bars) that the Universe is Infinite - 

Why do we still claim that we don't know the size of the Universe?

 

For the reasons already stated:(1) Perhaps the observed flatness could be just the arc of a much larger curvature...(2) We only observe the observable universe because that damn stuff  we call light has a finite speed, (3) the possibility still exists that it maybe torus shape or some other exotic geometry,  

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Even if the Universe is finite - do we have any idea what is it's minimal size?

Big!!!

Quote

What do you mean by "(space isn't quantised)".

It isn't made up of discreet units, rather according to GR, smooth and continuous, but to marry GR with Quantum physics, we will need a QGT...quantum gravity theory.

[Strange]

3 hours ago, Dan B. said:

Even if the Universe is finite - do we have any idea what is it's minimal size?

According to this, the diameter is at least 150 times larger than we can observe

http://scienceblogs.com/startswithabang/2012/07/18/how-big-is-the-entire-universe/

3 hours ago, Dan B. said:

How this data could affect the size of the Universe?

it doesn't have any effect on the size. 

It does change the answer to your question "Infinite number of finite observable Universes?" (which doesn't seem a very useful question)

[Dan B.]

10 hours ago, Strange said:

According to this, the diameter is at least 150 times larger than we can observe

http://scienceblogs.com/startswithabang/2012/07/18/how-big-is-the-entire-universe/

Thanks

So, as the Observable Universe is about 100 BLY then the minimal estimated size of our Universe is:

15 trillion Light year.

Is it correct?

12 hours ago, beecee said:

.(2) We only observe the observable universe because that damn stuff  we call light has a finite speed,

Sure.

However, can you please elaborate if the speed of light has any affect on the WMAP data as stated:

19 hours ago, beecee said:

Data from the WMAP probe showed the universe to be flat within very small error bars.

 

Edited September 19, 2017 by Dan B.

[Strange]

1 hour ago, Dan B. said:

Thanks

So, as the Observable Universe is about 100 BLY then the minimal estimated size of our Universe is:

15 trillion Light year.

Is it correct?

Maybe you should read the article:

"And what they teach us is that not only is the Universe consistent with being flat, it’s really, really, REALLY flat! If the Universe does curve back and close on itself, its radius of curvature is at least 150 times as large as the part that’s observable to us! Meaning that — even without speculative physics like cosmic inflation — we know that the entire Universe extends for at least 14 trillion light years in diameter, including the part that’s unobservable to us today."

 

[MigL]

There seems to be confusion between the 'observable universe' and 'universal domains'.

A domain is a volume of the universe, originally in causal contact, for which quantum fluctuations of the vacuum energy triggered inflation, and subsequent symmetry breaks, at different 'times' and in different ways. These domains would be separate from each other and may have different physical laws. IIRC they would be characterized by magnetic monopole production at the domain boundaries .
And they are purely speculative as they would lie outside our observable universe.

The observable universe, as Mordred has pointed out, is a causality sphere, and is different for each observer. It is a mathematical construct, defined by the distance light/information could have travelled to reach the observer since the Big Bang. In effect, the person standing a meter to your left, has a different observable universe than you; His extends a meter farther to the left, and is a meter shorter to the right.
So when Strange says there could be an infinite number of observable universes in a finite universe, if space isn't quantized, that means the universe can be infinitely subdivided into different observable portions, as each will always be different.

[Strange]

22 minutes ago, MigL said:

So when Strange says there could be an infinite number of observable universes in a finite universe, if space isn't quantized, that means the universe can be infinitely subdivided into different observable portions, as each will always be different.

Thanks for putting that so succinctly. I was going to say more, but I thought it might end up getting into different types of infinity, the continuum hypothesis and so on!

[Dan B.]

1 hour ago, Strange said:

"And what they teach us is that not only is the Universe consistent with being flat, it’s really, really, REALLY flat! If the Universe does curve back and close on itself, its radius of curvature is at least 150 times as large as the part that’s observable to us! Meaning that — even without speculative physics like cosmic inflation — we know that the entire Universe extends for at least 14 trillion light years in diameter, including the part that’s unobservable to us today."

 

Thanks

So now as we know that the Universe extends for at least 14 trillion light years in diameter -

How can we explain a creation of that Universe size in only 13.8 BY? How the BBT fits to this size of Universe?

[Strange]

1 minute ago, Dan B. said:

So now as we know that the Universe extends for at least 14 trillion light years in diameter -

How can we explain a creation of that Universe size in only 13.8 BY? How the BBT fits to this size of Universe?

There is no evidence (or explanation) for the "creation" of the universe.

If you mean, "how could the universe grow to be that big in that time" then I'm not sure what the problem is.

Imagine that, at some point, the observable universe was 1mm across (and is now 96 B light-years across) then at that time, the whole universe would have been 150 times larger (150mm) and would now have grown to 14 trillion light years.

[beecee]

4 hours ago, Dan B. said:

However, can you please elaborate if the speed of light has any affect on the WMAP data as stated:

My understanding of the WMAP experiment, was that it measured the temperature of the CMBR, and mapped the very tiny variations that existed, or the observed seeds for galactic formation.

[Dan B.]

On 19.9.2017 at 11:26 PM, Strange said:

If you mean, "how could the universe grow to be that big in that time" then I'm not sure what the problem is.

Yes, that is my intention.

 

On 19.9.2017 at 11:26 PM, Strange said:

Imagine that, at some point, the observable universe was 1mm across (and is now 96 B light-years across) then at that time, the whole universe would have been 150 times larger (150mm) and would now have grown to 14 trillion light years.

I have thought about this explanation for the last two days.

If I understand it correctly - even if the Universe is 14 Trillion LY, it must had been grown from the same Big Bang.

However, I couldn't understand the grow process from 150 mm to this size.

I had the impression that the maximal size of the Universe is limited by its age, the maximal speed of mass, speed of light, expansion and  some other factors from the BBT.

So, is there any technical limit for the Universe maximal size from the BB (in 13.8 BY)? Or can we just assume that as we increase the 150 mm we can get bigger and bigger Universe (For example - from 300 mm the Universe can grow to 28 trillion Light year and so on - without any limit).

 

 

Edited September 21, 2017 by Dan B.

[Strange]

6 minutes ago, Dan B. said:

I had the impression that the maximal size of the Universe is limited by its age, the maximal speed of mass (Let's assume - speed of light), expansion and  some other factors from the BBT.

No. That only applies to the observable universe.

If the whole universe is 150 times (or 1 million times) larger than the observable universe then it always been that much larger. (It may be that the expansion was not completely uniform so perhaps the ratios have not always been constant.)

Quote

So, is there any technical limit for the Universe maximal size from the BB (in 13.8 BY)? Or can we just assume that as we increase the 150 mm we can get bigger and bigger Universe (For example - from 300 MM the Universe can grow to 28 trillion Light year and so on - without any limit).

There is, as far as we know, no upper limit to how big the universe could be. It could be infinite.

13 minutes ago, Dan B. said:

it must had been grown from the same Big Bang.

It sounds like you are thinking of "the Big Bang" as a thing or an event.

It is a process: the universe is getting cooler and less dense over time.

[Dan B.]

 

On 21.9.2017 at 10:38 AM, Strange said:

It sounds like you are thinking of "the Big Bang" as a thing or an event.

It is a process: the universe is getting cooler and less dense over time.

On 21.9.2017 at 10:38 AM, Strange said:

No. That only applies to the observable universe

So, the observable Universe is an outcome of the BBT process.

Hence, if I understand it correctly, as long as our Universe is as big as the Observable Universe, we have a perfect fit.

However, based on the last valid data, the size of our real Universe is much bigger than the observable Universe. 

On 21.9.2017 at 10:38 AM, Strange said:

If the whole universe is 150 times (or 1 million times) larger than the observable universe then it always been that much larger. (It may be that the expansion was not completely uniform so perhaps the ratios have not always been constant.)

Why do you say "if"?

Is there any problem with this new data?

Somehow we need to give an explanation for a Universe which its minimal size is 150 times larger than the Observable Universe and its maximal size could be even infinite.

What do you mean by - "It always been that much larger"

If there was something before 13.8 BY ago, than why we do not start the BBT from that moment (even if it was always there)?

In any case, if I understand it correctly, the Impact of the BBT is up to a 96 BLY sphere.

So how the BBT set any impact on a space sphere at a distance of 10 trillion LY away from us?

Sorry that I ask too many questions.

I wonder if I'm the only person which asks those questions.