Is the Universe infinite?

[Strange]

26 minutes ago, Dan B. said:

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

The whole universe is (as far as we know) expanding in the way described by the Big Bang model.

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Why do you say "if"?

Because it might be 150 times larger or it might be 1 million times bigger or it might be infinite. So150 was just an example.

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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.

That explanation is the Big Bang model. I'm not sure what else you are looking for.

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

The whole universe has always been bigger than the observable universe by the same amount. 

So, for example, if the whole universe is now 150 times larger than our observable universe then it has always been 150 times larger.

And, for example, if the whole universe is now 1 million times larger than our observable universe then it has always been 1 million times larger.

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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)?

Because we don't know what was there before then. 

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

No. As far as we know, the whole universe is described by the same Big Bang model. There is an underlying assumption (the Cosmological Principle) that our observable universe is not special; that the rest of the universe is largely the same as what we see.

 

[Mordred]

1 hour ago, Strange said:

 

No. As far as we know, the whole universe is described by the same Big Bang model. There is an underlying assumption (the Cosmological Principle) that our observable universe is not special; that the rest of the universe is largely the same as what we see.

 

We can avoid some assumption of this beyond our Observable portion by looking for overlapping causality regions. So far we see no evidence that this isn't the case.

[Strange]

2 hours ago, Dan B. said:

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

Just to be clear, the thing I was saying only applied to the observable universe was this comment of yours: "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."

So the size of the observable universe is limited by the speed of light and the time from the Big Bang, because that defines how far we can see.

Note that there is no speed of light limit for matter in this case. We can see galaxies (i.e. they are in our observable universe) which are receding at more than the speed of light.

[Dubbelosix]

There seems to be a ''consensus'' that in honest-speaking terms, we only know the size of a universe up to its observable horizon. I have heard a few astrophysicists claim the universe may be many times more bigger than what we can observe.... but took the statement with a pinch of salt, until I heard Susskind say pretty much the same thing, that cosmologists are thinking the universe is many many times the size it is, outside the observable horizon.

 

Which is interesting, because this really places age problems on a universe, (without inflation) which was designed to make a universe... inconceivably large in just a very small time frame. Hows the horizon problem doing? Do scientists think inflation answers this as well?

Just took a read myself, yeah, they use inflation to answer this as well. Though, wiki really goes over the top on the homogeneity thing, that is a separate thing, though related. The horizon problem is that when you add up the time it takes for space to expand, the universe is still too large when you reconcile it's diameter. So inflation again answers it when you consider it became exponentially large in such a small time frame.

[Strange]

3 minutes ago, Dubbelosix said:

Which is interesting, because this really places age problems on a universe, (without inflation) which was designed to make a universe... inconceivably large in just a very small time frame.

Not really, no.

3 minutes ago, Dubbelosix said:

Hows the horizon problem doing? Do scientists think inflation answers this as well?

I think that is still the favoured explanation. But many are not happy with it (including Steinhardt, who was one of those who came up with it in the first place).

[Dubbelosix]

I'm not happy with it either. 

 

And yes, without inflation it would posit problems. This is my opinion anyway - that is not to say, we cannot find alternative models, but they need to be good. 

I am not happy with it, for much the same reasons as Steinhardt. I have never been a fan of the multiverse. 

[Mordred]

I always prefer the Higgs SO(10) proposal to inflation.

The aspects I like about it is that inflation can be regarded as thermodynamic phase change without introduction of quasi particles such as the inflaton and curvaton.

Its still viable according to Encyclopdia inflationaris 

Here is the arxiv with what it has tested out of the 70+ (at one time) viable inflationary models.

They regularly updated the article

https://www.google.ca/url?sa=t&source=web&rct=j&url=https://arxiv.org/abs/1303.3787&ved=0ahUKEwi0pLn3-LvWAhUS4GMKHfE8BxcQFggdMAA&usg=AFQjCNHCJmYI-_ntfQlZwIplFXA5w2JU_A

 

Sorry on messy link on phone atm, it has all the pertinant requirements on the horizon problem etc in terms of required e-folds

Edited September 23, 2017 by Mordred

[Dan B.]

On 23.9.2017 at 6:36 PM, Strange said:

That explanation is the Big Bang model. I'm not sure what else you are looking for.

With regards the Black body radiation:

https://ned.ipac.caltech.edu/level5/Sept02/Kinney/Kinney3.html

Recombination and the formation of the CMB"

The epoch at which atoms form, when the universe was at an age of 300,000 years and a temperature of around 3000 K is somewhat oxymoronically referred to as "recombination", despite the fact that electrons and nuclei had never before "combined" into atoms. The physics is simple: at a temperature of greater than about 3000 K, the universe consisted of an ionized plasma of mostly protons, electrons, and photons, which a few helium nuclei and a tiny trace of Lithium. The important characteristic of this plasma is that it was opaque, or more precisely the mean free path of a photon was a great deal smaller than the horizon size of the universe. As the universe cooled and expanded, the plasma "recombined" into neutral atoms, first the helium, then a little later the hydrogen."

Would you kindly explain:

How the black body radiation which is a direct product of: "The epoch at which atoms form, when the universe was at an age of 300,000 years and a temperature of around 3000 K "  could technically gets to a space sphere at a distance of 10 trillion LY in only 13.5 BLY?

 

 

 

[beecee]

2 hours ago, Dan B. said:

With regards the Black body radiation:

https://ned.ipac.caltech.edu/level5/Sept02/Kinney/Kinney3.html

Recombination and the formation of the CMB"

The epoch at which atoms form, when the universe was at an age of 300,000 years and a temperature of around 3000 K is somewhat oxymoronically referred to as "recombination", despite the fact that electrons and nuclei had never before "combined" into atoms. The physics is simple: at a temperature of greater than about 3000 K, the universe consisted of an ionized plasma of mostly protons, electrons, and photons, which a few helium nuclei and a tiny trace of Lithium. The important characteristic of this plasma is that it was opaque, or more precisely the mean free path of a photon was a great deal smaller than the horizon size of the universe. As the universe cooled and expanded, the plasma "recombined" into neutral atoms, first the helium, then a little later the hydrogen."

Would you kindly explain:

How the black body radiation which is a direct product of: "The epoch at which atoms form, when the universe was at an age of 300,000 years and a temperature of around 3000 K "  could technically gets to a space sphere at a distance of 10 trillion LY in only 13.5 BLY?

Spacetime was expanding, plus inflation.  Is this what you are after?   And it's 13.83 billion years, not light years.         

Edited September 26, 2017 by beecee

[Strange]

3 hours ago, Dan B. said:

How the black body radiation which is a direct product of: "The epoch at which atoms form, when the universe was at an age of 300,000 years and a temperature of around 3000 K "  could technically gets to a space sphere at a distance of 10 trillion LY in only 13.5 BLY?

I don't really know what you are asking. There isn't any connection between the CMB and the size of the universe.

The CMB we see comes from about 13.5 billion light years away because that is how far light has travelled in that time.

The CMB that someone 10 trillion light years away would have come from about 13.5 billion light years away from them, because that is how far light has travelled in that time.

 

[Dan B.]

sorry, but I really can't understand how the BBT works for a 14 trillion LY Universe.

As long as we have discussed about the observable Universe (let's say 96 BLY) - the BBT process was perfectly clear.

Actually, we call it observable - but in reality we can't see more than about 13 BLY at any direction.

Therefore, the maximal Universe which we can see is only 26 BLY (Let's call it visible Universe). 

Hence, I thought that the Observable Universe is the Maximal universe which could be developed by the BBT process, but we can only see just part of it (visible Universe). Is it correct?

In any case, now we discuss about a 14 trillion LY Universe. (Let's call it real Universe)

Is there any explanation for the real Universe process starting from t=0 (13.8 BY) ago?  

7 hours ago, Strange said:

The CMB we see comes from about 13.5 billion light years away because that is how far light has travelled in that time.

Yes, I fully understand this explanation.

7 hours ago, Strange said:

The CMB that someone 10 trillion light years away would have come from about 13.5 billion light years away from them, because that is how far light has travelled in that time.

I couldn't understand this explanation.

How a space sphere at a distance of 10 Trillion Light Year away could technically gets the same CMB from the same source as we do?

If they could get a CMB from a maximal distance of  "about 13.5 billion light years away from them," then by definition our CMB and their CMB must get from different sources.

So, could it be that they have a different Big Bang?

If so, how many bangs are needed for the whole real Universe?

However, diffrent BB meand different CMB.

So how a real Universe (14 trillion LY) had been developed out of a single BBT process which took place 13.8 BY ago?

any web site?

 

 

 

[Strange]

1 hour ago, Dan B. said:

Therefore, the maximal Universe which we can see is only 26 BLY (Let's call it visible Universe). 

Why call it the visible universe when it is already called the observable universe?

The size (now) is 96 Bly. 13 billion years is the time it took light to get here. 

1 hour ago, Dan B. said:

Hence, I thought that the Observable Universe is the Maximal universe which could be developed by the BBT process, but we can only see just part of it (visible Universe). Is it correct?

No. The observable universe is just the part of the universe that is visible. To us. Because of light travel time. 

1 hour ago, Dan B. said:

Is there any explanation for the real Universe process starting from t=0 (13.8 BY) ago?  

There is no explanation or evidence for anything starting at t=0. 

However, whatever explanation applies to the observable universe also applies to the rest of the universe. 

1 hour ago, Dan B. said:

If they could get a CMB from a maximal distance of  "about 13.5 billion light years away from them," then by definition our CMB and their CMB must get from different sources.

That's what I said. There is no single source for the CMB, it was created everywhere. So we see it coming from a sphere all around us and so does everyone else in the universe. 

1 hour ago, Dan B. said:

So, could it be that they have a different Big Bang?

No. 

1 hour ago, Dan B. said:

So how a real Universe (14 trillion LY) had been developed out of a single BBT process which took place 13.8 BY ago?

It is not a process that took place 13.8 by ago. It is a process that is happening now. The whole universe is expanding and cooling. And has been for 13.8 by.

Why does the fact that there are parts of the universe we can't see cause you such a problem?

 

[zapatos]

10 minutes ago, Strange said:

 not a process that took place 13.8 by ago. It is a process that is happening now. The whole universe is expanding and cooling. And has been for 13.8 by.

Why does the fact that there are parts of the universe we can't see cause you such a problem?

 

I think the problem is that the BBT seems to only apply to what was a very small space 13.8 bya, and that therefore 13.8 billion years does not seem like enough time for that very small space to grow into something 14 trillion light years in diameter.

Edited September 26, 2017 by zapatos

[Strange]

7 minutes ago, zapatos said:

I think the problem is that the BBT seems to only apply to what was a very small space 13.8 bya, and that therefore 13.8 billion years does not seem like enough time for that very small space to grow into something 14 trillion light years in diameter.

Yes. I have tried to explain that the whole universe was larger than the little bit that grew into the observable universe. But it doesn't seem to have worked.

1 hour ago, Dan B. said:

any web site?

This seems to answer lots of common questions: https://www.cfa.harvard.edu/seuforum/faq.htm

This is a good description of the source of the CMB (with a nice "surface of last screaming" analogy): https://ned.ipac.caltech.edu/level5/March03/Lineweaver/Lineweaver7_2.html

 

1 hour ago, Dan B. said:

sorry, but I really can't understand how the BBT works for a 14 trillion LY Universe.

The bit inside the blue sphere is our observable universe. The bit outside is the rest of the universe (or part of it). Everything (both inside the blue and outside) is expanding and cooling.

[MigL]

If I may...

About 13.5 billion yrs ago the temperature of the universe dropped below the ionization energy for simple atoms of H and He.
This temperature was slightly above 3000 deg. The current temperature of the background black body radiation ( CMB ) is 2.7 deg ( to one part in 10 000 ). Using simple gas laws we can say that the universe has expanded over 1000 times in volume since light became free to travel the universe.
Since volume expands at the cube of the radius, in 13,5 Billion years, the radius has increased by 10, so that what would have been 13.5 billion light years away if there was no expansion is, in effect, much farther away now ( approx. 3 times ).

This applies to our observable universe.
But we can infer that the same happened to adjacent observable universes.
And the Big Bang, although sometimes used ( wrongly, by myself included ) to describe an original event, is actually a continuous process, that did not happen in one place, or at one time.
 

[Antwerp]

I think Kant said something about it being a stupid question.

[Eise]

10 hours ago, Antwerp said:

I think Kant said something about it being a stupid question.

That is a rather perverted way of saying that.

Kant tried to show with his cosmological antinomies that if you try to answer questions about the reality we live in based on reason alone ("pure reason") you come to contradicting conclusions. See here (search in the page for 'FIRST CONFLICT OF THE TRANSCENDENTAL IDEAS'). It is one of his arguments against metaphysics as science. Therefore the title of his book: Critique of pure reason.

If our reasoning about the (in)finity of the universe is based on empirical data, it is not metaphysics anymore, but physics. And then it is not a stupid question anymore, but an empirical one.

[Dan B.]

On 26.9.2017 at 7:10 PM, Strange said:

On 26.9.2017 at 5:41 PM, Dan B. said:

So, could it be that they have a different Big Bang?

No

 

On 26.9.2017 at 9:15 PM, MigL said:

And the Big Bang, although sometimes used ( wrongly, by myself included ) to describe an original event, is actually a continuous process, that did not happen in one place, or at one time.

I still don't know if the whole 14 Trillion Universe is an outcome of just one bang or several bangs process.

In any case, let's take two space spheres at our current real Universe.

1. If the current distance between those two spheres is 10 Trillion LY, what might be the distance between those two spots 13.5 Years ago?

If it is still several trillions LY:

2. How could any kind of radiation cross this distance in a 13.5 BY (even if we add the expansion and any other requested feature)?

3. How a single bang or even several bangs could have the same affect on those two different space spheres?  I really can't understand this major issue.

4. With Regards to the black body radiation -

Based on our understanding the current Universe has no ability to generate Black body radiation.  

This black body radiation is a product of a single event which took place at a specific time frame (300,000 year old). No less, no more.

Therefore, when the Universe was 0.2 BY or even 0.4 BY - it couldn't generate a black body radiation. We get today some sort of an echo from age of 0.3 BY.

However, how long this echo could stay with us? How could it still be there in a Universe size of  14 Trillion LY or even infinite? There is no expedite date for this echo?

 

 

 

 

Edited September 28, 2017 by Dan B.

[Strange]

10 minutes ago, Dan B. said:

I still don't know if the whole 14 Trillion Universe is an outcome of just one bang or several bangs process.

One.

If there were separate universe created by separate Big Bang "events" (if there is any such thing) then they would be completely isolated from one another.

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In any case, let's take two space spheres at our current real Universe.1. If the current distance between those two spheres is 10 Trillion LY, what might be the distance between those two spots 13.5 Years ago?

Let's say at the time the CMB was released. In that case, the scale factor was about 1100 so the distance would be about 9 billion light years.

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2. How could any kind of radiation cross this distance in a 13.5 BY (even if we add the expansion and any other requested feature)?

Who says it could?

In fact, it couldn't. That is why it is outside our observable universe.

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3. How a single bang or even several bangs could have the same affect on those two different space spheres?  I really can't understand this major issue.

So, this is the "horizon problem": how could the universe be in the same state everywhere unless it was small enough for light to travel across it. The most generally accepted answer is inflation. But there is no solid evidence for that and there are other possibilities (like, the universe took an infinite time to evolve to the state where it started expanding and so the whole universe was in the same state at that point).

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4. With Regards to the black body radiation -

Based on our understanding the current Universe has no ability to generate Black body radiation.  

This black body radiation is a product of a single event which took place at a specific time frame (300,000 year old). No less, no more.

Therefore, when the Universe was 0.2 BY or even 0.4 BY - it couldn't generate a black body radiation. We get today some sort of an echo from age of 0.3 BY.

However, how long this echo could stay with us? How could it still be there in a Universe size of  14 Trillion LY or even infinite? There is no expedite date for this echo?

It will always be with us (but it will get cooler over time). The link I posted earlier explains how this works.

[Dubbelosix]

On 01/08/2017 at 2:32 PM, dordle-loddle said:

Is the Universe infinite or just really, really big?

 

 

If the universe is expanding, and has an origin, then it has a finite past. There are a few ways a universe could be infinite and I'll provide two such cases - 

 

1) The universe needs to expand forever to be infinite

2) The universe could be cyclic and without a beginning to time

 

In the realms of physics, the first suggestion doesn't seem like much of an option - when a universe gets really really big, the forces holding a universe together could very well split apart, something called a big rip. A more reasonable assumption is that a universe could suffer a heat death, which is just a fancy name to say the universe will eventually freeze over because the thermodynamic degree's vanish. That may not be entirely true either, because we have no precedence in nature that the fabric of spacetime can even fundamentally be in such zero Kelvin state. 

 

It's one of those, who knows (?) questions. For me, the universe is finite. That may not mean though, that the stuff the universe is made of has to come to an end. Our universe may just be a phase in the grand scheme, a temporary fluctuation in which living organisms like us, can sit and ponder these things. 

29 minutes ago, Dan B. said:

 

I still don't know if the whole 14 Trillion Universe is an outcome of just one bang or several bangs process.

 

 

The universe is 14 billion years old, not 14 trillion. 

Edited September 28, 2017 by Dubbelosix

[Strange]

4 minutes ago, Dubbelosix said:

If the universe is expanding, and has an origin, then it has a finite past.

There is no evidence that the universe has an origin.

If the "origin" were infinite in extent then the universe could be infinite.

If you "wind the clock back" on an infinite universe it can become zero sized in finite time.

[Dubbelosix]

Oh there is, we can trace the universe back to a point which we have called, the big bang. This is just another name for some origin point.

The reason why this was said, again, demonstrates the universe has a finite past. What happens for the future universe is for theorists... unless you believe in Cyclic universe theory, or pre-big bang phases, then this is the current trend of thinking - the universe has an origin and has been named the big bang.

[Strange]

1 minute ago, Dubbelosix said:

Oh there is, we can trace the universe back to a point which we have called, the big bang. This is just another name for some origin point.

Except we can't. The Big Bang model only goes back to a point where there is a hot, dense state (a quark-gluon plasma). Our current physics doesn't allow us to go further back than that.

2 minutes ago, Dubbelosix said:

The reason why this was said, again, demonstrates the universe has a finite past.

There are several models where that is not the case (even apart from the cyclic one).

3 minutes ago, Dubbelosix said:

the universe has an origin and has been named the big bang

The Big Bang model describes an evolving (expanding and cooling universe) not an "origin".

[Dubbelosix]

Yes, we can't literally look at it.... you are not one of these posters that gets into semantic dribble, because I quickly put those posters on ignore. 

 

Admit there is an origin point and the consensus is that it is called big bang, or did you reply to my comment just for an argument?

''The Big Bang model describes an evolving (expanding and cooling universe) not an "origin".'

What are you talking about???

Big bang is the point in which space and time come into existence, in current tend of thinking. 

 

[Strange]

3 minutes ago, Dubbelosix said:

'The Big Bang model describes an evolving (expanding and cooling universe) not an "origin".'

What are you talking about???

"The Big Bang theory is the prevailing cosmological model for the universe^[1] from the earliest known periods through its subsequent large-scale evolution.^[2][3][4] The model describes how the universe expanded from a very high density and high temperature state,^[5][6] "

https://en.wikipedia.org/wiki/Big_Bang

(Sadly, almost all popular descriptions agree with you.)