# The Finite Universe

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The universe had a finite size at the start. So no matter how fast the universe expanded, except for an infinite speed which it did not, the universe must still be finite, no matter how large. How does a finite universe become infinite in size? This is not about the "observable universe" but about the entire universe.

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The universe had a finite size at the start.

How do you know that?

So no matter how fast the universe expanded, except for an infinite speed which it did not, the universe must still be finite, no matter how large.

There are plenty of functions which go from finite to infinite values in finite time.

How does a finite universe become infinite in size?

Maybe it was always infinite?

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Infinite universe would have infinite quantity of protons, so it would have infinite mass and infinite energy, which would mean it would have to instantly collapse as black hole.. isn't?

It would be one of versions of Zeno paradox

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The universe had a finite size at the start. ...

... This is not about the "observable universe" but about the entire universe.

How do you know the entire Universe was finite at the start?

Edited by pzkpfw
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Lets compare the universe at the time just after the big bang to a number line.
Lets say at this time, t>0, where we can begin to make measurements of space-time, the size is 1 unit on the number line.

We can still subdivide that one unit into an infinite number of points.

If we subsequently consider the whole number line, extending to an infinite number of units, we can subdivide that into an infinite number of points.

Furthermore we can put each of the infinite points on the one unit length on a one-to-one correspondence with the infinite number of points on the whole number line.

Infinities are a funny business and not very intuitive.

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Infinite universe would have infinite quantity of protons, so it would have infinite mass and infinite energy, which would mean it would have to instantly collapse as black hole.. isn't?

The formation of a black hole requires a (spherical) concentration of mass in otherwise empty space. A homogeneous distribution of mass will not form a black hole.

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Strange:

'"A homogeneous distribution of mass will not form a black hole." I never knew that. Some clarification or links please. Also this need some have to determine the mass of the known universe while others wonder if the whole universe is infinite seems strange.

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How do you know the entire Universe was finite at the start?

Because Micheo Kaku, Hawking, and the other scientists always say that the [entire] universe was smaller than a proton at the moment of the big bang. I put "entire" in brackets because that is what they mean. They do not say the "observable" universe was smaller than a proton. Smaller than a proton is definitely a finite size. Nobody ever suggested a finite-sized object can expand to an infinite size in ANY length of time. Even cosmic inflation is not infinite acceleration, only faster than light.

Even Phi For All believes the universe was "no bigger than an atom" at the earliest moments:

"...a fraction of a second after it happened....the universe at that time was no bigger than an atom."

Edited by Airbrush
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Strange:

'"A homogeneous distribution of mass will not form a black hole." I never knew that. Some clarification or links please. Also this need some have to determine the mass of the known universe while others wonder if the whole universe is infinite seems strange.

The simplest description for a black hole is the Schwarzschild metric. This is only valid for a static mass in empty space: https://en.wikipedia.org/wiki/Schwarzschild_metric

The expansion of the universe is described by the FLRW metric which assumes a homogeneous distribution of mass: https://en.wikipedia.org/wiki/Friedmann%E2%80%93Lema%C3%AEtre%E2%80%93Robertson%E2%80%93Walker_metric

By an odd coincidence, the radius of the observable universe is roughly the Schwarzschild radius for the mass.

Because Micheo Kaku, Hawking, and the other scientists always say that the [entire] universe was smaller than a proton at the moment of the big bang. I put "entire" in brackets because that is what they mean. They do not say the "observable" universe was smaller than a proton.

Because Micheo Kaku, Hawking, and the other scientists always say that the [observable] universe was smaller than a proton at the moment of the big bang. I put "observable" in brackets because that is what they mean. They do not say the "entire" universe was smaller than a proton.

Nobody ever suggested a finite-sized object can expand to an infinite size in ANY length of time.

Nobody has (seriously) suggested it (as far as I know). But it is still possible.

Even cosmic inflation is not infinite acceleration, only faster than light.

Expansion is not a speed. There are now, and always have been, parts of the universe that are receding faster than the speed of light.

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Strange: i see what you mean so far.Thanx

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Because Micheo Kaku, Hawking, and the other scientists always say that the [entire] universe was smaller than a proton at the moment of the big bang. I put "entire" in brackets because that is what they mean. They do not say the "observable" universe was smaller than a proton. ...

If people don't specify entire or observable when they talk about "the" Universe, it's dangerous to make an assumption you base a whole theory on.

As Strange notes, in this case it's "observable".

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Because Micheo Kaku, Hawking, and the other scientists always say that the [observable] universe was smaller than a proton at the moment of the big bang. I put "observable" in brackets because that is what they mean. They do not say the "entire" universe was smaller than a proton.

Then every time a scientist neglects to state "OBSERVABLE" universe, before saying it was smaller than a proton, or even an atom for that matter, that is GROSS negligence because it implies the entire universe. Shame on them. Also, I would like to hear them clarify this and explain how a universe that is infinite in size could ever begin as a big bang.

I have seen many documentaries about this, and ALL those scientists ALWAYS blunder in this issue. Such stupidity for scientists! This tells me that scientists, who are often professors whose job it is to explain these subjects to students (such as Micheo Kaku), are besides being brilliant in their field, are raving idiots when it comes to lecturing. Oh well....nobody is perfect.

Edited by Airbrush
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If people don't specify entire or observable when they talk about "the" Universe, it's dangerous to make an assumption you base a whole theory on.

As Strange notes, in this case it's "observable".

This time I agree with Airbrush. Nobody can put words in anyone else's mouth.

And I have also heard Alan Guth talking about a universe smaller than a orange.

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Then every time a scientist neglects to state "OBSERVABLE" universe, before saying it was smaller than a proton, or even an atom for that matter, that is GROSS negligence because it implies the entire universe. Shame on them. Also, I would like to hear them clarify this and explain how a universe that is infinite in size could ever begin as a big bang.

I have seen many documentaries about this, and ALL those scientists ALWAYS blunder in this issue. Such stupidity for scientists! This tells me that scientists, who are often professors whose job it is to explain these subjects to students (such as Micheo Kaku), are besides being brilliant in their field, are raving idiots when it comes to lecturing. Oh well....nobody is perfect.

This time I agree with Airbrush. Nobody can put words in anyone else's mouth.

And I have also heard Alan Guth talking about a universe smaller than a orange.

Oh, give me a break. This is what backtracking the cosmic expansion leads us to. If you use the attic of your mouth a bit more thoroughly, you realize we can only analyze OBSERVABLE galactic redshifts to get this data. We use known physical laws to calculate the characteristics of the universe back to that time, but we have to use only the data we've observed.

Seriously, duh, how else did you expect science to do this? We don't look for proof, we use theory because we can't say for sure that what works here works everywhere every time. If anything is intuitive in science, it should be that.

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Then every time a scientist neglects to state "OBSERVABLE" universe, before saying it was smaller than a proton, or even an atom for that matter, that is GROSS negligence because it implies the entire universe. Shame on them.

I would say shame on you for putting words in their mouths instead of finding out what they mean.

This time I agree with Airbrush. Nobody can put words in anyone else's mouth.

Then why is Airbrush doing exactly that? And then pretending to be outraged. Pathetic.

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Oh. So you all seem to say that at the the BB, the singularity was infinite?

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Has anyone said that? I don't think so.

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Oh. So you all seem to say that at the the BB, the singularity was infinite?

1. No one said that.

2. "At" the big bang makes no sense as the big bang model describes the evolution of the universe from an earlier hot, dense state.

3. There is no evidence that the singularity has any physical existence.

4. What do you mean by "the singularity was infinite"?

5. Whatever you mean, it would only be true IF the universe were infinite. And there is no eveidence for that.

But apart from that ...

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1. No one said that.

2. "At" the big bang makes no sense as the big bang model describes the evolution of the universe from an earlier hot, dense state.

3. There is no evidence that the singularity has any physical existence.

4. What do you mean by "the singularity was infinite"?

5. Whatever you mean, it would only be true IF the universe were infinite. And there is no eveidence for that.

But apart from that ...

So where do we go wrong when we hear eminent scientists say that the universe began smaller than a proton, then became the dimension of a marble (from A. Guth, I must have mistaken the orange from another eminence)?
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So where do we go wrong when we hear eminent scientists say that the universe began smaller than a proton, then became the dimension of a marble (from A. Guth, I must have mistaken the orange from another eminence)?

I don't know where you go wrong. They are (I assume, given the lack of context) talking about the observable universe.

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My little dictionary defines "universe" as "the totality of all things that exist." It also gives a second definition as "the world".

All things that exist goes beyond the observable. So the assumption any English-speaker should make when a scientist says "the universe is ....." they mean the ENTIRE universe (all things that exist) and not merely what we can see.

I would say shame on you for putting words in their mouths instead of finding out what they mean.

Then why is Airbrush doing exactly that? And then pretending to be outraged. Pathetic.

I'm not putting words into their mouth. You are inserting the words by saying "universe" means observable universe. Oh...everybody knows that already. Scientists are being sloppy in their use of the word "universe".

There are plenty of functions which go from finite to infinite values in finite time.

Maybe it was always infinite?

Then please explain how the big bang function can cause a finite size to expand to an infinite size in any length of time.

What I would really like to know is how can an infinite-sized universe result from the big bang? The idea of a tiny size at the start is meaningless if the universe started out as infinite. No documentary, or episode of "The Universe" or "How the Universe Works" has ever suggested the universe could START out as infinite in size. Then all discussion of cosmic inflation becomes meaningless.

I am here to LEARN because I know very little about astronomy and cosmology. But when I hear inconsistencies in scientists' lectures, I have to call them on it in their ivory tower. What do you say about this issue Micheo Kaku? What do you say Stephen Hawking?

Why the assumption the universe started tiny? Why not the idea that the universe started huge, as a jagged rip, like a lightning bolt, trillions of light years across?.....IF it was caused by a collision of higher dimensions as string theory speculates.

Edited by Airbrush
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My little dictionary defines "universe" as "the totality of all things that exist." It also gives a second definition as "the world".

So, according to your dictionary, these scientists are saying that the world was the size of a proton?

You dictionary is not a good source for scientific information.

I'm not putting words into their mouth.

Only the word "entire".

Then please explain how the big bang function can cause a finite size to expand to an infinite size in any length of time.

I believe there are models where this is possible but I am not familiar with them and, as far as I know, they are not mainstream.

What I would really like to know is how can an infinite-sized universe result from the big bang?

The big bang is a model describing the evolution from an early hot dense state. It is equally applicable to a finite and an infinite universe.

The idea of a tiny size at the start is meaningless if the universe started out as infinite.

I agree. Which is why it I assume that the scientists you are citing meant the observable universe. (BTW, I see you mention Michio Kaku: I would take his pop-science stuff with a large pinch of salt. In fact, I would disregard it completely.)

As we have no idea how large the entire universe is, how could we know how large it was at some point in the past?

No documentary, or episode of "The Universe" or "How the Universe Works" has ever suggested the universe could START out as infinite in size.

Maybe those are not good sources of information.

Then all discussion of cosmic inflation becomes meaningless.

Inflation was proposed to solve some specific problems (http://wmap.gsfc.nasa.gov/universe/bb_cosmo_infl.html). I don't think it says anything about whether the universe is finite or not.

I am here to LEARN because I know very little about astronomy and cosmology.

Then you need to try and drop the "I don't understand this so it must be wrong" attitude and embrace the "what have I missed" once.

But when I hear inconsistencies in scientists' lectures, I have to call them on it in their ivory tower.

When I hear inconsistencies in pop-sci articles or documentaries, I go back to a more reliable source and try to find out what is really behind it.

Wikipedia has some reasonably good articles on the subject.

Why the assumption the universe started tiny?

It is not an assumption; it is a conclusion from the evidence.

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I am here to LEARN because I know very little about astronomy and cosmology. But when I hear inconsistencies in scientists' lectures, I have to call them on it in their ivory tower.

"I only know enough about science to understand when something is inconsistent. I find it usually means some scientist is out of touch with reality, separated from the facts, so I look for ways to point this type of thing out."

I changed this around to show you how the argument looks to me (trying NOT to put extra words in your mouth). I can't tell you how many times I've heard this same sentiment, like you could possibly have some kind of unlearned sense of when science is wrong or inconsistent. Do you have this ability with anything else you know very little about? Can you watch a ballet, or walk onto the trading floor of the stock market, or suit up for surgery, and somehow recognize inconsistencies in data and process, and shortcomings in the professional people involved? How do you do that?

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It is not an assumption; it is a conclusion from the evidence.

That the observable universe started out tiny is the conclusion from evidence. Ok.

Forgive me for trying to understand this. It looks to me like the evidence shows everything is expanding outward. Obviously that originated from a denser state, but how do they know that the entire observable universe was smaller than an atom? Or a proton? Maybe the observable universe blasted out of a region of unknown size, and that size was much larger than an atom. Why not?

As for an infinite-sized universe, no one has yet given me a hint at how an infinite sized universe can result from the big bang model.

What else can the entire universe be but one of 3 things:

It could be exactly as large as the observable universe, which is unlikely but possible.

It could be finite and just larger than the observable universe.

It could be infinitely larger than the observable universe, which is what I doubt. Can you change my mind?

"I only know enough about science to understand when something is inconsistent. I find it usually means some scientist is out of touch with reality, separated from the facts, so I look for ways to point this type of thing out."

I changed this around to show you how the argument looks to me (trying NOT to put extra words in your mouth). I can't tell you how many times I've heard this same sentiment, like you could possibly have some kind of unlearned sense of when science is wrong or inconsistent. Do you have this ability with anything else you know very little about? Can you watch a ballet, or walk onto the trading floor of the stock market, or suit up for surgery, and somehow recognize inconsistencies in data and process, and shortcomings in the professional people involved? How do you do that?

No, that is not my intention. I only know enough about science to be interested in it, and to accept it most of the time. When I discover inconsistencies I try to reconcile them. I'm not here to bore you with the consistencies of science, only what baffles me, even after searching for an answer. You appear to be saying, since I don't know much about science, I should just accept what the experts say, and not question authority. I have no business here. This discussion is only for experts who already understand the intricacies of the big bang.

Strange: "...I see you mention Michio Kaku: I would take his pop-science stuff with a large pinch of salt. In fact, I would disregard it completely."

Why should I? What Michio says is what Stephen Hawking, and Neil DeGrass Tyson, and a number of other very reputable, respected, televised experts ALSO say. It looks like a conspiracy to keep people confused, but it is certainly not intentional, just careless.

Edited by Airbrush
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Forgive me for trying to understand this. It looks to me like the evidence shows everything is expanding outward. Obviously that originated from a denser state, but how do they know that the entire observable universe was smaller than an atom? Or a proton? Maybe the observable universe blasted out of a region of unknown size, and that size was much larger than an atom. Why not?

There are many, many bits of evidence that lead to these conclusions. A lot of this is based on predicting what the universe would look like if there were conditions like that and then looking to see if observations match those predictions. Most of this is not stuff I know much about but, for example, the proportions of elements that should have been formed initially (given those early conditions) can be calculated and compared with the proportions of hydrogen and helium we see. There are quantum effects that should leave a (very tiny) imprint on the CMB. And so on.

Most of this is very complex and requires a lot of expertise to understand and probably won't be mentioned, except in passing, in the sort of sources you have mentioned so far.

As for an infinite-sized universe, no one has yet given me a hint at how an infinite sized universe can result from the big bang model.

If the original hot, dense universe were infinite.

What else can the entire universe be but one of 3 things:

It could be exactly as large as the observable universe, which is unlikely but possible.

It could be finite and just larger than the observable universe.

It could be infinitely larger than the observable universe, which is what I doubt.

There are other possibilities:

It could actually be smaller than the observable universe (so what we see at great distance is the same thing "wrapped round"). I don't think this is a serious contender but it is possible.

It could be much larger than the observable universe. There are varying estimates for the lower limit on the size of the entire universe, ranging from 250 times to 1023 times the size of the observable universe.

Can you change my mind?

I don't know. Some people seem emotionally convinced that the universe cannot possibly be infinite. Others are equally strongly attached to the idea that it must be. Currently, the evidence doesn't tell us which it is.

This is a good source for info on the big bang model and cosmology in general: http://www.astro.ucla.edu/~wright/cosmology_faq.html

If you feel up to it, you could work through his tutorial: http://www.astro.ucla.edu/~wright/cosmo_01.htm

This is good too: http://math.ucr.edu/home/baez/einstein/

It gets mathematical, but you might be able to follow some of the ideas even if you don't fully get the math.

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