# Finite or infinite Universe

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We are trapped in our horizon, we can't see outside observable universe. Physicist says that universe can be finite or infinite.

My Question is, we know that universe began 13.75 billion years ago. The universe isn't infinitely old, so how the universe can be infinitely big? If it had finite time until today?

Also if the universe began with certain amount of energy and had a definite size how can be universe infinite?

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We are trapped in our horizon, we can't see outside observable universe. Physicist says that universe can be finite or infinite.

Does a set of all sets contains itself?

Also if the universe began with certain amount of energy and had a definite size how can be universe infinite?

A process could repeat itself for infinity

Edited by KatzAndMice
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Does a set of all sets contains itself?

A process could repeat itself for infinity

When they say "Universe" I guess they mean whole universe. if they want to emphasis that we don't see the whole thing they say "observable universe". So they sometimes simply says - the universe may be infinite.

A process could repeat itself for infinity

You say that they mean cycles of the universe? not infinitely big in size?

Edited by mr.spaceman
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You say that they mean cycles of the universe? not infinitely big in size?

They seem the same to me, but cycle indeed, anything that can be perceived as infinite seems to be infinitely big

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They seem the same to me, but cycle indeed, anything that can be perceived as infinite seems to be infinitely big

I've never thought this way

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We are trapped in our horizon, we can't see outside observable universe. Physicist says that universe can be finite or infinite.

My Question is, we know that universe began 13.75 billion years ago. The universe isn't infinitely old, so how the universe can be infinitely big? If it had finite time until today?

Also if the universe began with certain amount of energy and had a definite size how can be universe infinite?

A flat universe is infinite in size. It was infinite in size when it was created. Think of a rod which is infinitely long and has tick marks on it to mark of space and there's an infinite number of tick marks. Let the distance between the tick marks increase with the distance between galaxies. Think of it like this - the distance between the tick marks before the big bang was zero meaning that the size of the universe was zero. Now let the Big Bang happen -> even the most smallest but finite distance between the tick marks being created would lead to an infinite universe.

Yes. It all sounds bizzare. Nobody said cosmology was going to be easy to understand. The fact is that nobody knows how it can be this way. We just have a good handle on how to describe it.

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A flat universe is infinite in size. It was infinite in size when it was created. Think of a rod which is infinitely long and has tick marks on it to mark of space and there's an infinite number of tick marks. Let the distance between the tick marks increase with the distance between galaxies. Think of it like this - the distance between the tick marks before the big bang was zero meaning that the size of the universe was zero. Now let the Big Bang happen -> even the most smallest but finite distance between the tick marks being created would lead to an infinite universe.

Yes. It all sounds bizzare. Nobody said cosmology was going to be easy to understand. The fact is that nobody knows how it can be this way. We just have a good handle on how to describe it.

thank you I think I understood principle,

But it confuses me when physicist say "the point of singularity was smaller than atom"

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thank you I think I understood principle,

But it confuses me when physicist say "the point of singularity was smaller than atom"

Smaller than a proton even

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To: KatzAndMice

For the following message"

mr.spaceman, on 1 July 2012 - 11:21 PM, said:Also if the universe began with certain amount of energy and had a definite size how can be universe infinite?

You have replied:

A process could repeat itself for infinity

So, how come that the Big Bang is a very singular process?

Is there any chance that it is a repeat process (Even one time more...)?

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We are trapped in our horizon, we can't see outside observable universe. Physicist says that universe can be finite or infinite.

My Question is, we know that universe began 13.75 billion years ago. The universe isn't infinitely old, so how the universe can be infinitely big? If it had finite time until today?

Also if the universe began with certain amount of energy and had a definite size how can be universe infinite?

Just suppose the universe did not begin in the first place.

To contemplate about this, let us first state that the universe is all there is in all time and all space.

What can we infer from that?

First I would think that the universe could not have an edge or boundary, there is no moment in time or place in space where the universe is not, and so there isn't a boundary between them.

This would imply in my opinion also the universe did not begin, because it would have to have started from nothing, but nothing is no begin and nothing contains no being. Nothing is only noting.

(That some part of the universe, like for instance the part we can observe now, could have started from an infinitsimal small patch in a quantum fluctuation, is something radically different, because it already presupposses that there exists space and time and quantum fluctuations happening in space and time, which is not nothing).

Edited by robheus
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To: KatzAndMice

For the following message"

mr.spaceman, on 1 July 2012 - 11:21 PM, said:Also if the universe began with certain amount of energy and had a definite size how can be universe infinite?

You have replied:

A process could repeat itself for infinity

So, how come that the Big Bang is a very singular process?

Is there any chance that it is a repeat process (Even one time more...)?

Yes... it is possible, they are called cyclic cosmological theories. Roger Penrose first solved equations to try and give evidence for this model. Where he once said nothing existed before big bang, he is now saying ... well... maybe something did. The reporter here is a bit arrogant

''Cosmic Bruises'' could be a way to detect this theory.

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To: KatzAndMice

For the following message"

mr.spaceman, on 1 July 2012 - 11:21 PM, said:Also if the universe began with certain amount of energy and had a definite size how can be universe infinite?

You have replied:

A process could repeat itself for infinity

So, how come that the Big Bang is a very singular process?

It is not. A singularity is only a mathematical point with zero dimension, but physical space time can not be a point, every part of spacetime has a minimum extension, like planck length and planck time.

Is there any chance that it is a repeat process (Even one time more...)?

If we would imagine that time extends to both past and future infinite, and there are infinite possibilities of arranging the universe, we would simply not know. Since the amount of possibilities might be a larger infinite then the infinity of time. But a subset of those infinite arrangements might of course re-occur.

Edited by robheus
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It is not. A singularity is only a mathematical point with zero dimension, but physical space time can not be a point, every part of spacetime has a minimum extension, like planck length and planck time.

precisely.

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precisely.

And we could add: the "singularity" in the theory of gravity (general relativity) is not in any way different then for intance the singularity in Newton's theory of gravity (which contemplates about point masses with zero dimensions), since if we would take point masses at zero distance, also in Newton's theory the force of gravity becomes infinite. We know from experience however, this does not happen. Firstly because besides gravity there also exists other forces, like electro-magnetism, and if two atoms are about to touch each other, what really happens is that the electron shells of the atoms are repulsing each other. Besides, as we also now from experiments, point masses of zero dimensions do not exist, matter (particles, fermions) take up some space. For the universe it can be explained that the point of singularity did not exist because 1. quantum mechanical effects need to be taken into account 2. zero dimensional spacetime does not exist, since space time is extended with a minimum of planck lengt and time.

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the planck scale is not necessarily an absolute limit. it is merely the energy scale at which quantum gravity effects will become apparent and important. At present it is not able to be investigated directly due to the vast energies required (and it is difficult to envisage how this could ever be overcome) - but it is hoped that large scale surveys of anisotropies in the future will be precise enough to reach the remnants of the planck era of the early universe when the forces were unified. the WMAP probe can hope to investigate the electroweak phase transition - but this is still many orders of magnitude off the planck scale.

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the planck scale is not necessarily an absolute limit.

In what way would it no be an absolute limit?

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In what way would it no be an absolute limit?

It is thought you can get smaller than it - ie before 10^-43 seconds we were in the planck era or epoch, in which all forces were unified and the entire universe was within the planck scale.

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It is thought you can get smaller than it - ie before 10^-43 seconds we were in the planck era or epoch, in which all forces were unified and the entire universe was within the planck scale.

Such epochs are usually impossible to promote, not that it's impossible. For the sake of relativity, the Planck Scales could be a type of limit... in the sense anything below this is hard to make sense of physically.

And we could add: the "singularity" in the theory of gravity (general relativity) is not in any way different then for intance the singularity in Newton's theory of gravity (which contemplates about point masses with zero dimensions), since if we would take point masses at zero distance, also in Newton's theory the force of gravity becomes infinite. We know from experience however, this does not happen.

In a recent force equation I posted here at this forum, I showed how the forces are really down to nature refusing to have particles be converged to a single point. The more you tried to squeeze particles into a single region of space the more nature wanted to fight it and the force becomes greater and greater. Space (and time) would become massively unstable due to the uncertainty principle. I wanted to make use of this instability - instead of seeing it as physics breaking down - the reason why spacetime expanded in the first place was because it wanted to avoid this instability. So as a way for the zero-dimensional vacuum to make sense of how to overcome this unstableness, was to expand spacetime between all objects that where converged to the same location. It could even explain why there was a rapid acceleration to begin with. Hell, the idea could even explain what kind of conditions where there before big bang.... even though you cannot speak of time per se, one could argue if there was anything before the big bang, it couldn't have existed for very long because of the instabilities spoke of.

Edited by Aethelwulf
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It is thought you can get smaller than it - ie before 10^-43 seconds we were in the planck era or epoch, in which all forces were unified and the entire universe was within the planck scale.

I don't think that it has any real meaning. You can think of so many things theoretically, but somewhere it stops to have any real meaning, and just becomes a phantom of imagination.

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Such epochs are usually impossible to promote, not that it's impossible. For the sake of relativity, the Planck Scales could be a type of limit... in the sense anything below this is hard to make sense of physically.

I don't think that it has any real meaning. You can think of so many things theoretically, but somewhere it stops to have any real meaning, and just becomes a phantom of imagination.

I never said it was easily imaginable (what the hell really is in either the super-macro scale of cosmology or the sub-micro of quantum mechanics) nor that it was easy to make sense of - but the lack of an intuitive or mentally accessible model really does not create a physical limit. It possibly is a physical limit - but if it is then our physics needs over-hauling and much cutting edge research will be shelved; however, we cannot in any way stop hi-energy physics just cos it gets weird, we cannot see its "real meaning" (wot's that then?) or it stops making intuitive sense physically.

ok.

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Just suppose the universe did not begin in the first place.

To contemplate about this, let us first state that the universe is all there is in all time and all space.

What can we infer from that?

First I would think that the universe could not have an edge or boundary, there is no moment in time or place in space where the universe is not, and so there isn't a boundary between them.

This would imply in my opinion also the universe did not begin, because it would have to have started from nothing, but nothing is no begin and nothing contains no being. Nothing is only noting.

(That some part of the universe, like for instance the part we can observe now, could have started from an infinitsimal small patch in a quantum fluctuation, is something radically different, because it already presupposses that there exists space and time and quantum fluctuations happening in space and time, which is not nothing).

As I comprehend

if the universe is infinite it hasn't beginning. it could not started from nothing

but if we talk about part of the universe like our observable universe it can be started from quantum fluctuations which exist in space time

am I right?

if only part of the universe can begin from quantum fluctuations, it sounds like an idea of multiverse. isn't it?

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As I comprehend

if the universe is infinite it hasn't beginning. it could not started from nothing

It's hard to talk about the beginning to anything without matter clocks which define time. Therefore, the universe could not have had a beginning within the framework of relativity simply because for a beginning to exist, you need to be able to define time.

Also another time-problem, is the fact that the universe arose with no geometry originally, so spacetime as geometry ceases to exist. Again, relativistically-speaking, we can't speak about ordered sets of events in your usual sense.

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We are trapped in our horizon, we can't see outside observable universe. Physicist says that universe can be finite or infinite.

My Question is, we know that universe began 13.75 billion years ago. The universe isn't infinitely old, so how the universe can be infinitely big? If it had finite time until today?

Also if the universe began with certain amount of energy and had a definite size how can be universe infinite?

If the universe were eternal we could never have reached the present "NOW" moment, because the "Arrow of Time" would be pushed back to the infinite past.

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If the universe were eternal we could never have reached the present "NOW" moment, because the "Arrow of Time" would be pushed back to the infinite past.

What does that mean? It would be pushed back from when? How do you 'push' the arrow of time? Also, I don't think mr.spaceman mentioned 'eternal'. He said 'infinite'.

Edited by zapatos

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