SauwIs the concept of finite space in infinite time scientifically valid?

[Eh]

Originally posted by heusdens
I don't think that the standard model describes that. The standard model is just the model of the observable universe (which extends beyond our obsevation) which was in the past more dense, smaller and more hot. In the standard model we can calculate back to perhaps the 10 to the minus 43 seconds, but then physical laws aren't able predicting anything. So the standard model can not make predictions about what was before.

The standard model, as well as comsology as a whole, is based on a classic description of space-time. That is, while general relativity cannot accuratley describe quantum scale events, it is the only theory we have to describe the big bang. And as it is, GR predicts a singularity and a beginning to space and time. While the notion of anything prior to the Planck era may not make much sense, GR does predict this. The singularity is expected to be replaced by something on the Planck scale at t=0, but even then many physicists expect a first moment of time.

Eternal / open or chaotic inflation models are built in such a way that the Big Bang theory becomes part of the inflationary regime.
That what is stated in this theory is that once inflation starts, it can reproduce eternally, and therefore does not need a begin.
I have not seen the 'proof' that such a regime can't be eternal.
But if that is proven, it just means that also that theory can predict about reality in a limited way. It does not urge us however to state then that time must had a beginning, but that some other material form, which can not be described within inflation theory, preceded inflation.

The problem seems to be with the expanding universe. Unless you've got a cyclic universe, eventually you will hit a singularity with those models. I read something authored by Vilenkin that showed that even eternal inflation models would likely require an initial singularity. I did some reading, and it seems this issue has been a popular topic for the past couple of years. I have some papers from the arxiv.org site that discuss some of the associated problems, but the PDF's aren't loading. I'm getting a file error, so I'll have to find the links somewhere else. Again, the expansion seems to be the main problem.

But a beginning of time is a very weird concept. It would urge us to conclude that everything existing came out of nothing.
No physical law can ever describe that. Physical laws can not be built on 'nothing'.

It's not created out of nothing. That there is a beginning does not mean there is a prior state from which the universe is created. The important thing to stress is that there is no before.

The logic inconsistency does occur however. When 'modelling' the state of the universe 'before' the begin of time, in fact we have to conclude that no model can describe it. Because a mere nothingness is either inexistent in time, or is just a concept of pure time, that is a concept of time without any foreign admixtures, without anything changing in time. The logic problem is that in such an eternal unchanging nothingness, a change did occur, 'causing' the material existence, time and space.

And therein lies the problem. The proposal is that there is no before at all, and you start talking about the logical problems of a timeless state that existed before the big bang. There is a difference in concepts here.

There is no logic that can work on that concept, if you ask me.

Probably not, but you've got the wrong concept.

This is just an indication of how good our models are. If the model comes up with such inconceivable concepts as the 'begin of time' it would merely indicate that a new theory must emerge.

The point is that if such a beginning suffers from no logical inconsistancy, there is no justification for that indication.

Philosophical note on Infinity of matter

The philosophical notion of the infinity of matter, does not reflect on a determined age or a detemined space. It denotes the eternal transformation of matter, the fact that matter can not be created or destroyed, but only can be transformed from one form, into another.
Infinity of matter means, that all finite development forms of matter in a finite spatial extent with a finite age transforms into another development form of matter, which also has a finite spatial extent and age.

Oddly enough, this old philsophy seems to be in trouble. Matter can be created from the vacuum, and this is an important feature of inflation models where the energy in the universe increases by enormous factors. Of course, this require net energy zero reasoning, and I don't know what relation it has to reality.

 

[Eh]

Originally posted by wimms
Sorry, that was too fast for me . Do I understand right, that because volume and area of brick can be well defined without any need for reference to outside space for definition, assumption that there must be something around the brick is plain stupid?

A brick wall is a bad example, since a building is necessarily embedded in something else. But the gist of it is correct. Since we have can define an area or volume by itself, we don't need infinite space. That doesn't mean the idea of infinite space is wrong, it's just not necessarily required.

Isn't definition of finite manifold simply postulate that needs no further consideration? As such, isn't it just assumption that is forbidden to be questioned? For working model, no problem. But when suppressing other intellect 'from higher ground'? Patience please, some understanding doesn't come easy.

It's not an assumption, it's just the definition. If there is something logically inconsistant about it, no one has of yet been able to show how. Still, the debate of finite vs. infinite space has a long pedegree and goes back as far as the ancient Greeks.
Many philosophers have tried to show why infinite space makes more sense with seeming paradoxes associated with finite space (ie. shooting an arrow at the edge of the universe). But such parodoxes are no longer taken seriously with the advent modern cosmology and such.

Logic doesn't reveal truth, it only checks consistency. Any theory is based on assumptions, intuitive or not.

Correct, and remember that the point I'm stressing is that finite space suffers from no logical inconsistency. Thus either infinite or finite could actually be an accurate description of reality.

Claim that a finite universe must be embedded in some infinite space may be unfortunate, but claim that universe cannot be finite comes from logical approach. I can't help but draw analogy with claim that set of _all_ integers can be finite.

I would seriously like to see a logically supported argument that the universe cannot be finite. Math can describe possible worlds, but only one of those descriptions will actually describe the world we live in. While infinity may be a more intuitive description of space, finite is equally possible.

 

[heusdens]

Originally posted by Eh
The standard model, as well as comsology as a whole, is based on a classic description of space-time. That is, while general relativity cannot accuratley describe quantum scale events, it is the only theory we have to describe the big bang. And as it is, GR predicts a singularity and a beginning to space and time. While the notion of anything prior to the Planck era may not make much sense, GR does predict this. The singularity is expected to be replaced by something on the Planck scale at t=0, but even then many physicists expect a first moment of time.

This is gross and widespread misunderstanding. Ask a physicist how they can make physics laws from nothing. Their answer will be, we can't.

It might be due to the fact that the ideas of Stephen Hawking (A brief history of time) has put forward such concepts. This included concepts like that real time had a definite begin, but imaginary time had not.

I don't think that such ideas will last long. What we have is a barrier to predict anything about what could have been before the Big Bang, cause the laws we an use to describe the event, break down at that instance.

I do not think physics can ever work with a begin of time, in whatever way. It just indicates that our models in that instance are ripped apart and can no longer describe reality.

So we need to look for different approaches to get past the problem.

The problem seems to be with the expanding universe. Unless you've got a cyclic universe, eventually you will hit a singularity with those models. I read something authored by Vilenkin that showed that even eternal inflation models would likely require an initial singularity. I did some reading, and it seems this issue has been a popular topic for the past couple of years. I have some papers from the arxiv.org site that discuss some of the associated problems, but the PDF's aren't loading. I'm getting a file error, so I'll have to find the links somewhere else. Again, the expansion seems to be the main problem.

It is to be expected that there is no material state of the universe or whatever material existing 'thing', that lasts forever.
But that just means that one state of the material universe, is transformed into another material state.
And that can go on without end, and doesn't require a begin either.

It's not created out of nothing. That there is a beginning does not mean there is a prior state from which the universe is created. The important thing to stress is that there is no before.

And therein lies the problem. The proposal is that there is no before at all, and you start talking about the logical problems of a timeless state that existed before the big bang. There is a difference in concepts here.

But this is altogether not much different from, for example a star formation. When the nuclear fusion starts, when the gasses that form the star are dense enough, the star can be said to be 'born'. It will exist for a certain amount of time.

Before the nuclear fusion started, it can be said that the star did not exist. But the gassed that formed the star, did exist.

What is expected from all other examples of the material world, is that such a thing is also true for the universe, that at one time, it started it existence, and can be existent for some definite amount of time.

But although it is difficult to even theoretically define a state prior to the existing universe, we should be confident that also the universe was preceeded by some or other material form. And also that form did not exist eternally, but also was caused by something else.

Probably not, but you've got the wrong concept.


The point is that if such a beginning suffers from no logical inconsistancy, there is no justification for that indication.


Oddly enough, this old philsophy seems to be in trouble. Matter can be created from the vacuum, and this is an important feature of inflation models where the energy in the universe increases by enormous factors. Of course, this require net energy zero reasoning, and I don't know what relation it has to reality.

The important thing to note is, that that vacuum is not empty, but contains fields. Now a field is as material as anyother material form.
It contains the basic properties of motion/change in a spatial and timely way.

So we are not talking about a concept of matter coming into existence from nothing, but from a previous and different material state.

 

[heusdens]

Originally posted by Eh
I would seriously like to see a logically supported argument that the universe cannot be finite. Math can describe possible worlds, but only one of those descriptions will actually describe the world we live in. While infinity may be a more intuitive description of space, finite is equally possible.

In what way would you think the universe is finite or infinite?

The way the material world exists, we see only finite material forms, in a finite space, and with a finite time. This can be stated for all of the material world.

Materialism however, while supporting this fact, says that while every existing material form is finite, it is always precedeed and will be followed by another material form.

Matter as such can not be destroyed or created, it can only be transformed from one form into another form.

In that sense, matter is said to be infinite, or eternal.

 

[Eh]

Originally posted by heusdens
This is gross and widespread misunderstanding. Ask a physicist how they can make physics laws from nothing. Their answer will be, we can't.

I don't of any models that propose such, either.

It might be due to the fact that the ideas of Stephen Hawking (A brief history of time) has put forward such concepts. This included concepts like that real time had a definite begin, but imaginary time had not.

That is also a source of confusion, because in those models, what we experience as "real time" isn't real at all. Imaginary time is, where a timeless 4D space-time exists. Of course that model has problems as well, and was discussed in another thread.

I don't think that such ideas will last long. What we have is a barrier to predict anything about what could have been before the Big Bang, cause the laws we an use to describe the event, break down at that instance.

I do not think physics can ever work with a begin of time, in whatever way. It just indicates that our models in that instance are ripped apart and can no longer describe reality.

But a beginning to time does not actually present a problem, because comsology is based on mathematical models. So long as the model does contain any internal inconsistency, there is no trouble. And that is the point I'm trying to stress. A beginning of time posses no mathematical inconsistency. What DOES give physicists problems is the notion of an infinitely dense point of zero volume.

It is to be expected that there is no material state of the universe or whatever material existing 'thing', that lasts forever.
But that just means that one state of the material universe, is transformed into another material state.
And that can go on without end, and doesn't require a begin either.

I'm not sure many physicists think a quantum theory of gravity will automatically allow the universe to have existed forever. It should give a minimum size for the universe, eliminating the singularity, however.

But this is altogether not much different from, for example a star formation. When the nuclear fusion starts, when the gasses that form the star are dense enough, the star can be said to be 'born'. It will exist for a certain amount of time.

Before the nuclear fusion started, it can be said that the star did not exist. But the gassed that formed the star, did exist.

There is a huge difference. For the star, there was a time when it did not exist. The proposal for the universe is merely that there is no before the big bang. That means exactly what it states. It does not mean there was a prior time (or timeless state) when there was no universe. There is no logical inconsistency with that, even though is goes against our intuition. But this is the same intuition that demands space to be infinite.

And that's really all it comes down to. Effectively, such a universe IS eternal, since it has existed for all time.

 

[Eh]

Originally posted by heusdens
In what way would you think the universe is finite or infinite?

There are the three. Space, time, and the divisibility of both. The infinity of time and the divisibility of both seem to be headed in a finite direction from cosmology and particle physics, so it seems more fitting that space also be finite.

The way the material world exists, we see only finite material forms, in a finite space, and with a finite time. This can be stated for all of the material world.

Materialism however, while supporting this fact, says that while every existing material form is finite, it is always precedeed and will be followed by another material form.

Matter as such can not be destroyed or created, it can only be transformed from one form into another form.

In that sense, matter is said to be infinite, or eternal.

The only problem is with the word matter. In science, matter has a very specific meaning, and it is neither fundamental nor eternal. So for physicalism, I think the word energy would be a better replacement, as energy cannot be created or destroyed and it avoids confusion over the word.

But wait, what if energy is not conserved either? Perhaps then the saying has to be changed again. Maybe some unified field is fundemental, where the geometry is constantly changing, but the field itself is eternal. Time will tell.

 

[heusdens]

Originally posted by Eh
Oddly enough, this old philsophy seems to be in trouble. Matter can be created from the vacuum, and this is an important feature of inflation models where the energy in the universe increases by enormous factors. Of course, this require net energy zero reasoning, and I don't know what relation it has to reality.

Oddly enough, it is not materialism itself that is suffering here, only your concept of matter. Note that the philosophical term matter denotes something different then the physical term matter. For philosophical materialism, matter is just the 'substance' that is in motion (and thus requires time and space to exist; time and/or space without matter would be inconceivable). What this 'substance' is, what form it has, is for science to explore and to define. So far we have the concept of matter in form of mass-having particles (the baryonic stuff and leptons), in form of energy (photons) and in form of fields.

The inflation model is not build on a concept of empty vacuum devoid of anything material., i.e. it is not a concept of 'nothing'.
It does contain 'something' for instance a scalar field that has the property of motion/change, and therefore it is material.
It is devoid however of any kind of 'normal' material stuff, like the atoms and particles and photons we know of, and where everything is made of.

 

[heusdens]

Originally posted by Eh
There is a huge difference. For the star, there was a time when it did not exist. The proposal for the universe is merely that there is no before the big bang. That means exactly what it states. It does not mean there was a prior time (or timeless state) when there was no universe. There is no logical inconsistency with that, even though is goes against our intuition. But this is the same intuition that demands space to be infinite.

And that's really all it comes down to. Effectively, such a universe IS eternal, since it has existed for all time.

What it comes down to that we cannot talk sensibly about the existence of space and time without the concept of matter. If it were not for matter, neither time or space would exist.

What the problem is however, is the problem where did the matter originate from. From 'the nothing'?

There was no existing state prior to the t=0 singularity.
All matter started out from that state, and 'created' time and space for it's existence.

This idea has been put in scientific theory by Hawkings, but also this idea is criticized, precisely because of the inconceivability of such an event.

What is good about this theory (even though it, as any scientific theory, it can be proven wrong) is that at least this is theory is not a form of theological doctrine, but is a scientific theory.
The debate in science is if such a model can explain the universe how it exists today. It must explain the large scale structure of the universe, the homogeneity and size of the universe and flatness.

It has been proven that the initital model (in form of the Hawking-Turok these, the Instanton pea) poses several problems that can not be dealt with in the original theory. Like for instance it would have modeled an universe which would already have crunched, and therefore can't explain the present universe.

There are competiting theories, like the theory of eternal inflation, that do better in the area of explaining observations, and solve some problems in the Big Bang theory.

Further more GR does not require perse that there was a singularity.

See for examle http://xxx.lanl.gov/abs/gr-qc/9810054".

 

[Eh]

Originally posted by heusdens
Oddly enough, it is not materialism itself that is suffering here, only your concept of matter. Note that the philosophical term matter denotes something different then the physical term matter.For philosophical materialism, matter is just the 'substance' that is in motion (and thus requires time and space to exist; time and/or space without matter would be inconceivable). What this 'substance' is, what form it has, is for science to explore and to define. So far we have the concept of matter in form of mass-having particles (the baryonic stuff and leptons), in form of energy (photons) and in form of fields.[/

Yes, I agree it's only a question of definitions. The word matter just seems a bit outdated, and it causes confusion when you use the word with the philosophical meaning for discussions about physics. I would consider myself a physicalist, but avoid using the word 'matter' only because it has a different meaning in science. Clarity is the key.

The inflation model is not build on a concept of empty vacuum devoid of anything material., i.e. it is not a concept of 'nothing'.
It does contain 'something' for instance a scalar field that has the property of motion/change, and therefore it is material.
It is devoid however of any kind of 'normal' material stuff, like the atoms and particles and photons we know of, and where everything is made of.

The vacuum IS a field, or failing a unified field theory, fields. The reason they call inflation a free lunch, is because the energy in the inflated region increases enormously, as if the energy conservation law is being violated. The claim however, is that because the net energy of the universe is zero, no such violation has occured.

 

[Eh]

Originally posted by heusdens
What it comes down to that we cannot talk sensibly about the existence of space and time without the concept of matter. If it were not for matter, neither time or space would exist.

This is what I mean about the use of the word matter. In physics, a field is not considered matter. Neither is energy. So when discussing physics, I don't mean fields or energy when I talk about matter. But just to clear things up, we are in agreement here. Space-time has no existence without fields.

There was no existing state prior to the t=0 singularity.
All matter started out from that state, and 'created' time and space for it's existence.

Since singularities aren't likely to be real, the initial state would have been a finite space-time, so to say time and space were 'created' would not have any meaningful definition. And that is the focus of the topic. A beginning is consistent mathematically and with observations. This doesn't mean it's correct, it just means it can't be discounted on the basis of intuition.

Now you mentioned that inflation and other models are better explanations for the observed universe. They are, but they aren't competing theories! Inflation occurs from a pre-existing space-time, and so is compatible with the big bang. In fact, inflation would be viable whether or not the big bang actually happened. Alas, no such models can deal with the expanding universe as you trace back the clock.

...Further more GR does not require perse that there was a singularity.

See for examle http://xxx.lanl.gov/abs/gr-qc/9810054".

The singularity theorems of Hawking take into account certain assumptions about the mass content in the universe. So if those assumptions are wrong, it has been said the singularity could be avoided. But we've still got a problem.

Let's assume the singularity is avoided, through quantum gravity or some other means. The universe is still expanding and as you go back into the past it gets smaller and denser. Once you hit the minimum size the universe can get (the Planck scale?) what then? Unless you want to argue the universe had existed for an eternity in that small and dense state before expanding, you're facing a beginning. But it's not really an option, because cosmology does not allow such a static state for the universe. So unless there is a mechanism present to allow for a cyclic universe, a minium size is likely to mean a minium time (beginning) for space-time.

 

[heusdens]

Originally posted by Eh
Now you mentioned that inflation and other models are better explanations for the observed universe. They are, but they aren't competing theories! Inflation occurs from a pre-existing space-time, and so is compatible with the big bang. In fact, inflation would be viable whether or not the big bang actually happened. Alas, no such models can deal with the expanding universe as you trace back the clock.



The singularity theorems of Hawking take into account certain assumptions about the mass content in the universe. So if those assumptions are wrong, it has been said the singularity could be avoided. But we've still got a problem.

Let's assume the singularity is avoided, through quantum gravity or some other means. The universe is still expanding and as you go back into the past it gets smaller and denser. Once you hit the minimum size the universe can get (the Planck scale?) what then? Unless you want to argue the universe had existed for an eternity in that small and dense state before expanding, you're facing a beginning. But it's not really an option, because cosmology does not allow such a static state for the universe. So unless there is a mechanism present to allow for a cyclic universe, a minium size is likely to mean a minium time (beginning) for space-time.

The eternal inflation theory, we are talking about, as far as I know it states otherwise. We are then not dealing with a Big bang, in which at the beginning there was inflation, but with an inflationary regime, which as a matter of fact "stands on it's own".
Big bang theory becomes then part of inflation theory, and not the other way around.

But I could be wrong, but this is the interpretation I have read from eternal / chaotic / open inflation, in the theory of Andrei Linde.

 

[Eh]

Apparently the expansion still must start in a singularity with eternal inflation models. Like I said, there have been a lot of papers on the subject of an infinitely old inflationary universe over the past few years, and there seem to be several problems with the idea. But nothing is certain.

 

[heusdens]

Originally posted by Eh
Apparently the expansion still must start in a singularity with eternal inflation models. Like I said, there have been a lot of papers on the subject of an infinitely old inflationary universe over the past few years, and there seem to be several problems with the idea. But nothing is certain.

There ain't anything wrong with that. Inflation theory is not and can not describe the endpoint to physics theories about the early universe.

Matter is eternal, in that it can not be created or destroyed.
But all material forms are always of a finite extend, never will we be able to perceive of infinity.

 

[wimms]

Originally posted by Eh
A brick wall is a bad example, since a building is necessarily embedded in something else. But the gist of it is correct. Since we have can define an area or volume by itself, we don't need infinite space. That doesn't mean the idea of infinite space is wrong, it's just not necessarily required.

No, I don't think brick is bad example. Creatures inside the brick don't know that building is necessarily embedded in something else. They check their math and calmly declare that there is nothing else, because its just enough to describe their existence without considering anything else. Their models work, ergo, they are right. And we outside the brick are puzzled, we knock-knock on the brick 'wait a minute, what about us??' And creatures inside brick doublecheck their math, watch out and say 'nope, sorry, you do not exist..next please..'

It's not an assumption, it's just the definition. If there is something logically inconsistant about it, no one has of yet been able to show how.

Well, how can there be something inconsistent, if that is defined to be true. I'm puzzled about this: we have those beautiful models, consistent with local observation, that don't need infinite space. Thats perfectly okay. But at which point in thinking process does scientist find justification to say that universe IS indeed finite? One thing is model, one thing is limits to our observable universe, but to stand up and say whew, now we know universe is finite??

Correct, and remember that the point I'm stressing is that finite space suffers from no logical inconsistency. Thus either infinite or finite could actually be an accurate description of reality.

Ahha, so we are still talking about assumptions of specific models?

But a beginning to time does not actually present a problem, because comsology is based on mathematical models. So long as the model does contain any internal inconsistency, there is no trouble. And that is the point I'm trying to stress. A beginning of time posses no mathematical inconsistency. What DOES give physicists problems is the notion of an infinitely dense point of zero volume.

Well, sure it does not present problem to a model. Model itself is finite, so its no surprise. I find suprising that we do not view time as something physical, while pondering about notions of infinitely dense point. We step onto infinite one way or other. We have point where time was created which is not a problem, we accept that energy was there, although there exists no meaning of energy that didn't include hidden concept of time.

The proposal for the universe is merely that there is no before the big bang. And that's really all it comes down to. Effectively, such a universe IS eternal, since it has existed for all time.

This can be understood. There are logical arguments to support finite minimum meaningful units of existence. For eg. distance between 2 points can be arbitrarily small, but it cannot be zero, for then there is no 2 points. For us Planck scales are minimum meaningful units, but this doesn't mean there isn't anything below, its just limits of our observable universe. Extrapolating existence to time zero is meaningless, for there is no existence without time.
Thus maybe existence was below Planck scales, but to say that time had a start is effectively creation from nothing. Not that is a problem that our models trace back to start of our observable universe together with our Planck scales, but claim of exact zero point of time. Do models actually predict zero time? They brake down well before that, its we who interpret the models come out and extrapolate.
Btw, we don't have problems with time dilation in SR, but what about that near BB? Observer near BB might not even know that he is part of spectacular BB event. For him its same calm boring expanding universe..

I would seriously like to see a logically supported argument that the universe cannot be finite. Math can describe possible worlds, but only one of those descriptions will actually describe the world we live in. While infinity may be a more intuitive description of space, finite is equally possible.

Well, its not math or physics question, would you agree? Its philosophycal question, besides perfectly working models.
At least by same logic as having no before BB makes universe eternal, having no beyond makes universe infinite. Is it intuitive? Universe, made from finite stuff, of which there is finite/infinite amount, is itself infinite. And growing.

Why not finite? Here's what confuses me, looking like unjust assumptions.
- what happened once, will happen again. assume: it can't happen again, it doesn't.
- energy cannot be created. assume: just once, and net energy is still zero.
- without time, there is no concept of energy, space, existence. No, time is just coordinate in our models. It can't be negative beyond BB though - because it makes no sense, obviously.
- fields are infinite although universe isn't. well, no problem..its big enuf
- there is no center of inflation. well, it was some bigass singularity..
- finite volume means finite radius, what about R+1? postulate: by definition there is no R+1!
- but, er, inflation? R is increasing!? postulate: its possible.
- if there is no beyond, where to does it inflates then? If R increases, there is no need for observable inflation.
- 13b years is like abit on low end. - sorry, that best we could do.

Question is about what is considered infinte? Extent, amount of energy/matter? Amount of differentiable concepts? Universe as Such is unique, single entity. It'd be unique eternally, no matter if it exists or actually doesn't. Similarily, its extent is infinite, has it one part or infinite parts. In same way as set of all reals is unique but has infinite parts. There is no beginning nor end of it, in any direction.

Inflation means that there is increase of differentiable spatial points. Where does this come from? It happens here and now. Is it creation or inflation of Planck scales? BB didn't just happen once, its eternal event?

I stress that I don't want to question validity of any theory, I'm just confused by the confidence with which we are told that BB was pointzero..

 

[Eh]

Originally posted by wimms
No, I don't think brick is bad example. Creatures inside the brick don't know that building is necessarily embedded in something else. They check their math and calmly declare that there is nothing else, because its just enough to describe their existence without considering anything else. Their models work, ergo, they are right. And we outside the brick are puzzled, we knock-knock on the brick 'wait a minute, what about us??' And creatures inside brick doublecheck their math, watch out and say 'nope, sorry, you do not exist..next please..'

It's a bad example because bricks are contingent upon a number of factors. But you're still missing the point. A finite space is logically consistent, but so is infinite space. No one is insisting space must be finite, only that it is a possibility. Nor is anyone suggesting the universe must be infinite, only that it is also a possibility.

Well, how can there be something inconsistent, if that is defined to be true.

I'm puzzled about this: we have those beautiful models, consistent with local observation, that don't need infinite space. Thats perfectly okay. But at which point in thinking process does scientist find justification to say that universe IS indeed finite?[/quote]

They cannot, unless the find that light from the same stars in several locations in the sky, which is only possible in a finite universe. As I said above, only the logical consistency is the subject here. Insisting space must be infinite is not based on reason.

One thing is model, one thing is limits to our observable universe, but to stand up and say whew, now we know universe is finite??

See above.

Ahha, so we are still talking about assumptions of specific models?

No, we're taking about the logical consistency of such models. It has nothing to do with whether or not they reflect reality. Math can describe possible worlds, but observation and experiment can tell us which world we actually live in.

Well, sure it does not present problem to a model. Model itself is finite, so its no surprise. I find suprising that we do not view time as something physical, while pondering about notions of infinitely dense point. We step onto infinite one way or other. We have point where time was created which is not a problem, we accept that energy was there, although there exists no meaning of energy that didn't include hidden concept of time.

No, that isn't what I'm talking about at all. The standard model does not predict a timeless state of energy before the big bang.

This can be understood. There are logical arguments to support finite minimum meaningful units of existence. For eg. distance between 2 points can be arbitrarily small, but it cannot be zero, for then there is no 2 points. For us Planck scales are minimum meaningful units, but this doesn't mean there isn't anything below, its just limits of our observable universe. Extrapolating existence to time zero is meaningless, for there is no existence without time.

Thus maybe existence was below Planck scales, but to say that time had a start is effectively creation from nothing. Not that is a problem that our models trace back to start of our observable universe together with our Planck scales, but claim of exact zero point of time. Do models actually predict zero time? They brake down well before that, its we who interpret the models come out and extrapolate.

No, this is incorrect. Saying time had a beginning is not saying the universe was created from a prior state of nothing. It's just the first moment where no such "before" can have any meaning. The stanard model predicts space and time vanish at t=0, but no one seriously suggests that is an accurate picture of the early universe. A quantum theory of gravity will be needed for that, but there is still likely to be a beginning, for reasons I covered in this thread.

Btw, we don't have problems with time dilation in SR, but what about that near BB? Observer near BB might not even know that he is part of spectacular BB event. For him its same calm boring expanding universe..

He might be a little hot though, with that damn temperature being trillions of degrees.

Well, its not math or physics question, would you agree? Its philosophycal question, besides perfectly working models.

Remember, the topic here is of the logical validity of these models. Math is just another form of logic, so it's certainly in the realm of philosophy.

At least by same logic as having no before BB makes universe eternal, having no beyond makes universe infinite. Is it intuitive? Universe, made from finite stuff, of which there is finite/infinite amount, is itself infinite. And growing.

I tried to point out that "effectively eternal" is not the same as having infinite time. So no, finite space is not infinite.

Why not finite? Here's what confuses me, looking like unjust assumptions.

- what happened once, will happen again. assume: it can't happen again, it doesn't.

I don't understand the meaning of this? How is this an argument against finite space?

energy cannot be created. assume: just once, and net energy is still zero.

Energy can be created from the vacuum. But the big bang does not suppose energy was necessarily created, though the classic singularity has some problems with that.

without time, there is no concept of energy, space, existence. No, time is just coordinate in our models. It can't be negative beyond BB though - because it makes no sense, obviously.

Since no one is proposing a timeless state prior to the big bang, this is a non-issue.

fields are infinite although universe isn't. well, no problem..its big enuf

Who says fields must be intinite? Actually, space-time itself is just the gravitational field. It can be finite or infinite.

there is no center of inflation. well, it was some bigass singularity..

What are you talking about?

finite volume means finite radius, what about R+1? postulate: by definition there is no R+1!

Again, what?

but, er, inflation? R is increasing!? postulate: its possible.
- if there is no beyond, where to does it inflates then? If R increases, there is no need for observable inflation.
- 13b years is like abit on low end. - sorry, that best we could do.

As I pointed out before, the universe expands but does not need to be expanding into something else. Much like how volume is defined without the need for outside space, the volume of the universe increases without the need for space-time to be embedded in some extra dimensional space.

Question is about what is considered infinte? Extent, amount of energy/matter? Amount of differentiable concepts? Universe as Such is unique, single entity. It'd be unique eternally, no matter if it exists or actually doesn't. Similarily, its extent is infinite, has it one part or infinite parts. In same way as set of all reals is unique but has infinite parts. There is no beginning nor end of it, in any direction.

This has already been covered in this thread. 3 potential infinites (spatial extent, time, divisibility space) with addtional infinities that necessarily come with infinite space or infinite time. For example, an infinite universe necessarily has an infinite amount of mass, galaxies, etc.

Inflation means that there is increase of differentiable spatial points. Where does this come from? It happens here and now. Is it creation or inflation of Planck scales? BB didn't just happen once, its eternal event?

I don't know exactly what you're asking here.

I stress that I don't want to question validity of any theory, I'm just confused by the confidence with which we are told that BB was pointzero...

The point I have been stressing is NOT that the BB must have been the beginning of time (though there are good reasons to believe so) but that it is logically consistent.

 

[heusdens]

What is infinite?

The only candidate for infinity is matter itself, which does not necessarily imply infinite space or time, or infinite amount of matter, but it denotes that material forms are infinite, and relations between material forms are infinite.

 

[heusdens]

Originally posted by Eh
The point I have been stressing is NOT that the BB must have been the beginning of time (though there are good reasons to believe so) but that it is logically consistent.

What is the 'logic' of a beginning of time?
Matter appearing from nowhere for no appearant reason??
That is just supernatural!

 

[Eh]

The universe appearing out of nowhere is a strawman. If you can find a logical inconsistency with a beginning to time, simply point it out. Strawman arguments don't cut it.

 

[Eh]

Originally posted by heusdens
What is infinite?

The only candidate for infinity is matter itself, which does not necessarily imply infinite space or time, or infinite amount of matter, but it denotes that material forms are infinite, and relations between material forms are infinite.

Since space has no existence without matter/energy, infinite matter is also necessarily infinite space.

 

[heusdens]

Originally posted by Eh
Since space has no existence without matter/energy, infinite matter is also necessarily infinite space.

Einfuhrung in der dialektischen und historischen materialismus (Dietz Verlag 1980 Berlin)

Kapitel V

Materie und ihrer Existenzformen

4. Die Unendlichkeit der Materie

(...)

"Die philosophische Erkenntnis von der Unendlichkeit der Materie widerspiegelt nicht ein bestimmtes Alter oder einen bestimmten Raumbereich. Sie widerspiegelt die Ewigkeit des materiellen Formwandels, die Unerschopflichkeit der Entwicklungsformen der Materie und ihrer raum-zeitlichen Beziehungen. Unendlichkeit der Materie bedeutet, daß sich jede endliche Entwicklungsform der materie I am endlichen Raumbereich mit endlichem Alter bei ihre Umandlung wider in eine andere Entwicklungsform der Materie verwandelt, ebenfalls I am endlichen Raumbereicht mit endlichen Alter".

Translation:

"The philosophical acknowledgment of the infiniteness of matter does not reflect a determined age or spatial extent. It denotes the eternity of material transformations, the [Unerschopflichkeit] (uncreatability?) of material forms and their timely/spatial inter-relations. Infinitness of matter means, that all development forms of matter in a finite space and finite time change in their transformation into a new development form of matter, which is also within finite time and spatial extents".

Nb. the translation is far from perfect, I hope I expressed the meaning correctly though

 

[Eh]

Oh, I thought you meant an infinite quantity of matter.

 

[heusdens]

Originally posted by Eh
Oh, I thought you meant an infinite quantity of matter.

The quantity of matter is not determinable, I think. Well scientificially said, there is only the possibility of determine it to be of finite extend, but a lack of proof for a finite amount of matter is no proof for an infinite amount of matter.

But you might be right that somewhere I have said that, it must have slipped from the keyboard.