The Universe: Finite or Infinite?

[cragar]

could we say that there is only so much space but its a finite volume .
like an infinite series it goes on forever but it can converge to a finite area. A fixed number. So could space go on forever and have a finite volume.

 

[x→∞]

could we say that there is only so much space but its a finite volume .
like an infinite series it goes on forever but it can converge to a finite area. A fixed number. So could space go on forever and have a finite volume.

So according to what you said, space can contain a finite amount of matter (finite volume), although space itself is infinite? If the volume is finite, it must have a finite shape and boundaries in which the finite volume is contained. Then what is beyond those boundaries? It's impossible to tell, but theoretically speaking, what you are saying implies that there must be some sort of boundary.

 

[cragar]

there does not neccessarily have to be a boundry for example the improper integral from -inf to +inf of 1/(x^2+1) the bounds go forever i both directions but it has a finite area of (pi) 3.14 the limit as x approaches infinty of arctan(x) =pi/2 then multyply it by 2 cause we have 2 sides so we get pi . even tho the bounds go for ever we have a finite area .

 

[kenny30]

this is a question and not a reply.
when we look at very distant galaxi,we go back in time and we see the state of that galaxi supposing 12 billion years ago.
but 12 billion years ago the matter making the universe was very close to each other due to the theory of the big bang.
and here we are now looking at that galaxi 12 billion years later,looking at the light emitted by,that blob of matter when we were very close to it.and because the speed of light is ultimate and much faster than the matter making our beiing ,
(telescopes,eyes,brains,solaire systeme and galaxy ...Etc)that light should have passed by the matter that make us long time ago.

we should be moving with that light at the same speed,impossible!
is there a paradox or something wrong with big bang or the speed of light theories.

 

[Gan_HOPE326]

Hmm... I'm not 100% sure of what I'm going to say cause I'm not a physicist, but

this is a question and not a reply.
when we look at very distant galaxi,we go back in time and we see the state of that galaxi supposing 12 billion years ago.
but 12 billion years ago the matter making the universe was very close to each other due to the theory of the big bang.
and here we are now looking at that galaxi 12 billion years later,looking at the light emitted by,that blob of matter when we were very close to it.and because the speed of light is ultimate and much faster than the matter making our beiing ,
(telescopes,eyes,brains,solaire systeme and galaxy ...Etc)that light should have passed by the matter that make us long time ago.

we should be moving with that light at the same speed,impossible!
is there a paradox or something wrong with big bang or the speed of light theories.

I think this could be because speed of light limitation doesn't apply to universe expansion. During the "inflation" universe should have expanded actually faster than light. Lightspeed is a limitation due to our space-time construct: expansion is the creation of that same space-time. Then, after all, probably 12 billions year ago that galaxy was already very far from us - 'cause the universe experienced its biggest expansion in its first moments. If it was, say, 8 billions LY from us, then it took 8 billion years for light to reach our former position - but in the meanwhile, we went a little further. So it took a little more and so on - finally, it's 12 billion years. More or less ...

Or maybe the universe definitely is a curved, finite one (meaning, with curved, it has a "Riemann" or spherical geometry), and light just went round and round since it came to us... again. Maybe we're just looking our own galaxy how it was 12 billion years ago, after its image turned the whole universe. Ok, this is madness .

 

[honzik]

Hi,
Finity of the universe for me doesn't mean that it has finite volume but that it is space-ly bounded (ie. there exists distance D that every two points in the universe have distance between them lower than D).

I think that a) inflation theory implies finite universe or b) I don't understand inflation theory.

So to be able to discuss about inflation we have to define what we understand under this term. Or to be less strict - what are the exhibitions of inflation.

The first and major question of all is:

(*) Did inflation took place in the whole universe (no matter whether it is finite or infinite)?

I think both possible answers (yes or no) can lead into contradiction if we suppose the universe is infinite. But please answer the question first to lead our discussion in one direction only.

Thank you very much.

Honzik

 

[TalonD]

Hmmm..

b)

 

[kenny30]

thanks to Gan_HOPE326 for answering my question.
i think the concept of inflation that u described should apply not only to space but to time too i guess.
so in this case cosmologist will be having another problem in giving our universe an age which is between 13.5 and 13.7 billion years old.
because if there is an inflation in time,the flow of time in the early universe would be much different than the flow of time in the actual universe .
i mean a second won t be a second as we know it know ,
and a year won t be a year as we know it now.
so the universe could be 20 or 30 billion years older or more
and probably the constant of speed of light could have been much different than the (c)
as we know it in the actuel universe .but who knows.?

 

[DevilsAvocado]

thanks to Gan_HOPE326 for answering my question.
i think the concept of inflation that u described should apply not only to space but to time too i guess. so in this case cosmologist will be having another problem in giving our universe an age which is between 13.5 and 13.7 billion years old.
...

I'm just a layman (not avocado, nor advocate ), but I think I can help you.

This question about light from very old (and at that time near) "objects" almost drove me crazy , before I found the logical answer on Wikipedia. Inflation could be some part of the answer, but the real "heavy" thing here is Einstein's General Relativity, which describes gravity as a geometric property of spacetime (the curvature of spacetime).

The key thing to understanding this, is that the light from very old objects, actually were emitted at an angle of 45° towards Earth, and furthermore had to work its way "upstream" the expansion of spacetime.

I strongly doubt that speed of light (c) has varied... That's the only constant thing Einstein left for us to hold on to...

Here is the link (including nice pictures):
http://en.wikipedia.org/wiki/Expanding_universe#Understanding_the_expansion_of_space"

 

[DevilsAvocado]

Dear Pjpic,
George Jones who is both a PF mentor and someone with academic specialization in cosmology effectively answered the question. But you couild reasonably ask for more elaboration and say that what you've been able to find in your other readingon it is either:
1. not spelled out in simple language, or
2. too contaminated with noise and disagreement about the meaning of words.
So I'll make a stab at clarifying for you.

I think what Mattex is asking is if you could freeze expansion at the present instant of cosmological time and then were able to wander freely around and explore all of space,then would it turn out to have infinite volume or would it have finite volume?

...

(Perhaps I'm throwing stones in a glass house, with this question...? marcus, you have to excuse me for this... )

But I think the real "forbidden" question here is - What is the universe expanding into?

I.e. mattex & Pjpic are very "polite", but I guess the (traumatic) underlying problem/question is - what the heck is that extremely generous "thing" providing bigger and bigger "living room" for our maniac accelerating universe. (Packman seems like a nice guy in comparison)

(Please note; I'm NOT religious at ALL)

We can get lost in formal discussions about finite versus infinite, flat versus open/closed, etc. And if we calculate with spacetime and gravity (GR) - it becomes impossible to just talk in words about where we are and what is now, and what happened first, etc.

So, the one thing we surely can agree on (in words), is that our observable universe is expanding at accelerating rate. This no-one can deny.

Thus, if our universe is finite - there MUST be "new room" for this expanding monster at almost twice the speed of light. Where does this "new room" come from??

And if our universe is infinite - there MUST be "extra room" for this expanding monster at almost twice the speed of light. Where does this "extra room" come from??

I know it's "forbidden" to talk about things that we never ever will be able to come in contact with. But if guys like http://en.wikipedia.org/wiki/Multiverse" can talk about Multiverse and "bubbles" we never ever will be able to come in contact with...? Why can't I talk about what we are expanding into??

You can twist this as much as you want. The bottom-line is that our universe is like BIG expanding aquarium (with some stupid fishes = me) in a room that is providing more and more space for the aquarium.

In my head this construction doesn't work! It's not a real thing... And the thing that finaly makes me throw up is – WHAT THE HECK IS OUTSIDE THIS LIVING ROOM?? HELP!

(I'm not crazy... yet... )

 

[Gan_HOPE326]

WHAT THE HECK IS OUTSIDE THIS LIVING ROOM?? HELP!

(I'm not crazy... yet... )

But I'm not sure this question really makes sense... think of it: the universe being "bigger" means, more or less, it has "room for more matter". What determines matter's dimensions? Mainly, Planck's Constant, from which we can deduce an electron's cloud vastness, and then how big an atom is. And the constants which determine the intensity of the four interactions, then (consequently) the speed of light, and so on. The "scale" of our universe is all comprised into this kind of stuff. But, they're all internal laws to OUR universe, right? So, why should our universe need "space" to expand? It's just that it can "contain more matter" second after second.
Plus, expansion is a temporal concept: but if we want to take a look to our universe from outside, it's got to be four-dimensional (or even worse...). Then, its shape is already determined in all of the four dimensions: the space for the future, bigger versions of our universe is already booked!

 

[Dmitry67]

And if our universe is infinite - there MUST be "extra room" for this expanding monster at almost twice the speed of light. Where does this "extra room" come from??

No.
Take an infinite line: -inf .. +inf
every point on that line is defined by the real number X

Now expand this line to 200%: every point on then new line will be 2*X
All distances now doubled.

Where did the line expand into? :)

In mathematics, you can not use the naive common sense measurements of 'space', 'volume', etc to compare infinite sets. For infinite sets, there are other methods (cardinality for example).

Note that even the law of conservation of mass/energy is not applicable tot he WHOLE universe (even it is valid in every small region)

 

[Dmitry67]

I know it's "forbidden" to talk about things that we never ever will be able to come in contact with. But if guys like http://en.wikipedia.org/wiki/Multiverse" can talk about Multiverse and "bubbles" we never ever will be able to come in contact with...? Why can't I talk about what we are expanding into??

You can talk about it in the context of superstrings, the BULK, and the multidimensional "landscape"

So yes, you can talk about it.

But, it is possible that there are NO other entities except our universe. Mathematically, the curved spacetime does not require it to be 'embedded' into some more highly dimensional euclidean space.

It is just curved, for us it is easier to understand to when we look at it 'from the outtside', but it is just a limitation of our brains. Flat/euclidean space is not more 'natural' then curved space; we just got used to it in our everyday life, so it got hardwired in our brains.

 

[Gan_HOPE326]

Note that even the law of conservation of mass/energy is not applicable to the WHOLE universe (even if it is valid in every small region)

Really? I thought this had to be one of the few things we could hold for certain. I mean, except for instantaneous quantum fluctuations (like virtual particles being born and disappearing in the blink of an eye). You mean mass can be created - or disappear? Under what circumstances?

 

[Dmitry67]

The problem is that when you take 'time slices' of the universe say, ‘the whole Universe Now’ or ‘the whole universe 1 year after the Big Bang’, these ‘slices’ do not form valid rest frames. So the conservation laws are not applicable to such entities – I repeat – laws are not VIOLATED, they are just NOT APPLICABLE. So no particles magically 'created' from nothing or disappeared into nothing.

So, if you look at the universe from any observer perspective, mass/energy IS conversed, but you observe just a tiny bit of the Universe and in different times (you see very far objects on their early stage of the evolution).

If you take the Cosmology point of view, which is really a ‘God’s eyes view’, or ‘Bird’s view’ in the terminology of Max Tegmark, then the picture becomes simpler, but energy is not conserved there.

For example, when our Universe becomes 10 times bigger, the matter becomes 1000 times less dense. But the radiation becomes 10’000 times less dense! In the Bird’s view, the extra energy is gone. For any observer, we just see it more and more red-shifted when we look further and further.

 

[Gan_HOPE326]

The problem is that when you take 'time slices' of the universe say, ‘the whole Universe Now’ or ‘the whole universe 1 year after the Big Bang’, these ‘slices’ do not form valid rest frames. So the conservation laws are not applicable to such entities – I repeat – laws are not VIOLATED, they are just NOT APPLICABLE. So no particles magically 'created' from nothing or disappeared into nothing.

So, if you look at the universe from any observer perspective, mass/energy IS conversed, but you observe just a tiny bit of the Universe and in different times (you see very far objects on their early stage of the evolution).

If you take the Cosmology point of view, which is really a ‘God’s eyes view’, or ‘Bird’s view’ in the terminology of Max Tegmark, then the picture becomes simpler, but energy is not conserved there.

For example, when our Universe becomes 10 times bigger, the matter becomes 1000 times less dense. But the radiation becomes 10’000 times less dense! In the Bird’s view, the extra energy is gone. For any observer, we just see it more and more red-shifted when we look further and further.

Right, I didn't think about that.

Which makes me think something different... I'm expanding space, so distances increase as well. If two bodies have, say, gravitational potential energy -U, after the universe has expanded tenfold it's got to be -U/10, and this is rough, since I'm not using Einstein's general relativity, but just classical gravitation. Here energy pops out of nothing. Can't it be that the missing energy from radiation goes here, to potential energy for the interactions? Id est, that radiation pressure is just the force which gives the work needed to expand universe, creating new space? If so, mass/energy conservation would still hold.

 

[DevilsAvocado]

But I'm not sure this question really makes sense...
...
But, they're all internal laws to OUR universe, right? So, why should our universe need "space" to expand? It's just that it can "contain more matter" second after second.
Plus, expansion is a temporal concept: but if we want to take a look to our universe from outside, it's got to be four-dimensional (or even worse...). Then, its shape is already determined in all of the four dimensions: the space for the future, bigger versions of our universe is already booked!

Thanks Gan_HOPE326, for taking the time to try to answer this 'impossible' question.

I know this is a 'little bit' outside the mainstream cosmology, and extremely difficult to 'talk' about. Ned Wright gives this explanation in his FAQ - http://www.astro.ucla.edu/~wright/cosmology_faq.html#XIN":

"This question is based on the ever popular misconception that the Universe is some curved object embedded in a higher dimensional space, and that the Universe is expanding into this space. This misconception is probably fostered by the balloon analogy which shows a 2-D spherical model of the Universe expanding in a 3-D space. While it is possible to think of the Universe this way, it is not necessary, and there is nothing whatsoever that we have measured or can measure that will show us anything about the larger space. Everything that we measure is within the Universe, and we see no edge or boundary or center of expansion. Thus the Universe is not expanding into anything that we can see, and this is not a profitable thing to think about."

This is perfectly clear to me. And the odds to get the Nobel Prize in studying "the thing outside" our universe, is not outstanding. The Holy Grail of this question is this line:

"Thus the Universe is not expanding into anything that we can see, and this is not a profitable thing to think about."

This is also perfectly clear to me. Why should a professional scientist spend valuable time on this 'impossible' question? There are thousands and thousands other questions with much better prognosis for a real solution... Reasonably - this is 'stupidity' and a waste of time (for a pro).

But for me, as a layman, it's extremely interesting and fun to speculate about. And it doesn't cost me much (in status or money).

I also have come to the conclusion that "the thing outside" probably must have extra dimensions, additional to our four-dimensional spacetime. But I'm not sure I can follow your reasoning all the way:

"... the space for the future, bigger versions of our universe is already booked!"

Take a look of http://upload.wikimedia.org/wikipedia/commons/3/32/Embedded_LambdaCDM_geometry.png" (Lambda-Cold Dark Matter) cosmological model, showing one dimension of space and one of time (the red line is the path of a light beam emitted by the quasar about 13 billion years ago and reaching the Earth in the present day).

How can we state that geometrical status of our universe in 13 billion years from now "is already booked"!?

I could be wrong? But doesn't this mean that our universe is perfectly deterministic?? This is NOT what the QM-guys (quantum mechanics) are telling us?? We can make very good mathematical predictions, but noting is absolutely written in stone - about the future?

So, how can we state anything 100% sure about our universe in 13 billion years from 'now', and how can the 'future space' already be "booked"??

(An easy way to get rid of this problem is to say - Yeah, yeah Dude! And what do we know of the determinism in "the thing outside"!? Absolutely nothing, nada, zero, zip! )

Another thing that often pops up in this kind of discussions is "extra dimensions". But I'm not sure this satisfies me. Take one thousand extra dimensions, and you still have the problem of a physical reality that seems (in some way) impossible...

Dmitry67 (thanks!) talks about "the Cosmology point of view, which is really a ‘God’s eyes view’, or ‘Bird’s view’" (and I like that very much!). Now with this view - visualize our observable universe - 14 billion parsecs (46.5 billion light-years) at least. And according to Alan Guth (founder of the theory of cosmic inflation), the entire Universe could be at least 1023 to 1026 times as large as the observable universe.

Imagine the enormous amount of matter/energy in our giant universe. And recall that only 4% of the universe is ordinary matter/energy that we can see - 96% we cannot see (Dark Matter & Dark Energy).

How on Earth can this extremely 'heavy thing', that is our universe, just 'float around' in some weird nothingness? That furthermore doesn't exist!? And at the same time provides more 'room' for our extremely fast 'expanding giant'??

This is an absolutely mind-blowing thought - no matter how many dimensions you add to this scenario - you always run into the 'irrational wall'. To me it seems as an impossible construction: A never-ending series of a "Russian Nested Doll"-reality. If you find the answer for "one doll", then instantly a new question needs to be answered - Okay, AND what kind of "doll" is this one 'floating' around in??

My guess is that our brains are not developed enough (yet ) to comprehend this 'recursive reality loop'. Or... the universe and our existence is a fundamentally impossible construction that really cannot exist - in the way we percept the world...

(And I still claim; I'm not crazy... yet... )

(Dmitry67, thanks! I'll be back...)

 

[Gan_HOPE326]

I also have come to the conclusion that "the thing outside" probably must have extra dimensions, additional to our four-dimensional spacetime. But I'm not sure I can follow your reasoning all the way:

"... the space for the future, bigger versions of our universe is already booked!"

Take a look of http://upload.wikimedia.org/wikipedia/commons/3/32/Embedded_LambdaCDM_geometry.png" (Lambda-Cold Dark Matter) cosmological model, showing one dimension of space and one of time (the red line is the path of a light beam emitted by the quasar about 13 billion years ago and reaching the Earth in the present day).

How can we state that geometrical status of our universe in 13 billion years from now "is already booked"!?

I could be wrong? But doesn't this mean that our universe is perfectly deterministic?? This is NOT what the QM-guys (quantum mechanics) are telling us?? We can make very good mathematical predictions, but noting is absolutely written in stone - about the future?

So, how can we state anything 100% sure about our universe in 13 billion years from 'now', and how can the 'future space' already be "booked"??

(An easy way to get rid of this problem is to say - Yeah, yeah Dude! And what do we know of the determinism in "the thing outside"!? Absolutely nothing, nada, zero, zip! )

Thanks to you, for popping out such a mind-breaking question. As for you (a layman), for me (actually, right now, a PhD student in Physics... but in a completely different field. And anyway, my life changed a lot and in unpredictable ways since my first post in this topic. Another demonstration that the universe definitely isn't deterministic ) this kinda speculation is fun. Anyway, what I meant was not about universe being deterministic or not... Even if it's quantum-mechanical, our universe (I'd like to point out I'm saying our. If we believe in the many-worlds interpretation of QM, universe doesn't evolve randomly, it's just that there's a lot of them) has a past, a present, a future. Time is really a convention, a dimension perfectly equivalent to others (try reading Julian Barbour's work... look for his "Platonia" website. He's got some interesting ideas up his sleeve!), so it's not like our universe is a three-dimensional one evolving through time. Our universe is a four-dimensional thing, it's us that we're seeing it frame-by-frame. Like an avi file: the whole lot is there, it occupies a certain space on your hard-disk; different frames may occupy different space because of the compression algorithm, but the total is fixed. Seeing it in a time sequence doesn't mean it stops occupying all of his size. That's more or less what I meant with "space already booked". I don't think that when a physics says trying to answer to this question isn't proficient he means he can't make a living out of it, it's just that it's "gnoseologically" not proficient. It's beyond our knowledge; more or less like debating if God exists or not. You can go on with similar debates for thousands years, but you just won't get an answer, cause, even if it exists, it's not for us to know. Or so it seems.

 

[DevilsAvocado]

Thanks to you, for popping out such a mind-breaking question. As for you (a layman), for me (actually, right now, a PhD student in Physics... but in a completely different field. And anyway, my life changed a lot and in unpredictable ways since my first post in this topic. Another demonstration that the universe definitely isn't deterministic ) this kinda speculation is fun.

Thanks again. Yeah, this forum definitely determine the indeterministic nature of the universe (and soon I'm going to be classified as an hopelessly incorrigible topic hijacker ).

This question is probably, as you say, "beyond our knowledge". But then again, we do have Max Tegmark, Sean Carroll, Multiverse and "bubbles"! If you could crack that nut - why not crack mine!?

I see you are into QM Many-worlds interpretation. Personally I don't like that solution. It's cheating. You can explain anything with that:

- Why can't I understand "the thing outside" our universe?
- Ohh, but you can! It's just happened that the "QM-one of you", that DID understand this, was split into another world in the same second you found the solution! Sh*t happens!

Julian Barbour is an interesting man, ...on a very thin line... I think... even as a layman I react when he says:

"If all distances in the universe were doubled over night, nothing would tell us this had happened."

Huuum... is this really true?? I think that the guy who measure the distance to the Moon every day is going to sh*t in his (new big 2x) pants, if this happened - since the laser beam (speed of light) would take twice the time yesterday, to make it to the Moon and back!

Maybe you're AVI-analogy is the real movie of our universe. Time is weird. Everyone who has been in love and to the dentist (but not at the same time!) knows this for sure. Or as my hero says:

The only reason for time is so that everything doesn't happen at once -- Albert Einstein

 

[DevilsAvocado]

No.
Take an infinite line: -inf .. +inf
every point on that line is defined by the real number X

Now expand this line to 200%: every point on then new line will be 2*X
All distances now doubled.

Where did the line expand into? :)

In mathematics, you can not use the naive common sense measurements of 'space', 'volume', etc to compare infinite sets. For infinite sets, there are other methods (cardinality for example).

Note that even the law of conservation of mass/energy is not applicable tot he WHOLE universe (even it is valid in every small region)

Dmitry67, thanks for taking the time to answer. Your answers were what I hoped fore from a real math-pro.

I realize that infinity is not a 'problem' for a mathematician. Even I can grasp mathematical infinity:

A = 1;
while (A > 0) {A++}

This code will continue forever and variable A will grow bigger and bigger and bigger (i.e. if you have the right 'hardware').

But can we really convert this to our physical world?? More and more and more and more and more and more and more energy/matter ... forever and ever and ever and ever and ever... ?

I could be out, knee-deep in the "Amateur Guessing Swamp" - But I thought that if you get infinity large (e.g.) energies in an equation, describing our universe, then something must be wrong with that equation?? (Or did I just drown in the "swamp"!?)

You can talk about it in the context of superstrings, the BULK, and the multidimensional "landscape"

So yes, you can talk about it.

But, it is possible that there are NO other entities except our universe. Mathematically, the curved spacetime does not require it to be 'embedded' into some more highly dimensional euclidean space.

It is just curved, for us it is easier to understand to when we look at it 'from the outtside', but it is just a limitation of our brains. Flat/euclidean space is not more 'natural' then curved space; we just got used to it in our everyday life, so it got hardwired in our brains.

This is so damn interesting! I do understand that very beautiful mathematical equations (Einstein/GR?) don't require our universe to be 'embedded' into something more. But just think about it for a sec or two - without the equations:

Our Universe; 46 billion light-years of 4% ordinary matter and 96% DM & DE (and maybe 1000 times as large in the cosmic inflation model)... Could ALL this stuff just 'HANG' out there?? Surrounded by nothingness that doesn't exist!? A nothingness providing more 'room' for our extremely fast (~2c) expanding universe??

Does this really look like a physical working picture for you?

 

[Chronos]

The observable universe appears to be temporally finite.

I do not see how a temporally finite universe can be infinitely large. A temporally finite universe can be unimaginably large, but, not infinite. Olber's paradox, imo, suggests an infinitely old universe should be in thermal equilibrium. This is not observed - e.g., :

Molecular Hydrogen in a Damped Lyman-alpha System at z_abs=4.224
http://www.arxiv.org/abs/astro-ph/0602212
. . . The high excitation of neutral carbon in one of the components can be explained if the temperature of the Cosmic Microwave Background Radiation has the value expected at the absorber redshift, T=14.2 K.

http://babbage.sissa.it/abs/astro-ph/0012222
The microwave background temperature at the redshift of 2.33771
Authors: R. Srianand (IUCAA, Pune), Patrick Petitjean (IAP, Paris), Cedric Ledoux (ESO, Munich)
Comments: 20 pages, 5 figures, accepted for publication in Nature, Press embargo until 1900 hrs London time (GMT) on 20 Dec 2000

The Cosmic Microwave Background radiation is a fundamental prediction of Hot Big Bang cosmology. The temperature of its black-body spectrum has been measured at the present time, $T_{\rm CMBR,0}$ = 2.726$\pm$ 0.010 K, and is predicted to have been higher in the past. At earlier time, the temperature can be measured, in principle, using the excitation of atomic fine structure levels by the radiation field. All previous measurements however give only upper limits as they assume that no other significant source of excitation is present. Here we report the detection of absorption from the first {\sl and} second fine-structure levels of neutral carbon atoms in an isolated remote cloud at a redshift of 2.33771. In addition, the unusual detection of molecular hydrogen in several rotational levels and the presence of ionized carbon in its excited fine structure level make the absorption system unique to constrain, directly from observation, the different excitation processes at play. It is shown for the first time that the cosmic radiation was warmer in the past. We find 6.0 < T_{\rm CMBR} < 14 K at z = 2.33771 when 9.1 K is expected in the Hot Big Bang cosmology.

 

[Dmitry67]

1 But can we really convert this to our physical world?? More and more and more and more and more and more and more energy/matter ... forever and ever and ever and ever and ever... ?

2
I could be out, knee-deep in the "Amateur Guessing Swamp" - But I thought that if you get infinity large (e.g.) energies in an equation, describing our universe, then something must be wrong with that equation?? (Or did I just drown in the "swamp"!?)

3
Does this really look like a physical working picture for you?

1
As a proponent of Mathematic Universe Hypotesis,
http://arxiv.org/abs/0704.0646
- this is very good reading,
I don't see any difference between physical and mathematical.

2
For that reason Newtonians gravity theory was not valid, because when applied to the infinite Universe, you got infinities. In General Realitivity you don't run into infinities even for the infinite Universe.

3
If a theory is a) self-consistent, b) is compatible with the observations I don't see reason to cry all the time "wow, but wait, the whole Universe is hanging in the nothingness! or wow, but it is infinite!" :)

 

[Dmitry67]

Our Universe; 46 billion light-years of 4% ordinary matter and 96% DM & DE (and maybe 1000 times as large in the cosmic inflation model)... Could ALL this stuff just 'HANG' out there??

Yes, it can, without any help of the turtles :)

 

[Gan_HOPE326]

I see you are into QM Many-worlds interpretation. Personally I don't like that solution. It's cheating. You can explain anything with that:

- Why can't I understand "the thing outside" our universe?
- Ohh, but you can! It's just happened that the "QM-one of you", that DID understand this, was split into another world in the same second you found the solution! Sh*t happens!

Julian Barbour is an interesting man, ...on a very thin line... I think... even as a layman I react when he says:

"If all distances in the universe were doubled over night, nothing would tell us this had happened."

Huuum... is this really true?? I think that the guy who measure the distance to the Moon every day is going to sh*t in his (new big 2x) pants, if this happened - since the laser beam (speed of light) would take twice the time yesterday, to make it to the Moon and back!

About the first thing: I'm not really into the many-worlds intepretation, meaning I don't really have chosen my way to look at QM. I was taught the Copenaghen interpretation, of course, so it still has deep roots in my mind; and I don't think that objective-collapse intepretations are really satisfactory. I find the many-worlds a definite possibility that I just don't want to discard. But, it's true, it seems quite easy. It's more or less admitting in this field too our inability to really understand the truth. But if we keep on surrendering at every single tiny difficulty...

But I think what Barbour says is absolutely true. He's not saying he's just pulling apart the moon, so its distance is doubled. He says "double every distance". It's like drawing something on a rubber sheet, then pulling it making it larger. You can see the difference because you're not part of the sheet; but if you were on it, with your deformed eye you'd see deformed rays of light that, on your point of view, would travel exactly at the same speed (but, seen from outside the sheet, they'd appear to travel faster). The scale factor between what's inside the universe and what supposedly is outside of it doesn't matter at all, simply because there's no known interaction between the two, so you can't make comparisons.

 

[Dmitry67]

DevilsAdvocado, regarding the QM ManyWorlds you are a victum of popular junk about the MWI.

1. There are no 'MANY' universes in MWI - everything happens in the same universe, just some parts of the omnium (almost) loses an ability to communicate forming 'branches'
2. When I make an experiment with different outcomes, I don't 'split' the whole Unvierse. The effect propagates at speed of light (or slower) via experimentally observed process called 'Qunatum Decoherence'
3. MWI does not make any additional assumptions expect we already have in QM. In that sense it is minimalistic. It does not even postulate the existence of the other branches: all that is derived using the standard QM stuff + Quantum Decoherence

 

[DevilsAvocado]

About the first thing: I'm not really into the many-worlds intepretation, meaning I don't really have chosen my way to look at QM. I was taught the Copenaghen interpretation, of course, so it still has deep roots in my mind; and I don't think that objective-collapse intepretations are really satisfactory. I find the many-worlds a definite possibility that I just don't want to discard. But, it's true, it seems quite easy. It's more or less admitting in this field too our inability to really understand the truth. But if we keep on surrendering at every single tiny difficulty...

But I think what Barbour says is absolutely true. He's not saying he's just pulling apart the moon, so its distance is doubled. He says "double every distance". It's like drawing something on a rubber sheet, then pulling it making it larger. You can see the difference because you're not part of the sheet; but if you were on it, with your deformed eye you'd see deformed rays of light that, on your point of view, would travel exactly at the same speed (but, seen from outside the sheet, they'd appear to travel faster). The scale factor between what's inside the universe and what supposedly is outside of it doesn't matter at all, simply because there's no known interaction between the two, so you can't make comparisons.

Okay, now I'm really confused...?

http://en.wikipedia.org/wiki/Copenhagen_interpretation#Nature_of_collapse"
"So if an electron passes through a double slit apparatus there are various probabilities for where on the detection screen that individual electron will hit. But once it has hit, there is no longer any probability whatsoever that it will hit somewhere else. Many-worlds interpretations say that an electron hits wherever there is a possibility that it might hit, and that each of these hits occurs in a separate universe."

Is it my brain that has split into impossible many QM-states?? Or... isn't the Copenhagen interpretation <> Many-worlds interpretation...??

I follow your reasoning about Barbour. But didn't he miss one very important factor? Doesn't Barbour also have to double the speed of light, for example, if the distance between Earth and Moon has doubled, and you want the same result as yesterday?? Or, Barbour has to decrease the speed of our atomic clocks to half?? But that's maybe comes automatically? From the increased (doubled? quadrupled?) gravitation of a doubled-sized Earth... (even if it seems like a too big 'effect' for a layman...)

And further more. Doesn't Barbour have to redesign ALL of the four fundamental interactions of nature, In the Standard Model of particle physics, the strong and weak nuclear force etc? If the all distances in the atom also get doubled??

A practical example: If our Sun would double in size overnight, and Barbour doesn't adjust the laws of physics accordingly, we would know something strange had happened last night! The Sun 2.0 would burn its fuel much faster, and hence would die much quicker. And the end of the Sun 2.0 would be a whole different enchilada, than the end of Sun 1.0!

Please, tell me I'm right on this one? I suddenly feel a clear mind!

 

[Dmitry67]

Copenhagen interpretation <> Many-worlds interpretation
Copenhagen interpretation (together with the 'collapse') is almost abandoned in 21th century. So forget about the 'collapse'

 

[DevilsAvocado]

Okay Dmitry67, thanks! I'm working on your other replays. I'll be back.

 

[Gan_HOPE326]

I follow your reasoning about Barbour. But didn't he miss one very important factor? Doesn't Barbour also have to double the speed of light, for example, if the distance between Earth and Moon has doubled, and you want the same result as yesterday?? Or, Barbour has to decrease the speed of our atomic clocks to half?? But that's maybe comes automatically? From the increased (doubled? quadrupled?) gravitation of a doubled-sized Earth... (even if it seems like a too big 'effect' for a layman...)

And further more. Doesn't Barbour have to redesign ALL of the four fundamental interactions of nature, In the Standard Model of particle physics, the strong and weak nuclear force etc? If the all distances in the atom also get doubled??

A practical example: If our Sun would double in size overnight, and Barbour doesn't adjust the laws of physics accordingly, we would know something strange had happened last night! The Sun 2.0 would burn its fuel much faster, and hence would die much quicker. And the end of the Sun 2.0 would be a whole different enchilada, than the end of Sun 1.0!

Please, tell me I'm right on this one? I suddenly feel a clear mind!

No, that's the point. Doubling distances means doubling everything: light speed is 3e8 meters per second, but in such a 2.0 universe, the very concept of "meter" would be doubled. It's not about enlarging objects: it's about stretching the fabric of space itself. That's why he says that nothing changes: or better, you could say it's even meaningless to think such a concept, because, how can you tell Universe 2.0 is twice the size of Universe 1.0 if you don't have anything external to the universe to measure it?

P.S. if we're talking about doubling linear distances, anyway, volumes, and then, roughly, masses, would be multiplied per 8. Yet still, since gravity goes as mass/square of radius, a "double radius" Earth, provided it had the same density than ours, would have a doubled gravitational force. And here's the trick: in Barbour's hypotesis, Planck constant, dielectric constant, Newton's gravitational constant etc. would change as well; as a result, we'd have an Earth made of bigger (less dense) atoms, with different laws, etc., so that its gravity wouldn't change from the original value.

 

[DevilsAvocado]

And here's the trick: in Barbour's hypotesis, Planck constant, dielectric constant, Newton's gravitational constant etc. would change as well; as a result, we'd have an Earth made of bigger (less dense) atoms, with different laws, etc., so that its gravity wouldn't change from the original value.

Okay Houston, I Read You Loud and Clear!

But as "Cranky Layman" I still argue that Barbour maybe should express his hypothesis in this way:

"If all distances, scales and (physical) constants in the universe were doubled over night - nothing would tell us this had happened."

This I will have for breakfast tomorrow!
(i.e. if the QM-guys do high-five as wel)

With all the respect for Barbour (and your interest in his theory), it does make me 'nervous' when he tries to visualize Eternity with this "thing" (that looks like a drying rack to me)...

http://www.youtube.com/watch?v=WKsNraFxPwk"

(Says the man who 'believes' Extra-Universal Space! )