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Thread: The Expanding Universe + Time (??)

  1. #1 The Expanding Universe + Time (??) 
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    I've been looking all over the internet for an answer to this question, and I am yet to find one, so I've decided I'll just have to ask. So, could someone explain to me what exactly is meant when it is said that the universe is expanding AND YET we supposedly live in a block universe, how can a tenseless universe expand? Wouldn't expansion of the system require time to exist outside the system as opposed to being a feature of the system.


    I did assume that the expansion was a referrence to the shape of the universe, in the sense that the further along the time axis you are, the larger the spatial dimensions would be, increasing the potential states for energy and matter to occupy and thus explaining the increase in entropy from low when space was constrained at the big bang to high when space is big and cold (so to speak) and subsequently the apparent arrow of time, etc. However, lately I've gotten the impression from reading up on things that this model isn't the accepted view, so now I'm just lost. Can someone please steer me back on track? Would be appreciated, thanks


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    Quote Originally Posted by Scientits View Post
    So, could someone explain to me what exactly is meant when it is said that the universe is expanding AND YET we supposedly live in a block universe, how can a tenseless universe expand?
    Can you please explain a bit more what you call a "block universe"? Please note that according to the accepted Big Bang paradigm, there is no "outside". The universe is the whole thing. Expansion simply means that the distance scale increases with time.


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    I am aware of that, I never said (or even implied) that the universe has an outside. On the contrary, I was making the claim that for a block universe to expand there would need to be a temporal dimension outside the universe for this to be possible, and since the universe does not (as far as we know) have an outside, this can't be right.

    And uhh, what do you mean? You've not heard of the block universe? I thought it was common knowledge in astrophysics
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    Quote Originally Posted by Scientits View Post
    And uhh, what do you mean? You've not heard of the block universe? I thought it was common knowledge in astrophysics
    Nope, this is the first time I come across this term, but that does not mean much, because cosmology is actually not my prime expertise. To me it sounds like "solid", "inert", "static". Maybe you can share a reference?
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    An infinite big universe implies infinitely much matter (infinitely many starts, galaxy...). When we say that the universe is expanding, you should't think of it as the volume of the universe getting bigger (the volume is already infinite). It's easier to understand through finite parameters, such as the distance between neighbouring galaxies.
    Below is an illustration. The o's are galaxies. I'll do it in 1 dimension for you, and let your imagination crank it up to 3.
    This universe have 1 dimension, and is infinitely big (long). That means there are an infinite amount of galaxies. Let's say they are evenly spread out at all time. Let's choose some random neighbouring galaxies, and see how they behave over time. On the first line of galaxies (the past) you see 17 galaxies, as they where some time ago. Today (present) all the distances has increased. The black galaxies doesn't fit on the illustration anymore, but they are still there, because they have an infinite "volume" to expand in! In the future, the distances will be even bigger, and the green galaxies will be out of view of this illustration too. I picked the blue galaxy to be the center on (thus, the illustration shows how it would look to us if we lived in the blue galaxy). Choose any other galaxy (including one far out the infinite line) as the center one, and you'll see the same thing.

    oo o o o o o o o o o o o o o o o oooooo<--- Past
    ooooooooooooooooooooooooooooooo<--- Present
    ooooooooooooooooooooooooooooooo<--- Future

    As to the "block universe"; no, it is not common language in astrophysics.
    Last edited by jmd_dk; August 16th, 2011 at 04:57 PM. Reason: Fixing the galaxies
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    I understand what you're saying, however, I was also under the impression that the universe was not thought to be infinite? I thought the current consensus was that the universe is finite but unbounded?
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    Okay, I researched a bit, and I think I understand now that the term "block universe" means that instead of time being considered as an agent that flows, it is regarded as something rather fixed and laid out and it is us that is actually "travelling" along it. From what I understand is that it is rather a philosophical concept than actually a physical hypothesis. To me, it seems to be derived from a misunderstanding of what relativity of time actually means, in particular in the framework of General Relativity. From my understanding, there are more alternatives than only the so called "block universe", where all "times" co-exist and a flowing and developing time.

    If you can comment on this, I think, we could start finding answers to your questions.
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    Just thought i would add this.
    From what i know about the time flow idea(s) is that, it is based on time passing in an absolute/fixed way.wind time backwards and we have a pre bb era...and a time before that...and so on..
    (My view however is ,im not suggesting a pre bb time,as it could indeed be an infinite time ago that the bb started)
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    Quote Originally Posted by Dishmaster View Post
    Okay, I researched a bit, and I think I understand now that the term "block universe" means that instead of time being considered as an agent that flows, it is regarded as something rather fixed and laid out and it is us that is actually "travelling" along it. From what I understand is that it is rather a philosophical concept than actually a physical hypothesis. To me, it seems to be derived from a misunderstanding of what relativity of time actually means, in particular in the framework of General Relativity. From my understanding, there are more alternatives than only the so called "block universe", where all "times" co-exist and a flowing and developing time.

    If you can comment on this, I think, we could start finding answers to your questions.
    Yeah, that's partly right, except that there is no flow of time in a block universe. All of space and time merely 'is', and the flow is just a subjective experience caused by the fact that at any given moment, we remember the past and not the future, due to the arrow of time, which itself is considered to be a consequence of the increase in entropy the further one is along the temporal axis. I certainly wouldn't call it a misunderstanding of general relativity, firstly because it derives more from Minkowski's work on special relativity in 1908. But also, because it seems that Einstein himself believed in the universe as a tenseless structure, as does Stephen Hawking and many others today, so even if it is wrong, it can't be called a misunderstanding of relativity.

    And yeah, it's often thought of as philosophical, but I'm not sure why, it seems like a natural consequence of special relativity, much the same way that extra dimensions are implicit in the mathematics of string theory, so it's as much a philosophical issue as the implications of string theory are.
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    Is this concept compatible with QM? To me it sounds very deterministic.
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    Quote Originally Posted by Scientits View Post
    I understand what you're saying, however, I was also under the impression that the universe was not thought to be infinite? I thought the current consensus was that the universe is finite but unbounded?
    Nope, the current consensus is that the universe is infinite in size (and thereby also unbounded). The flatness of space on cosmic scales is what leads to this belief.
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    Quote Originally Posted by Dishmaster View Post
    Is this concept compatible with QM? To me it sounds very deterministic.
    It is deterministic, and determinism in and of itself is pretty self-evident on the macro-level. Any supposed indeterministic occurrences on the quantum level have no impact on the on scales larger than that, unless you're a cat in a box inside some Austrian's head. The apparent probabilistic nature of quantum reality may only be an illusion anyway, or merely our macrocosmic way of interpreting it, who knows.



    Quote Originally Posted by jmd_dk View Post
    Quote Originally Posted by Scientits View Post
    I understand what you're saying, however, I was also under the impression that the universe was not thought to be infinite? I thought the current consensus was that the universe is finite but unbounded?
    Nope, the current consensus is that the universe is infinite in size (and thereby also unbounded). The flatness of space on cosmic scales is what leads to this belief.
    Fair enough, though the consensus view on the shape of the universe seems to change pretty often, being such a speculative branch of physics and all. Wouldn't surprise me if it turned out that the universe was in fact finite in size, it would certainly make a lot more sense for it to be. Hopefully the evidence will lead cosmology in this direction in the future.
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    There is no concensus.
    Wether infinite or finite and unbounded, the fact that inflation enlarged the universe by a factor of between 10^30 and 10^100 in a time of 10^-35 sec. is what accounts for the impression of flatness. Just like the world looks flat locally but is actually curved globally. See Alan Guth's inflationary Big Bang theory.
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    on the subject of expansion ,what i find hard to comprehend is that the big bang (the beggining of our universe)was actualy a microscopic event in the quantum world according to likes of profs brian cox and jim al-khalili, if this is so, how could all of the physical matter in the universe actually have expanded to the size it is now.
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    The simple answer is because all of the physical matter in the observable universe was contained in that microscopic event.
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    Quote Originally Posted by Scientits View Post
    Fair enough, though the consensus view on the shape of the universe seems to change pretty often, being such a speculative branch of physics and all. Wouldn't surprise me if it turned out that the universe was in fact finite in size, it would certainly make a lot more sense for it to be. Hopefully the evidence will lead cosmology in this direction in the future.
    Two things come to mind in response to your statement. One, Cosmology includes a consensus cosmology which evolves as the questions about the nature of the universe get addressed by the scientific community, as well as alternatives to the consensus. So there is always a consensus and it is very hard for a layman to stay abrest of what the current consensus is, and that includes me of course. Check this out for a 2010 update: BBC Horizon 2010: 1/6 What Happened Before the Big Bang - YouTube

    Two, though you would find the universe easier to understand if it was finite, some of us would find it easier to understand if it was infinite, lol. Immediately, those two view points focus on the Big Bang; if the Big Bang was the beginning then the universe had no preconditions. Those comfortable with a beginning with no preconditions will be more comfortable with a finite universe.

    To me however, "no preconditions" means that something came from nothing; and "preconditions to the big bang" means that the Big Bang event occurred within a pre-existing universe that could be infinite and eternal, IMHO.
    Last edited by Dark Speculator; August 26th, 2011 at 03:27 PM.
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    Quote Originally Posted by Dark Speculator View Post
    To me however, "no preconditions" means that something came from nothing; and "preconditions to the big bang" means that the Big Bang event occurred within a pre-existing universe that could be infinite and eternal, IMHO.
    And in the "consensus cosmology", which currently has no preconditions, if something "comes from nothing", it doesn't matter whether that something is finite, or infinite in extent.

    Simply put, the singularity (or whatever that represents) can become an infinite universe just as easily as it can become a finite universe.
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    Quote Originally Posted by SpeedFreek View Post
    The simple answer is because all of the physical matter in the observable universe was contained in that microscopic event.
    yes but how can matter grow in size ,and if this is the case then surly it is still growing.
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    Quote Originally Posted by SpeedFreek View Post
    Quote Originally Posted by Dark Speculator View Post
    To me however, "no preconditions" means that something came from nothing; and "preconditions to the big bang" means that the Big Bang event occurred within a pre-existing universe that could be infinite and eternal, IMHO.
    And in the "consensus cosmology", which currently has no preconditions, if something "comes from nothing", it doesn't matter whether that something is finite, or infinite in extent.

    Simply put, the singularity (or whatever that represents) can become an infinite universe just as easily as it can become a finite universe.
    It sounds like you are referring to the "shape" of the universe as predicted by General Relativity, i.e. open, flat, or closed. Am I correct to that extent?

    If so, then your reference to "the singularity can become an infinite universe" would be a reference to the open "shape" which can expand forever, right? Of course if the universe is open, flat, or closed in terms of GR, it is still finite at any point in time. An open universe can expand forever but is not ever going to be infinite in extent (spatially). Or would you disagree?

    Have you ever viewed the link I gave in my last post to the BBC Horizon 2010 series? If not, why not do so?
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    Quote Originally Posted by Dark Speculator View Post
    Quote Originally Posted by SpeedFreek View Post
    Quote Originally Posted by Dark Speculator View Post
    To me however, "no preconditions" means that something came from nothing; and "preconditions to the big bang" means that the Big Bang event occurred within a pre-existing universe that could be infinite and eternal, IMHO.
    And in the "consensus cosmology", which currently has no preconditions, if something "comes from nothing", it doesn't matter whether that something is finite, or infinite in extent.

    Simply put, the singularity (or whatever that represents) can become an infinite universe just as easily as it can become a finite universe.
    It sounds like you are referring to the "shape" of the universe as predicted by General Relativity, i.e. open, flat, or closed. Am I correct to that extent?
    It is a little more subtle than that. In topological terms, the manifold is either compact (finite), or non-compact (infinite), but it always describes a universe with stuff in it. For instance, you can have a flat universe that, depending on the topology, is either finite or infinite in extent, and homogeneous - i.e. there is no place where the universe stops and there is empty space beyond - the universe does not expand into empty space (at least not in our spatial dimensions!), there is no valid model for that, as far as I know.

    Of course, in a nod to the Horizon program, if it is finite, this could all be going on in our "bubble" universe, a compact manifold embedded in a higher dimension, along with other bubble universes.

    Quote Originally Posted by Dark Speculator View Post
    If so, then your reference to "the singularity can become an infinite universe" would be a reference to the open "shape" which can expand forever, right? Of course if the universe is open, flat, or closed in terms of GR, it is still finite at any point in time. An open universe can expand forever but is not ever going to be infinite in extent (spatially). Or would you disagree?
    I would disagree. The universe, full of stuff, might have been infinite in extent (spatially) from the start, i.e at t>0, even if it were a singularity at t=0. There is no difference between going from a singularity to a finite amount of stuff, or from a singularity to an infinite amount of stuff.

    A closed universe is finite, whereas both a flat and an open universe can be either finite or infinite in extent.

    Quote Originally Posted by Dark Speculator View Post
    Have you ever viewed the link I gave in my last post to the BBC Horizon 2010 series? If not, why not do so?
    I watched it when it was broadcast. I liked Roger Penrose's idea, that scale means nothing at the end of the universe.
    Last edited by SpeedFreek; August 26th, 2011 at 07:45 PM.
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    Quote Originally Posted by penfold View Post
    Quote Originally Posted by SpeedFreek View Post
    The simple answer is because all of the physical matter in the observable universe was contained in that microscopic event.
    yes but how can matter grow in size ,and if this is the case then surly it is still growing.
    The matter didn't grow in size, it changed in form. Matter could not exist in the form it is currently in, if it were all in such a small region. When the contents of the observable universe were all within a volume the size of a grapefruit (theory is a little more solid by this stage!), it would have been in a form of energy.

    And at that time, it would have been part of a larger volume* - the universe outside of our observable part. That volume could have been any size larger than that grapefruit, and full of energy. It could even have been infinite in extent, and full of energy.

    *It would be an almost insurmountable coincidence if our observable universe was the whole universe, for many reasons!
    Last edited by SpeedFreek; August 26th, 2011 at 07:52 PM.
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    Quote Originally Posted by SpeedFreek View Post
    Quote Originally Posted by Dark Speculator View Post
    If so, then your reference to "the singularity can become an infinite universe" would be a reference to the open "shape" which can expand forever, right? Of course if the universe is open, flat, or closed in terms of GR, it is still finite at any point in time. An open universe can expand forever but is not ever going to be infinite in extent (spatially). Or would you disagree?
    I would disagree. The universe, full of stuff, might have been infinite in extent (spatially) from the start, i.e at t>0, even if it were a singularity at t=0. There is no difference between going from a singularity to a finite amount of stuff, or from a singularity to an infinite amount of stuff.

    A closed universe is finite, whereas both a flat and an open universe can be either finite or infinite in extent.
    That is a perfect example of how the standard cosmology evolves. I was around when the consensus was that the Big Bang was finite, .
    Quote Originally Posted by Dark Speculator View Post
    Have you ever viewed the link I gave in my last post to the BBC Horizon 2010 series? If not, why not do so?
    Quote Originally Posted by SpeedFreek View Post
    I watched it when it was broadcast. I liked Roger Penrose's idea, that scale means nothing at the end of the universe.
    Scale may mean nothing and the alternative theory "Eternal Inflation is a good example of the concept being put to use, lol. As i mentioned, the BBC Horizons series that you saw was a good 2010 update of the consensus cosmology as well as an update on the main alternatives. I have a thread going in another forum about Laura Mersini-Houghton's recent paper about Bubble universes and addressing the question of "Is Eternal Inflation Eternal". If you haven't read her paper yet, go here:
    [1106.3542] Is Eternal Inflation Eternal?

    If you want to have a look at the footnotes to her paper go here:
    SciForums.com - View Single Post - Lorentz invariance and the multiverse, possible or not?
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    Quote Originally Posted by SpeedFreek View Post

    The matter didn't grow in size, it changed in form. Matter could not exist in the form it is currently in, if it were all in such a small region. When the contents of the observable universe were all within a volume the size of a grapefruit (theory is a little more solid by this stage!), it would have been in a form of energy.

    And at that time, it would have been part of a larger volume* - the universe outside of our observable part. That volume could have been any size larger than that grapefruit, and full of energy. It could even have been infinite in extent, and full of energy.

    *It would be an almost insurmountable coincidence if our observable universe was the whole universe, for many reasons!
    maybe the space surounding the atomic nuclei in an atom is expanding just like our universe ,only thing is we don`t realize this.
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    maybe higgs field...i hope so,saves some speculation.a good hypothosis..i agreee.maybe random,but how do we define dimensions?
    is zero dimension 0...why do i start there ? is zero the beginning or it 1st dimension.? not that im stuck there....? excuse my grammar,mose precisely,do we start from 0 or 1?
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    Quote Originally Posted by Dark Speculator View Post
    As i mentioned, the BBC Horizons series that you saw was a good 2010 update of the consensus cosmology as well as an update on the main alternatives.
    I think you might be confusing terms here, as the consensus cosmology is still the Lambda-CDM concordance model. What you are talking of are speculative ideas that might find their way into the consensus in the future, but they are not part of the current model.
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    Quote Originally Posted by penfold View Post
    maybe the space surounding the atomic nuclei in an atom is expanding just like our universe ,only thing is we don`t realize this.
    Perhaps, but the forces holding the atom together would far outweigh the expansion at that scale, so the atom does not "grow".
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    Quote Originally Posted by SpeedFreek View Post
    Quote Originally Posted by Dark Speculator View Post
    As i mentioned, the BBC Horizons series that you saw was a good 2010 update of the consensus cosmology as well as an update on the main alternatives.
    I think you might be confusing terms here, as the consensus cosmology is still the Lambda-CDM concordance model. What you are talking of are speculative ideas that might find their way into the consensus in the future, but they are not part of the current model.
    Maybe so, but I don't think I'm confused about the difference between the standard model and the alternative cosmologies and I thought the BBC Horizons series presented a good update for the thread starter, Scientits and others who are interested in exploring cosmology and the alternatives.

    Curious why you didn't comment to me in return for the links I offered to the Mersini-Houghton paper. If Mersini-Houghton is too speculative for your taste I hope you would say so. Some people like to advocate to standard model and avoid alternatives as too speculative.
    Last edited by Dark Speculator; August 27th, 2011 at 08:18 AM.
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    I am simply making the distinction between speculative theories (or more accurately hypotheses) about the origins of the universe, and the "consensus cosmology" that you refer to, which does not include those speculations. They are not "alternative cosmologies" in the sense that they are not in conflict with the current consensus cosmology, as they have different domains of applicability.

    Hence, our standard Lamba-CDM concordance model may well accurately describe the inside of a "bubble universe", within its domain of applicability
    Last edited by SpeedFreek; August 27th, 2011 at 11:54 AM.
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    Of course.
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