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Low entropy big bang Where am I going wrong with this interpretation?

  1. Oct 30, 2011 #1
    Hello. This is my interpretation of what is currently known in cosmology, as regards the low entropy state of the early universe. If it is a poor interpretation, then I apologise, but in all fairness, I can only blame the industry professionals for not explaining the data clearly enough. I am not a scientist, I am a mere student, and I cannot possibly be the first person to have this interpretation, but since I cannot find it anywhere on the internet (I've looked long and hard, but I'm running out of search terms at this point), I've been forced to conclude that it must just be so stupidly wrong that no one has ever bothered to write about it. But I must satisfy my curiosity, so I would like someone here to explain to me where I am going wrong in my interpretation, as I must be going wrong somewhere.

    The Problem

    1) The universe is an isolated system that began with the big bang, a point of very low entropy.

    2) The universe is expanding and its entropy is increasing. We are living at a point of low to moderate entropy.

    3) Entropy will eventually reach maximum and the universe will be in complete thermal equilibrium. I think this point in time is referred to as heat death.

    4) Since entropy tends to increase due to probability favouring disorder, it is considered somewhat paradoxical that the universe should have begun with low entropy, when the probability of a high entropy beginning was orders of magnitude more... well, probable.

    Furthermore

    1) General relativity posits that the universe is composed of spacetime, a phenomenon which for reasons I cannot fathom is frequently referred to as a fabric. Spacetime is four-dimensional, thus the three dimensions of space are equivalent to a single axis on a 2D graph with relation to time as the other axis. So, the faster one traverses space, the slower one traverses time, and vice versa.

    2) An often overlooked implication of this is that since space and time are two facets of the same thing, it follows that time is a dimension, and thus, it doesn't flow, it merely is. We perceive the flow of time due to our only remembering the past at any given point in spacetime. Our forward momentum through time is just an illusion. Time is real, but it doesn't flow.

    3) The universe therefore has no beginning or end, it merely is. It is a four dimensional structure within which we exist but are only able to perceive the three dimensional manifold that is embedded in the fourth dimension. The fourth dimension is in fact spatial in the sense that it is already there, but we perceive it as being temporal because at any given point along our world line, we can only see a cross section of the fourth dimension, we call this the present. This, coupled with our memory of the past gives us the illusion that we are flowing through the fourth dimension, and that the fourth dimension is therefore only temporal, when in reality the fourth dimension is spatial and we are distributed across it.

    The Solution

    1) The universe had no beginning, because time is a feature of the universe, it is not something within which the universe is situated. Thus, the big bang was not the beginning. Rather, the big bang should be thought of as being the furthest most point at one end of the temporal axis. Likewise, at the other end of the temporal axis, at the furthest most point, is where heat death is to be found.

    2) The universe is not expanding, because time is a feature of the universe, it is not something within which the universe is situated. Thus, just as we don't consider the universe to be expanding into anything spatially, it also follows that we should not think of the universe as expanding through something temporally.

    3) What we perceive as the expansion of the universe is in fact the increase in spatial volume of the universe, the further one is along the temporal axis.

    4) The universe could therefore be thought of as a four dimensional cone, with the big bang at the apex and heat death at the base. The radial dimension of the cone is equivalent to our three spatial dimensions, with the proverbial height dimension from base to apex being equivalent to our temporal dimension. The apparent expansion of the spatial volume along the temporal dimension is due to the sloping of the cone from apex to base.

    5) The universe did not begin with low entropy, because it has no extrinsic beginning. Likewise, entropy is not increasing, because the universe is not extrinsically expanding.

    6) The reason that entropy is low at the apex is because the spatial dimensions at that point are compressed so much that there is simply not enough spatial volume for disorder; the more confined the space, the higher the probability of low entropy, as there are fewer (in this case perhaps zero) potential states of disorder.

    7) The reason that entropy is high at the base is self-explanatory. At this end of the temporal dimension, the universe is at its largest volume spatially, and thus the probability of disorder is much greater.

    Conclusion

    Well, whether this is what cosmologists currently believe or not, I am uncertain. But if it is not, then could someone explain to me where am I going wrong in my interpretation? I'm sure I am going wrong somewhere (perhaps everywhere), so in all humility I ask that someone set me on the right track, thank you.

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    Edit: Apologies for my poor (and possibly confusing) use of terminology, as I said earlier, I am not a scientist, and I am still fairly new to all of this.https://www.physicsforums.com/editpost.php?do=editpost&p=3588395 [Broken]
     
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  3. Oct 30, 2011 #2

    phinds

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    I don't know enough to give you a comprehensive answer to your discourse, but here are a few comments.

    "Fabric" is a metaphorical term, not to be taken literally, which is carried over from something Einstein, I think it was, once said.

    To say that the universe had no beginning is not an arguable position. That is, you may be right or you may be wrong but there's no way to know so arguing about it is just silly. But to say that the thing we call t=0 didn't exist is totally contrary to experimental evidence and solid theory. The state of the universe from the Plank time forward is remarkable well understood and that's just 10E-43 or so after what we call, variously "the singularity", "the big bang", or "t=0", all of which terms are just shorthand for "we don't know squat about what happened there". Now there MAY have been time before that but no one knows. It was one HELL of a state change, though, if there was something prior to it.

    Your argument that the universe is not expanding sound to me like you are saying that it's not expanding because it's expanding. I don't really follow it, but you're going to have to do a lot better than what you have here to convince physicists that current theory, backed by observational evidence, are wrong just because you don't understand it.

    I vaguely see where you get the cone analogy but it doesn't work for me, mostly because the "base" doesn't exist ... it's off in infinity and we can't go there. Current theory says that in upteen scadzillion years, the universe will experience heat death, but nothing says it just STOPS at that point. It might as well just stop, of course, since at that point absolutely nothing is happening and the passage of time becomes meaningless but since it doesn't stop, you don't ever get a base for your cone.

    Speaking of time, I don't even want to get into your concept of time, other than to say politely that I don't agree with it.
     
  4. Oct 30, 2011 #3

    marcus

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    The public is in part responsible for watching Brian Greene popularization specials and the like. History channel stuff. The "industry" you are talking about is part of the media/entertainment industry. They have the money to persuade individual scientists to produce misleading oversimple soundbites which they then mix in with dazzling special effect imagery. What they sell is celebrity hyperphysics, not actual physics. The illusion of understanding.

    That's just my two cents on the pop-sci scene. If you are starting from TEXTBOOKs you've read then I apologize (but it does not sound like it.)

    I'm just an interested observer and other people will differ at least on some details but here is my view of "what is known in cosmology" It is not like what you say.

    Real cosmologists don't say they know how the U began. The conventional math models only kick in once the expansion got started. Future models may do better and go back further in time.

    There are various guesses about what could have preceded and they are just beginning to reach the stage of observational testing.

    And even if someday one of these new models is accepted (having passed some tests) it still would not say how U began. It would just push the time horizon back a ways to before the expansion started. (I dont say "big bang" because it is a misleading picture---I just say start of expansion.)

    Cosmologists still don't have a standardized definition of the entropy of the U's geometry. And that would be crucial to any application of the entropy idea to the start of expansion.

    Because the matter in the very Early was apparently in great disorder. Uniform super-hot soup. So where was all this low entropy? In the gravitational field (which means in the geometry). The geometric entropy was low and it was the dominant component. But how do you define it mathematically? No standardized defintion yet.

    Cosmologists do not claim their model of the Very Early is certain or complete. (Misleading pop-sci media makes it look like they do.)

    The model is great! But it is still a work in progress. There are unanswered questions. Patience and humility are required.
    As general advice to all of us including me: above all be aware of the limits of the model you are using---know how far you can push it (back in time, for example) and still get meaningful numbers. Try not to talk like you understand more than you do, or have more certainty. Be patient with the cosmologists too. Don't ask them to answer bigger questions than what they are currently working on. Science grinds ahead gradually. There is always a leading edge of speculative (not yet sufficiently tested) ideas but that may be a very narrow margin with only very modest ambitions for the moment. Don't ask for too much of certainty, but also do not even ask too much of legitimate Speculation!

    BTW I like your reasoning style. You seem careful organized and thorough. Probably you will get a lot of answers.
     
    Last edited: Oct 30, 2011
  5. Oct 30, 2011 #4

    marcus

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    Some comments?

    The Problem

    1) The universe is an isolated system that began with the big bang, a point of very low entropy.
    How is geometric entropy defined? Without that you cannot talk about the entropy of the U, especially at a very early stage.
    Furthermore

    1) General relativity posits that the universe is composed of spacetime, a phenomenon which for reasons I cannot fathom is frequently referred to as a fabric.​

    Yeah "fabric" is a dumb word. Gen Rel does not postulate the existence of a fabric. That is Brian Green hyperphysics. Gen Rel is about the evolution of geometry. Einstein pointed out already in 1917 or so that he was not claiming space and time had objective physical reality. (He said the basic GR principle of covariance denies a fabric-like reality.)

    And one should not say the Universe expands. Spatial distances are increasing according to a certain law or pattern. It is sloppy to say "expanding universe" and it misleads and confuses people.

    The Solution

    1) The universe had no beginning, ​

    Well, I agree with much of what you say in the first four points. There is a usable concept of universal time. Lorentz symmetry might appear or emerge at familiar scale without being fundamental. A 4D block universe might not physically exist (it seems to be in conflict with basic quantum ideas like uncertainty). So maybe you can picture the expansion of spatial distances (not the universe) proceeding with time as you do without offending Nature too much.
    After points 1-4) I'm not sure what I think.

    Conclusion

    Well, whether this is what cosmologists currently believe or not, I am uncertain. ​

    You are right to be uncertain, in my opinion. A mathematical science like Cosmo is not based on uniform belief so much as on people making explicit definite math models and comparing them with the data. Different people can have different suspicions and hunches and degrees of doubt and different itches and disatisfactions about the models.

    But we can all see the data (there is a lot and it is open) and we can all see the models, you can put one in your computer and try it out for yourself. That is what it is ostensibly about, rather than belief.

    Translating features of a widely shared math model into English words is already risky. If you hear someone translating, listen closely for how he describes the limitations of the model. If he glosses over the limitations...
     
    Last edited: Oct 30, 2011
  6. Oct 31, 2011 #5

    Chalnoth

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    Aside from some pedantic nitpicks, I would say this is generally an accurate description of one of the fundamental problems in modern cosmology: why was the entropy lower in the past?

    Note that you can't get out of this by stating that the universe doesn't expand. Not only does it expand empirically, but entropy is also growing in terms of stuff in the universe. Eventually, for instance, all of the fuel for stars will be burned up and there won't be anything left but the dead cores of old stars. Even more basic than that, you need an increase in entropy to have an arrow of time at all. All of the microscopic physics which we know are invariant in direction in time (to be pedantic, they're invariant under the CPT transformation). The only way you can get a direction of time is to have a low-entropy starting point.

    So the question of why the entropy was lower in the past is a fundamental one that demands an answer, and cannot simply be avoided by claiming that entropy hasn't actually increased (because it so very obviously has).

    Multiple solutions to this problem have been proposed. One is inflation. Inflation grows a really, really tiny region of space-time into a very large region. So if you have a big universe with high entropy but low entropy density, the change of a small region of that universe to an inflating universe isn't such a tremendous leap. In this way, there actually isn't any equilibrium and the universe just keeps increasing in entropy forever. New inflating regions can be thought of, in this picture, as a way for the entropy of the universe to increase faster.
     
  7. Oct 31, 2011 #6
    This confuses two different things. When you are talking about t=0, you can make up pretty much anything you want because we haven't got a clue what happened there. If you are talking about t=now, then you can't make up anything because we can take a telescope and point it at a galaxy and see what happens.

    At t=0, everything is guesswork. As you move from t=0 to t=now, the amount of guesswork and stuff that you can make up decreases until the point where you really can't make up very much. For example at t=0, you can make up any theory that you want. At t=1 to 3 minutes, you are temperatures at which you have nuclear fusion processes that we think we understand pretty well, so anything you make up has to explain why the universe is 25% helium-4.
     
  8. Oct 31, 2011 #7
    The place where you are going wrong is that it's not obvious how you can kill your theory. What can I show you with a telescope that would convince you that you are totally and utterly wrong?

    Also don't take that too personally, this is a general problem with talking about what happened at t=0. You can make up anything you want, and it's *REALLY* hard to show that what you just made up is totally wrong.

    Now if you go to t=10 seconds, then it's easy to come up with models that are provably wrong.
     
  9. Oct 31, 2011 #8
    Thank you all for the responses.

    Based on the general theme of what is being said, I've concluded that my description of my interpretation (and it is just that, I'm not proposing a theory here, I'm just interpreting the existing theory) doesn't accurately convey what I mean. So I will attempt to clarify it by adding three further points, if I may.


    1) Because it is just my interpretation of what is currently known, it is technically a metaphysical (quite literally in fact, as metaphysics means after the physics) analysis, rather than a proposed theory, and as such, I think I was in error for using the phrase 'The Solution' as a subheading, as this implied that I was putting more stock in what I was saying than I actually was. Furthermore, as it is just an interpretation, the requirement for falsifiability is absent. I am looking for criticisms rather than evidence, since as you all noted, there is no way for what I'm saying to really be tested, at least not yet. So it is something of an orbiting teapot I suppose.

    2) As regards the responses I have received, it seems that I should have been more clear when I was discussing the nature of time. When I said that the universe had no beginning, I did not mean that there was no t=0; rather I meant to imply that the Universe is (as one of you did appear to pick up on in fairness) a 4D block. Now, I realise that this too is merely an interpretation and is not testable, and I also realise that there are many who disagree with it, and that's fine by me (though I do have my doubts about the quantum uncertainty rebuttal of block time, as I believe that the uncertainty is epistemological rather than ontological); the main reason I subscribe to it is because it just feels right to me, and I don't believe that it is merely a case of mistaking the map for the territory; not a scientific way of thinking about things I'll admit, hence this is more metaphysical than physical. Likewise, I wasn't saying that the Universe isn't expanding in an intrinsic sense, but rather I was implying that the extrinsic nature of the expansion is more geometrical in nature, a kind tapering of volume in the direction of t=0; and that the temporal notion of expansion is only applicable within the Universe, where time exists.

    3) I understand that nobody knows what happened at t=0, but immediately following that point in time, it does seem logical that the smaller volume would have left less space for disorder. One of you noted that the early Universe is thought to have had low entropy due to the gravitational forces involved; admittedly, my grasp of the subject begins to diminish at this point, and this is where formal education in the future should come in handy.


    None of this negates anything that was said in any of your responses though. All of your points still stand regardless of whether or not I made myself clear in the OP. So I do appreciate your responses. Thanks again.
     
    Last edited: Oct 31, 2011
  10. Oct 31, 2011 #9
    Could part of the OP's difficulty be in seeing time as simply another vector? The first three dimensions can be manipulated easily, in any direction, but the fourth can only be manipulated in one direction (unless we can figure out how to travel faster than c), which kind'a makes the fourth dimension different to the other three.
     
  11. Oct 31, 2011 #10
    Well, I don't know that our inability to manipulate the fourth dimension would necessarily mean that it isn't just another vector. I mean, in some ways we were unable to manipulate the third dimension to any significant degree until we developed the technology necessary to reach escape velocity. Okay, so that's a terrible analogy, and pretty inaccurate I know. But I suppose my point is that our inability to manipulate a vector doesn't mean it isn't a vector. I think that the dimension of time could very well be a dimension of space that we simply lack the ability to perceive as such. Once again, an epistemic problem rather than an ontological one.

    After all, has it not been hypothesized that particles with negative mass could possibly exist? Such particles would move faster than C, and would therefore appear to be pointing in the opposite direction along the temporal vector.
     
  12. Oct 31, 2011 #11

    marcus

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    "One of you noted" I don't know whose comment you are remembering. I said something about gravitational field order/disorder, but my intent was opposite what you say here so I will repeat some.

    Our understanding is based on GR which says "gravity = geometry". GR is our current law of gravity and it is NOT primarily about "forces". It is about the gravitational field, which is what describes the geometry (e.g. curvature, expansion/contraction of distance...)

    The early U is NOT thought to have been quite disordered. Of course all we have is a best-fit model, but FWIW the model does not say "quite disordered".

    The basic reason for the low entropy in our picture of the early U is that the geometry was smooth and even. The gravitational field (i.e. the geometry) was LEVEL.

    Like a baby's skin it had not yet begun to develop wrinkles. Later on, with time, the geometry would develop creases and dents and pits. This is just natural evolution of geometry according to Einstein GR equation, because of clumping of matter.
    Normal aging brings disorder to geometry.

    The overwhelming determining factor in the low entropy of the Early is the low entropy of the geometry. As I picture it anyway, whatever the matter is doing and whatever entropy it might contribute (separate from its effect on geometry) is a minor footnote.
     
  13. Oct 31, 2011 #12
    Apologies, I actually meant ordered, not disordered, I should proof-read my posts in future. I'll edit it to fix.
     
  14. Oct 31, 2011 #13

    marcus

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    Good. I should have seen that it was just a minor typo. I didn't need to get all concerned :biggrin: Glad you are still able to edit. (Something like a 12 hour limit?)
     
  15. Nov 12, 2011 #14
    I’m no physics guru, but in an attempt to do some self-motivated research on entropy and thermodynamics I happened across this forum. I read all the posts and understood it fairly well, but I was surprised that nobody found the same flaw with the argument as I did. Now I’m wondering if it was really a flaw at all.

    “Spacetime is four-dimensional, thus the three dimensions of space are equivalent to a single axis on a 2D graph with relation to time as the other axis. So, the faster one traverses space, the slower one traverses time, and vice versa.”

    The issue there is for any movement to occur or “to traverse” in a 3D space there has to be a passage of time, otherwise any object in three dimensional space is simply stationary without time. So in order for you to traverse on your graph you have to include time on the same axis as the other three dimensions. Or put more clearly, you can’t have motion without time, therefore you can’t split time and space on a graph and talk about relative speed of each.

    Does that make sense or am I just poking my uneducated brain where it don't belong?
     
  16. Nov 13, 2011 #15

    Chalnoth

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    Well, you can make this sensible by adding a reference time. We could use the time on a particular stopwatch, for example. Since two stopwatches will not always tick at the same rate, we can pick one particular stopwatch to measure the (relative) flow of time in a fully-consistent manner. So if I use the stopwatch I am holding as a reference, the stopwatches that I see ticking most rapidly are those that aren't moving in space relative to my stopwatch. The stopwatches that I see ticking most slowly are those that are moving in space at high speed relative to my stopwatch.

    So the geometrical argument of moving quickly through space or time is perfectly reasonable. You just have to add a reference. Though which particular reference you add is arbitrary.
     
  17. Nov 16, 2011 #16
    I just have a specualtion regarding something marcus said in his discussion with Geodesik worm. It seems to me our ability to comrepehend, or interpret the U seems to drasticly decrease in very early times. (I think). Doesnt this imply something very strange at the very beggining of time? I think marcus is right when he sais that we have yet to have gained a theory for geometric gravity. (Is this the same as quantum qravity?) But the fact that this earliest moment in time is so strange, to me, gives way something to the nature of it's character. We can inver now, for example, that pre plank time IS something, or has the quality of being very different in a profound way, then times just moments following. This seems stange to me, I was just wondering what you guys thought. Even if the U 'inflated' we wouldnt be able to explain why.
     
  18. Nov 16, 2011 #17

    phinds

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    Read Weinberg's "The First Three Minutes"
     
  19. Nov 16, 2011 #18
    I'll do that
     
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