Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Finite Big Bang, Infinite universe?

  1. Mar 30, 2008 #1
    What is wrong with the idea that the Big Bang is a finite structure a million or more times the diameter of the visible universe, and the universe surrounds it in the same way that the visible universe surround the Milky Way?

  2. jcsd
  3. Mar 30, 2008 #2


    User Avatar
    Science Advisor

    Nothing. Current theory about inflation describes the universe exactly that way (except for the multiple).
  4. Mar 30, 2008 #3
    When I say "in the same way that the visible universe surrounds the Milky Way" I mean that fairly literally, like the Big Bang eventually dissipates entirely at some distant point and gives way to relatively empty space for some arbitrary span whereupon some other disposition of matter is encountered. Does inflation theory allow for at least the possibility of this type of material disposition?
    Last edited: Mar 30, 2008
  5. Mar 30, 2008 #4
    You say "dissipates" to "relatively empty space" yet as is presently conceived "space" is a product of the Big Bang. So no, not as presently conceived.

    ETA: I do find these assumption ripe for theoretical and possibly empirical questioning. They are however empirically consistent thus far.
    Last edited: Mar 30, 2008
  6. Mar 31, 2008 #5
    Surely the Big Bang under the current tenets of the cosmological principle is perfectly consistent for a region at least 1,000,000 times the dia of the visible universe (based on the CMB uniformity) without modification. But for 1,000,000,000 times the vis. u.? Maybe not; For 1,000,000,000^^2 times?... Who among us seriously thinks that we won't need to modify the theory of relativity in some fashion over the next 1000 years?

    As far as relativity goes, any characterization of "super-regional" material dispositions surrounding us at vast distances beyond the ultimate extent of the Big Bang would themselves presumably exhibit the same internal tensor relationship between matter and space that the Big Bang does as well as collectively exhibiting these relationships inter-structurally over whatever interstitial spans exist at such scales. We could expand into such immense interstices and perhaps be only very slightly tugged (acceleration of our local expansion profile) by the influences of such hypothetical structures, all without unduly disturbing the overall tensor relationships.

    The thing that I feel behooves us to presume the extension of the material hierarchy is that it predisposes us to look for diversity beyond our current data set that has always been the case. Every time we humans have tried to devise a complete description of the cosmos we find there is a larger structure beyond the range of our instrumentation that each time reconfirms the hierarchy. Yet even though the previous cosmology always turns out to be a hierarchical subordinate of the following cosmology, we still try to terminate the hierarchy each time. Why not anticipate this process?

    Formalizing the notion that there will always be more diversity beyond the limits of our examinations is the better strategy even if the hierarchy does terminate at some point. That is, if there are only two more tiers of ever larger structures beyond the Big Bang, we will be better off always searching for the next discovery and being surprised just once when the search is over, rather than falsely presuming an end to the hierarchy and having to be stubbornly convinced two more times before the search ends. It's just an efficiency thing, of course. The data will take us where it takes us, no matter what. But why not expedite the process?
  7. Apr 1, 2008 #6
    Who makes the claim the the Big Bang is a finite structure?
  8. Apr 1, 2008 #7
    I do.

    -<[{( Speculation Alert!)}]>-

    I base my presumption of the Bayesian probability that the unbroken material hierarchy we see across 40 orders of spatial magnitude continues beyond the Big Bang. I presume the cosmological principle to apply out to many millions of times the diameter of the visible universe and the Big Bang to range far beyond that, but neither to abide indefinitely. It seems purely philosophical, but it addresses a certain psychological pathology we humans have always suffered at the limits of our understanding.

    Basically this theory limits the first two axioms of the cosmological principal --(1) the homogeneous and (2) isotropic universe)-- by suggesting the following two axioms as more universal:

    1) The Finite Rule: All material phenomena are finite in extent and constituent to a larger structures.

    2) The Plurality Principal: All material phenomena are multiply manifest.

    (numerical justification: http://www.thegodofreason.com/rules-of-discovery.pdf)

    If the Big Bang were just a million times the diameter of the visible universe then we would only see one part per million difference in the homogeneity of the visible universe from one side of the sky to the other. (WMAP data only goes to about 25 parts per million resolution.)

    This video poses a rationale for the above two rules:

    This video offers an improvement of the Cosmological Principle:

    And this video is a speculation on how we might imagine the large scale
    structure of the Big Bang under the constraints of the two rules:
    Last edited by a moderator: Sep 25, 2014
  9. Apr 1, 2008 #8


    User Avatar
    Staff Emeritus
    Science Advisor

    Erm... labelling your post with "crackpot alert" is not a good start. Have your read the PF rules?
  10. Apr 1, 2008 #9
    Yeah, Cristo, I've read 'em, and that's kinda why I prefaced the balance of my post. The rules say that I should discuss with informed people as to the prevailing technical realities before I post. I started this thread in order to do exactly that. As the thread developes I am inevitably prodded for further explanation of why I might be asking my original question. So, for those uninterested in my more speculative points, I warn them off with the alert. Is that a bad thing?
  11. Apr 1, 2008 #10
    I could take that as a -<[{( Speculation Alert!)}]>- iif (yes 2 i's) your rants had a thread of empirical content. I will not even let the official advisor's here get away with overstating the veracity of certain standard model claims. Why then would I give some claim from left field any consideration whatsoever. Especially one that purports to derive legitimacy from argument alone.

    My personal experience when trying to actually give such ideas a fair trial is objections that it simply must be that way. Followed often by accusations of ignorance. Capernicus even prefaced his questions with such accusations. So I'll not bother.
  12. Apr 1, 2008 #11


    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    It sounds to me like it doesn't belong here at PF Cosmology subforum.

    Empirical science depends on theorists restricting themselves to making predictive theories. Theories that predict new phenomenal (not already predicted by previously established theory) so that they can be tested.

    It is not about imagining the universe in emotionally satisfying ways, or whatever else, it is about making quantitative predictions. And at this subforum we only deal with mainstream theories of this sort. Models of the universe that appear in peer-review professional publications. We don't dream up our own models, because we are interested in learning about and studying mainstream cosmology models. Typically the focus here is on the prevailing consensus LambdaCDM model.

    I think this thread will probably be locked, or moved somewhere like Philosophy. I don't know what to advise you to do. Obviously you are pushing your website with your writings and visuals about the way you fantasize the universe. It is not appropriate to do that here. I don't know where it would be appropriate for you to go.

    I think the big gap in what you are talking about is you don't have any equations describing gravity, that is, describing the dynamics of spacetime geometry. You are proposing a picture of the geometry of the universe but it seems kind of vague and unmathematical. In conventional mainstream cosmology we SEE the universe evolving geometrically and that evolution is related to our best understanding of gravity. The cosmological model is based on General Relativity (which has been tested). The universe is laid out the way it is and behaves the way it does because it obeys the equation of GR.
    So there are all sorts of checks and interrelated things that you can test.
  13. Apr 2, 2008 #12
    Why does this not count as an empirical examination?


    I only ask that you are equally diligent in restricting yourselves to my predictive theory and not "imagining the universe in emotionally satisfying ways."

    My prediction is that the probability is 99% that the homogeneity of the Big Bang will dissipate and give way to a larger structure made up at least in part by other Big Bang structures.

    The most obvious test of this theory would be to examine the WMAP data for a faint dipole. Such a dipole would only show up in the WMAP data if the Big Bang was in the neighborhood of 100,000 times (or less) the size of the visible universe. Based on the relative sizes of other scalar successions (say star system to galaxy) it would likely be much larger.

    How is this not empirical?
  14. Apr 2, 2008 #13
    I actually read the paper.. You did say predictions, oh well. In the conclusions it admits that the assignment of priors is subjective and therefore more qualitative than quantitative.

    Your first prediction stated here requires a few billion years to be a prediction. Your dipole prediction assumes an upside down picture of what is being observed. It is the past we are observing. In fact I see nothing in the dipole thinking that is not supporting the standard model.

    Now you quoted marcus, "imagining the universe in emotionally satisfying ways", and turned it into a characterization of those supporting the standard model. The realities are that this model started out hotly debated and mostly rejected until new information kept strengthening it. Even so, if it could be knocked off its pedestal I and many thousands of others would fight to do it first. Your accusation is nothing more than a red herring.

    You had your say, it's time to end it....
  15. Apr 2, 2008 #14


    User Avatar
    Science Advisor

    We can already measure much more than you seem to realise or give credit for. Inflation predicts a particular power spectrum (or equivalently, correlation function) that describes the density field of the Universe. These statistical measures describe the amount of structure present on any given length scale. We can test these predictions against the density field seen in the CMB, and the theory passes with flying colours. We can also test it by observing the correlation function of the density field of galaxies from galaxy surveys and also the density field of dark matter through weak gravitational lensing surveys. These are less 'clean' measurements that the CMB however that do find a correlation function in agreement with the theory. This gives us confidence, empirically, that the theory has some merit.

    Now, the theory doesn't cut off at the length scales corresponding to the largest lengths scales we could ever observe but instead makes definite predictions about what kind of structure is likely to be present in 'super horizon sized' perturbations (meaning structures larger than the observable Universe). We obviously cannot directly test this, however since it is a prediction from a theory that we can test at other scales we can have some (but not complete) confidence in it. The prediction is that on those large scales the perturbation amplitude is quite small, so we would not expect that the Universe outside of the observable chunk would be much different from the part we can see.

    You seem to be enamored with Bayesian statistics, this is good, cosmologist now use Bayesian statistics almost exclusively since data is at a premium and we wish to make the best guess we can when things are not always obvious 'to the eye' in noisy data. But don't forget that the essence of Bayes's theorem is that your state of knowledge is always updated based on new evidence. If your theory does not include all the current evidence, including the observations that the amplitude of the correlation function reduces as lengths scales increase (so would be expected to be even smaller on super horizon scales), then it cannot be considered to be a 'Bayesian Cosmology'.

    Still, I don't want to come across as being too harsh, it's great to toss different possibilities around, but the current cosmology theories weren't just dreamed up at the Pub one afternoon, they are the result of many years of theoretical and observational work by many people. Therefore it's hard to come up with something new that does a better job of explaining the data. I'm sure eventually that will happen, I suspect at least a few aspects of our current theories will eventually be drastically altered, but it's only by considering all of what we know that we can achieve any next step.
  16. Apr 2, 2008 #15
    Thanks Wallace for being patient with me. I didn't post this stuff to insult people. I just wanted some responses like yours telling me how exactly my views are naive in light of the conventional wisdom. This definitely gives me something to work with. I've searched some of your terminology and and found some papers I need to try and understand. Thanks again.
  17. Apr 2, 2008 #16


    User Avatar
    Science Advisor

    Another useful term to look for is 'scale of homogeneity', I think that might get you quickly to the heart of the matter.
  18. Apr 2, 2008 #17
    If the slight was good enough for Marcus to characterize the presumption that the Big Bang may be finite as feel-good idiocy on my part, then it's good enough for me to put back to him for being so dismissive of my wanting peoples honest reaction.

    I'm not refuting the standard model. I'm saying that the effort to make any model a complete and sufficient description of everything is precisely where that model will ultimately be found weakest. If this idea is cause for disdain and derision, knock yourself out.
  19. Apr 2, 2008 #18
    Oh yeah, that's it. Thanks again.
  20. Aug 4, 2008 #19
    Well, gentlemen, (and MeJennifer) after carefully examining these articles on the scale of homogeneity, I don't think they are as conclusive as a few of you might imagine. I looked at some of these papers and they fall into two general categories to extend the homogeneity beyond the range of the visible universe. One category uses the recession data and another uses the CMB data.

    One typical article in support of the cosmological principle is Martinez’s "Searching for the Scale of Homogeneity:"


    Using the red shift recession data, it claims "no hope for unbounded fractal distributions," which basically supports a total projection of the visible homogeneity. However, he bases his presumption on the two point correlation function which is dependent on the fair sample hypothesis which is itself a derivative of the cosmological principle. This is like saying, if the universe were homogeneous then it could be modeled like this and since the model is so beautifully compliant with respect to relativity then it is undoubtedly true.

    This approach constitutes the same potentially true but ultimately false presumptions we have always made when characterizing the universe beyond the data at hand. We always make the presumption that the data we have is sufficient to explain "everything." This is what the cosmological principle is doing for us in modern cosmology. It makes an infinite universe compliant to a finite data set. But historically, the universe has always proven to be more diverse than is possible to determine from any finite local data set.

    You may be surprised to find that there are also articles that do not explicitly support a totally homogeneous universe. Take Patricia Castro’s "Scale of Homogeneity from WMAP" which states:


    "We review the physics of the Grishchuck-Zel'dovich effect which describes the impact of large amplitude, super-horizon gravitational field fluctuations on the Cosmic Microwave Background anisotropy power spectrum. Using the latest determination of the spectrum by WMAP, we infer a lower limit on the present length-scale of such fluctuations of 3927 times the cosmological particle horizon (at the 95% confidence level)."

    Attacking the problem from a lower limit perspective is a far better strategy than presuming homogeneity and trying to indicate the absence of an upper limit. This approach addresses only what we can be confident in with respect to the local data rather than trying to corroborate an impossible thesis with a potential to range infinitely beyond the local data set.

    If we were living on an electron of a hydrogen atom in the middle of the ocean, we would be perfectly justified in presuming the universe was made entirely of water molecules, and all our calculations would work perfectly, but we would still be wrong. All I'm saying is that a Bayesian examination across the widest possible spectrum of the existing data (the hierarchical structure of of the known material universe from quarks to galaxy clusters and across the history of scientific investigation) says that the universe is hierarchical and not homogeneous across all scales and that whenever we try to terminate that hierarchy is precisely where our theories have historically proven weakest. And the CP is that point of weakest presumption in modern cosmology.

    For people to get upset to the point of indignation over the suggestion that the Big Bang may ultimately be a finite phenomenon is more an artifact of psychology than of science. The universe is not ours to claim total understanding beyond a reasonable projection of the data to a statistically relevant degree. That it is possible for the cosmological principle to be true is not the same thing as being inevitable.

  21. Aug 4, 2008 #20


    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    I did not. You were not being slighted. You must not have understood. I have often discussed the possibility that standard cosmology is spatially finite, in the sense of finite spatial volume. Several of us have (I am not alone in my interest in that case.) Several threads here at the forum about this.

    By itself, bigbang finiteness is hardly a revolutionary idea :smile: there is even some data supporting it (not conclusive though).

    Again I think you must have misunderstood the point of others' comment. I don't see anyone who responded to you acting upset or indignant at all!

    It's a general observation which bears repeating that we have to distinguish between universe models that are supported in detail by data, and make quantitative predictions so they can be tested by practical observations, on the one hand, versus, on the other hand, concepts that appeal to somebody's imagination and are proposed without some currently feasible method of testing.

    If you want to call the latter "feel-good idiocy" well, those are your words and it is your perogative. But I wouldn't choose such language. Practical testability of scientific theories is a serious point and, as I say, bears repeating----no one should take offense at the reminder.
    Last edited: Aug 4, 2008
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook