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The finite bang fallacy rears its head again

  1. Aug 24, 2003 #1


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    "In short - the Big Bang could not have occured if the universe is infinite - and the Big Bang has mounds of evidence."

    this is a common fallacy
    the particular instance was recently posted in mathforum's "infinity" thread

    people who actually study the big bang, the CMB, inflation scenarios, do not assume finite universe
    because there is no logical implication
    BB does not imply finiteness

    you can see this graphically in e.g. lineweaver's figure 5
    or you can read it in words (if you understand the terminology) in any recent survey of contemp cosmology

    The misconception that BB implies finiteness is a naive one and surprisingly common.

    Whether the universe has a finite volume or an infinite volume is not the point here. That is a separate issue. What I am calling attention to is the the fallacy that evidence for BB constitutes evidence for finiteness.

    You pay the experts millions of tax dollars to put satellite observatories like COBE and WMAP into orbit to study the oldest light---the CMB---and to write articles about the Bang
    and you entrust these expensive projects to Bang experts who do not see any reason to suppose the universe is finite

    Maybe it is finite---that would be fine with me---but that would be on the basis of entirely different evidence. That evidence has yet to be found (some type Ia supernova data might reveal it, depending on what turns up).

    But if you say silly things like BB implies finite then you are not getting your money's worth from the satellite observatories and the people you pay to study universe beginnings and such.
    Last edited: Aug 24, 2003
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  3. Aug 24, 2003 #2


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    more quotes from B.Forums

    If you limit your cosmology reading to stuff that has some formulas in it and was written since 2000 then you wont see it suggested that BB implies finite.

    On the other hand, here's a clear example of this widespread fallacy. This poster (a newcomer signing his posts "Biologyforums") is getting ideas from somewhere. Non-technical books by Hawkings from the Reagan Years? I don't know where----maybe someone familiar with non-technical science writings has a clue.

    If possible it would be nice to have some links to current non-popular sources by reputable people. Anyway, here goes with more quotes, exerpted from several posts:

    -------------B.Forums says----------------------

    Let's recall that the big bang is the energy source of the universe expanding.

    The big bang expanding created the spatial dimensions - thus the universe is finite. It's that simple.

    In short - the Big Bang could not have occured if the universe is infinite - and the Big Bang has mounds of evidence.


    The Big Bang has never had anything to do with compression, but just the opposite. I've read plenty of Big Bang explanations including Hawking - never heard him mention anything but the opposite of what you just said.

    And also that indeed the big bang does NOT coincide with an infinite universe.


    Well then if it was once more concentrated - and now it is less concentrated, and continuing to expand - how could it be infinite?

    It can't be expanding if it's infinite, and it could never have been compressed if it is infinite.

    -------------end of quotes---------
  4. Aug 24, 2003 #3


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    How do you explain to a person like that (preferably in a nice way) that he is wrong?

    The issue is not whether cosmos is finite or infinite (about which it would be foolish to take sides since the supernova data is still coming in). I think it would be neat if it turned out finite but also would be swell if infinite.
    Infinite is the simplest picture since so far no suggestion of closure.

    The point is that BB---roughly speaking the notion that the cosmos was at one time much denser and has been getting less dense for estimated 13.8 billion years----does not imply finiteness

    and no working observational cosmologist that Ive sofar read suggests that there any such "BB implies finite" logic. Where does this misconception come from?

    It sounds like something B.Forum just made up on his own initiative and decided to believe in without much comprehension of what's involved! Or something he read in the Eighties back when cosmology was more vague and speculative.

    Cosmology used to be more of an Armchair Philosophy subject
    and all kinds of harum-scarum notions floated around. I dont remember but it was a couple of PF mentors conversing on some thread (Damgo, Tom?) and one of them remarked that it was too bad Stephen Hawking hadnt been pushed out a third story window long ago because of the wealth of misconceptions he had caused the general readership.
    Last edited: Aug 24, 2003
  5. Aug 24, 2003 #4


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    George Smoot (Berkeley) and Charley Lineweaver (Melbourne) are examples of the kind of observational cosmologist you entrusted COBE to.
    COBE was one of the greatest scientific projects of all time and all thru the Nineties you were seeing the blue and red oval maps of the CMB which came from it.

    You let them drive your car but you refuse to read their papers

    Try this---go to google and type in one word: Lineweaver

    You'll find lots of journal articles including a great 2003 general audience survey of the whole cosmology field
    "Inflation and the Cosmic Microwave Background"
    posted both at CalTech and at the LosAlamos archive
    Figure 5 shows big bang of infinite universe graphically
    Does anyone want a specific link?

    Lineweaver also has an article about people's BigBang popular misconceptions that he wrote with Tamara Davis. It is called something like "Expanding Confusion, popular misconceptions about the Big Bang" but I havent looked at it.

    George Smoot has taught the General Relativity and Cosmology course at Berkeley for several years---actually several different cosmology courses---and has GR lecture notes on line.
  6. Aug 24, 2003 #5
    I think your personal attacks are uneeded.

    And all you have said so far has shown absolutely no evidence that the BBT allows for either a finite or infinite universe.

    You said "How do you explain to ..... that he is wrong?"

    Well you could provide actual evidence, and not bothering to single someone out and then say nothing to support your claim.

    The BB was an expansion of matter which caused the spacial dimensions, and thus the time dimension.

    As the matter expanded outward (in all directions) it expanded the dimensions, and thus the universe.

    If the universe is infinite - which is non-existant - than it cannot ever have been expanding, because and expansion can never reach infiniti.

    Furthermore, just the proof (undeniable)that the universe IS expanding is enough to prove it is not infinite.

    If it is infinite, it could not possible be expanding.
  7. Aug 24, 2003 #6
    The big bang was an expansion of space, not of matter, and it is still occuring.

    And the Universe could be infinite and still expanding. But that is just one possibility.
  8. Aug 24, 2003 #7

    I know quite well what the BB is thank you. And you (and others) still have shown no proof as to why this is possible, and shown not why my assertions or false!

    To be honest, it seems like nobody here so far has any particular idea why this is possible, which is fine because I'm not expecting experts. But please show where my claims are false!
  9. Aug 24, 2003 #8


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    What exactly do you object to, or feel that makes the expansion of an infinite universe impossible in the first place? I really don't know how to argue "it's possible" except through logical consistency.
  10. Aug 24, 2003 #9


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    finite, infinite.
    my garden is finite it is BOUNDED,the boundery is specified in the deeds, all the properties private houses, farms etc have bounderies,
    the UK is bounded by water.
    but all these bounderies do not prohibit infinite travel around
    the earth, they are just local bounderies.
    if something has limits it must have dimentions its," bounded",
    in other words its finite,
    if our universe is finite what is it bounded by?
    best wishes.
  11. Aug 24, 2003 #10

    Bounded by the speed of light. It grows at the speed of light.
  12. Aug 24, 2003 #11


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    And the Universe could be infinite and still expanding. But that is just one possibility.


    I know quite well what the BB is thank you. And you (and others) still have shown no proof as to why this is possible,


    It is routinely assumed by cosmologists to be possible that the universe is infinite and expanding. I do not have to prove the possibility to you because it is a normal assumption made by people who understand the subject and work in it professionally.

    You have made a false statement, namely "expansion implies finite". this is what you should retract.

    You are welcome to claim to "know" that the universe is finite or to say that God told you this or that. I do not care. I also do not care if the universe is in fact finite or infinite. Both could be awesomely beautiful and wonderful.

    Your mistake is to assert that "A implies B" when, in fact, the implication is false. I am not saying the CONCLUSION is false (I dont think anybody knows if the U is finite or infinite). What I say is your statement of implication is false.

    Not only do you go against normal professional opinion but what you say seems totally unintuitive. How could you possibly imagine that a space of unlimited extent would be logically prevented from having uniformly increasing distances?

    Global solutions of the 1916 equation governing the metric (essentially the only model we have of a dynamic spacetime metric, nobody has succeeded in improving on Einstein yet)
    tend to be of two kinds: either the metric is uniformly increasing or it is uniformly decreasing. It is pretty clear that the case we are in is where distances between stationary objects are increasing (which is called "expansion)----the case with increasing metric. This case is completely compatible with infinite space (the so-called "flat" or "open" models). No contradiction between expansion and infinitness has ever been seen by any competent person.

    If, to the contrary, you think expansion is logically incompatible with unbounded spatial extent, and are under the misconception that expansion implies finiteness, then the burden on you is to LEARN some cosmology---teach yourself something, study some articles where the meaning is in the formulas----not just impressionistic mass-market verbal blathering. Get your head around the two Friedmann equations, for starters.
  13. Aug 24, 2003 #12


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    The big bang can give rise to an expanding spatially infinite universe in the sense that although it's total volume would remain infinite, bounded regions within it would be expanding and thus decreasing in density. In other words, unlike with spatially finite universes, expansion in spatially infinite universes is a local but not a global property.

    In fact, current theory suggests that universes may be finite in some directions and infinite in others, as in kaluza-klein models and string theory.
  14. Aug 24, 2003 #13
    Marcus - I apoligize but I've had to use the report button a few times, and I'm sure others have. I definetely consider this a personal attack and have asked that it be removed. I would think one who is so sure of themself would rather teach someone else than attempt to attack them.
    Last edited by a moderator: Aug 24, 2003
  15. Aug 24, 2003 #14


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    Hi Jeff
  16. Aug 24, 2003 #15
    Jeff - I don't see where you actually said the quote of Marcus, but if you did then well, strength in numbers perhaps. Thanks.
  17. Aug 24, 2003 #16
    You're making the specific claim that if the Universe is infinite it can't be expanding, but it's possible to construct logically consistent models where it is both infinite and expanding.

    My personal suspicion is that at any givn time it is finite, and it may even have a boundary, but that would be very far away, but these are only possibilites and there is no convincing evidence to choose between many different models.

    Where you set Marcus off was you made very dogmatic replies to someone's questions that gave the impression that you were an authority on the subject and knew answers that no one else was privy to. If you want to present your personal views on something don't put them as a reply to some newbie's question, make a new thread and put it in theoretical physics or theory developement where it belongs. Then you'll get along a lot better with everyone.
    Last edited: Aug 24, 2003
  18. Aug 25, 2003 #17


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    I think the original argument was that the big bang cannot produce a spatially infinite universe since it must produce an expanding universe and spatially infinite universes cannot expand.

    The point that spatially infinite universes may expand locally has already been made by myself and hurkyl.

    So consider this: The big bang theory implies that the universe must have begun in a singular state, so the question becomes can spatially infinite universes have begun in a singular state a finite time ago?. According to the singularity theorems in GR, under reasonable assumptions - which by the way observation seems to support - the answer is yes.
  19. Aug 25, 2003 #18


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    Oh well, it seems the OP has been banned.
  20. Aug 25, 2003 #19


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    Yes, B.F. was a previously banned member starting up again under a new name.

    Seems this topic is done...
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