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

Logic, Metaphysics, and the Idea of an Expanding Universe

  1. Aug 5, 2005 #1

    Tom Mattson

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    This thread is an offshoot of The fundamental concepts of physics are all based upon metaphysics.

    Hmmmm, OK...

    ex·pand
    v. intr.
    1. To become greater in size, volume, quantity, or scope: Air expands when heated. This critic's influence is expanding.
    2. To speak or write at length or in detail: expand on a favorite topic.
    3. To open up or out; unfold: The chair expands to form a day bed.
    4. To feel expansive.

    u·ni·verse
    n.
    1. All matter and energy, including the earth, the galaxies, and the contents of intergalactic space, regarded as a whole.
    2. The earth together with all its inhabitants and created things.
    3. The human race.
    4. The sphere or realm in which something exists or takes place.
    5. Logic. See universe of discourse.
    6. Statistics. See population.

    I see nothing in the definitions of "expand" that requires a larger embedding space for a universe to expand into.

    In fact your charge of language abuse is a bit ironic because it is in fact the position taken by yourself that I see more frequently charged thus. You haven't explicitly stated your reasons for your quote above, but I'm going to go out on a limb and assume that they are the usual reasons that I have seen for similar conclusions on philosophy boards all over the internet. My apologies if your argument is better than the following.


    Physicist: The universe is all that there is, by definition. It is also expanding.

    Skeptic: Well, if it's expanding, then what's it expanding into.

    Physicist: Nothing. The universe is all that there is, remember?

    Skeptic: Well, the universe can't expand into 'nothing', because 'nothing' does not exist. So if the universe is expanding into 'nothing' then that's just another way of saying that it isn't expanding at all!


    The above argument by Skeptic pays lip service to the truth that 'nothing' does not exist (by definition). But it tacitly (and mistakenly) denies that truth by treating 'nothing' as an existent in drawing the conclusion. In more formal terms, the conclusion is reached by committing a linguistic (!) fallacy known as reification of the zero. When Physicist said "nothing" he didn't mean that the universe was expanding into something, and that thing is called 'nothing'. He meant simply, "the universe isn't expanding into anything", which is far from being the same thing.

    It would be the same if Physicist were to tell Skeptic that "no one can travel at the speed of light", and then Skeptic turn around and start looking for this mysterious person called "no one" who is zipping around, keeping pace with his own reflection in the mirror.

    (This analogy with the speed of light was originally brought up by the member Eh. Credit where credit is due, and all that.)

    Now you, Hector, say that logic prohibits the universe from expanding. But since you didn't state your reasons for saying this, I have to ask, does the above argument by Skeptic reflect your logic? I'm curious because there are big problems with his logic!
     
    Last edited: Aug 5, 2005
  2. jcsd
  3. Aug 5, 2005 #2
    Hector's logic is impeccable

    Hector's logic is impeccable. It is at the crux of understanding Reality.

    Technically, I prefer the term Reality, to Hector's use of the term "universe" (this is a semantical problem that can easily be satisfied), which is a singularity; and thus, always "there", relaitivistacally, as a function of speed.

    Galactic dispersion is expanding in an accelerating manner; not the Universe or Reality.

    The Universe exists within Reality; and, has Reality as it limit. Thus, the difference between Reality and the Universe is quite subtle; and, in this context of no comsequence.

    Any other interpretation will defy logic.

    Brunardot@Brunardot.com
    ”Click” to directly E-mail Me
     
    Last edited: Aug 5, 2005
  4. Aug 5, 2005 #3

    Tom Mattson

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    :confused: How would you know? How would anyone but Hector know? Hector hasn't presented his logic yet. All he did is make an assertion.

    As for the rest, I'm afraid I couldn't make any sense of it. For instance I have no idea of what it means for the universe to be a function of speed. But fortunately that's got nothing to do with this topic.
     
  5. Aug 6, 2005 #4
    Scientists need only define enough well their terms in order to obtain successful scientific theories, enough empirically adequate; this is their primary task not to engage in possible endless debates regarding the exact meaning of terms. As Karl Popper puts it well in 'Two kinds of definitions':

    "The view that the precision of science and of scientific language depends upon the precision of its terms is certainly very plausible, but it is none the less, I believe, a mere prejudice. The precision of a language depends, rather, just upon the fact that it takes care not to burden its terms with the task of being precise. A term like 'sand-dune' or 'wind' is certainly very vague. (How many inches high must a little sand-hill be in order to be called 'sand-dune'? How quickly must the air move in order to be called 'wind'?) However, for many of the geologist's purposes, these terms are quite sufficiently precise; and for other purposes, when a higher degree of differentiation is needed, he can always say 'dunes between 4 and 30 feet high' or 'wind of a velocity of between 20 and 40 miles an hour'. And the position in the more exact sciences is analogous. In physical measurements, for instance, we always take care to consider the range within which there may be an error; and precision does not consist in trying to reduce this range to nothing, or in pretending that there is no such range, but rather in its explicit recognition."

    Thus scientists never engage in endless debates like 'what is really a dune, how many grains does it have?' when they devise a certain theory, all they need is a clear enough definition. Of course they are free to question further the terms under the umbrella of philosophy, there is nothing wrong with this, actually it is adviceable to enquire basically everything. But the terms 'expansion' or 'universe' as used by cosmologists in the Big Bang/inflationary theory fully comply to the 'enough well defined' approach, we do not need more at this stage all that count is that the inflationary theory not only makes novel predictions but is also enough empirically adequate (as corroborated by the COBE satellite). The Inflationary Theory comply to the requirements of the scientific method (under the current acception of rationality), fully deserving to be the normal science of today, provisionally accepted.

    By the way no serious scientist, at least those accustomed with the modern philosophy of science, claim that we have established once and forever that the Big Bang theory is approximately true (though some may believe now that it is approximately true); all we can say is that under the actually accepted definition of rationality scientists prefer this theory to all other existing alternatives but they are fully prepared to realize in the future that other approaches are actually more accurate, fallibilism in a nontrivial way is never dropped (they are always open to the possibility of strongly nontrivial paradigm shifts). Now science might be 'erected on a swamp' to paraphrase Popper and the [acception] of what is rational may vary in time indeed but the actual methodology (minimal) of science is (still) our best 'tool' to make sense of observed facts...
     
    Last edited: Aug 6, 2005
  6. Aug 7, 2005 #5
    Well, you seem to think I'm wrong, so you must have some hypothesis as to what is on my mind.

    I don't know if that makes sense, it doesn't make sense to me but in any case it's not where I'm coming from anyway.

    I think you are misrepresenting the scientific position when you say the expansion of the universe means it is growing in size. The universe includes all empty space within it; you can measure an increase in distance between celestial bodies but you cannot measure an increase in the size of the total empty space around them.

    But physicists are not saying the total amount of empty space, which is part of "all there is", is increasing. Furthermore, they don't say stars are getting far apart from each other. The correct notion, as I have seen several times, is that it is spacetime that is expanding.

    So I can't properly offer you what you consider a logical refutation of an idea if we are not talking about the same idea. Would you agree that what physics says is that it is spacetime that is expanding? If so, then we may make progress, otherwise I fear you will misunderstand me to the point you will be tempted to censor me, as you have hinted at recently.
     
  7. Aug 7, 2005 #6

    Garth

    User Avatar
    Science Advisor
    Gold Member

    Actually no! Space-time cannot do anything, it just sits and suffers (curvature)!

    In the standard model it is the cosmologically foliated space-like hyper-surfaces of simultaneity that we call "space" that expand as one progresses in the positive time-like direction.

    What do we mean by "expansion"? Answer: that physical distances between representative particles increases with time.

    How do we measure such distances? Ah - that is another story!

    Actually we cannot measure cosmological distances and conclude that they grow larger as time progresses, you would have to wait too long, all we can measure is cosmological red shift and interpret it as such.

    Garth
     
  8. Aug 7, 2005 #7

    Tom Mattson

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Yes, and I presented it in blue. I was supposing that you took the point of view of Skeptic in that dialog.

    I'd rather not do that sort of thing, but you post very little in the way of actual philosophical argumentation.

    So where are you coming from? You have yet to say.

    I didn't even attempt to represent the scientific postion in my last post. I'm acting on what little you have given to go on to understand your position. You said to take a look at the meaning of the words "universe" and "expand" and that it should be clear as to why an expanding universe is illogical.

    I did, and it isn't.

    Not sure if I agree exactly, because in GR the scale factor (which accounts for cosmological expansion) affects only the spatial part of the metric, not the temporal part.

    I didn't say anything about censoring you. What I said is that I would not ignore you, as long as you make statements without even attempting to support them with argumentation.

    I started this thread in response to your statement that an examination of the words "universe" and "expand" should lead one to acknowledge that an expanding universe is impossible, because there is nothing for the universe to expand into. Since you provided not one jot of support for that statement, I posted what I thought your argument might be. I really should not have had to do that, because our policies here at PF (see the Sticky at the top of the General Philosophy Forum) require that claimants make their own cases.

    So by all means, don't refrain from posting supporting argumentation for your claims out of fear of censorship. If anything you are more likely to be censored if you don't post your supporting arguments.
     
  9. Aug 8, 2005 #8
    Philosophically there is still place for debate indeed but not this is the real problem (the situation is more or less similar with that regarding Zeno's paradoxes arguing against the existence of motion). Are the definitions given by actual science enough well defined and non contradictory for developping a successful theory (at the observational level)? The answer is yes since spacetime itself is postulated to stretch, being 'elastic', creating its own dimensions alongside (there is no 'outside' only spacetime and matter exist). Gribbin's cosmological model pushes this even further, our universe appears from a Black Hole in a parent universe but probably there is a great number of parallel universes, forever unknowable, each expanding into its set of dimensions.

    Gribbin's hypothesis is speculative indeed but the standard Big Bang/Inflationary theory fully complies to the actual standards of rationality defining what can be accepted as 'objective' knowledge. There is, still, nothing paradoxical with this view, moreover it is fully rational to prefer such a solution as the first choice program as much as the possibility of strongly nontrivial paradigm shift is held.
     
    Last edited: Aug 8, 2005
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Logic, Metaphysics, and the Idea of an Expanding Universe
  1. Metaphysics (Replies: 6)

  2. Expanding universe (Replies: 2)

  3. Universe Logical? (Replies: 18)

  4. Universal logic (Replies: 36)

Loading...