Page 1 of 2 12 LastLast
Results 1 to 30 of 37

Thread: The usual doubts about expansion

  1. #1
    Join Date
    Jun 2005
    Posts
    9,078

    The usual doubts about expansion

    I'm sure others have asked this before, but I just wonder what others think of this. If the cosmological principle holds and the universe is expanding, then everybody everywhere sees an equal expansion. People often use the analogy of the surface of a balloon to illustrate the situation. So my question is, the number of points on a balloon is finite, because the surface curves back on itself. You can travel in a straight line and get back to where you started. So in our universe, either the universe is infinite, or it curves back on itself, and so if we had a powerful enough telescope we might be able to see the earth. So of course, if the universe started with a big bang, then there can't be an infinite number of stars, so the possibility that remains is that it curves back on itself. Is this a fair conclusion?
    As above, so below

  2. #2
    Join Date
    Dec 2004
    Posts
    12,771
    The largest point of contention I have had with others here
    in recent years has been with my assertion that the Universe
    starting with the Big Bang means that it is finite. Or more
    precisely, the part of the Universe which was involved in the
    Big Bang and continues to participate in the cosmic expansion
    must be finite. There may be more to the Universe than was
    involved in the Big Bang. Something may have existed before
    the Big Bang, and / or other "universes" may exist. Or there
    might be infinite empty space beyond the part of the Universe
    involved in the Big Bang. I don't agree that the part of the
    Universe which was involved in the Big Bang must either be
    infinite or curve back on itself. A wide range of possibilities
    even with my restriction.

    But several others here dispute my restriction, asserting that
    the Big Bang could somehow produce an infinite Universe.

    I think that's crazy, but modern physics in general is crazy...

    If the Universe does curve back on itself, my understanding
    is that the most basic description of the geometry (no longer
    relevant with the discovery of the acceleration), where the
    Universe eventually stops expanding and collapses again,
    would allow light which started travelling at the Big Bang
    to get only halfway around the Universe by the time of the
    Big Crunch. So even the Superduper ultra-mega hyper-dyper
    telescope wouldn't be able to see its home galaxy off in
    the far distance.

    If I failed to address your question, please say so. I can
    try again.

    -- Jeff, in Minneapolis
    http://www.FreeMars.org/jeff/

    "I find astronomy very interesting, but I wouldn't if I thought we
    were just going to sit here and look." -- "Van Rijn"

    "The other planets? Well, they just happen to be there, but the
    point of rockets is to explore them!" -- Kai Yeves

  3. #3
    Join Date
    Jun 2007
    Posts
    4,377
    Quote Originally Posted by Jens View Post
    I'm sure others have asked this before, but I just wonder what others think of this. If the cosmological principle holds and the universe is expanding, then everybody everywhere sees an equal expansion. People often use the analogy of the surface of a balloon to illustrate the situation. So my question is, the number of points on a balloon is finite, because the surface curves back on itself. You can travel in a straight line and get back to where you started. So in our universe, either the universe is infinite, or it curves back on itself, and so if we had a powerful enough telescope we might be able to see the earth.
    If the universe is closed, and if it stopped expanding for long enough, this would eventually be true. As it is, the furthest and oldest thing we can see is the universe when it was still opaque plasma, and estimates of curvature mean the universe is either infinite or the visible universe must only be a small fraction of the whole...the CMB is what we see from a small circle on the balloon.

    Also, expansion means the circle representing the visible universe won't necessarily ever reach the "far side" of the balloon.


    Quote Originally Posted by Jens View Post
    So of course, if the universe started with a big bang, then there can't be an infinite number of stars, so the possibility that remains is that it curves back on itself. Is this a fair conclusion?
    No. There's no reason to conclude there isn't an infinite number of stars in an infinite universe that resulted from a big bang. The big bang does not require that the universe was ever of finite size.

  4. #4
    Join Date
    Jun 2005
    Posts
    9,078
    Quote Originally Posted by Jeff Root View Post
    The largest point of contention I have had with others here
    in recent years has been with my assertion that the Universe
    starting with the Big Bang means that it is finite. Or more
    precisely, the part of the Universe which was involved in the
    Big Bang and continues to participate in the cosmic expansion
    must be finite.
    I can't say that I understand the idea of the big bang all that well, despite having read quite a bit about it. I tend to agree with you on that point. But something has occurred to me. Using an analogy, suppose that the universe were an infinitely long ruler made up of integers, and an algorithm was implemented that basically said: all even numbers become mountains, and all odd numbers become valleys. In that case, we would get an infinite number of mountains from a sudden event. I suppose the problem is how that algorithm would be implemented. It would seem naively to me to violate the "speed limit" for the information to be available to all places simultaneously.
    As above, so below

  5. #5
    Join Date
    Nov 2005
    Posts
    421
    Quote Originally Posted by Jens View Post
    So my question is, the number of points on a balloon is finite, because the surface curves back on itself. ... So of course, if the universe started with a big bang, then there can't be an infinite number of stars. Is this a fair conclusion?
    The Balloon analogy is used as a simple everyday picture to show a situation where every point expands away from every other point, and the velocity is proportional on the distance between them. Expecting it to remain valid for other implications all the way back to the Big Bang is expecting too much from it.

    Let's take an alternative 2D analogy - our visisble universe as a flat sheet of (elastic) paper. Imagine at time t=(very small), this measured 1cm square. We stretch it, doubling it's size in each direction. Do that again, and again, and again. As with the Balloon, every point on the sheet expands away from every other point, proportional to the distance between them.

    However, using this analogy, we are not restricted to a finite number of stars. Unlike the Balloon that starts at a single point, there's nothing that restricts our initial 1cm square to be all that there is. Indeed, this square could be sitting on an infinite 2D plane, that could all be expanding with us. Our universe could well be infinite.
    Last edited by RobA; 2012-May-14 at 02:31 AM. Reason: Fixed typo, and got rid of rhetorical question

  6. #6
    Join Date
    Mar 2010
    Location
    United Kingdom
    Posts
    4,458
    Quote Originally Posted by Jeff Root View Post
    The largest point of contention I have had with others here in recent years has been with my assertion that the universe starting with the Big Bang means that it is finite.
    The Big Bang describes the visible universe expanding from a finite sized hot dense state. It says pretty much nothing about the areas outside that volume. So there could have been an infinite spacetime filled with 'bang' that led to an infinite universe. Most of the arguments I have seen on this come from an attempt to push the model back to a singular point and say that the entire universe came from that. It is important to put limits on what the theory is actually describing.
    Last edited by pzkpfw; 2012-May-14 at 04:48 AM. Reason: Fix tags

  7. #7
    Join Date
    Jun 2008
    Posts
    4,222
    My understanding is kind of drifting towards Jeffs and here is why.

    The big bang assumes an existing state of the universe where it is extremely hot and dense.

    This existing state may or may not be infinite. If it is infinite then, like Jeff points out, how would the entire universe suddenly know to inflate at the same "time". That said I don't think our physics is good enough, obviously, so I don't have to much of an issue thinking that there is a time before the big bang where the universe went from zero dimensions to infinite in expanse and the subsequent inflation was triggered by that first null->infinity transition.

    I don't know if that will ever be in the realm of science though while the "bubble universe" from an existing bulk might be more testible.

    So I guess I'm agnostic on the finite/infinite issue still but it really depends when that first inflation happened. If we are a bubble universe I'd have to say we have to be finite but there maybe a bigger bulk we may or may not be still attached to.

    If we are finite and detached from some large bulk we came from then I kind of require, in my mind, us to some how be looped back on ourselves even if it is never possible to make that trip. If we are part of some bigger universe where the inflation/expansion is "local", and by "local" I mean orders of magnitude larger then our visible universe then the topology can change.

    I heard a cosmologist talk about the fact that the topology of the larger, non visible universe, may be like the surface of a raisin and it is that the amount of inflation/expansion makes it just seem that the universe is flat but we could still be on a section that has either positive or negative curvature.

    The science is way beyond me but I understand some topologies would leave signs on the visible universe but we have not even seen a single hint on any of those signs.

    So how is that for a big non answer. To Jeff, thanks for opening my eyes to the causality issue which I agree with but only if the initial inflation was from some T>0 and not a direct result of space/time going from null->infinity and at the same time kicking off the initial inflation (note to lurkers, this is not part of the big bang theory but would be another theory that describes T<1x10-48 if "time" even had the same meaning at that point.)

  8. #8
    Join Date
    Mar 2010
    Location
    United Kingdom
    Posts
    4,458
    Imagine two flat plates, infinite in extent, moving towards each other face on. How does every point in them 'know' to collide at the same time?

    Similarly if (as some brane theories hint at) the universe is generated by some kind of topological interaction in a higher dimensional space it is perfectly feasible that an infinite 4D space came into being at one point in that 4D spaces time.

  9. #9
    Join Date
    Dec 2004
    Posts
    12,771
    My argument doesn't depend on the Universe starting
    from infinitesimal size. It depends on the notion that
    everything involved in the Big Bang had to be causally
    connected to the Big Bang in order to be involved in
    the Big Bang (that is pretty much a tautology), and the
    notion that things which are infinitely far away from
    each other cannot be causally connected to the same
    event which occurred a finite time in the past.

    -- Jeff, in Minneapolis
    http://www.FreeMars.org/jeff/

    "I find astronomy very interesting, but I wouldn't if I thought we
    were just going to sit here and look." -- "Van Rijn"

    "The other planets? Well, they just happen to be there, but the
    point of rockets is to explore them!" -- Kai Yeves

  10. #10
    Join Date
    Jun 2008
    Posts
    4,222
    Quote Originally Posted by Shaula View Post
    Imagine two flat plates, infinite in extent, moving towards each other face on. How does every point in them 'know' to collide at the same time?

    Similarly if (as some brane theories hint at) the universe is generated by some kind of topological interaction in a higher dimensional space it is perfectly feasible that an infinite 4D space came into being at one point in that 4D spaces time.
    Yes and that is my point, no pun intended. It would have to have happened in a pre-existing, bad terminology, universe/multi-verse. I see Jeff posted right after you and I can say something he might agree with like.
    Well what is the odds that 2 infinite plates would be perfectly aligned? My explanation is that the initial inflation might just be a property of space/time. Just Hydrogen doesn't need to coordinate the energy levels of each of its electron shells space/time might just have a property that reacts in a certain way when energy densities are a certain level.

    Regardless this steps outside of the Big Bang and science into a metaphysics at this point since there is no way, even in principal, for us to verify it right now.

  11. #11
    Join Date
    Jun 2008
    Posts
    4,222
    Quote Originally Posted by Jeff Root View Post
    My argument doesn't depend on the Universe starting
    from infinitesimal size. It depends on the notion that
    everything involved in the Big Bang had to be causally
    connected to the Big Bang in order to be involved in
    the Big Bang (that is pretty much a tautology), and the
    notion that things which are infinitely far away from
    each other cannot be causally connected to the same
    event which occurred a finite time in the past.

    -- Jeff, in Minneapolis
    That is where you loose me. If, and these are big speculations, space/time has a property that causes it to inflate at a certain condition and our universe came into existence from zero volume to infinite volume with everywhere being the same then everywhere can inflate at the same "time" even though they are not in contact. IE the physical laws space/time obeys and the fact that the universe popped into existence and started to equalise could be enough.

    I guess where I really differ is I put the causality link back to the point where the laws of our universe where solidified or how they may have evolved.

  12. #12
    Join Date
    Dec 2004
    Posts
    12,771
    Quote Originally Posted by WayneFrancis View Post
    That is where you loose me. If, and these are big
    speculations, space/time has a property that causes it
    to inflate at a certain condition and our universe came
    into existence from zero volume to infinite volume with
    everywhere being the same then everywhere can inflate
    at the same "time" even though they are not in contact.
    IE the physical laws space/time obeys and the fact that
    the universe popped into existence and started to
    equalise could be enough.
    What do you mean by "at a certain condition"?

    If everywhere inflates at the same "time" without any
    causal event, then is it by coincidence?

    If the Universe popping into existence is the causal
    event which resulted in inflation, then you need to
    explain how an infinite volume of space would all pop
    into existence at the same "time". Coincidence?

    If the Universe instantaneously inflated from a "point"
    to infinite size when it popped into existence, then that
    inflation is in addition to the observed expansion and
    the inflation hypothesized by Inflation theory. (Plus
    the observed acceleration of the observed expansion.)

    -- Jeff, in Minneapolis
    http://www.FreeMars.org/jeff/

    "I find astronomy very interesting, but I wouldn't if I thought we
    were just going to sit here and look." -- "Van Rijn"

    "The other planets? Well, they just happen to be there, but the
    point of rockets is to explore them!" -- Kai Yeves

  13. #13
    Join Date
    Mar 2010
    Location
    United Kingdom
    Posts
    4,458
    It depends on the notion that everything involved in the Big Bang had to be causally connected to the Big Bang in order to be involved in the Big Bang (that is pretty much a tautology)
    But you are going beyond the model here. You are trying to include a creation event - which we know nothing about. The Big Bang as it stands is the evolution of the universe from a given set of initial conditions. How it got into those initial conditions is all totally speculative right now. We do not even know that there was a time-like dimension right at the start.

  14. #14
    Join Date
    Jun 2006
    Posts
    2,914
    Quote Originally Posted by Shaula View Post
    Imagine two flat plates, infinite in extent, moving towards each other face on. How does every point in them 'know' to collide at the same time?

    Similarly if (as some brane theories hint at) the universe is generated by some kind of topological interaction in a higher dimensional space it is perfectly feasible that an infinite 4D space came into being at one point in that 4D spaces time.
    Any observer at any point on either of the plates sees the collision occurring at any other point other than his own after his collision . . .

    The time is relative.

    Regards, John M.
    I'm not a hardnosed mainstreamer; I just like the observations, theories, predictions, and results to match.

    "Mainstream isnít a faith system. It is a verified body of work that must be taken into account if you wish to add to that body of work, or if you want to change the conclusions of that body of work." - korjik

  15. #15
    Join Date
    Aug 2003
    Location
    The Wild West
    Posts
    7,794
    Quote Originally Posted by Jens View Post
    ...if the universe started with a big bang, then there can't be an infinite number of stars, so the possibility that remains is that it curves back on itself. Is this a fair conclusion?
    You've reached two conclusions here. I like the first one, but not the second. I don't see how the big bang could produce an infinite amount of matter. Yes, that's an argument from incredulity, but if someone knows how this could be reasonably accomplished, please let me know. Where did all this matter come from? Well, at least one scenario has it that when the inflaton field decayed, all its prior energy converted to particles that filled the space. This just sounds like a finite operation to me.

    But the question of a finite extent to the universe is quite different. The expansion doesn't look like it's going to be stopping, so it will apparently go on forever. That sounds like an infinite operation. So the mass-energy density of the universe will become less and less, approaching zero. Kind of a bleak-looking future. Fortunately, we're not anywhere near such a future, and all our personal futures are cheery and bright, I hope.
    Everyone is entitled to his own opinion, but not his own facts.

  16. #16
    Join Date
    Mar 2010
    Location
    United Kingdom
    Posts
    4,458
    Remind me not to use throwaway analogies on here again... The point of the flat plates comment was not to get into a debate about time being relative (I know it is) or the odds of two plates being perfectly aligned (irrelevant) but to show the implicit assumption in the comments about one side of the universe 'knowing' that it had to go bang at the same time as the other side. The implicit assumption is that there is a signal or propagation of an effect whereas it is perfectly possible that (as in the inflation field ideas) this 'knowledge' was contained in the initial conditions. As it would be in the two plates.

  17. #17
    Join Date
    Dec 2004
    Posts
    12,771
    I think that the total failure of the imaginary plates to
    be able to collide everywhere at once is a perfect analogy
    to show that physics needs to be involved, not just math.
    Mathematically, two infinite planes can easily collide
    everywhere at once. Physically such a thing can't be.

    My criticism of the idea of an infinite universe resulting
    from an event which occurred a finite time in the past
    is based as much on physics as on mathematics.

    If some particular initial conditions existed throughout
    an infinite volume of space, was that a coincidence, or
    did something cause the conditions to be the same
    everywhere?

    -- Jeff, in Minneapolis
    http://www.FreeMars.org/jeff/

    "I find astronomy very interesting, but I wouldn't if I thought we
    were just going to sit here and look." -- "Van Rijn"

    "The other planets? Well, they just happen to be there, but the
    point of rockets is to explore them!" -- Kai Yeves

  18. #18
    Join Date
    Dec 2004
    Posts
    12,771
    Quote Originally Posted by Shaula View Post
    Quote Originally Posted by Jeff Root View Post
    It depends on the notion that everything involved in
    the Big Bang had to be causally connected to the Big
    Bang in order to be involved in the Big Bang (that is
    pretty much a tautology)
    But you are going beyond the model here. You are
    trying to include a creation event - which we know
    nothing about.
    My statement quoted above has nothing to do with
    a creation event or any model. As I said, it is pretty
    much a tautology. It does not say much, and what
    it does say should be completely noncontroversial.

    -- Jeff, in Minneapolis
    http://www.FreeMars.org/jeff/

    "I find astronomy very interesting, but I wouldn't if I thought we
    were just going to sit here and look." -- "Van Rijn"

    "The other planets? Well, they just happen to be there, but the
    point of rockets is to explore them!" -- Kai Yeves

  19. #19
    Join Date
    Mar 2010
    Location
    United Kingdom
    Posts
    4,458
    If some particular initial conditions existed throughout an infinite volume of space, was that a coincidence, or did something cause the conditions to be the same everywhere?
    Really not interested in having this debate about what you think and what I think is logical and what causality means. We've done it to death a couple of times and never got even close to agreeing. So I will just leave it there.

  20. #20
    Join Date
    Jun 2008
    Posts
    4,222
    Quote Originally Posted by Jeff Root View Post
    What do you mean by "at a certain condition"?
    Well... like pure water freezing at 0c at sea level pressures. Water everywhere we know will behave predictably when you lower its temperature.

    Quote Originally Posted by Jeff Root View Post
    If everywhere inflates at the same "time" without any
    causal event, then is it by coincidence?

    If the Universe popping into existence is the causal
    event which resulted in inflation, then you need to
    explain how an infinite volume of space would all pop
    into existence at the same "time". Coincidence?
    I don't see this as a problem. It is just that instead of a finite amount of space time popping into existence it is infinite.

    Quote Originally Posted by Jeff Root View Post

    If the Universe instantaneously inflated from a "point"
    to infinite size when it popped into existence, then that
    inflation is in addition to the observed expansion and
    the inflation hypothesized by Inflation theory. (Plus
    the observed acceleration of the observed expansion.)

    -- Jeff, in Minneapolis
    I didn't say a point. That implies a location and the only location I say that matters is the location in time. The T[sub]0[/sup] point. The extent of x,y,z at T[0] is not an issue. Just as t∅→t∞ is not an issue x∅→x∞ is not an issue. In a 4 dimensional manifold do you have a problem with time having a start but being infinite in extent?

    "t" might be finite in our universe. So may the spatial dimensions but I don't have any issue with any of the dimensions being infinite in extent.

    Another way I think of this is if you have a problem with an infinite amount of energy coming into existence to satisfy a universe that is infinite in one or more spatial dimensions then you should have the same issue with a finite amount of energy coming into existence to satisfy a spatially finite universe that has a start but lasts for an infinite amount of time.

  21. #21
    Join Date
    Jun 2008
    Posts
    4,222
    Quote Originally Posted by Shaula View Post
    Remind me not to use throwaway analogies on here again... The point of the flat plates comment was not to get into a debate about time being relative (I know it is) or the odds of two plates being perfectly aligned (irrelevant) but to show the implicit assumption in the comments about one side of the universe 'knowing' that it had to go bang at the same time as the other side. The implicit assumption is that there is a signal or propagation of an effect whereas it is perfectly possible that (as in the inflation field ideas) this 'knowledge' was contained in the initial conditions. As it would be in the two plates.
    I was agreeing with you...I don't think I made that clear. I think we are saying the same type of thing just your words are a bit more elegant then mine :P

  22. #22
    Join Date
    Jun 2008
    Posts
    4,222
    Quote Originally Posted by Jeff Root View Post
    My statement quoted above has nothing to do with
    a creation event or any model. As I said, it is pretty
    much a tautology. It does not say much, and what
    it does say should be completely noncontroversial.

    -- Jeff, in Minneapolis
    No but I did. I'm the one that said that I don't have a problem with a creation event causing a universe infinite in all 4 spatial dimensions and I fully recognise that it is not provable. You say you don't like the chance of that happening. I say as long as there is a chance it could have happened that way and there is no data to indicate that it isn't that way.

  23. #23
    Join Date
    Mar 2010
    Location
    United Kingdom
    Posts
    4,458
    You say you don't like the chance of that happening. I say as long as there is a chance it could have happened that way and there is no data to indicate that it isn't that way.
    That is really the crux of it. Until we have more data, more complete models and so on all this speculation and attempt to logically constrain the nature of the universe is really just speculation. Any strong stance taken is essentially driven by belief because we do not know that our reasoning is valid under the unknown conditions way back when. The scientific position is: Don't know.

  24. #24
    Join Date
    Dec 2004
    Posts
    12,771
    Quote Originally Posted by WayneFrancis View Post
    Quote Originally Posted by Jeff Root View Post
    What do you mean by "at a certain condition"?
    Well... like pure water freezing at 0c at sea level pressures.
    Water everywhere we know will behave predictably when
    you lower its temperature.
    Ah. Of course.

    The problem is then either:

    How the conditions came to be the same throughout an
    infinite volume simultaneously, or

    How the initially zero-volume or very-small-volume
    Universe could become infinite in finite time.

    Quote Originally Posted by WayneFrancis View Post
    Quote Originally Posted by Jeff Root View Post
    If everywhere inflates at the same "time" without any
    causal event, then is it by coincidence?

    If the Universe popping into existence is the causal
    event which resulted in inflation, then you need to
    explain how an infinite volume of space would all pop
    into existence at the same "time". Coincidence?
    I don't see this as a problem. It is just that instead
    of a finite amount of space time popping into existence
    it is infinite.
    You have space popping into existence here, and
    simultaneously you have space popping into existence
    a meter to the left, and simultaneously you have space
    popping into existence a meter to the right, in exactly
    the same way as it popped into existence in the other
    two places, just by coincidence. And you have more
    space popping into existence five meters behind you
    and more space popping into existence five meters
    above you, again in exactly the same way as in the
    first three cases, all at exactly the same time, and all
    just by pure chance. Pure coincidence. Plus you have
    more space popping into existence fifteen meters in
    front of you and yet more twenty meters in front of you,
    and more twenty-five meters in front of you, all at the
    same time, all just by coincidence. And it just goes on
    and on and on and on and on and on, without end.

    It isn't a trillion coincidences, or a sextillion or a googol
    or a googolplex coincidences. It isn't even a googolplex
    raised to the googolplex power coincidences. It is
    infinitely more than that. Infinitely many coincidences
    have to occur in order for space to pop into existence
    everywhere simultaneously.

    That is infinitely less likely than, say, every snowflake
    that forms in the Milky Way galaxy during the next ten
    million years having exactly the same number of water
    molecules in the same hexagonal pattern.

    I can compare the likelyhoods of those two possibilities
    even though I don't know the absolute probabilities of
    either because one is finite and the other is infinite.

    Quote Originally Posted by WayneFrancis View Post
    Quote Originally Posted by Jeff Root View Post
    If the Universe instantaneously inflated from a "point"
    to infinite size when it popped into existence, then that
    inflation is in addition to the observed expansion and
    the inflation hypothesized by Inflation theory. (Plus
    the observed acceleration of the observed expansion.)
    I didn't say a point. That implies a location and the
    only location I say that matters is the location in time.
    I agree that you didn't say anything about a point.
    The term was the best I could come up with at that
    moment and I agree it is not a good one.

    The idea is that the Universe went from zero or very
    small size to infinite size in zero or very short time,
    as opposed to simultaneously popping up everywhere
    at once. The former permits the expansion to have
    a single, common cause, while the latter requires
    infinitely many coincidences.

    But as I say, it is still another expansion in addition
    to those already proposed by the Big Bang theory
    and Inflation theory.

    Quote Originally Posted by WayneFrancis View Post
    ... The T[sub]0[/sup] point. The extent of x,y,z at
    T[0] is not an issue. Just as t∅→t∞ is not an issue
    x∅→x∞ is not an issue. In a 4 dimensional manifold
    do you have a problem with time having a start but
    being infinite in extent?
    Time does not instantaneously become infinite in extent.

    Time does not become infinite in finite time.

    I have a big problem with space becoming infinite in
    finite time. But my point here was that if it happens,
    it is an additional expansion needing explanation.

    Quote Originally Posted by WayneFrancis View Post
    "t" might be finite in our universe. So may the spatial
    dimensions but I don't have any issue with any of the
    dimensions being infinite in extent.
    I'm going to repeat myself yet again... I don't have
    any problem with an infinite universe, either. I just
    have a problem with an infinite universe coming from
    an event which occurred a finite time in the past.
    We can be sure that the Big Bang occurred roughly
    14 billion years ago, so we can be sure the Universe
    which resulted from it is not infinite in extent.

    Quote Originally Posted by WayneFrancis View Post
    Another way I think of this is if you have a problem
    with an infinite amount of energy coming into existence
    to satisfy a universe that is infinite in one or more
    spatial dimensions then you should have the same
    issue with a finite amount of energy coming into
    existence to satisfy a spatially finite universe that
    has a start but lasts for an infinite amount of time.
    I don't really understand it, but I'm attracted to the
    view (expressed by Hawking, if I recall correctly)
    that the net energy of the Universe is zero. Positive
    energy of matter and inertia balanced by the negative
    (potential) energy of gravity. In this view, any finite
    amount of positive and negative energy could separate
    from each other, though I can't imagine what the
    mechanism could be.

    -- Jeff, in Minneapolis
    http://www.FreeMars.org/jeff/

    "I find astronomy very interesting, but I wouldn't if I thought we
    were just going to sit here and look." -- "Van Rijn"

    "The other planets? Well, they just happen to be there, but the
    point of rockets is to explore them!" -- Kai Yeves

  25. #25
    Join Date
    Nov 2008
    Posts
    458
    Quote Originally Posted by Jens
    So of course, if the universe started with a big bang, then there can't be an infinite number of stars, so the possibility that remains is that it curves back on itself. Is this a fair conclusion?
    Hello Jens,

    You might find the work of Julian Barbour relevant:

    http://platonia.com/ideas.html (his website)

    http://discovermagazine.com/2001/feb/letters (old response letter)

    http://www.edge.org/3rd_culture/barbour/barbour_p1.html (old interview)

    http://discovermagazine.com/2012/mar...g-didnt-go-far (front page story from Discover, March 2012)

    http://www.youtube.com/watch?v=WKsNraFxPwk (a popular science piece about "Killing Time")


    Personally, I'm still trying to figure out these ideas, but the most fascinating path for me is trying to let go of anthropocentric thinking as much as possible: from the Copernican Revolution to the Cosmological Principle, this way of thinking has proven very successful.

    Barbour is exploring to what degree Mach's Principle is implicit in Einstein's GR and suggests that time itself is an abstraction (not real per se).

    What you may find intriguing about his model of the universe is that it is both static and eternal. Barbour demonstrates a relatively simple, yet illuminating, metaphor for his model in that youtube link. If one were to imagine a universe comprised of only three particles, one could imagine that it would be fully described by all the possible configurations these particles could take. This configuration space would be defined by three axes: each corresponding to the three inter-particle separations. These configurations occupy a tetrahedral volume in the configuration space with a natural "alpha" point (each point in the volume corresponding to a single triangle in position space) while having an infinite extent.

    In this way, universal expansion becomes an unavoidable consequence of time.


    I think reading his writings and watching the video would do his ideas better justice than I can as I am still trying to digest them.

    One might put it this way: the universe (the totality of existence) is static and eternal, yet, as Mach said: "It is utterly beyond our power to measure the changes of things by time. Quite the contrary, time is an abstraction at which we arrive through the changes of things."



    Quote Originally Posted by Jeff

    My argument doesn't depend on the Universe starting
    from infinitesimal size. It depends on the notion that
    everything involved in the Big Bang had to be causally
    connected to the Big Bang in order to be involved in
    the Big Bang (that is pretty much a tautology), and the
    notion that things which are infinitely far away from
    each other cannot be causally connected to the same
    event which occurred a finite time in the past.
    Jeff,
    I think I agree with your sentiment: you are arguing in favor of holism, are you not? In that case, I would say, what does causality even mean if the behavior of any entity (say particle) is governed by the entire observable universe? To me, causality only makes sense if there is such thing as independent entities; it's a convenient approximation of reality.

    For example, one might say that an asteroid caused the extinction of the dinosaurs, but why stop there? Why not blame the sun for having overwhelming influence on the other bodies in the solar system? Or why not blame the stars that spilled their guts into the interstellar medium, paving the way for the formation of the sun? This leads one to the conclusion that all of history is to "blame" for the extinction of the dinosaur for no event in the universe is singularly caused. In this sense causality is just an illusion and so questions like "what caused the big bang?" are incoherent.


    M74

  26. #26
    Join Date
    Jun 2008
    Posts
    4,222
    Quote Originally Posted by Jeff Root View Post
    Ah. Of course.

    The problem is then either:

    How the conditions came to be the same throughout an
    infinite volume simultaneously, or

    How the initially zero-volume or very-small-volume
    Universe could become infinite in finite time.


    You have space popping into existence here, and
    simultaneously you have space popping into existence
    a meter to the left, and simultaneously you have space
    popping into existence a meter to the right, in exactly
    the same way as it popped into existence in the other
    two places, just by coincidence. And you have more
    space popping into existence five meters behind you
    and more space popping into existence five meters
    above you, again in exactly the same way as in the
    first three cases, all at exactly the same time, and all
    just by pure chance. Pure coincidence. Plus you have
    more space popping into existence fifteen meters in
    front of you and yet more twenty meters in front of you,
    and more twenty-five meters in front of you, all at the
    same time, all just by coincidence. And it just goes on
    and on and on and on and on and on, without end.

    It isn't a trillion coincidences, or a sextillion or a googol
    or a googolplex coincidences. It isn't even a googolplex
    raised to the googolplex power coincidences. It is
    infinitely more than that. Infinitely many coincidences
    have to occur in order for space to pop into existence
    everywhere simultaneously.

    That is infinitely less likely than, say, every snowflake
    that forms in the Milky Way galaxy during the next ten
    million years having exactly the same number of water
    molecules in the same hexagonal pattern.
    But you've got the same problem. Why does it matter if and infinite amount of space come into existence at once or just 1x10-43m3?
    Your logic is why any 2 points in space would have the same properties if they are to far away. I ask "what is your definition of 'far' and why does it matter?"

    If they universe came into existence at a single point in time then what does it matter about the distance between any 2 point having the same physical laws. At T[sub]0[/sup] any 2 points you pick will be causally disconnected in our 4D space time. So you have the problem if the universe was 2 Planck units wide or if the universe was ∞ Planck units wide. If there is no reason, in your mind, why 2 points in space-time separated by an ∞ amount of distance at T0 should have the same physical laws because they are not causally linked then you have to have that problem for ANY distance at T0.

    Quote Originally Posted by Jeff Root View Post
    I can compare the likelyhoods of those two possibilities
    even though I don't know the absolute probabilities of
    either because one is finite and the other is infinite.
    Its like trying to say you have problem with numbers because they go on for ever.

    Quote Originally Posted by Jeff Root View Post
    I agree that you didn't say anything about a point.
    The term was the best I could come up with at that
    moment and I agree it is not a good one.

    The idea is that the Universe went from zero or very
    small size to infinite size in zero or very short time,
    as opposed to simultaneously popping up everywhere
    at once. The former permits the expansion to have
    a single, common cause, while the latter requires
    infinitely many coincidences.
    Let me make this clear I don't believe, and I don't know any scientist or mathematician that believes, you can get an infinite volume from a "small size". ∅→∞ not a problem. n→∞ big problem as I understand it. As far as a "short time" it is not applicable. T∅→T0 is not a "short time". The question of "time" is undefined. It just is. It doesn't matter about the spatial dimensions being finite or infinite. T∅→T0 can't be used for complaining about a causal link in our space-time. Its like asking someone outside a black hole to compare clocks with someone inside a black hole. It isn't even a question scientifically.


    Quote Originally Posted by Jeff Root View Post


    But as I say, it is still another expansion in addition
    to those already proposed by the Big Bang theory
    and Inflation theory.


    Time does not instantaneously become infinite in extent.

    Time does not become infinite in finite time.
    Our perception doesn't but just like I can't get from work to home instantly I can't travel through time instantly. The fact that it takes me 5 minutes to get 5 minutes into my future doesn't matter just like it doesn't matter if it takes me 5 metres to get 5 metres from where I am. Just because I'm "Here" at Tn in time doesn't mean Tn + 5 minutes does not exist in the space-time manifold. So unless you want to show how T can't exist then I say at the time dimension of a 4d space time manifold did instantly become infinite in extent.


    Quote Originally Posted by Jeff Root View Post
    I have a big problem with space becoming infinite in
    finite time.

    Good, so do I. T∅→T0 is not a finite amount of time. It is no time. It is undefined with the question of time. So no problem there.

    Quote Originally Posted by Jeff Root View Post
    But my point here was that if it happens,
    it is an additional expansion needing explanation.

    I've already shown that if you follow that logic then you have to have a problem T∅→T0 and any spatial distances regardless of them being finite or infinite. While I'm agnostic on the question if the universe is infinite in any one of its spatial dimensions or not I see faults in the logic about claiming it can't be so far. I guess that is why I'm still agnostic on the issue.

    Quote Originally Posted by Jeff Root View Post
    I'm going to repeat myself yet again... I don't have
    any problem with an infinite universe, either. I just
    have a problem with an infinite universe coming from
    an event which occurred a finite time in the past.
    We can be sure that the Big Bang occurred roughly
    14 billion years ago, so we can be sure the Universe
    which resulted from it is not infinite in extent.


    I don't really understand it, but I'm attracted to the
    view (expressed by Hawking, if I recall correctly)
    that the net energy of the Universe is zero. Positive
    energy of matter and inertia balanced by the negative
    (potential) energy of gravity. In this view, any finite
    amount of positive and negative energy could separate
    from each other, though I can't imagine what the
    mechanism could be.

    -- Jeff, in Minneapolis
    And that problem of the universe having a net energy of zero would mean that time would have to end at some point. Something the data doesn't support at all. Could be...but no support for it. So if you have no problem with a finite amount of energy being created to create our universe for an infinite amount of time then you're already past the point of complaining about an infinite amount of energy being created for a finite or infinite amount of time. Well that is the way I see it.

    as always I'm open to being corrected especially by those with the skills in mathematics to show me where my logic breaks down. But I've got here by others showing me, using mathematics over my head, that it isn't inconsistent or impossible.

  27. #27
    Join Date
    Aug 2003
    Location
    The Wild West
    Posts
    7,794
    Quote Originally Posted by m74z00219 View Post
    You might find the work of Julian Barbour relevant:
    his model of the universe is that it is both static and eternal.
    Well, we know the "static" part is wrong. I'm not sure why one would pick Barbour out of the thousands of physicists working at the cutting edge of our current knowledge. It's not disqualifying, but it's a little weird that Barbour completed his PhD in 1968 and has worked outside the academic environment ever since. But more importantly, how can someone claim the Universe is static in the face of so much contrary evidence?
    Everyone is entitled to his own opinion, but not his own facts.

  28. #28
    Join Date
    Dec 2004
    Posts
    12,771
    Quote Originally Posted by WayneFrancis View Post
    But you've got the same problem. Why does it
    matter if an infinite amount of space comes into
    existence at once or just 1x10-43m3?
    It doesn't. You've missed the point.

    In an *infinite* universe, a fraction of a second
    or an hour or a millenium has the same problem:
    There is no way that the required information can
    reach all parts of the Universe in time to cause
    whatever event we are talking about.

    It isn't necessary or important that the event be
    exactly simultaneous everywhere. But it needs to
    be approximately simultaneous, and that requires
    either a cause which somehow affects the entire
    Universe, or an infinite number of separate, nearly
    identical coincidences.

    Quote Originally Posted by WayneFrancis View Post
    Your logic is why any 2 points in space would have
    the same properties if they are too far away. I ask
    "what is your definition of 'far' and why does it matter?"
    "Too far apart" is "Too far for one location to have
    had an effect on the other."

    If two places have never had any causal connection,
    there is no reason to expect that they would have
    any properties in common. When I see the same
    thing occur at many different places, I can be sure
    that those events have been causally connected.

    The more complex the event, the more sure I am
    that the events have been causally connected.
    Perhaps "space popping into existence" or "space
    inflating" are very, very simple events...

    The larger the number of events, the more sure I
    am that they have been causally connected. When
    you are talking about infinite space being affected
    in the same way in a short period of time, you are
    talking about infinitely many events. Infinitely
    many places where space pops into existence or
    existing space inflates. I can be sure in that case
    that the events must have been causally connected.
    Except that it is impossible for them to have been
    causally connected because they are separated
    from one another by infinite distances. Neither
    way works. It is a reductio ad absurdum.

    Quote Originally Posted by WayneFrancis View Post
    If the universe came into existence at a single point
    in time then what does it matter about the distance
    between any 2 points having the same physical laws.
    At T[sub]0[/sup] any 2 points you pick will be causally
    disconnected in our 4D space time. So you have the
    problem if the universe was 2 Planck units wide or if
    the universe was ∞ Planck units wide.
    That may be your problem. It is not mine.

    In the real Universe, it is obvious to me that all parts
    of the Universe have been causally connected in the
    past. They would not be so similar if they had not
    been causally connected. Your problem is to extend
    that causal connection to infinite distances in finite
    time. I say that is impossible.

    As an alternative to all parts of the Universe having
    been causally connected in the past, you posit a
    coincidence of infinite proportions. Everywhere in an
    infinite universe just happened to do the same thing
    at the same time. I say that is impossible, too.

    Quote Originally Posted by WayneFrancis View Post
    If there is no reason, in your mind, why 2 points in
    space-time separated by an ∞ amount of distance
    at T0 should have the same physical laws
    because they are not causally linked then you have
    to have that problem for ANY distance at T0.
    Real events really affect the Universe around them.
    It takes time for effects to propagate to a distance.
    I have no doubt that all parts of the Universe that we
    can see -- and all parts of the Universe that came out
    of the Big Bang -- have been causally connected.

    Quote Originally Posted by WayneFrancis View Post
    Quote Originally Posted by Jeff Root View Post
    I can compare the likelyhoods of those two possibilities
    even though I don't know the absolute probabilities of
    either because one is finite and the other is infinite.
    Its like trying to say you have problem with numbers
    because they go on for ever.
    No.

    I think you are grasping at straws.

    I compared a finite event which is obviously absurdly
    unlikely to an event which is infinitely unlikely. You
    are the one positing the infinitely unlikely event, so
    the problem would be yours, not mine.

    Quote Originally Posted by WayneFrancis View Post
    Quote Originally Posted by Jeff Root View Post
    I agree that you didn't say anything about a point.
    The term was the best I could come up with at that
    moment and I agree it is not a good one.

    The idea is that the Universe went from zero or very
    small size to infinite size in zero or very short time,
    as opposed to simultaneously popping up everywhere
    at once. The former permits the expansion to have
    a single, common cause, while the latter requires
    infinitely many coincidences.
    Let me make this clear I don't believe, and I don't
    know any scientist or mathematician that believes,
    you can get an infinite volume from a "small size".
    ∅→∞ not a problem. n→∞ big problem as I
    understand it.
    And let me check that you were as clear as you were
    trying to be.

    Are you saying that something can increase from
    zero size to infinite size, but something cannot
    increase from small size to infinite size?

    If so, can you give any examples of things increasing
    from zero size to infinite size?

    If you can't do that, can you give any examples of
    things increasing from zero size to very large size?

    So that I can be sure I understand you correctly.

    Also -- if I did understand correctly -- can you
    explain why increasing from small size to infinite size
    is a problem while increasing from zero size to infinite
    size is not?

    Quote Originally Posted by WayneFrancis View Post
    As far as a "short time" it is not applicable.
    T∅→T0 is not a "short time".
    You are saying that zero time is something distinctly
    different from a "short time". Okay.

    Quote Originally Posted by WayneFrancis View Post
    The question of "time" is undefined. It just is.
    What is undefined? Time, or "the question of time"?
    What "just is"? Time, or "the question of time"?

    I don't get what you were saying there, or why.

    Are you saying that you don't want me to apply the
    idea of passage of time to the infinite universe-filling
    event you posit?

    Quote Originally Posted by WayneFrancis View Post
    It doesn't matter about the spatial dimensions being
    finite or infinite. T∅→T0 can't be used for
    complaining about a causal link in our space-time.
    Its like asking someone outside a black hole to
    compare clocks with someone inside a black hole.
    It isn't even a question scientifically.
    You appear to be asserting that because something
    occurs instantaneously, causality is irrelevant.

    Is that at all close to what you meant?

    Can you provide any examples of what you are
    talking about?

    Can you provide any examples of events which
    occur in zero time?

    Quote Originally Posted by WayneFrancis View Post
    Quote Originally Posted by Jeff Root View Post
    Time does not instantaneously become infinite in extent.

    Time does not become infinite in finite time.
    Our perception doesn't but just like I can't get from
    work to home instantly I can't travel through time
    instantly. The fact that it takes me 5 minutes to get
    5 minutes into my future doesn't matter just like it
    doesn't matter if it takes me 5 metres to get 5 metres
    from where I am. Just because I'm "Here" at Tn
    in time doesn't mean Tn + 5 minutes does
    not exist in the space-time manifold. So unless you
    want to show how T can't exist then I
    say at the time dimension of a 4d space time
    manifold did instantly become infinite in extent.
    That looks like word soup. Everything up to the last
    sentence may be true, but it doesn't say anything
    of any consequence. It is pure tautology. The final
    clause appears to be a completely baseless assertion.
    You are simply asserting that the Universe could
    (or did!) instantaneously become infinite in extent.
    There is no reason to think so.

    Quote Originally Posted by WayneFrancis View Post
    Quote Originally Posted by Jeff Root View Post
    I have a big problem with space becoming infinite in
    finite time.
    Good, so do I. T∅→T0 is not a finite
    amount of time. It is no time. It is undefined
    with the question of time. So no problem there.
    What is "the question of time"?

    What makes you think that zero time is "undefined"?

    What makes you think that zero time being undefined
    makes it not a problem for your idea?

    And -- nit-picking -- What makes you think that zero
    is not considered "finite"? I defy you to present a
    credible source for that assertion.

    Quote Originally Posted by WayneFrancis View Post
    Quote Originally Posted by Jeff Root View Post
    But my point here was that if it happens,
    it is an additional expansion needing explanation.
    I've already shown that if you follow that logic then
    you have to have a problem T∅→T0 and any
    spatial distances regardless of them being finite or
    infinite.
    What?

    What logic of mine are you referring to? The logic that
    the expansion you posit (of space inflating instantly from
    zero size to infinite size) is in addition to the expansion
    posited by the Big Bang theory and the inflation posited
    by Inflation theory? Or the logic that the expansion you
    posit requires an explanation? Or what?

    I don't understand the rest of what you said.

    Quote Originally Posted by WayneFrancis View Post
    Quote Originally Posted by Jeff Root View Post
    I don't really understand it, but I'm attracted to the
    view (expressed by Hawking, if I recall correctly)
    that the net energy of the Universe is zero. Positive
    energy of matter and inertia balanced by the negative
    (potential) energy of gravity. In this view, any finite
    amount of positive and negative energy could separate
    from each other, though I can't imagine what the
    mechanism could be.
    And that problem of the universe having a net energy
    of zero would mean that time would have to end at
    some point.
    Can you explain that? I've never heard such a thing.

    -- Jeff, in Minneapolis
    http://www.FreeMars.org/jeff/

    "I find astronomy very interesting, but I wouldn't if I thought we
    were just going to sit here and look." -- "Van Rijn"

    "The other planets? Well, they just happen to be there, but the
    point of rockets is to explore them!" -- Kai Yeves

  29. #29
    Join Date
    Oct 2009
    Location
    a long way away
    Posts
    9,104
    Quote Originally Posted by Jeff Root View Post
    It isn't necessary or important that the event be
    exactly simultaneous everywhere. But it needs to
    be approximately simultaneous, and that requires
    either a cause which somehow affects the entire
    Universe, or an infinite number of separate, nearly
    identical coincidences.
    There is a third possibility, which I think has already been mentioned in this thread (and every thread where you bring this up). It may be an essential characteristic of [whatever was there at the time] to start expanding; and so it all started doing it at (about) the same time.

    If two places have never had any causal connection,
    there is no reason to expect that they would have
    any properties in common.
    On the other hand, it doesn't say they can't have properties in common.

    As an alternative to all parts of the Universe having
    been causally connected in the past, you posit a
    coincidence of infinite proportions. Everywhere in an
    infinite universe just happened to do the same thing
    at the same time. I say that is impossible, too.
    It doesn't have to be "coincidence"; it may be part of the underlying nature of the universe.

    I know you believe that to be impossible, but that doesn't mean it is.

    And just to be clear, I am not arguing in favour of a finite universe or an infinite universe, one that sprang from nothing or one that always existed in some form, the big bang being unique or the big bang happening multiple times (in time and/or in different regions of space), or even the big bang never happening. (It could be any of these.) I am just pointing out that you are attempting to prove what you believe by using a logical argument where the premises are based on your beliefs. It is just an example of begging the question.

  30. #30
    Join Date
    Dec 2004
    Posts
    12,771
    Quote Originally Posted by Strange View Post
    Quote Originally Posted by Jeff Root View Post
    It isn't necessary or important that the event be
    exactly simultaneous everywhere. But it needs to
    be approximately simultaneous, and that requires
    either a cause which somehow affects the entire
    Universe, or an infinite number of separate, nearly
    identical coincidences.
    There is a third possibility, which I think has already
    been mentioned in this thread (and every thread
    where you bring this up). It may be an essential
    characteristic of [whatever was there at the time]
    to start expanding; and so it all started doing it
    at (about) the same time.
    That possibility is covered by the the two I stated.
    If something has a particular characteristic, then
    either it has that characteristic because it was
    caused to have it or because it acquired the
    characteristic by chance.

    Quote Originally Posted by Strange View Post
    Quote Originally Posted by Jeff Root View Post
    If two places have never had any causal connection,
    there is no reason to expect that they would have
    any properties in common.
    On the other hand, it doesn't say they can't have
    properties in common.
    Certainly. But the more places we are talking about,
    the less likely it is that they will have any specific
    property in common by chance.

    Quote Originally Posted by Strange View Post
    Quote Originally Posted by Jeff Root View Post
    As an alternative to all parts of the Universe having
    been causally connected in the past, you posit a
    coincidence of infinite proportions. Everywhere in an
    infinite universe just happened to do the same thing
    at the same time. I say that is impossible, too.
    It doesn't have to be "coincidence"; it may be part of
    the underlying nature of the universe.
    Why is the underlying nature of one part of the
    universe anything at all like the underlying nature
    of another part? Either it was caused to be that
    way or it is by chance.

    -- Jeff, in Minneapolis
    http://www.FreeMars.org/jeff/

    "I find astronomy very interesting, but I wouldn't if I thought we
    were just going to sit here and look." -- "Van Rijn"

    "The other planets? Well, they just happen to be there, but the
    point of rockets is to explore them!" -- Kai Yeves

Similar Threads

  1. Betelguex is much brighter than usual tonight -maybe?
    By Messier Tidy Upper in forum Space/Astronomy Questions and Answers
    Replies: 48
    Last Post: 2011-Jan-17, 07:41 AM
  2. As usual - can't do the maths
    By Cheap Astronomy in forum Space/Astronomy Questions and Answers
    Replies: 14
    Last Post: 2009-Mar-28, 11:34 AM
  3. The usual New Year's resolution post
    By banquo's_bumble_puppy in forum Off-Topic Babbling
    Replies: 26
    Last Post: 2005-Dec-17, 09:38 PM
  4. Sunset as usual in Germany
    By Sunflower in forum Against the Mainstream
    Replies: 5
    Last Post: 2003-May-20, 09:13 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
here
The forum is sponsored in-part by: