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Does the universe have infinite mass?

  1. Yes

  2. No

  3. Yes and No

    0 vote(s)
  4. Don't know

  1. Jun 20, 2008 #1

    Do you think that the universe has infinite mass?

    If you think that the universe has infinite volume and has isotropic and homogenous density everywhere on large scales then your answer should probably be yes.

    The question is specifically about "our" universe and does not include concepts of infinite multiverses. The question does however include mass that is beyond the visable universe that we see.
    Last edited: Jun 20, 2008
  2. jcsd
  3. Jun 20, 2008 #2


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    Properly speaking, it isn't known which is right. The Omega parameter hasn't been measured accurately enough. The errorbar is around 1.01 (which would say finite spatial volume) but includes the case that it is exactly 1.00 (which would make for infinite spatial volume).

    But it didn't seem much fun to just answer "don't know".

    I took the poll to be asking what is our personal hunch or private opinion. Admittedly we don't know, but which way do you lean?

    I lean towards the view that it's likely to be finite spatial volume. that is, the density ratio Omega actually is slightly bigger than 1, say something like 1.01.
    And matter seems to be approximately evenly distributed throughout space, so that leads to a finite estimate for matter.

    Good poll. It would be interesting to see what other people think, which way they are leaning.

    No rigorously correct answer, since the standard cosmological model, LambdaCDM, includes both cases depending on whether Omega exactly one or slightly bigger than one.
  4. Jun 20, 2008 #3
    Yes, it is probably more about personal belief or leaning. I believe there are some theories that require Omega to be exactly one but the experimental data does not not confirm that yet but it is tantalizing close and not excluded by the error bars. Maybe some people here know of reasons why it should logically be one from quantum theories or whatever and it would be interesting to hear what those arguments are. I started this poll, because I got to replies in another thread that felt strongly that the universe is definately infinite in mass. Personally my hunch or gut feeling is that the universe can not be infinite in mass, for what to me seem logical reasons, but may just be a prejudice brought about by the seeming absurdity or impossibility of anything physical actually being infinite.

    Anyway, it would be very interesting if anyone can present arguments as to why it would be impossible for the universe not to be infinite in mass or point to experimental evidence possibly in other fields that suggest that the universe must be infinite in mass.

    If you are one those in the "don't know" catagory here is a flow chart that gives some of the things to consider that may help you make up your mind: http://www.astro.umd.edu/~ssm/mond/flowchart.html
  5. Jun 21, 2008 #4


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    "It cannot be that axioms established by argumentation should avail for the discovery of new works, since the subtlety of nature is greater many times over than the subtlety of argument." --Francis Bacon (Novum Organum, 1620)
  6. Jun 22, 2008 #5
    This is surprising. :O

    I thought the poll would show a majority of "yes" votes followed closely by "don't know" votes. So far it is showing quite the opposite.
  7. Jul 3, 2008 #6
    Yes. IMO the universe is infinite. The universe is not just our observable universe and its environment. I can and will not give all my ideas about this infinite universe for which I think there is evidence in this thread (at least not in this post).
  8. Jul 3, 2008 #7
    Please note that the poll was worded specifically to address whether the universe has infinite mass and does not address whether the universe has infinite volume, which is a completely different issue. I mentioned this, because you mention "infinite universe" without making it clear whether you meant infinite mass or infinite volume.

    Thanks for your honest opinion. To be honest I thought there would be more votes like yours, and I get the impression from discussions in other threads that more people in this forum believe the same as you do, than is indicated by the vote so far.
  9. Jul 3, 2008 #8
    Hi Kev,
    I change my mind about every two months, so my vote shouldn't count for much.

    I vote that the universe indeed has infinite mass. My preference de jour is that the universe has a very large but finite quantity of matter and free radiation, located in a finite but expanding region. Beyond that region is an infinite expanse of empty vacuum.

    I do not currently believe that the universe has a closed topology, in the sense of being simply connected to itself, such as a sphere. Such curvature of space apparently requires 4 spatial dimensions. I think the scientific method requires that the physical existence of a 4th spatial dimension must remain categorized as pure conjecture until all reasonable 3-dimensional alternatives are demonstrated to be unlikely.

    Since there currently seems to be no better alternative to a cosmological constant (although I wish there were), I currently favor its existence. I believe that such a cosmological constant would fill all of the infinite vacuum beyond the matter/radiation domain of our universe. Since the cosmological constant has mass/energy, this requires the infinite universal vacuum to contain infinite mass/energy.

    The definition of "our universe" in my answer includes only our own matter/radiation domain plus the empty vacuum beyond. If there are other matter/radiation domains distant from and causally independent from ours, I exclude them from my definition. I have no opinion on whether such additional domains exist.

    Last edited: Jul 3, 2008
  10. Jul 3, 2008 #9
    If space is infinite, then mass is also infinite.
  11. Jul 3, 2008 #10
    Hi kev
    I agree with your remark , I was too quick in responding, but I really wanted to say that IMO the infinite universe has infinite mass. Even if you don't considder all local areas (domains) only containing energy then still there will be an infinite amount of areas (domains)containing mass. This results in infinite mass.
    Our observable universe with its environment is (IMO) not the centre of the infinite universe.
  12. Jul 3, 2008 #11

    Infinite mass would require infinite volume, would it not?
  13. Jul 3, 2008 #12
    Possibly, but infinite volume with finite density does not necessarily imply infinite mass.. or does it?

    Sorry for being vague, but infinite has some odd properties. For example if you pick a point anywhere on logarithmic spiral it requires an infinite number of rotations to reach the centre but the total path length that you travel is finite. Wierd! Another example is that an infinite flat slab of mass has finite gravity perpendiclar to the slab. I am sure there other examples.

    I hope some of the better mathematicians on this forum can clear up some of the properties of infinite for us :biggrin:
  14. Jul 3, 2008 #13
    Hi Kev,
    I'm uneasy with the whole concept of infinite too. Particularly as relates to singularities.

    The weirdness illustrated in your examples seems to arise from the fact that you've identified objects which are infinite in one or two spatial dimensions but not in all 3. Spaces which are infinite in all 3 spatial dimensions seem to be better behaved.

  15. Jul 3, 2008 #14
    I wouldn't think so. You could have an infinite volume with zero mass, but mass needs somewhere to go, so if you have infinite mass you must have infinite volume IMO.

    ...unless you have infinite density, which doesn't make much sense to me. It seems to me that pre-BB densities must be a maximum.
  16. Jul 3, 2008 #15
    I am in doubt here about what you see as "multiverses".
    This is maybe not unambigious. Same as for "our universe".

    Let me try to explain:
    When we talk about the spatial and time dimension, we normally talk then about a continuous, connected space, and without making special assumptions, without boundaries, edges or gaps.

    And my metaphysical assumption then is that neither space nor time have "begin" or "end" points.
    Nor is there a closed loop, and to my knowledge, this would only allow for infinite space and time.

    Now a multiverse can arise in diverse ways.
    For example, if you allow there to be gaps, you could end up with multiple seperated universes, for which there is no connection between them.
    They would be for all practical purposes (and based on scientific reasoning) to be considered "non existent" for the reason that they could not in any way effect us or each other and are by definition unobservable.

    A different "multiverse" is from the idea (such as in inflation) that they were co-developed with ours, or otherwise, but for which in any case it is true that there is some spatial/temporal connection possible.

    The latter I assume is simply part of "our universe".

    But perhaps you use a different reasoning to define "multiverse"?

    And for the question itself, the amount of mass in a universe which would not have any spatial extend and flat, and with an overall density > 0, there would indeed be no limit to the amount of mass.
    But in the physics meaning, all observables have finite values. Like: even on an infinite line, the distance between any two points on such line always yield a finite distance. Infinite distance does not exist, neither as infinite mass, at least not as observable measurements.
    Yet, as there is no upper limit that can be defined, in that sense they can be said to be infinite.
    Last edited: Jul 3, 2008
  17. Jul 3, 2008 #16
    As the infinite is not a precise quantity and never can be a measurement result yielding the infinite, in that sense nothing is infinite. On an infinite line, all distances between points are still strictly finite values, wherever you place the two points. Yet that doesn't make the line itself in any way finite, since you can always get a larger distance by selecting two points farther away.

    So, if density is said to be finite, it would mean that some upper limit to the density would apply.
    Perhaps there is. Maybe a Planck mass devided by the cube of a Planck lenght?
  18. Jul 3, 2008 #17
    The kind of multiverse I had in mind is the parallel universes (many worlds interpretation)often used in quantum discussions. Everytime a decision is made the universe splits off into two parallel universes, but I hope it reasonable to consider that every time a new parallel universe is made, that it does not double the mass acting on the universe that we experience.
  19. Jul 3, 2008 #18
    So it does contain other "inflationary bubble universes"?

    In that case it is a safe bet to say infinity (although I could reason for zero mass/energy also.....)
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