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

Infinte space infinte earths?

  1. Dec 9, 2006 #1
    Infinte space... infinte earths???

    Hi all, i am only a year 12 student so this may seem completely stupid to some of you haha... i was thinking the other day and came up with some kind of theory.

    If space is infinite then, assuming that our universe was created by random events... i.e. the Big bang then there has to be, at least matematically, a universe or earth exactly the same as the one known to us somewhere else in space.

    Also for this "second" univerese would there not also be another third universe.... and so on.

    So now i have myslef thinking that if space is infinite then there is an infinite amount of our universes... or soace repeats itself.. which it cant because it is infinite.

    hahaha this must seem pretty stupid to you all but would someone pleasde
    explain this to me?? thanks alot:smile:
  2. jcsd
  3. Dec 9, 2006 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Welcome to PF.

    Please be careful with what you post here -- we have high intellectual standards, and we don't permit personal theories, no matter how well-intended. There are no "mathematics" which support such an argument about multiple universes, and, indeed, your argument is not necessarily true.

    - Warren
  4. Dec 9, 2006 #3
    could you explain why it is impossible because i cant understand it....

    if there is infinite space doesnt it mean that the same environment needed to form this earth must exist somewhere else... or in many places because space is infinite?
  5. Dec 9, 2006 #4


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    I didn't say it was impossible that an almost identical planet exists elsewhere in the universe.

    I simply said there are no "mathematics" which demand that that must be true. In fact, there is no reason to believe the universe is infinite; many people believe that it is simply finite yet without bound, like the two-dimensional surface of an orange.

    - Warren
  6. Dec 9, 2006 #5
    If it is finite without bound, it implies a finite pattern which is inescapable. A finite universe cannot have an infinite number of stars. It would have to be like the game asteriods. A finite universe without exact symmetry would require a property reminescent of a "Hall of unfocused mirrors". An infinite universe beyond our particle horizon, as far as I know, has nothing to do with the balloon analogy. I am right about that?
  7. Dec 9, 2006 #6
    kmarinas86... do u think what i proposed is logical? if not why? that is all i really wanted to know.. assuming that space is infinite
  8. Dec 9, 2006 #7

    It has the property of being valid. But that does not mean it is true or that it has the property of soundness.

    It's still "logical", but being "logical" doesn't automatically make it the truth.
  9. Dec 10, 2006 #8
    i see that it cannot be classified as true because there is no evidence to support the claim..

    but could the event of an identical earth .. even down to this conversation... occur simply because of space being infinite, as in the problem of the monkey in front of a typerwriter eventually creating a sheakspere novel given infinite time?
  10. Dec 10, 2006 #9
    Could? yes. Really? We don't know.
  11. Dec 12, 2006 #10
    Don't worry Spoon, I understand what you are saying. Yet at the end of the day, we don't really know enough about our own universe to make claims that there are multiple universes. However if our universe "magically" appeared, then what would keep alternative universes from doing the same?

    Of course though, the universe most likely didn't "magically" appear. Read "The Big Crunch" theory. However one question I always posed and never get a clear answer is: if our universe was once a super dense singularity, then erupted causing the expansion of the universe, cooler temperatures for the formation of atoms, etc... then what stops a Black Hole's singularity from also creating a universe.. Seems pretty similiar in my opinion... condensed singularity. And while one may think that the universe a black hole would create would be small, size is relative and what makes us think our universe is big...

    Right now on our current understanding of the universe says that there are no multiple universes, and most likely the universe does have limits, though they are expanding. And to your earth like planet question, who knows! If the universe consists of the same atoms everywhere, then with 200 + billion stars in our galaxy 10+ billion galaxies in the universe, who knows, it could happen :)
  12. Dec 12, 2006 #11


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    ||spoon|| - I recall seeing an article about this idea (hmm...it was either Scientific American or Astronomy magazine about a year or two ago...maybe I can dig it up). The line of argument was something about there being a finite number of possible particle arrangements (e.g., finite number of particles in the observable universe) therefore, the patterns would eventually repeat in an infinite space. Not sure I buy it, but you're not alone in thinking along those lines.
  13. Dec 12, 2006 #12


    User Avatar
    Science Advisor

    The problem with talking about 'multiple universes' is that it is a contradiction in terms. The Universe, by definition, is everything. We used to think of what we now call the Milky Way as 'The Universe' but then discovered what were first called 'spiral nebulae' which turned out to be other objects that we called 'galaxies' and we decided that we also lived inside such an object.

    We changed our concept of the universe, rather than talking about other galaxies as 'universes'. Likewise if one of the many weird ideas about Black Holes seeding new 'universes' proves to be testable, and passes such as test then we will come up with some phrase like 'disconnected space time regions' or some such thing to describe the newly discovered add-ons to our Universe, rather than change the definition of the term 'universe'.
  14. Dec 12, 2006 #13


    User Avatar

    Staff: Mentor

    To me the flaw seems ovious: there aren't a finite number of possible particle arrangements.
  15. Dec 13, 2006 #14


    User Avatar
    Science Advisor
    Gold Member

    The blue collar explanation is, while the universe may be spatially infinite, it is not temporally infinite [i.e., we can only observe it back to the surface of last scattering]. Since the region beyond the surface of last scattering is unobservable, it is not casually connected to us, as observers. Hence, the concept is the same as a mathematical artifact that has no physically meaningful [e.g., testable] consequences.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook