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Infinite Universe?

  1. Oct 19, 2013 #1
    I was watching a video about how if the universe is infinite, that there is a possibility there is another galaxy exactly like ours and doing the same thing. Every possibility that I can imagine of do exist if the universe is infinite.

    Then I imagined me from another universe visiting me. He never came. Surely if the universe is infinite, that is a possibility.
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  3. Oct 19, 2013 #2


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    How could it be possible? If he's exactly like you that means that everything else on his world is exactly like ours, which means they don't have FTL travel in which to get from their galaxy to ours.
  4. Oct 22, 2013 #3
    I am sorry. My earlier explanation is awfully bad. If the universe is infinite, there has to be a possibility that myself somewhere else in another galaxy has created a machine where he can come see me on our earth. There are some that are visiting other earths too, but since the universe is infinite, there is a chance that one, many, or even infinite amount of me coming to visit me.

    I know it sounds weird, but it's logical in my head. By the universe being infinite, every possibility is infinite as well. Not only things that I can think about, but also things that I cannot should exist, and correlates with me, and everyone else too.

    Just like there is a possibility that you could have been the president of earth. You were never born. etc.
  5. Oct 22, 2013 #4


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    That's the problem with infinities, you get swamped with paradoxes. Fortunately, our universe has a temporal cutoff, otherwise known as the finite age of the observable universe, which spares us such indignities. We are causally disconnected from any regions beyond this boundary.
  6. Oct 22, 2013 #5


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    Assuming that machine is possible, yes.
    This means that someone called howabout1337 gets visited. It does not mean all howabout1337 get visited.
  7. Oct 22, 2013 #6


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    No, only those things that do not violate the laws of physics are possible.
  8. Oct 23, 2013 #7


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    We have no compelling reason to posit the laws of physics are the same everywhere in an infinite 'universe'. I'm bold enough to suggest they are the same everywhere in the observable universe - which is finite.
  9. Oct 23, 2013 #8
    I think what Cronos mentioned about a temporal cutoff is pretty important. Space may very well be infinite but time (at least as we understand it) is not infinite and holds little relevance once we get to Planck times and physics just breaks down.

    I may be wrong but I think that:

    Even if there was a very small amount of finite objects with an accordingly small configuration of states but they existed for an infinite time, they would not necessarily repeat the same state. For example, if we take 3 x wheels of equal size, rotating on the same access, one point marked on the same point on each wheel (same point on the circumference) and they all lined up in a straight line, the second wheel rotates twice as fast as the first. If the third wheel is 1/ π then the initial configuration of state would never reoccur – even given an infinite amount of spinning. This is how an infinity can be denied by a simple lack of return to initial configuration of state.
    So for a clone Earth to exist (an exact clone) would require a recreation include every fermion, photon, all electromagnetic wave, every single point of chance occurring the same including Quantum Indeterminacy randomness – basically everything across a bubble at least the size of the Observable Universe which is the current Hubble volume (28 billion light years diameter) and then you would need to account for factors outside the current volume but do have an impact on the initial state equations of the Observable Universe.

    Open to corrections or guidance from more knowledgeable posters here at PF.
  10. Oct 23, 2013 #9
    If there are infinite of visitors, then ALL howabout1337 gets visited. How can you limit to few only gets visited when there are infinite of them?

    If we take entropy as a general rule, with the universe being infinite, there is a possibility that a machine could randomly appear out of nowhere that can do this.

    Am I not getting the concept of INFINITY here? If the universe is infinite, the possibility of anything CAN and DOES exist, and that possibility will be infinite. Seems like all the answers given other than Chronos' are not taking my original question into consideration.
  11. Oct 23, 2013 #10
    No, I dont think so. Are you quoting something here or are you saying what you personally believe? It has been shown that in dimensions greater than two a random walker will not necessarily cross the origin after an infinite amount of time. http://mathworld.wolfram.com/PolyasRandomWalkConstants.html

    If you consider a physical state to be a point or a collection of points randomly walking in phase space they will not cover every point in an infinite amount of time. In an infinite universe after an infinite amount of time all that can happen does not necessarily happen.
  12. Oct 23, 2013 #11
    In a graduate course in probability I learned measure theory, which has to do with probability in infinite spaces. In infinite spaces then events with probability zero can occur. The canonical example is integers in the space of real numbers. The chance that any given real number is also an integer is zero. But it isn't impossible.

    In a finite sample space if we observe an event occurring then we can conclude its probability is greater than zero. In an infinite sample space that probability could be zero.

    The way I see it, in an infinite universe whatever exists exists. Said universe is indifferent to our mathematical models.
  13. Oct 23, 2013 #12
    Well, if you have countably many vistors and uncountably many howabout1337, then you can prove not all get visited.
  14. Oct 23, 2013 #13
    What is your probability measure on the space of real numbers?
  15. Oct 24, 2013 #14


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    How can you have "uncountably many" discrete physical objects?
  16. Oct 24, 2013 #15
    It was 18 years ago, let's see whether I can remember.

    Begin with the set of reals. Construct the set that is the union of all subsets [x,x+1/2) with x an integer. Assign it the measure 1/2. Similarly each union of all subsets [x,x+e) with x an integer and 0<e<1 has measure e. Build up a sigma algebra on that. Then you can show that the subset of integers has measure zero.
  17. Oct 25, 2013 #16
    Thank you Hubble. One thing you need to keep in mind is that the further The Hubble Telescope looks out into space, the further back in time it is looking too. The furthest Hubble has seen is a galaxy that is roughly 13 billion light years away.This means it took the electromagnetic wave (light wave) that Hubble is receiving 13 billion years to arrive. We are in fact seeing that Galaxy as it was 13 billion years ago.

    With that said, we would now have to review Hubble's Law. Hubble's Law says that we are sitting in a uniformly expanding universe and the expansion looks the same, regardless of your location. Also Hubble's Law states that the Speed at which a galaxy is traveling away from is is proportional to its distance. This is proven using the Doppler Effect. All galaxies in the universe (except for Andromeda and any other galaxy that is gravitationally locked with the Milky Way) will be redshifted.

    Apparently, nothing can travel faster than the speed of light right? Well there is a theory that the expansion of space itself can travel faster. Which would make sense giving the fact that the expansion of space is not an actual particle that has mass.

    I would think that if this is true, then galaxies that are far enough away would eventually get to the point were it was traveling faster than the speed of light away from us, Canceling out the velocity of light itself.

    Imagine being in the back of a pick up truck, traveling 50 kph in one direction. If you were to throw a baseball in the opposite direction, for that baseball to have any advancement in the opposite direction, you would have to throw that ball faster than 50 kph. If you throw the ball exactly the same speed as the truck but in the opposite direction, shouldn't it not move position from spot of release from your hand?

    I would think that the expansion of the universe would work the same way. Anything traveling the speed of light way from us would cancel out the velocity of light traveling towards us. This would make it to where were would see nothing at all because there are no light waves traveling towards us at this point.

    So I would think that the OBSERVABLE Universe is not the same size as the ACTUAL Universe itself. Please correct me if I am wrong at any point of this. Thanks
  18. Oct 25, 2013 #17


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    Last edited: Oct 25, 2013
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