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B Trouble with Infinity

  1. Dec 16, 2016 #1
    How is it possible that there is a infinite amount of density at a point? I understand how number can be infinite but how does something tangible like matter reach infinity?
     
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  3. Dec 16, 2016 #2

    Orodruin

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    What do you think "matter" is? It is not some esoteric substance. It is made up of components that on a (sub)microscopic level behave according to the predictions of quantum mechanics.

    Only on larger scales does the "intuitive" approach of a continuum make sense.
     
    Last edited by a moderator: Dec 16, 2016
  4. Dec 16, 2016 #3
    okay, then how is it possible that infinite particles are in one spot in the universe, say at a singularity in a black hole? I'm having trouble comprehending how a never ending amount of particles can fit into a finite area. Wouldn't this area run out of space to fit the particles?
     
  5. Dec 16, 2016 #4

    Orodruin

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    They are not. In the case of standard classical GR, the singularity is (1) not "somewhere" - it is in the future of all observers - and (2) not a part of the universe.

    It is also highly likely that classical GR breaks down before you reach the singularity.
     
  6. Dec 16, 2016 #5
    So it's a mathematical entity not a physical one?
     
  7. Dec 16, 2016 #6
    also, what do you mean by in the future?
     
  8. Dec 16, 2016 #7

    Orodruin

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    If it was part of the universe, it would be more like a moment in time than a place in space. That "moment in time" would be in the future of all observers.
     
  9. Dec 18, 2016 #8

    Meir Achuz

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    "How is it possible that there is a infinite amount of density at a point? I understand how number can be infinite but how does something tangible like matter reach infinity?"
    'Infinity' is not a number at a point. A limit is 'infinite' if the number increases without limit as a point is approached,
    but the value at the point is undefined.
     
  10. Jul 3, 2017 #9
    Also, a different perspective: it exists along a different axis per se, more of a time measure than anything. Since it is a finite amount of energy / mass in a given infinitely small space, although the curvature of spacetime would be undefined, it would still exist within regular reasonable standards of Thermodynamics.
     
  11. Jul 5, 2017 #10
    Leptons and quarks are usually considered to be point particles, so you could perhaps consider them to have infinite density. But we humans invented the term density to be the ratio of mass to volume, so why shouldn't density be infinite? Any time we define a quantity as a ratio, we risk having infinities or undefined results. This isn't really a problem with Nature, but our choice of mathematical model.

    For example, we could consider the neutron to have an infinite mass to charge ratio. How could Nature allow such an aberration? It didn't. We did.
     
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