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I Do particles create space over time? Is that expansion?

  1. May 1, 2017 #1
    If a particle can potentially be transported to any place in space limited only by the speed of light, does that potential amount to an expansion of space? And another question: Does it make sense to define space as any place a particle could go to?
     
  2. jcsd
  3. May 1, 2017 #2

    PeterDonis

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    "Space" in General Relativity, which is the applicable theory in cosmology regarding the overall structure of the universe, is not a fundamental concept; spacetime is. "Space" depends on your choice of coordinates.
     
  4. May 1, 2017 #3

    Drakkith

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    Before even getting into this in terms of cosmology and spacetime, I recommend that you start with learning more about basic geometry. The concepts used in 2d Euclidean geometry (the kind we all learn of in school) don't go away. They just get extended to more dimensions and different types of spaces.

    To most people, the phrase "expansion of space" means that "space itself" is expanding. This idea is problematic, as space is part of spacetime and spacetime is not an object. General relativity is a geometric theory, meaning that it tells us what the geometry of space is like, and this geometry will cause objects to behave certain ways. For example, gravity is the result of the geometry of local spacetime causing objects to get closer together over time, despite the fact that there are no forces acting on them. An vaguely analogous situation is when two people start walking due north from the Equator. Although they start off walking parallel to each other, the geometry of the surface of the Earth means that they get closer together over time despite the fact that both of them have been walking straight without turning.

    It's not really a wrong definition, it's just very incomplete.
     
  5. May 1, 2017 #4
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    i can't figure, out how to ask a single question about spacetime. If gravity has cousins, which would be dark energy and dark matter, and the cousins origins are basically geometric and emergent, like gravity . i can't figure it all out. But that is a nevermind.
    .
    Excuse me, but i think my basic simple question hasn't been answered. Does the mere existence of momentum over time imply space/time? And would that be expansion? More possible places to go in space/time= more space, in my naive interpretation anyway. It just looks like expansion to me.
    .
    And, i would like to add, thank you for your kind informative attention.
     
  6. May 1, 2017 #5

    PeterDonis

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    I'm not sure what you mean by "existence of momentum over time". In our best current theory, General Relativity, spacetime geometry and the presence of matter and energy are connected by the Einstein Field Equation.

    This doesn't make sense. Spacetime is a 4-dimensional geometry. It's not something that changes with time; "time" is already included in the 4-dimensional geometry.
     
  7. May 1, 2017 #6
    i refer you to Smolin. He saw an "emergence" of space, given the assumption that time is real.
     
  8. May 1, 2017 #7

    PeterDonis

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    Reference, please?
     
  9. May 1, 2017 #8
    Let's just go back to why i even showed up on this site.
    i kept getting messages from physicsforums informing me that i was seriously missed.
    Now i wonder if perhaps that was not entirely accurate.
    .
    You want a "reference".
    i can't find it now. i watched Smolin's 90 minute long lecture three times. i made detailed notes on it and posted them here, on this forum. Perimeter Institute lectures as i remember. He had this simple T-space geometry and he floated the notion that he could see space emerging from [as far as i could tell] a simple observation of the developments of his simple math---oh wait! No! It was geometry.
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    It's not my fault. Smolin said it.
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    Smolin is GR; you are GR.
    Duke it out.
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    And now irregardlessly i'm giving up cosmetology.
    Bye!
     
  10. May 2, 2017 #9

    PeterDonis

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    Those happen automatically if you haven't posted in a while, which it appears you hadn't until this thread, looking at your profile page.

    I'm sorry you feel that way; that was not the intent.

    Can you give a link to the thread where you did this? It would help a lot in understanding where you're coming from. I have never watched Smolin's video; and even if I had, I wouldn't know which particular things in it gave you the ideas you have. We don't ask for specific references here just for kicks; we do it because without them we don't know what background knowledge and context you have for the question you are asking, and without that we can't give you a good answer.
     
  11. May 2, 2017 #10
    The papers I've read from Smolin don't say that. LQG thrives on a discrete spacetime!

    Here is one of his papers where spacetime emerges: https://arxiv.org/pdf/1308.2206v1.pdf
     
  12. May 2, 2017 #11
    Thanks for responding. But i can only go by my measly memory and a couple of GR guys came up and said i was not welcome, and so now i'm gunna ban myself again for a couple of years. Being not welcome and all.
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    It's not a hard question: Do particles create more space by just sitting there, being particles?
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    Anyway, two exits is one too many.
     
  13. May 2, 2017 #12
    It's your site.
    You don't have archives?
    Please!
    i'm not going to go thru this again.
    GR.
    GR.
    GR.
    Huh?
     
  14. May 2, 2017 #13

    Drakkith

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    As far as I understand things, space isn't "created" at all. Objects simply move further apart over time. Distances between objects increase, but space isn't created as if it were something akin to an object.

    No one said that. We volunteered our own time to try to answer your questions and in return you act as if we've spat in your face for some reason.

    We aren't going to go out of our way to try to find which one of your 100+ posts contains your notes.

    I'm not sure what it is that you don't want to go through again, but it's clear this thread is done.

    Thread locked.
     
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