Space expand faster than light, why?

Discussion in 'Physics & Math' started by Secret, Aug 5, 2012.

  1. Secret Registered Senior Member

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  3. AlexG Like nailing Jello to a tree Valued Senior Member

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    It's the ultimate speed for anything moving in space. But the expansion is not movement through space. It's the creation of new space, and it happens at such a rate that light can never cover the ever growing distance.
     
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  5. Secret Registered Senior Member

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    Thanks for the explanation!

    Mind boggling indeed
    P.S. I need to wait 2 more years before I can finally touch GR in uni

    Btw where does the energy required to create the new space come from?
     
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  7. AlexG Like nailing Jello to a tree Valued Senior Member

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    Good question. Another question is does it take energy to create new space?

    It was originally thought that the universe was sort of coasting on the initial burst of inflationary energy. Then is was discovered that the expansion has been accelerating for the last 6.5 billion years. This has lead to the introduction of Dark energy, which is just a place holder term until we (hopefully) figure out what it is.
     
  8. Syne Sine qua non Valued Senior Member

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    It is specifically the speed limit for anything with a non-zero rest mass. Space is not known to have any mass.

    Space is only relative to the units of measurement associated with objects. We cannot know anything about space directly, only the relation between objects.
     
  9. AlphaNumeric Fully ionized Registered Senior Member

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    It actually depends on things like the cosmological constant. If the sign of the cosmological constant is right then it generates energy to make more space, which leads to a run away exponential effect, which is what we're observing via supernova detections and the expansion of the universe accelerating.

    Presently in GR it's a bit 'put in by hand', in the sense that if the universe has a particular metric, like the FRW metric, then you can get inflation and expansion of the type we see. But why should that happen? There are string theoretic constructions which describe inflation in terms of the compact dimensions. The curled up dimensions have various degrees of freedom and they all obey horribly complicated equations of motion. It just so happens that these small dimensions can have an impact on the big ones, with an unstable configuration in the compact dimensions leading to exponential growth in the bigger ones. The compact dimensions then stabilise and the inflation stops. Think of it like a ball starting at the top of an almost flat hill with an almost cliff on it. It hangs there for a long time, moving very very very slowly but once it reaches the cliff it makes a sudden transition to the bottom. This is the behaviour seen in the expansion parameter during inflation.
     
  10. kaduseus melencolia I Registered Senior Member

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  11. Fraggle Rocker Staff Member

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    Isn't it also the precise speed for anything with a zero rest mass? Have we established a scenario in which anything can travel faster?
     
  12. Syne Sine qua non Valued Senior Member

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    Yes to the former, and no to the latter. I would guess that you mean to infer that space should move at c? That would only be feasible of space were a substance.
     
  13. wlminex Banned Banned

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    Secret post #3: Btw where does the energy required to create the new space come from?

    Please see my recent post in the "There's a Black Hole at the Cosmic Core" thread - wlminex
     
  14. origin In a democracy you deserve the leaders you elect. Valued Senior Member

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    Or in lieu of that you could read a comic book.
     
  15. AlexG Like nailing Jello to a tree Valued Senior Member

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    The comic book has more information.
     

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