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Why galaxies are further from us

  1. Sep 11, 2013 #1
    Sorry to harp on the same subject but here's a point of view - without a reasonable explanation of why galaxies are further from us this year than they were last year, why isn't the proposition that new space is coming into existence from out of extra dimensions given any credibility?
    Do mathematical explanations of geometry really give a cause to increasing distances?
     
  2. jcsd
  3. Sep 11, 2013 #2
    There is a reasonable explaination for expansion. A major contributor is vacuum energy or the cosmological constant. You keep wanting to give space substance. Space itself is just geometric dimensions.

    Take a read through the two articles I posted in this thread.

    Perhaps with a better understanding of geometry and expansion you will see there us no need to invoke alternate dimension sources.

    https://www.physicsforums.com/showthread.php?t=709478
     
  4. Sep 11, 2013 #3
    I'm just a rank amateur so believe me, i feel silly being argumentative here, but anyway - as i understand it the cosmological constant is just a mathematical description, not a mechanism. Is vacuum energy the same?
     
  5. Sep 11, 2013 #4
    Ok think of it this way. Energy-mass density/volume is the same as pressure. So vacuum energy is the same as negative pressure. Gravity sources are positive pressure. Locally gravity pressure is stronger than the negative pressure.
    However in the voids between galaxy clusters. vacuum pressure becomes dominant. As the amount of space increases the vacuum pressure does not change. Hence constant. Ie cosmological constant. As the volume of the dominant vacuum pressure increases expansion rates also increase overall. However not per cubic metre
     
  6. Sep 11, 2013 #5
    As i understand it vacuum energy is a viable mechanism but as i understand it the numbers don't add up correctly. I hate to be simplistic but where does that leave us?
     
  7. Sep 11, 2013 #6
    The fact that vacuum pressure exists isn't in question in point of fact Einstein predicted either a contracting or expanding universe. The question as to why that pressure is constant as to the source of energy to maintains that constant pressure is the mystery. Is it one or many contributors. Dark energy is one strong candidate, others include quantum processes.
     
  8. Sep 11, 2013 #7

    Drakkith

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    Staff: Mentor

    My understanding:

    You're right in that the constant isn't "physically acting" on space, it is simply a part of the math. But without the constant the math simply wouldn't work at a universal scale. Since GR is a theory of geometry, this constant is an important part. Dark energy is an attempt to put a physical mechanism in place to explain the expansion. But it really isn't necessary, as the geometry of the universe can simply cause an expansion regardless of a physical mechanism. Space doesn't need something to cause it to behave that way if it's "built in" to the geometry.

    Does that make sense?
     
  9. Sep 11, 2013 #8
    Thanks Drakkith. What if it's a multidimensional geometry that is causing measurements to expand i.e. Calabai yau space moving in and out of our 3 dimensions?
     
  10. Sep 11, 2013 #9
    Its one of many possible conjectures, although string theory has a ways to go to prove the possibility. string theory is not one of my strong suits. Thus far I have never heard of a testable string theory prediction. Not to say that their aren't any, super strings have the same problem. Without being testable its difficult to validate beyond conjecture.
     
  11. Sep 11, 2013 #10

    Drakkith

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    If it happens to be multidimensional geometry, then that's what it is. But as of now we only know of our own 3 spatial dimensions. I'm not sure what kind of answers you're seeking.
     
  12. Sep 11, 2013 #11
    i asked my question in a vague way for lack of a more precise way. I guess i'm just fishing for ideas.
     
  13. Sep 11, 2013 #12
    if the LHC validates the possibility of extra dimensions, what will that say about space being more than nothing?
     
  14. Sep 11, 2013 #13

    Drakkith

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    Staff: Mentor

    It will remain nothing. The math just gets more complicated.

    I don't understand the concept of more space coming from some other dimension. That seems like asking if space from the Y dimension moves into the X dimension or Z dimension. (Where X, Y, and Z are our normal 3 dimensions)
     
  15. Sep 12, 2013 #14
    Mordred,
    maybe i misunderstood but you said "It's one of many possible conjectures". Could you point me to some research on the possibility?
     
  16. Sep 12, 2013 #15
    Not sure I still have the paper. I will look. Been a coupke of years since I last read the article
     
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