If Space is Expanding?

Discussion in 'Astronomy, Exobiology, & Cosmology' started by Bowser, Feb 17, 2018.

  1. Bowser Life is Fatal. Valued Senior Member

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    If space is expanding, taking the stars with it, much like a balloon filling with air, would it be reasonable to conclude that space is being filled with some unknown either (dark energy)?
     
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  3. nebel Valued Senior Member

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    just for fun. how about a negative energy void sucking it out into a bigger volume? . hope the balloon does not pop.
     
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  5. Bowser Life is Fatal. Valued Senior Member

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    Or the idea that our universe is a bubble extruding from one larger than itself.
     
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  7. RainbowSingularity Registered Senior Member

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    if for arguement sake we used string theory...
    expansion is the continual creation of matter being converted from convergant axis of harmonics.
    i tend to lean toward this idea as it makes enough room for Dark Energy, mean-while i also beleive it is possible that Dark Energy is the dominant energy and we are yet to be able to scientifically isolate & study.
    Thus Dark energy is the source of Expanding space and Dark Matter is the source of the balance holding Galaxys together.
    this is a very loose concept(opinion of mine) and i am mostly postulating the idea.
     
  8. DaveC426913 Valued Senior Member

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    Don't think of it as space expanding. Space is not a thing.
    It is simply things getting farther apart.
     
  9. Bowser Life is Fatal. Valued Senior Member

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    I'm not certain I agree with you here. Space certainly does seem to be a "Thing."
     
  10. Q-reeus Valued Senior Member

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    Then how will you explain GW's within GR paradigm? Pure spatial curvature propagating as a wave at speed c. Methinks space is indeed a 'thing' of sorts. At least GR insists so.
     
  11. Q-reeus Valued Senior Member

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    DE or cosmological constant is within GR a logical explanation for observed late-time (from ca 5 or so billion years ago) accelerated Hubble expansion rate.
    However expansion per se requires no such exotic addition. Better to think of it as expanding matter-energy taking space along with it for a ride. The two are intimately coupled.
     
  12. Bowser Life is Fatal. Valued Senior Member

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    Thanks. My understanding is that space can be warped, stretched and compressed, which seems to imply it is a thing.
     
  13. Q-reeus Valued Senior Member

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    Current astronomical observations indicate the large-scale curvature of space is extremely small - some think zero. That despite the universe being filled with matter and a presumed DE. Some rival gravity theories dispense with DE, but regardless, space is expanding. In another thread I pointed out that to explain GW's properly, one cannot resort to 'stretching' or squeezing' of space, but rather to it's creation or destruction.

    Flat space implies a spatial metric that is unvarying with time. Hence cosmological scale expansion of space means creation of more space over time. The distinction between stretching/squeezing and creation/annihilation may seem pedantic, but it's actually necessary to make that distinction in certain situations e.g. GW's.
     
  14. RainbowSingularity Registered Senior Member

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    if everything is expanding, how do we know because all our Tape measures will be expanding also.

    did you notice that the thing is not only suggestively expanding(for want of a more technical word) but also (supposedly)accelerating in its expansion.

    if getting bigger was not enough, getting faster at getting bigger seems to be the thing of the thing.

    Though if Dave is correct and the thing is not a thing and things are just getting father apart, then how do we know as we have yet to find the edge of the bigger thing, or so i had come to understand.
     
  15. DaveC426913 Valued Senior Member

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    No.

    Think of pennies glued to a balloon. Inflate the balloon. Do the pennies grow as well? No. The balloon's expansion is far, far too weak to affect the penny's structure. The penny's simply get further apart.

    Likewise, the expansion of the universe is far, far too weak to affect anything but the most tenuously-bound structures. Galaxies are too cohesive to be affected - even galaxy clusters. It is only strong enough to affect the spaces between clusters.
     
  16. Bowser Life is Fatal. Valued Senior Member

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    That sounds like a substantial force.
     
  17. Vociferous Registered Senior Member

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    The metric expansion of space, in GR, includes time. So it's an expansion of space-time. Since it's much harder to imagine time as a "thing", it may help to think of the expansion as being the same in both time and space. For time to expand, the only thing added is more time. Not some exotic form of time.
     
  18. Xelasnave.1947 Valued Senior Member

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    How do scientists determine the Universe is expanding.
    I presume they cant take a measurement today and another in say a year or two.
    How can they tell that say one group of galaxies is moving away from another?
    How did Hubble determine the Universe was expanding.
    Alex
     
  19. Vociferous Registered Senior Member

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    Red-shift in the frequency of light. The further away a light source, determined by "standard candles" (luminosity to rotational velocity relationship) , the more red-shifted it's frequency.
    We can experimentally verify the red-shift of a receding light source on earth.
     
  20. Xelasnave.1947 Valued Senior Member

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    Thank you for your reply.

    I thought that was how it is worked out.
    Is there anything other than that method in play.
    And what I am really asking is ...could our determination that the universe is expanding be in any way flawed?
    Thanks again.
    Alex
     
  21. Vociferous Registered Senior Member

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    Not in the broad strokes, but possibly in accuracy of measurements.
     
  22. Q-reeus Valued Senior Member

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    Most of that 2nd to last sentence was ok, presuming 'in the very large cosmological scale' is implied, but as for that in red highlight - not so. Nothing to do with rotational velocity. The (current) standard candle is actually SNIa (type Ia supernovae). Owing to it's presumed highly predictable relationship between spectral luminosity as a function of time: https://en.wikipedia.org/wiki/Type_Ia_supernova
    Angular momentum/rotation-rate of the inspiraling binary star system is not important. The accretion mass limit before a/the white dwarf member goes SN is. There was a fairly recent challenge to that presumed regularity, but it seems to have petered out - much like a supernova does in fact.
     
    Last edited: Feb 19, 2018
  23. Vociferous Registered Senior Member

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    There are several classes of standard candles.
     

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