Is Dark energy a fudge factor ?

Discussion in 'Physics & Math' started by timojin, Apr 12, 2017.

  1. timojin Valued Senior Member

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    Can dark energy be measured if so, how is it measured ?
     
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  3. DaveC426913 Valued Senior Member

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    Not directly**. We see an expansion of our universe that appears to defy the physics we know.
    Whatever is doing that requires energy to do so.
    We can place some constraints on the nature of that energy, we don't know yet the details of its manifestation.

    Essentially, DE is measured by the rate of expansion of the universe.


    ** nothing wrong with that. We can't directly measure gravity either. We can only measure its effect on mass.
     
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  5. timojin Valued Senior Member

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    The team’s virtual universe evolved much as the real one has, with its expansion accelerating over the past few billion years. That happened even without adding space-stretching dark energy to the simulation, the researchers report in a paper in press at the Monthly Notices of the Royal Astronomical Society. The results suggest that it may be possible to explain away dark energy as an illusion, Dobos says.

    Others are cautious. Giblin notes that the simulation he and his colleagues performed differs from the new one. The new work tracks the evolution of the universe to finer spatial scales, but involves certain assumptions and approximations, he says. In spite of the differences, Giblin says, his work suggests that backreaction would change the expansion rate of the universe by less than a percent, whereas the new simulation suggests an effect in excess of 20%.

    Kaiser also expects the effects of inhomogeneity to be small. He notes that the best evidence for the accelerated expansion of the universe comes from measuring the distances and ages of stellar explosions known as type 1a supernovae in the relatively nearby universe. However, in the local universe, plain Newtonian gravity should work well enough. That suggests the difference in how the scale factor is determined in a relativistic theory shouldn’t exert a big effect. “If they’re right, there’s something very funny going on,” he says.
    http://www.sciencemag.org/news/2017...ily_2017-04-04&et_rid=41087911&et_cid=1255428
     
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  7. rpenner Fully Wired Staff Member

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  8. Michael 345 Valued Senior Member

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    Has any Scientist looked into / considered the acceleration of the Universe is due to it still being under the influence of the Big Bang?

    With (as far as we know) nothing outside of our Universe

    there is nothing out there to impede its expansion

    The internal force of gravity acting as a sort of bungie cord to acting as a restraint, as I understand it, is becoming weaker

    Just like a bungie cord being stretched

    if it goes to far it will break

    My thoughts are that
    • gravity will break
    • when it breaks
    • there will be no further acceleration
    • everything in the Universe
    • will continue expanding
    • at the rate it was moving
    • at the moment gravity broke
    • for eternity
    • unless parts of our Universe
    • bunp into something
    • Another Universe?

    Please Register or Log in to view the hidden image!

     
  9. Q-reeus Valued Senior Member

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    Anyone else using Firefox clicked on that arXiv link in #4 got the warning "Your connection is not secure!"? Doesn't affect Chrome browser.

    From the Intro of that article:
    "...Given the non-linear nature of Einstein’s equations, it has been known for a while that local inhomogeneities influence the overall expansion rate, whereas the magnitude of such backreaction effect is debated..."
    That article is not about effect of local inhomogeneity skewing our perspective of the true average value, but claims inhomogeneity everywhere effects the true average Hubble expansion rate. The rationale behind 'backreaction' causing any such change is at odds with implication of Birkhoff's theorem: https://en.wikipedia.org/wiki/Birkhoff's_theorem_(relativity)#Implications
    To put it simply: Authors claim net gravitating mass in a given average sample of the universe decreases as gravitational clumping proceeds within. Strange that, getting back to Birkhoff's theorem, such 'backreaction' is never claimed to manifest during say stellar gravitational collapse. Another example imo of internal conflict within GR.
     
  10. rpenner Fully Wired Staff Member

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    The link is to https :// www.arxiv.org when the certificate is for arxiv.org .

    There was a Subject Alternative Name (SAN) field which should be filled out with www.arxiv.org and the literal names of hosts that serve pages from that domain, if any. But they filled out the certificate request wrong and put (only) arxiv.org there also.
     
  11. Q-reeus Valued Senior Member

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    OK well I'm not up with the web technicalities there, but note that stripping out www to https://arxiv.org/abs/1607.08797 cures the issue in Firefox.
    Also within the article https://www.ras.org.uk/news-and-pre...expansion-of-the-universe-without-dark-energy
    linked to in #3, a further link is provided to the non-paywalled full article evidently identical to the arXiv version: https://www.ras.org.uk/images/stories/press/Cosmology/slx012.pdf
     
  12. The God Valued Senior Member

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  13. origin Trump is the best argument against a democracy. Valued Senior Member

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    He simply gave the source for the article Timojin cited.
     
  14. The God Valued Senior Member

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    Lot of issues with this offhand post.
    We do not see the expansion. It is just the interpretation which could be incorrect.

    There is no mechanistic relationship between DE and this expansion. Once you insert mechanics the SR comes into picture.

    There is apparently no constraints on this energy, it has problem of the order of 10^120.

    Cite the work which measures or quantifies DE based on expansion rate.

    If you were to measure gravity directly, how would you do that? Directly?
     
  15. DaveC426913 Valued Senior Member

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    We see acceleration of recessional velocity empirically.

    This goes without saying. That's why they're theories.

    Since we can't measure gravity directly, this question makes no sense. So neither would an answer.

    With unicorns?
     
  16. The God Valued Senior Member

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    Such argument comes from over reading of pop science.

    Recessional velocity is not velocity, and there is no acceleration. Why don't you do some simple dimension analysis (Chapter 00 of physics) and see if 'recessional velocity' has the dimension of m/t or something else.

    Unquestioned over belief in anything tantamounts to belief in Unicorn. You seem to accept mainstream hands down, thats like believing in Unicorns.
     
  17. karenmansker HSIRI Banned

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    "Amen" . . . . to The God
     

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