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Question regarding accellerating expansion of the universe.

  1. Mar 26, 2005 #1
    How do scientists compensate for relativistic effects when measuring the expansion of the universe using type 1a supernove?

  2. jcsd
  3. Mar 27, 2005 #2
    Interesting question. I'm not an expert and would love to see a reply from someone more knowledgable in this area, but from my reading of the literature the only relativistic correction applied to the data seems to be a time-dilation correction in the apparent magnitude data (see for example http://arxiv.org/abs/astro-ph/9805200).

    Anybody else got any idea?

    MF :smile:
  4. Mar 27, 2005 #3
    I'm not an expert either but why is redshift supposed to determine recession velocity? Is redshift a reliable indicator of distance? Is the CMB radiation basically uniform in all directions?

    These two discoveries might poses a challenge to the BB cosmology:

    1) Can A 'Distant' Quasar Lie Within A Nearby Galaxy?


    2) Is the low-l microwave background cosmic?

    Last edited: Mar 27, 2005
  5. Mar 27, 2005 #4
    I checked out all three links, but I couldn't access the first one X-43D provided. How fast does a supernova expand...ball park idea.
  6. Mar 27, 2005 #5
    i couldn't find anything about your supernova, but here some background on the expansion of the universe (hubble constant). run with it. also go to your library and find the book "the whole shebang" by Timothy something, i read it not too long ago and it talked about some of that stuff.


  7. Mar 27, 2005 #6
    my pet idea is Quasars are more then one black hole
    and are a group of 2 or more black holes coming together
    to form a supermassive black hole
    so they could have very high speeds and red shifts
    as they wiz around eachother
    and red shift canbe based on speed not distance

    once they combine into a super massive single hole
    the show is over no more quasar
    only a resting massive black hole
  8. Mar 27, 2005 #7
    A last name would be very helpful if that's ok. :wink:

    I'll see if I can find the book. Thanks. Couldn't access the link, stupid computer. :devil:

    The quasars might be part of the answer. Something to think about. :rolleyes:
  9. Mar 27, 2005 #8


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    1) Here is the paper about the quasar in NGC 7319.


    Don't expect standard cosmologists to spend much time considering its implications, at least in public. They have rejected every known example of interacting objects with discordant redshifts, and have labeled Arp, the Burbidges, et al as "cranks" for their efforts.

    2) I believe that the CMB is the local signature of the ZPE EM fields, and that the strong dipole anisotropy is an artifact of our galaxy's proper motion through that field. Smaller anisotropies will be the result of smaller proper motions (galactic rotation, Sun's path through the galactic arm, Earth's path around the Sun, etc) Perhaps someday :mad:, the 2nd year WMAP data will be released. If in fact my ZPE model is correct, I predict that the data will show that the small-angle anisotropies do not agree with those of the 1st year data, and therefore the CMB is not the echo of the Big Bang, but is the local ground-state of the quantum vacuum. The longer the release is delayed, the more I suspect that the delay is due to a "problem" of this magnitude.
  10. Mar 27, 2005 #9
    So if the big bang would not be the way the universe had begun, then what theory would best describe how our universe came to be?
  11. Mar 27, 2005 #10


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    How about a Universe that is infinite in extent, both spacially and temporally? It's a mind-blower for many folks (OK, I grew up in the '60s :smile:), because humans seem to naturally want to define our place relative to some beginning and some ending. It is just as likely (given our sample set of ONE universe) that the Universe is infinite in any respect, as it is that the Universe is finite in that respect.
  12. Mar 27, 2005 #11


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    If you mean the time dilation from cosmological redshift, then you just have to scale your light curves by 1+z, just as you do the spectrum. If you mean relativistic effects due to the compact objects, then it's not really necessary to consider it. The measurement of cosmological expansion can be done without understanding the physics of the supernova, you just have to verify observationally that they follow some sort of "standard candle" relationship.
  13. Mar 27, 2005 #12
    Heard of Olber's paradox?
    I disagree with your comment here - in fact there are very many humans who seem to naturally NOT want to define our place relative to some beginning or some ending - including some of the greatest names in historical science - both Newton and Einstein intuitively believed in a static, infinite universe (though Einstein, on deeper reflection, recanted). I would suggest that it is in fact naive intuition that leads to thinking of a universe infinite in both space and time.

    Not sure I understand this, can you explain a little more?
    If there is an additional relativistic effect on the redhsift (for example gravitational redshift, but I am not restricting myself to that alone) then this will surely be the same for all SN1a (if they are "standard candles" then any gravitational redshift for example will result in a similar magnitude gravitational redshift correction regardless of distance?) and therefore require a "constant correction" to all the SN1a redshift data rather than correction by a z-shift "factor"?
  14. Mar 27, 2005 #13


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    Yes, I have heard of Olber's paradox, and no, I do not think that it is naive intuition to believe that the Universe might be infinite in both space and time. These concepts do not follow from naive intuition, but arise from informed study. Newton believed that the Universe must be infinite, to prevent any gravitational instability that would have caused collapse, and Einstein introduced the CC in order to ensure that such a collapse would not happen. I might be a dummy, but these are a couple of pretty smart guys.
  15. Mar 27, 2005 #14
    Hey, we all have naive intuitions, it's what we learn as we grow up. Please don't take it as an insult, I have many naive intuitions too, and I know its hard sometimes to fight against them. I never said that either Newton or Einstein were not smart, but like all of us they were not perfect and they also had naive intuitions. Newton never really thought through the implications of his infinite universe properly, I suspect he had a deep religious conviction that the universe was infinite and therefore selectively favoured such a model (I admit this is my personal opinion of his motivations).

    The first implication of an infinite (in time and space) universe that Newton failed to address properly is the paradox of gravity. In an infinite universe filled with stars, the gravitational force becomes undefined because there is an infinite force in each direction. The net force on the Earth, for instance, is then not dominated by the Sun but by any asymmetry in the distribution of distant stars. In his correspondence with Newton, Richard Bentley had put his finger on the problem, although Newton had fobbed him off by claiming that the infinite forces from the distant stars exactly cancelled; essentially this was an appeal to his theorem that a uniform shell of matter had no gravitational force on objects within it. In fact this theorem cannot be extended to an infinite shell, and in any case it was obvious that the stars are not uniform in space. Newton's manuscripts show that he was worried enough by Bentley's question to set to work to compare the numbers of stars of different magnitudes with a model of stars uniformly distributed in space (this came to nothing because there was no quantitative definition of magnitudes). Finding no obvious solution, Newton chose not to publicise the problem and it was only re-discovered by Hugo Seeliger in 1895.

    Secondly, in his correspondence with Bentley, Newton had claimed (correctly) that if matter was distributed evenly throughout infinite space, it would be highly unstable:
    "And much harder it is to suppose that all ye particles in an infinite space should be so accurately poised one among another as to stand still in a perfect equilibrium. For I reckon this as hard as to make not one needle only but an infinite number of them (so many as there are particles in an infinite space) stand accurately poised upon their points."
    Newton concluded from this that the particles would collapse into "an infinite number of great masses scattered at great distances from one to another... And thus might ye Sun and Fixt stars be formed...". Bentley took the argument a step further and argued that the stars themselves would collapse into each other without God's active intervention.

    (Leibniz criticised Newton's cosmology for this very reason : "According to their Doctrine, God Almighty wants to wind up his Watch from Time to Time: Otherwise it would cease to move. He had not, it seems, sufficient Foresight to make it a perpetual Motion. Nay, the Machine of God's making is so imperfect, according to these Gentlemen, that he is obliged to clean it now and then...and even to mend it...")

    And then there's Olber's famous paradox. You say you have heard of it - can you explain how you escape Olber's paradox in a universe infinite in space and time?


    MF :smile:
  16. Mar 28, 2005 #15


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    MF this is a great post. I nominate it for post of the month or something.
    I really like the quotes from newton correspondence with bentley, and most especially the Leibniz quote is priceless.
    More power to you!
  17. Mar 28, 2005 #16


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    That's right. That was the second category I was talking about. Those things are irrelevant for the standard candle analysis.

    That's just cosmological time dilation. Not only is the light redshifted, but the time interval is also dilated. It doesn't come up a lot because we don't usually measure time intervals in cosmology, but it's an issue for quasar variability and GRB studies. Here's an example paper on the subject.
  18. Mar 28, 2005 #17
    Thanks for the reference, but I think we are talking at cross-purposes.
    There should be at least 2 different gravitational relativistic effects?
    One is gravitational time-dilation (addressed in the paper you reference).
    The other is gravitational redshift (not addressed)

    The gravitational redshift will be in addition to, but mixed up with, any cosmological expansion redshift.
    But the gravitational redshift should be distance-independent, whereas the cosmological expansion redhsift will be distance dependent.
    Therefore to get the correct distance-dependency out of the measured redshift, we would have to correct the measured z for the gravitational redshift, to get the correct cosmological expansion z.
    This should be a fixed redshift correction, not a (1+z) multiplying factor?

    MF :smile:
  19. Mar 28, 2005 #18


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    Not sure I follow. Here's the basic process that I'm picturing:

    - Measure the redshift based on the spectrum (no time dilation correction).
    - Measure the flux (no time dilation correction).

    That used to be all that they did to get the distance and no time dilation correction was necessary, but they found out that it wasn't exactly a standard candle. They could more precisely measure the distance by fitting a relationship between luminosity and the timescale of the supernova burst. Thus,

    - Measure the light curve (redshift-dependent time dilation correction required).

    That is, the times they measured required a 1+z correction factor. They could use this to find the luminosity and the flux to find the distance. Then they just plot on a Hubble diagram and they're done.
  20. Mar 28, 2005 #19
    Sorry, point taken. I was confusing gravitationally-induced time-dilation & redshift with velocity-induced time-dilation. Of course the gravitational effects on photon frequency will be negligible with the particular supernovae being studied (but might be significant for quasars?). Anyway, sorry for muddying the waters here.

    By the way, there is an excellent review paper at http://www.publish.csiro.au/?act=view_file&file_id=AS03040.pdf
    for anyone interested in a non-specialist account of cosmological expansion and all the associated measurement issues.

    MF :smile:
  21. Mar 28, 2005 #20


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    Hi, MF! I am very pleased to encounter someone who will bother to study the motivations of the masters. Thank you for the elucidation.

    Yes, you can escape Olber's paradox in an infinite Universe. In my model, light interacts with the EM fields of the quantum vacuum as it traverses space and is redshifted proportional to the density and extent of the EM fields that it traverses. Light emitted sufficiently far away from us is redshifted out of detectability, limiting the extent of the universe that we can see. Like any other wave, light cannot traverse the EM fields of the vacuum without "paying the fare".
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