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Just a Little Mind Game re: Superluminal Neutrino Velocities

  1. Nov 26, 2011 #1
    By now, I've listened several times to Brian Greene's talk about the OPERA experiment. And, although I largely agree with him, there's one nagging question I have:

    Gravitation was, at a time soon following the Big Bang, a repulsive force.

    The existence of "Dark Energy" suggests the persistence of repulsive gravitation in our universe.

    If gravitation was once, and, within certain contextual constraints regulating our universe, apparently still is, a repulsive force, does it not make perfect sense, well within the bounds of Einsteinian Special Relativity, that particles under the influence of "Dark Energy"/repulsive gravity would, although possessing mass, exhibit the characteristics of RELATIVE negative mass, with respect to our observational perspective? Relative negative mass would REQUIRE relative superluminal velocity of particles under the influence of repulsive gravity/"Dark Energy".

    Am I an idiot? (I sure feel like one right now!!!)

    Does anybody have any other idea?
     
    Last edited: Nov 26, 2011
  2. jcsd
  3. Nov 26, 2011 #2

    mathman

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    Inflation (right after the big bang) and accelerated expansion (dark energy) are not the same as ordinary gravity, although there is some connection through general relativity. Ordinary gravity is attractive, as you well know.
     
  4. Nov 26, 2011 #3
    Correct you are. But the fact remains that gravitation was, and, in certain cases, still is, a repulsive force. The only thing I can think of that would allow for this apparent anomaly is for the particles under the influence of this repulsive gravity to exhibit characteristics of relative negative mass, while, simultaneously, possessing positive mass sufficient to account for the "missing mass" in our universe.
     
  5. Nov 27, 2011 #4

    Chalnoth

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    I don't see any connection here.

    But if you ask me, the observation of the neutrinos from supernova 1987A pretty much entirely rules out the possibility of the OPERA experiment being valid.
     
  6. Nov 27, 2011 #5
    OK, let me test that. The neutrino emission from SN1987A preceded the visible light emission by three hours. How do I find out the radial size of the star so I can model the interval between core collapse and the shockwave reaching the surface? Do stellar seismic events travel at the speed of light, or some other speed? (Obviously it must be less than the speed of light in a vacuum, as a star is hardly a vacuum.)

    ***

    As I said, Professor Greene is most likely right, but I'm just trying to figure out what the odd chance would look like.
     
  7. Nov 27, 2011 #6
    In fact, negative mass would not amount to superluminal speeds. That would be negative squared mass (or, equivalently, imaginary mass).
     
  8. Nov 27, 2011 #7

    Chalnoth

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    It's not necessary to delve into the details of the physics of the supernova. Just note that SN1987A occurred 168,000 light years away. Three hours is two parts in a billion of the travel time. So the simple, back-of-the-envelope estimate makes it so that the speed of neutrinos differ from the speed of light by no more than two parts in a billion. You can get better than this, obviously, by taking into account the physics of the supernova in some detail, but ignoring it is good enough for our purposes here.

    The OPERA team claims that these neutrinos differ from the speed of light by one part in 40,000. I don't see any possible way to reconcile these two results, even taking into account the fact that the neutrinos measured by OPERA had higher energy.
     
  9. Nov 27, 2011 #8
    Parlyne and Chainoth:

    You're both correct. I concede the point.
     
  10. Nov 27, 2011 #9

    DaveC426913

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    I'd like follow that. Link please?
     
  11. Nov 27, 2011 #10
  12. Nov 28, 2011 #11
    Chainoth:

    If the time difference between the observation of neutrinos from SN1987A and the observation of visible light from that event is not calculable with finesse equivalent to the OPERA experiment, due to the limitations on resolution obviously operating at such a vast space-time scale, than how does the SN1987A event have any bearing on the validity of the OPERA results? Are man-made scientific instruments really capable of producing energies greater than those produced by massive stellar events? Or is the energy bleed-off involved in motion across such vast distances sufficient to account for lower-energy naturally-propelled neutrinos as compared with neutrinos propelled by man-made devices measured just a few hundred kilometers from their source?
     
  13. Nov 28, 2011 #12

    Chalnoth

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    I don't understand what you mean. It is far, far easier to get a fine-grained measurement of the relative speed of light and neutrinos from SN1987A. The difference is travel time. The total travel time between CERN and the OPERA detector was a mere 2.4ms. So in order to detect differences in the travel time, you need your timing apparatus to detect differences that are vastly, vastly smaller than 2.4ms.

    By contrast, SN1987A occurred some 168,000 light years away, so you can get the exact same accuracy as the OPERA measurement by being able to detect the arrival time within a span of 4.2 years. So in practice, you just do not need obscenely-accurate estimates of the arrival time from SN1987A. A few hours' discrepancy leads to a vastly more accurate estimate of the relative speed of neutrinos and light than can realistically be done with an OPERA-type experiment.

    Total energies, no, certainly not. But typical energy per particle? Absolutely, because the typical energy per particle of those particles emitted from a supernova usually isn't that great. Though I should mention that there do exist particles that we detect here on Earth which have energies more than a million times greater than can be produced by the LHC. See here:
    http://en.wikipedia.org/wiki/Ultra-high-energy_cosmic_ray
     
  14. Nov 28, 2011 #13
    Thanks! So the OPERA measurements were taken by means of instruments proportionally too large for the objects whose activity they were measuring, and over a "race course" too short, to allow for either instrument resolution or sample size to produce a reliable result.

    Matter concluded.
     
  15. Nov 28, 2011 #14

    Chalnoth

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    Well, it's not so much that it's too large, but rather that the distance between CERN and OPERA is too small, so that it is incredibly difficult to get the timing right. It's a very tricky, finicky experiment, and the best guess right now is that something is wrong with their timing apparatus.
     
  16. Nov 28, 2011 #15
    The speed of light in a non vacuum is different to the speed of light in a perfect vacuum. Space is not a perfect vacuum so could this explain the delta between the speed of neutinos and the speed of light from supernova?
     
  17. Nov 28, 2011 #16
    I know that, as I already stated in my post above: "Obviously it must be less than the speed of light in a vacuum, as a star is hardly a vacuum.".

    Also, you may be missing the point that neutrinos are emitted from supernovae at the time of core collapse, whereas visible light isn't emitted until the countercoup from the core collapse strikes the stellar surface. Therefor, visible light will always follow the neutrinos.
     
  18. Nov 29, 2011 #17

    Chalnoth

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    The difference in the speed of light is due to interactions between the light and the matter is it moving through. So no, it can't explain this discrepancy because neutrinos hardly interact at all with matter.
     
  19. Nov 29, 2011 #18
    Yes the neutrinos are not slowed so I thought this explains why the neutinos arrive a few hours earlier than the light?

    Perhaps the speed of light should be re-defined as the speed of neutrinos since we know that they cannot ever get slowed down by any matter along the way?
    A new yardstick reference perhaps?
     
    Last edited: Nov 29, 2011
  20. Nov 29, 2011 #19

    Chalnoth

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    The speed they're being compared to is the speed of light in a vacuum. But no, it can't be something simple as this because it wouldn't agree with our experiments with high-velocity matter.
     
  21. Dec 4, 2011 #20
    I was wondering if the discrepancy could be due to the presence of a gravity well of rather significant depth compared to the distance traveled between the source and detector?

    If we observe a supernova on the far side of a massive galaxy cluster, might the neutrino travel time have been lessened by some mechanism which we wouldn't have seen from the SN1987a event due to the flatter spacetime along the path?
     
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