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Intergalactic Race Shows That Einstein Still Rules

Posted by samzenpus on from the the-speed-of-right dept.

Ponca City, We love you writes "The NY Times reports that after a journey of 7.3 billion light-years, a race between gamma rays ranging from 31 billion electron volts to 10,000 electron volts, a factor of more than a million, in a burst from an exploding star, have arrived within nine-tenths of a second of each other. A detector on NASA’s Fermi Gamma-Ray Space Telescope confirmed Einstein’s proclamation in his 1905 theory of relativity that the speed of light is constant and independent of its color, energy, direction or how you yourself are moving. Some theorists had suggested that space on very small scales has a granular structure that would speed some light waves faster than others — in short, that relativity could break down on the smallest scales. Until now such quantum gravity theories have been untestable because ordinarily you would have to see details as small as the so-called Planck length, which is vastly smaller than an atom — to test these theories in order to discern the bumpiness of space."

21 of 227 comments (clear)

  1. i'm confused by circletimessquare · · Score: 2, Insightful

    they arrived within 9/10th of a second of each other

    which indicates the opposite of the story's summary

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    1. Re:i'm confused by schnikies79 · · Score: 2, Insightful

      If it wasn't instantaneous, or nearly, how can we even use this data? They could have been released minutes or more apart.

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    2. Re:i'm confused by zerosomething · · Score: 5, Insightful

      9/10th of a second is only about 3/4th the distance from earth to the moon. I don't know for sure but I think that's a rather small difference and could be accounted for just by the size of the star that exploded. Our own sun is about 4 seconds across isn't it?

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    3. Re:i'm confused by hotair · · Score: 1, Insightful

      That was my thought exactly. Then it occurred to me that an exploding star might actually have diverse points of origin as far apart as 0.9 light-seconds. If 7.3 billion light-years of travel is insufficient to create greater divergence than 0.9 seconds, we may have to wait for a much more distant event. My guess is that they decided that the noise of diverse points of origin sufficiently overrides the question of 0.9 seconds to the point that absent other evidence, it confirms rather than invalidates the theory of relativity.

    4. Re:i'm confused by natehoy · · Score: 5, Insightful

      Actually, it really indicates nothing, except that any "bumpiness" of space doesn't have a profound effect on the speed of light within the wavelength range tested. It's good data. However, this neither proves nor disprove there was an effect, just proves that the effect (if it exists) is very insignificant at the tested wavelengths.

      Insignificant != Nonexistent
      Tested Wavelengths != All Wavelengths

      In order to prove or disprove the theory that light changes speed based on wavelength or other factors, you'd need to be sure that both pulses started the race at the exact same moment, that the two pulses travel through the same space without interfering with each other,and that they complete the race at the exact same moment (ie, within the margin of error of your testing equipment). The margin was almost one second, which is terribly insignificant when compared to 7 billion years, of course, but demonstrates clearly one of the following three things:

      1. The pulses left about a second from each other, which we can neither prove nor disprove.
      2. The test equipment was flawed and they really did arrive at the exact same time (which leads to #1, maybe they left at different times and just happened to arrive at the exact same moment).
      3. The speed of the various wavelengths WAS affected by "space potholes", but it took 7 billion years to accumulate less than one second of variance.

      If #3 is possible, which it still is even after this test, then the theory of bumpiness of space has not been disproven, it just appears that evidence points toward the bumps being really, really small or somehow only marginally effective at affecting the speed of light.

      Plus, the original article goes on to explain that the tested wavelengths were relatively large, and that much smaller wavelengths might be more susceptible to the "bumpiness" of space depending on the size of the bumps. If the bumps are really tiny, then they might have just tested wavelengths that were too large to be affected by them. If we can measure some really high-frequency (low-wavelength) pulses against the ones we think are nearly identical, that would be much more compelling data.

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    5. Re:i'm confused by radtea · · Score: 5, Insightful

      I don't know for sure but I think that's a rather small difference and could be accounted for just by the size of the star that exploded.

      You're confused because the summary, and the press release on which it is based, are misleading and wrong.

      This is a gamma ray burst (GRB), which originate from neutron stars, not a super-nova (which is the only reasonable meaning one can give "exploding star".) Neutron stars are small, resulting in much finer burst timescales.

      The paper discusses the time-structure of GRB's, which has been extensively studied. The fundamental result they get is from a single high-energy gamma ray at the end of the last spike in the burst, which comes 0.9 s after the onset of that spike (seen in the lower-energy photon flux). They do a lot of analysis to argue that the most plausible explanation of that single photon is that it is a member of that spike rather than a random cosmic ray. Anyone familiar with modern statistical techniques will see that this is straightforward, albeit non-trivial.

      This is the way science works: we squeeze limited and imperfect experimental evidence as hard as we can using established theory and other, supporting, observations. All the "yeah, well, it could be something else" kind of commentary we see so much of on /. is irrelevant to the scientific process, because it is doing nothing but repeating what everyone already knows: sometimes the most plausible explanation turns out to be wrong.

      The exciting thing about this measurement is that they have shown it is possible to put quantum gravity to a rather good test using entirely conventional gamma-ray spectroscopy techniques, and repeating this kind of measurement over the next few years or decades on different bursts will rapidly push down the limits on potential planck-scale effects, because eventually we'll see bursts where there are a few high-energy photons closer to the onset, or we will see bursts from objects at larger (known) distances.

      The present authors argue, rightly, that their observation makes theories that have a linear dependence of light velocity on wavelength less plausible. At some point in the next few years it is likely that those theories will be dead, and there's really nothing so beautiful as a theory killed by a fact.

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    6. Re:i'm confused by LordLimecat · · Score: 2, Insightful

      No. Gravity has exactly the same effect on all photons

      How do we know this is true over long distances? Seems to me a lot of this is conjecture.

    7. Re:i'm confused by Sean+Hederman · · Score: 2, Insightful

      Because if gravity randomly affected photons differently, our night sky would look a LOT different than it does.

  2. How do they know by 2.7182 · · Score: 4, Insightful

    that the photons all left at the same time?

    1. Re:How do they know by jabuzz · · Score: 5, Insightful

      Not true, if the theory requires that they would be separated by say 900 seconds, they left within 2.2 seconds of one another maximum, and we observe them at 0.9 seconds apart, then the theory is proved wrong.

    2. Re:How do they know by csartanis · · Score: 3, Insightful

      Perhaps your theory is _not_ plausible, and the scientists know more than the average slashdot commenter?

    3. Re:How do they know by gnick · · Score: 4, Insightful

      Your post makes sense except that "more accurate" implies that "proved wrong tomorrow" is somehow better than "proved wrong today".

      "Proved wrong tomorrow" IS better than "proved wrong today". "Proved wrong tomorrow" means that we've got nothing contradicting it yet and it's the best we've got. I'm perfectly happy to accept that everything we know is wrong and go through life using our best-available models for how the world works. If you wait for a perfect model of everything before you start using the models at hand, you'll never get anything done. So what's wrong accepting what we've got as a possibly-flawed, but best-available model and refining it as we learn more?

      Either its right, and will never be proved wrong, or it is wrong, and may eventually be proved as such.

      You left out an important option. There's "right", "wrong", and "unproven but useful and not yet proven wrong". Very few things in science or life can really be "proven" right. A lot of science is made of reasonable (sometimes radical) guesses that haven't yet been discredited. Even the "law" of gravity is still just a theory, but that fact doesn't make me mistrust my scale because we may be able to refine our knowledge of heavy-body attraction in the future.

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    4. Re:How do they know by bidule · · Score: 2, Insightful

      0.9 seconds over 7.3 billion years is... at most a 10^-16 speed difference. IOW, the speed of light is not affected by the wavelength.

      Suppose there was a negligible 1 in a million speed variation between those wavelengths, and this speed variation occurred in a magic part of space representing 1 millionth of the total distance. We'd still get 2-3 days of lag between our reception of both wavelengths.

      That should tell you why your question is meaningless.

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      ID: the nose did not occur naturally, how would we wear glasses otherwise? (apologies to Voltaire)
    5. Re:How do they know by lgw · · Score: 4, Insightful

      Science doesn't deal in "proven right" and rarely in "proven wrong". That would be math with the proofs. Science deals in "accurate over the available data", and looks for "more accurate" models over time.

      --
      Socialism: a lie told by totalitarians and believed by fools.
  3. Re:Slow news day. by VShael · · Score: 1, Insightful

    That would be big news, if some smart people had put forward the idea that water, at the molecular level, isn't wet.

    (Which it isn't, by the way.)

  4. how do we know by Anonymous Coward · · Score: 3, Insightful

    that these rays are all from a star which exploded 7.3 billion light years away? what was monitored to predict arrival?

  5. Re:Slow news day. by Tibia1 · · Score: 5, Insightful

    What a time we live in where a "slow new day" consists of a 7.8 million year race being recorded (regardless of the results), a fusion reactor is being developed, and a real time speech translator was released.

  6. Re:Slow news day. by Anonymous Coward · · Score: 2, Insightful

    Some people just like to get offended. It validates their existence.

  7. Re:Obligatory analogy by Anonymous Coward · · Score: 1, Insightful

    Better analogy (RTFA)

    A - My brother and my parents left the same destination within 2 seconds of each other
    B - They traveled along the same path without stopping to my house in different vehicles
    C - They arrived at the same time
    D - therefore they traveled at the same speed

  8. Re:Einstein still being proved correct by Anonymous Coward · · Score: 1, Insightful

    "The sky is blue." Yeah, that's the same as Einstein's four amazingly insightful theories.

  9. Re:Planck length by Man+Eating+Duck · · Score: 2, Insightful

    size of the known universe (15 billion light years across--itself an almost unimaginable distance)

    Nitpicking: It's 93 billion light-years (radius 46.5 billion), see Misconceptions.
    It doesn't really matter, as the distances involved are so mindbogglingly large that in most cases the only explanation you need will be: "So large that your mind can't cope with it". The same thing goes for the infinitesimal size of an atomic nucleus. An error of an order of magnitude still gets the point across :)

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