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Space Science

Intergalactic Race Shows That Einstein Still Rules 227

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."
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Intergalactic Race Shows That Einstein Still Rules

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  • Re:How do they know (Score:5, Interesting)

    by Richard_at_work ( 517087 ) <richardpriceNO@SPAMgmail.com> on Thursday October 29, 2009 @12:57PM (#29912519)
    Its also plausable that they left at the same time, and arrived 0.9 seconds apart. How do we tell though?
  • So-Called? (Score:3, Interesting)

    by Afforess ( 1310263 ) <afforess@gmail.com> on Thursday October 29, 2009 @01:06PM (#29912651) Journal
    I'm curious, why is the Plank-length "So-called"? Hasn't it been firmly established as a unit of measurement?
  • Re:How do they know (Score:5, Interesting)

    by gnick ( 1211984 ) on Thursday October 29, 2009 @01:14PM (#29912785) Homepage

    Not true. If we know that the event that generated the rays lasted only 2.2 seconds and we have a theory that would delay one of the rays by more than 3.1 seconds (2.2 + 0.9) relative to the other, we can invalidate that theory. From my understanding, that is exactly the case we're dealing with. You are correct though that this cannot completely validate any specific theory - All it can do is reinforce the assumption that our current theory is more accurate than some others proposed and eliminate some competing ideas.

  • Re:i'm confused (Score:1, Interesting)

    by Anonymous Coward on Thursday October 29, 2009 @01:28PM (#29913029)
    So...just to be difficult...is it worth pointing out that the measurement of the distance is dependent upon an assumption of the constancy of the speed of light? FWIW, I fully believe the laws of physics haven't "changed" over the course of the history of the universe, but if you're trying to argue with someone who believes that the speed of light isn't constant, I'm not certain how this helps. Of course, for people who actually are interested in real science, it's a useful and important result, but it doesn't seem likely to convince a disbeliever
  • by wowbagger ( 69688 ) on Thursday October 29, 2009 @01:44PM (#29913231) Homepage Journal

    OK, here's one for the physicists in the audience (and pardon the simplification of terms here, but...)

    1) Being deeper in a gravity well slows time relative to being further out.
    2) All things which have mass have gravity wells.
    3) Photons have mass (NOTE TO THE CLUELESS: "mass" and "rest mass" are two different things - photons have no rest mass, but they most certainly have relativistic mass).
    4) By 2 and 3 photons should have a (small) gravity well. More massive photons (higher energy and thus shorter wavelength) have deeper wells.

    Thus, wouldn't 1 and 4 lead to higher energy photons "clocks running slower" (since they are deeper in a gravity well) and thus propagating as a lower speed as viewed by an observer outside their gravity well - and that effect would be negligible for all but the most massive photons.

    (for the physicists: feel free to expand and clarify on the oversimplifications I've made here. This is, after all, targeting a Slashdot audience which has rather a wide spread of backgrounds).

  • Re:i'm confused (Score:5, Interesting)

    by Rary ( 566291 ) on Thursday October 29, 2009 @01:48PM (#29913299)

    We know that the pulses were caused by an event that lasted 2.2 seconds, therefore we know that they left anywhere from 0 to 2.2 seconds apart. However, the point isn't to determine a simple boolean result to the question "did they arrive at the same time", the point is to invalidate the predictions of theories. The existing theories predicted that the arrival times of these pulses, having left at most 2.2 seconds apart, would be at a minimum significantly more than 0.9 seconds. However, they were not, therefore the theories' predictions are wrong, and thus the theories are invalid. The one theory that predicted that they would arrive at most 2.2 seconds apart remains — not proven, but still not disproven. That's how science works.

  • by mea37 ( 1201159 ) on Thursday October 29, 2009 @01:49PM (#29913305)

    "Thus, wouldn't 1 and 4 lead to higher energy photons 'clocks running slower'"

    It's been too long since I've really looked at relativity for me to agree or disagree with this bit, but let's assume you're right...

    " thus propagating as a lower speed as viewed by an observer outside their gravity well "

    I think not. Your clock has nothing to do with how fast I see you moving. That's why it's your clock and not mine.

  • Re:How do they know (Score:2, Interesting)

    by Anonymous Coward on Thursday October 29, 2009 @01:57PM (#29913423)
    Because it is incredibly unlikely that:
    1) the event lasted 10 minutes
    2) produced gamma rays steadily decreasing in energy
    3) such that the effects of the difference of the speed of light on the particles over 7.3 billion years would compress the burst to 2.2 seconds
    4) that we would be located at the exact location to observe a burst of only 2.2 seconds (closer or farther away and the burst would still be spread out)

    Since all gamma ray bursts are short and have different energy radiation, there are only two possibilities. Either space time is not bumpy at plank distance, therefor the speed of light is not dependant on wavelength, or we are magically located at the perfect distance from gamma ray burst events that they all compress to such a short time, requiring divine providence to explain the happenstance.

  • Dispersion (Score:3, Interesting)

    by sugarmotor ( 621907 ) on Thursday October 29, 2009 @02:21PM (#29913799) Homepage

    I thought the speed of light does depend on the medium through which light travels.

      * http://en.wikipedia.org/wiki/Dispersion_(optics) [wikipedia.org]
      * http://en.wikipedia.org/wiki/Prism_(optics) [wikipedia.org]

    What they measured is a bit surprising that way.


  • Re:How do they know (Score:3, Interesting)

    by SleazyRidr ( 1563649 ) on Thursday October 29, 2009 @03:00PM (#29914403)

    We all know that isn't the way science is done, but I (and a lot of other people) get rather pissed off by the inevetable commenters who read the summary and then seem to think the researchers are retarded monkeys who didn't finish high-school. They've spent a long time on this, they've thought out a lot of possibilities, you aren't going to prove them wrong with your 30-second insight.

  • Re:Slow news day. (Score:3, Interesting)

    by The_Wilschon ( 782534 ) on Thursday October 29, 2009 @03:30PM (#29914821) Homepage

    One interesting thing that stood out is they used the assumption that the effect of quantum gravity would be proportional to the energy of the light; is this what the theories suggested or is this another case of science getting lost in the translation to newspapers?

    As far as I understand from my colleagues who worked on this analysis (now departed for other groups/institutions), the theories of quantum gravity which predict a linear relationship between photon energy and propagation speed are the simplest to test. There are other theories, and they are worth testing too, and some of them would no doubt also be falsified by the Fermi data, but the analysis to do so is more difficult and more complicated, so nobody has done it yet.

  • by shoor ( 33382 ) on Thursday October 29, 2009 @04:35PM (#29915819)
    I thought electromagnetic radiation of different frequencies traveled at different speeds through a medium (as opposed to a vacuum). In this case, the medium would be intergalactic gas, very thin, but there's 7 billion light years of it. How come that didn't spread things out? Is it because the frequencies involved are so high?
  • lots of authors (Score:2, Interesting)

    by rgravina ( 520410 ) on Thursday October 29, 2009 @09:06PM (#29919293)

    Funny... I sent the link to a friend who does GRB-related research, and she said "thanks, I already know about it though, I'm one of the authors" :). Apparently there are 210 authors on that paper though. Imagine coordinating that.

    Anyway, I don't know a thing about astrophysics so that's about all I can contribute to this discussion.

  • Re:How do they know (Score:3, Interesting)

    by MaskedSlacker ( 911878 ) on Friday October 30, 2009 @12:03AM (#29920461)

    I hope your science profs failed you, because you don't understand science.

    Everything in science is WRONG, strictly construed. Newton's theory of gravity is WRONG (gravity is not proportional to 1/R^2), but it's reasonably close for many applications. Einstein's theory of general relativity is WRONG, strictly construed, but it is LESS wrong than anything else we've managed to come up with (for certain applications).

    Science is the continual quest for explanations that are less wrong, not right ones. Even if we found THE right answer, we'd never know it. We'd only ever be able to know that it was the least wrong answer ever thought up.

  • by mbone ( 558574 ) on Friday October 30, 2009 @12:36AM (#29920639)

    Is it because the frequencies involved are so high?

    Yes. That's true even for visible light, much less gamma rays.

Can anyone remember when the times were not hard, and money not scarce?