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Science

Einstein's Theory To Go Beta Testing 326

Posted by timothy
from the relawhatnow dept.
pinqkandi writes: "This article over at CNN looks into the relativity of Einstein's theory of relativity (pun intended) as equipment becomes more and more precise. Soon atomic clocks will be placed in the International Space Station to analyze the accuracy of Einstein's theories. One of the lead researchers says that if Einstein's theory is not right, it will only need minor adjustments to account for changes in space-time, due to its deadly accurate precision."
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Einstein's Theory To Go Beta Testing

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  • by qurob (543434) on Wednesday June 05, 2002 @07:04AM (#3643967) Homepage

    If you don't understand either one, take a look
    here [bartleby.com]:
  • Hasn't this been proved already? What's wrong with those older proofs? Like the atomic clock in the airplane and GPS satellites?
    • It hasn't been proved, it just hasn't been disproved. That's why it's a theory.
    • by DarkState (116388) on Wednesday June 05, 2002 @07:43AM (#3644105) Homepage
      The tests that Kostelecky is proposing are somewhat different than the earlier tests. In the previous tests researchers looked for changes in the frequency difference between two clocks when they were moving at different velocities or when they were at different heights in the earth's gravitational field. These tests looked at standard relativity theory (either special or general) and checked that the predictions it made were correct. In the new tests, one looks for changes in the frequency of a clock as it points in different directions (which would be akin to an ether, picking out a prefered direction in space) or a similar effect as the velocity of the clock changes.
      These tests have been performed on the ground recently by measuring the frequency of a clock as its direction relative to the stars changes due to the rotation of the earth. (For example, see Phillips, et al., Physical Review D 63, 111101 (2001) or Physical Review Letters 85, 5038 (2000)- showing off is always good.) In space, one could use the faster rotation of the space station as the atomic clocks in space which may substantially outperform ground based clocks.
    • What is wrong with using existing equipment, like that hive of atomic clocks in the GPS system? They already transmit their time to just anybody that wants to receive it and all of the adjustments for relativity, etc., are known and can be removed for "raw" time measurement.

      I guess the hammer and feather experiment just gets more expensive in proportion to the expansion of the beurocracy.
    • by danro (544913) on Wednesday June 05, 2002 @08:04AM (#3644225) Homepage
      Hasn't this been proved already? What's wrong with those older proofs?

      You can't prove anything in physics, you can try to disprove something and fail, and thus you may have reason to believe that the theory was correct.
      But there is always a posibility that your theory may be disproved later. (Which doesn't mean the theory is rendered useless. Newton's mechanics for example, stood for a very long time, until they were replaced by the theories of relativity. But they are still used, because in most "normal" conditions they work good enought, and the math is easier to work with.)
  • deadly? (Score:3, Funny)

    by tps12 (105590) on Wednesday June 05, 2002 @07:07AM (#3643989) Homepage Journal
    Deadly precision? What has space-time done to you lately?
  • by brejc8 (223089) on Wednesday June 05, 2002 @07:10AM (#3643997) Homepage Journal
    I remember in the seventies they got two atomic clocks and stuck one on a plane and after two years of the plane flying around aimlessly they found a minute difference
    in time.

    The joke of it all is that after a year some journalist asked why they didn't just stick it on a regular commercial jet but they didn't think of it at the time.
    • Was that MIN-ute or min-UTE?

      -JPJ
    • they got two atomic clocks and stuck one on a plane and after two years of the plane flying around aimlessly they found a minute difference

      I've heard of this experiment, but I have a serious question about it that's always bothered me.

      This assumes that Clock A is stationary at 0 mph and Clock B is traveling at 400 mph, right? But, given that the Earth rotates AND orbits the Sun that assumption isn't really true. Relative to a given point, sometimes they're going faster and other times slower. Also, since Clock B is ideally flying in a big circle (around the Earth) doesn't its velocity (in relation to a set point) average out to 0 as well?

      I would think that this experiment would only work if Clock A was dropped off somewhere in space and Clock B was launched in a straight line relative to Clock A. Where am I wrong?
      • One clock moved slower, the other moved faster, relative to the surface of the earth.
    • The joke of it all is that after a year some journalist asked why they didn't just stick it on a regular commercial jet but they didn't think of it at the time.

      Can you imagine the excess baggage allowance on an atomic clock?


  • While we might think that we are equipped to carry out the beta test on Einstein's theory, methinks we may not yet be ready.

    Practically, what we understand from the Theory of Relativity is what we BELIEVE we understand, and that will influence what type of outcome we are searching for.

    Plus, the equipments that we think are ready may not be ready.

    Take the Atomic Clocks for instant ... so far, the way we test the atomic clock is under normal condition, and we have NO IDEA how the atomic clock will behave under the relativity condition - that is, the very basic function of the atomic clock, the vibration of the atoms itself, may CHANGE if time itself is change.

    After all, the "ticks" of the atomic clock, no matter which type of "atoms" we base it on, still depends on the variable TIME - as "ticks per second".

    • I don't think you understand this theory at all, do you?
      You should read it.
      Einstein was a pretty good writer, and his examples are still used today.
      Go to your library!
  • Kostelecky's page... (Score:5, Informative)

    by doru (541245) on Wednesday June 05, 2002 @07:15AM (#3644010) Homepage
    is here [indiana.edu], with a little more information on Lorentz and CPT violation.
  • Zero gravity? (Score:2, Interesting)

    by tdemark (512406)
    Maybe it's just the way the guy was quoted in the article, but if they need to test in a "zero gravity" environment, how would the ISS be applicable?

    I'd consider it a "weightless" environment, but not "zero gravity".

    - Tony
    • And for the slow ones out there, how does a satelite (such as the ISS) stay in orbit?

      Might it just have something to do with gravity?
      • More like speed, inertia, and gravity. Gravity is constanting trying to pull the ISS to the ground, the speed and inertia of the ISS keep it in orbit.

        There is also such a thing as a Lagrange Point [montana.edu].

        Kierthos
    • Re:Zero gravity? (Score:5, Informative)

      by delta407 (518868) <slashdot@nOSPAM.lerfjhax.com> on Wednesday June 05, 2002 @07:55AM (#3644168) Homepage

      Technically, you're never going to get zero gravity. And yes, you're right, ISS isn't anywhere near that -- it's in orbit, and uses gravity to stay that way. ISS and the like are weightless (or near weightless) because they are effectually in a free fall; this state is termed "microgravity".

    • Maybe it's just the way the guy was quoted in the article, but if they need to test in a "zero gravity" environment, how would the ISS be applicable?

      I'd consider it a "weightless" environment, but not "zero gravity".


      True, but I'm sure they've taken that into account. The problem is, when the results come back a certain way, the same persons responsible for this article will write another about how "Einstein was wrong" because they don't understand what was actually decided here.

      It's like testing the lifespan of Goldfish in water. But I didn't have any water, so I used Tequila. By the way, it's 26 seconds, but after about 15 the fish started using emacs. But the example remains the same...you can "prove" or "disprove" anything depending on who's reading it. It's all relative.

  • by fisman (66079) on Wednesday June 05, 2002 @07:28AM (#3644056)
    AFAIK the current GPS satelite system makek adjustments for relativity in the signals it is sending around and they have been adjusting for this for years. See the articles at Metaresearch [metaresearch.org] and lsu.edu [lsu.edu] for more info.
    • GPS sats make adjustments for relativity on, well, relatively large scales. What these researchers are interested in is the small scale(both temporal and spatial I would think) fluctuations. Basically I get the impression that they are attacking the gap b/w quantum theory (small) and relativity(large) from above, so to speak.
    • From the site you gave:
      "The accuracy of this comparison [ground-based clocks to satellite clocks] is limited mainly because atomic clocks change frequencies by small, semi-random amounts (of order 1 ns/day) at unpredictable times for reasons that are not fully understood."

      Sounds pretty unscientific to me. Here's one researcher's papers on the subject, which conclude that the GPS systems aren't following relativity. http://www.stcloudstate.edu/~ruwang/ [stcloudstate.edu]

      • And also from one of the links:


        For GPS satellites, GR predicts that the atomic clocks at GPS orbital altitudes will tick faster by about 45,900 ns/day because they are in a weaker gravitational field than atomic clocks on Earth's surface. Special Relativity (SR) predicts that atomic clocks moving at GPS orbital speeds will tick slower by about 7,200 ns/day than stationary ground clocks. Rather than have clocks with such large rate differences, the satellite clocks are reset in rate before launch to compensate for these predicted effects. In practice, simply changing the international definition of the number of atomic transitions that constitute a one-second interval accomplishes this goal. Therefore, we observe the clocks running at their offset rates before launch. Then we observe the clocks running after launch and compare their rates with the predictions of relativity, both GR and SR combined. If the predictions are right, we should see the clocks run again at nearly the same rates as ground clocks, despite using an offset definition for the length of one second.

        We note that this post-launch rate comparison is independent of frame or observer considerations. Since the ground tracks repeat day after day, the distance from satellite to ground remains essentially unchanged. Yet, any rate difference between satellite and ground clocks continues to build a larger and larger time reading difference as the days go by. Therefore, no confusion can arise due to the satellite clock being located some distance away from the ground clock when we compare their time readings. One only needs to wait long enough and the time difference due to a rate discrepancy will eventually exceed any imaginable error source or ambiguity in such comparisons.


        This in the other hand sound pretty scientific and conclusive to me ...

  • by meringuoid (568297) on Wednesday June 05, 2002 @07:28AM (#3644058)
    Soon accurate telescopes will be installed to make extremely careful measurements of Mercury's orbit to analyze the accuracy of Newton's theories. One of the lead researchers says that if Newton's theory is not right, it will only need minor adjustments, due to its deadly accurate precision.
  • "Beta testing"? (Score:1, Interesting)

    by PhysicsGenius (565228)
    Even as a joke this makes no sense. Relativity was alpha tested in the 1913 (IIRC) eclipse and has been tested very very thoroughly since then. This is just another fine-grained test.
    • This is just another fine-grained test.

      Agreed. This whole thing is a lot more like benchmarking. Those geeks want to find a way to squeeze another nanosecond out of reality.

      • Heh, that was funny. It kind of reminds me of Arnold Rimmer (from the book Red Dwarf) using a '0 time stasis field' to spend his free time 'not existing'. The idea was that in 5 years, he'd age only 4! That way, when his bunkmate Dave Lister was 80 years old, Rimmer'd only be 71. Not bad, eh?

        (I may have misquoted bits of the story, but you get the idea...)
    • I have to believe that this test is somewhat different from the previous ones, not just a more accurate version. What I'd like to see is a test which pits Relativity against Ether Gauge Theory [egtphysics.net] or some other similar theory which assumes the existence of an ether and has not yet been disproven.
  • Like, they put one of those into an airplane and flew it half around the globe or something.. That might have been another aspect of the theory though.

    But one thing is for sure: They won't 'prove' Einstein in any way by doing this - but they might *prove* him wrong. Only negative proof can be done by example.
  • So sad (Score:5, Funny)

    by NiftyNews (537829) on Wednesday June 05, 2002 @07:42AM (#3644094) Homepage
    Too bad Einstein isn't around anymore...

    He would have made for one heck of a great match on Fox Celebrity Boxing 3 with Stephen Hawking.
  • Can a clock really be DEADLY accurate? A rifle, a smart bomb, maybe even a rolling pin weilded by an angry wife when her husband comes in late.... THESE can be deadly accurate... I don't think a clock can be.

  • The CNN article is not very clear as to what it says. This comes from the fact that There are two different theorys of relativity.

    1 The special theory
    2 the General theory.

    The special theory concerns what happens to the laws of physics as a person is traveling at a constant velocity, whereas the general theory is concerned with bodys that are accelerating ( In general relativity acceleration and gravity are equivalent).

    So since the ISS is in orbit it experences an outwards accerleration( the same as one experences as one goes round a corner fast in a car.) In space there is gravity on the ISS but it is very little. This means that the ISS will experence a slight change in the ticking rate that is recorded. But this is explained by the general theory of relativity and not the special theory.
    • by volpe (58112)

      whereas the general theory is concerned with bodys that are accelerating ( In general relativity acceleration and gravity are equivalent).


      Common misconception. Acceleration and gravity are not equivalent in General Relativity. They are *locally* (that word is extremely significant here) indistinguishable. The fact of the matter is that Special Relativity can handle acceleration just fine by using calculus. General Relativity is only needed where spacetime is not flat (i.e. in the presence of gravity), since the two postulates of Special Relativity only hold in regions of flat spacetime.
      • A good explanation of the difference between acceleration and gravity can be found on the Eot-Wash webpage [washington.edu]. This is the good part:

        "All objects fall the same way under the influence of gravity; therefore, locally, one cannot tell the difference between an accelerated frame and an unaccelerated frame. Consider the famous example of a person in a falling elevator. The person floats in the middle of an elevator that is falling down a shaft. Locally, that is during any sufficiently small amount of time or over a sufficiently small space, the person falling in the elevator can make no distinction between being in the falling elevator or being in completely empty space, where there is no gravity.

        We could imagine two apples floating on either side of the person; as the elevator approached the earth, the apples would approach eachother. This happens because their paths, both toward the center of the earth, eventually converge. But this is not an effect that can be detected in a local experiment.

        This statement of the equivalence principle makes an important suggestion. In special relativity--and all classical mechanics--we are used to the idea that objects travel at constant velocity unless a force acts on them. Now, if we can't locally tell the difference between falling in a gravitational field and travelling at constant velocity, then, locally, they must be the same thing. The paths of free bodies define what we mean by "straight" and if we observe an object deviate from constant velocity, it must be because spacetime itself is curved.

        Formally, we state the equivalence principle this way: in any and every locally Lorentz (inertial) frame, the laws of special relativity must hold. From this, we conclude that the only things which can define the geometric structure of spacetime are the paths of free bodies."
      • "General Relativity is only needed where spacetime is not flat (i.e. in the presence of gravity)"

        So basically, everywhere in the known universe, except in our minds?
        • Strictly-speaking, yes, gravity is everywhere. However, the amount by which SR's predictions deviate from measurement depends on the amount by which spacetime, in the region of the experiment, deviates from being flat. In other words, in places where gravity is negligible (and to the extent to which this holds), SR is applicable, regardless of how much accelerating your rocket is doing.
  • "If variations in the ticking rate were discovered, Kostelecky says, it would be a "striking signal" that the laws of nature may be based on fundamental theories other than Special Relativity -- or perhaps in addition to it."

    I thought this was precisely what special relativity does predict, that a moving observer experiences less passage of time than a stationary one, increasingly so as the speed becomes a significant fraction of the speed of light. If the ticking rate does not vary, then special relativity would be invalidated.
    • Re:Backwards? (Score:2, Insightful)

      by Chuck Lane (583571)
      I thought this was precisely what special relativity does predict, that a moving observer experiences less passage of time than a stationary one, increasingly so as the speed becomes a significant fraction of the speed of light. If the ticking rate does not vary, then special relativity would be invalidated.

      You're correct about special relativity, but we're considering a different sort of effect.

      Special relativity predicts (among other things, as you describe above) that the ticking rate of a clock, when always viewed from its own rest frame, is independent of the clock's orientation and velocity with respect to everything else in the universe. We're studying this idea by watching very sensitive clocks as they rotate or change velocities. Any dependence of a clock's rate on its orientation would imply that some directions are different from others, i.e, it would show a violation of rotational symmetry, which is a subgroup of Lorentz symmetry.

      Chuck

  • by micromoog (206608)
    One of the lead researchers says that if Einstein's theory is not right, it will only need minor adjustments to account for changes in space-time, due to its deadly accurate precision.

    This just in, from a 1903 Einstein press release:

    One of Einstein's lead researchers says that if Newton's theory is not right, it will only need minor adjustments to account for changes in space and possibly time, due to our upcoming theory's deadly accurate precision.

  • This is an honest question. Most theories I know of have things they cannot account for, but I have not heard where relativity fails.
    • The biggest outstanding problem with relativity is that it doesn't completely work on the quantum scale. One of the biggest outstanding problems with quantum theory is it doesn't completely work on the macroscopic scale. A fully-complete theory of the universe should explain both.

      For more details and clarifications, consult an appropraite source, not Slashdot. ;-) There's probably a good FAQ on this somewhere.
      • Unless by "macroscopic" you mean "size of the entire universe", I don't believe that QM is known to have any problems, except for incorporating gravity. The problems with QM & gravity generally are associated with extremly microscopic (as in Planck length), that is, high energies, where the gravitational contributions to QM are comparable to the other fundamental forces.

        The problem of the quantum--classical transition (a.k.a. the measurement problem) is not really a physics problem. Read Gottfried's QM text for a pretty clear description of how physicists come to grips with it. The people working on quantum computing have to deal with this all the time, and as far as I can tell, quantum decoherence for them is an engineering problem, not a physics problem.
        Strictly speaking, on very large length scales (like the size of the earth or larger), gravity is the most prevalent force, because matter tends to be neutral in large clumps. However, gravity is still relatively weak on those scales, so you don't need a full theory of quantum gravity to understand it---the weak gravitational fields can be treated accurately as an plain-old potential. Only in the neighborhood of a black hole, or trying to describe the entire universe being in a single quantum state, or trying to understand the first few moments of the big bang, does QM seem not to work.
  • by cybrpnk2 (579066) on Wednesday June 05, 2002 @08:06AM (#3644233) Homepage
    Atomic clocks on ISS are a trivial test of relativity compared to Gravity Probe B [stanford.edu], hopefully to be launched soon after DECADES of development. A one-pager "GPB for Dummies" is here [nasa.gov]. GPB tests not for alterations in time but another phenomenon known as "frame dragging" which has never been directly measured. There's been lots of criticism about GPB as being too ambitious, so there's been lots of independent reviews [nas.edu].
  • by peter303 (12292) on Wednesday June 05, 2002 @08:27AM (#3644338)
    An article [aip.org] (membership requires) in May Physics Today details the extensive corrections GPS must make for both special relativity (velocity corrections) and general relativity (gravity corrections). This has tested Einstein every day of the past 20 years, and he has held up.
    • You're correct that the GPS system provides a great test of relativity. However, the theories of relativity make many predictions, and GPS doesn't test all of them. Clock-comparison experiments study another aspect of relativity: Lorentz symmetry.

      Chuck

  • I heard GPS sattelites use atomic clocks to keep in synch with earth. They use the Theory of Relativity to adjust their times so that they stay in synch with earth because they move at a different speeds and in a different field of gravity.
  • by DeadBugs (546475) on Wednesday June 05, 2002 @08:45AM (#3644434) Homepage
    I wonder if Scientists ever play practical jokes on each other and sneak into the lab to make the Atomic Clock blink 12:00
  • by jbarr (2233)
    "One of the lead researchers says that if Einstein's theory is not right, it will only need minor adjustments to account for changes in space-time, due to its deadly accurate precision."
    You mean like e=mc2+1?
  • But I do believe in uncertainty.

    Does this mean my GPS will stop working now?

    :)
  • Actually, GPS knows about this and takes advantage of it. It is the only consumer relativity application I know of.

    The GPS SV's are going about 3900 m/s which is a sufficient percentage of the speed of light for relativity to come into play. If relativity weren't taken into account and Einstein obeyed, you'd be off by ~100 meters.

    The correction could be done in the receiver or the signal could be biased in the SV. Following the Principle of Alice's Restaurant:

    One Big Pile Is Better Than Two Little Piles

    Factoring this correction into the SV, the onboard clocks use a frequency of 10.22999999543 MHz and your GPS receiver uses 10.23 MHz. This simplifies the GPS receiver software immensely.

    GPS was designed during the 1970's by some really smart forward thinking guys.

  • Horrible (Score:2, Insightful)

    by Fatllama (17980)
    The CNN article is one of the worst examples of science writing I've *ever* seen. I even thought of submitting it for that purpose alone. Now, what does it mean that Slashdot took it seriously? Good lord.
  • by xihr (556141) on Wednesday June 05, 2002 @01:30PM (#3646809) Homepage
    The CNN article is a good example of journalism's tendency to misrepresent scientific news, even subtly. The URL contains the string "einstein.wrong," and the headline on the CNN article is, "Has time run out on Einstein's theory?" suggesting that there is some new doubt that general relativity is accurate. (Note also that the article's description of the special theory of relativity is pretty meaningless, particularly to a layman -- and it isn't even special relativity that is being tested.)

    In fact the opposite is the case. No one has any reason to believe that general relativity is in error, but as part of good science it is being tested anyway. One can never prove a theory; one can only disprove it. So the best you can do is test your theories with greater and greater precision as the opportunities present themselves.

    It's a case where this is, in effect, a pretty mundane story (a very well-established theory is being routinely tested), but the journalist in question is implying that there is some doubt as to its validity. Of course, it's possible the experiment will reveal deviations from general relativity's predictions, which would indeed involve "minor corrections" to the theory since it is so accurate in other areas, but there is a definite spin being put on the story which isn't in the underlying facts.

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