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NASA Gravity Probe Set for Launch

Posted by michael on from the weighty-concepts dept.

The Real Dr John writes "NASA announced yesterday that its longest running program, Gravity Probe B, was ready and scheduled for launch on April 17th. The project has taken 44 years to complete, at a cost of approximately $700 million. The reason for the high cost is that the probe contains the most sensitive gyroscopic equipment ever created, which will be used to test Einstein's theory of gravity. Einstein predicted that the gravity created by a large body warped space-time, but he also predicted that if the large body was rotating it would create a drag effect on space-time known as frame dragging. Gravity Probe B will be able to test Einstein's theory using Earth's relatively small gravitational field because the instruments are so sensitive."

20 of 250 comments (clear)

  1. Too sensitive by pholower · · Score: 5, Interesting

    The slightest bit of interference could deem it unusable data with as much precision the gyroscopes will be operating. I have a feeling that even interference they are not thinking about (who am I kidding, this is nasa) such as solar radiation, and the magnetic north shift (which as of late, has been about 10 miles a year) will alter the results of this test dramaticly.

    --
    -- johntracy.com, because everybody else is wrong.
    1. Re:Too sensitive by jabberjaw · · Score: 2, Interesting

      Given that you have worked on this project, would you care to comment on the other projects such as SUMO and LATOR which also aim to test Einstein's relativity?

    2. Re:Too sensitive by Anonymous Coward · · Score: 2, Interesting

      This is sooo cool! Very elegant. I notice from some of the numbers that it appears to be using superfluid helium (current cryostat temp ~1.77k)

      Will it be using a high or low, circular or elliptical, equatorial or inclined orbit?
      (i'm sure the info is at the GP-B site, i just missed it)

      The electrostatic suspension system also reminds me bit of a Stargate SG-1 episode, Serpent's Venom.

      kudos and good luck. You launch on my birthday.

    3. Re:Too sensitive by Anonymous Coward · · Score: 2, Interesting

      I think you're confused. The train analogy isn't likening two different particles to being ferrous or non-ferrous.

      The magnet example was saying this: if you're an observer inside a magnetic substance, you will notice a "preferred direction": the direction the spins in the magnetic are pointing. Thus, there will be a "preferred observer" or "absolute reference frame": one oriented in the same direction as the spins. An observer inside the magnet can absolutely determine whether he is in such a frame: he merely has to measure the magnetization and see whether he's oriented in the same direction as it.

      This is despite the fact that the laws of physics, and the laws of electromagnetism, have no preferred direction. Space itself doesn't come with magic arrows pointing in some particular direction. So how did the magnet acquire a spontaneous magnetization in a specific direction? That's spontaneous symmetry breaking. The spins start out aligned randomly, but just by chance, some spins will happen to be pointing more in one random direction then another, and they will pull others into alignment with them, so the entire material becomes magnetized.

      Thus, the "total equation" -- the laws of atomic physics and electromagnetism -- do not and cannot predict a specific "absolute direction" in space. They are perfectly rotationally symmetric. Nevertheless, it is possible for a solution of those equations to break the rotational symmetry and acquire a preferred direction, just due to the random dynamics of interacting particles.

      In the train example, the symmetry of relativity is not a rotational symmetry but a Lorentz symmetry, saying that there is no preferred state of inertial motion: there is no "absolute reference frame", and so you cannot perform an experiment to determine your "absolute velocity" in space with respect to such a frame. But if Lorentz symmetry is violated (spontaneously broken), then there is such a preferred frame, and an observer inside the train could tell whether or not the train was moving with respect to such a frame.

    4. Re:Too sensitive by Anonymous Coward · · Score: 1, Interesting

      I am not aware of any magnets that form up only by spontanaity.


      Magnets which do that are called "ferromagnets". Iron is one (obviously).


      There is always some macro force that organizes the discreet magnetic spins.

      No, that's not true. If there is some external magnetic field that the material is placed in, then that will certainly bias the magnetization in the direction of the external field. But even if you completely isolate the material from all external fields, the spins will still self-align in some direction (picked out by the total magnetization, which is theoretically zero but in practice is always nonzero in some direction) -- provided the temperature is below its Curie temperature. (If the temperature is too high, then random thermal fluctuations will cause the spins to flip too much to remain aligned.)

      Now the claim of the symmety breaking in a magnet has some logic but doesn't seem real life to me.

      It is real life. Real magnets experimentally behave the way that this theory predicts.

      So the combining of the magnetized particle on the train with the non magnetized one still seems like simply the addition of another variable affecting only one of the two particles.

      Again, you're missing the point. There is no "magnetized particle" and "unmagnetized particle". There is a material, made of lots and lots of magnetic particles (spins), and observers sitting inside the material, looking in some particular direction and measuring the magnetization of the material.
  2. Interesting... by Mr.+Certainly · · Score: 2, Interesting
    It'll be interesting what the results would be -- was Albert right about all these theories?

    More interestingly enough, what can we use this for? No, this isn't sarcasm, but how can we apply these scientific principals to help our daily lives and to understand the universe better?

    Comments anyone?

  3. Gravity Probe A by Anonymous Coward · · Score: 2, Interesting

    So what happend to Gravity Probe A?

    (sorry had to ask)

  4. considering string theories by spacepimp · · Score: 5, Interesting

    i viewed the elegant universe, the other day by brian green, and am currently reading the text, much has changed in theory over the last 44 years, string theory for one, currently holds the possiblility that gravtiy strings are looped and therefore capable of jumping from our current brane/dimension. will this allow and or test for this theory or is the device antiquated before deployment? I guess thats a risk involved with such a long dev cycle. hopefully it will take this into account, or has the CERN project already made this redundant?

  5. Re:Gravity dragging? by Anonymous Coward · · Score: 5, Interesting

    Frame dragging occurs when a massive object is rotating. It turns out that a when a body rotates, it 'pulls' the surroundng space around in the direction of rotation. This means that if you drop an object toward the rotating body, it will not just fall radially tooward the centre but will aquire a component of velocity tangental to the surface.

    Of course, this effect also applies to light rays, so the question of what one would actually see is a bit tricky.

    Another situation that 'frame dragging' alters from classical theory is orbits around the body. Imagine an observer fixed at a particular set of coordinates in orbit around a rotatng body. If they send photons in orbits around the body opposite directions, they will not be recieved at the same time; that which travels in the direction of rotation will arrive sooner than that travelling in the opposite direction. In extreme cases, it is possible that the photon opposing the direction of motion, although locally moving at the speed of light, won't appear to move at all from the point of view of a distant observer.

  6. An experiment whose time has passed? by David+Hume · · Score: 4, Interesting


    In addition to the sensitivity problem, I wonder if this could be an experiment whose time has passed.

    In 1995, the GP-B was described as the "only experiment ever devised to test [the existence of frame-dragging]."

    However, in 1997 NASA announced that it had successfully tested frame dragging. See also here.

    --
    Only Women Bleed (Sex, Sharia remix)
  7. Re:Einstein was a (gravitational) drag... by kfg · · Score: 1, Interesting

    Yeah, I get the joke, but it's the same thing really. What Einstein meant by this statement is that God doesn't gamble with the fate of the universe. The universe follows rules such that God always knows the outcome in advance.

    I'm afraid I'm of the opinion that Einstein was partially incorrect in this matter. God does, indeed, not gamble with the fate of the universe, but he may well play dice/roulette with it. The universe is a macro object, even if it made up of an, ummmmmm, unGodly number of small "dice."

    God is the house, and thus has house odds. The number of dice, and thus the sample size, at every instant, is always equal to that unGodly number of dice.

    Thus God himself may lack omniscience in that he never knows what the outcome of any particular roll of a die is going to be, but on the scale that's relevant to anyone who isn't an atom or smaller ( and few of us are) things are perfectly mechanistic nontheless.

    The idea that God is perfectly omniscient is a matter of religious dogma, even when applied to a sectarian pursuit such as science. Maybe God ( or whatever) made it that way on purpose because he isn't omnicontent and likes a bit of entertainment now and again. Just as he made that rock that's too heavey for he himself to lift for the challange of it. He'll be the judge of that, not the Pope or scientific theory. Empirical data always trumps dogma.

    None of this has anything to do with the Copenhagen "Interpretation" or other such wishy-washy, quasi-mystical philosophies that have grown up around quantum theory. It's simply straight statistical analysis, such as is applied in the kinetic theory of gases.

    KFG

  8. Re:Gravity dragging? by dragons_flight · · Score: 2, Interesting

    It sounds more complicated than it is because it is usually phrased in geometrical language.

    You may be aware that elctricity and magnetism are intimately connected. In one sense magnetism is an extra force that moving electrical charges exert on other moving electrical charges.

    Einstein discovered that gravity can work much the same way. Moving gravitational charges (i.e. masses) generate an extra force on other moving masses. This extra force is sometimes refered to a gravito-magnetism and is usually very weak except when high velocities or enormous masses are involved.

    Gravito-magnetism works like ordinary magnetism in that the force is exerted tangetial to the direction of motion of the object. So if you are falling into towards a massive rotating object, then the net effect of all of the moving mass in the rotating body is to give you a little kick sideways, towards the direction of rotation. This makes in look like the straight paths near the rotating body have been twisted around and people refer to this effect as "frame dragging", like the massive body has put a twist into space.

  9. unclear whether it's worth it by hak1du · · Score: 2, Interesting

    Many theories of gravity, even those disagreeing wildly with GR, have frame dragging. If there are no decent alternative hypotheses that make different predictions, is it really worth spending hundreds of millions of dollars on conducting this experiment?

    1. Re:unclear whether it's worth it by Anonymous Coward · · Score: 1, Interesting

      Many theories of gravity, even those disagreeing wildly with GR, have frame dragging.


      So what? It's usually possible to construct a bunch of theories that all describe one particular phenomena (though they don't agree on all phenomena). Should we stop observing phenomena?

      Besides, while many of them have frame dragging, they don't all agree on the amount of frame dragging. GPB is sensitive enough to measure the strength of the dragging.


      If there are no decent alternative hypotheses that make different predictions, is it really worth spending hundreds of millions of dollars on conducting this experiment?


      Well, we should always ask whether a given experiment is worth its cost. But we don't do experiments merely to judge between competing hypotheses. If GPB measured frame-dragging whose magnitude was incontroveribly different from that predicted by GR, then we'd know we'd have to develop a "decent alternative hypothesis" -- even if we don't have any now -- because GR would simply be wrong.

  10. Very Cool Experiment by QuantumFTL · · Score: 2, Interesting

    Very cool experiment (well worth the cash) however I think the LATOR relativity experiment would be much more interesting and scientifically useful.

    And probably not much more expensive.

    LATOR is capable of testing string theory, an exciting but so far merely theoretical development in high energy physics. LATOR also seems to be much more accurate, and less likely to receive interference.

    I do hope that this experiment works out, however as other posters have mentioned, there only has to be one unexpected source of error to totally screw this up.

    Cheers,
    Justin Wick

    1. Re:Very Cool Experiment by Anonymous Coward · · Score: 2, Interesting

      LATOR is capable of testing string theory, an exciting but so far merely theoretical development in high energy physics.


      Or rather, it might conceivably be capable of testing some rather speculative models within string theory; there are plenty of other string theory models that LATOR can't test, and no good reason to believe in one over the other. That's one of the problems with string theory: it's too flexible. People can cook up all sorts of artificial string models, but that doesn't mean that any of those models are likely to be true, even if string theory itself is true.


      LATOR also seems to be much more accurate,


      It is, but it's also a test of something that we've already measured extensively (albeit much more sensitively). Our existing measurements of frame-dragging are extremely crude.


      and less likely to receive interference.


      Why? And, so what? (Unless you're suggesting that GPB will receive so much interference that it won't work.)


      I do hope that this experiment works out, however as other posters have mentioned, there only has to be one unexpected source of error to totally screw this up.


      The same is true of LATOR or of any other experiment, especially highly sensitive ones.
    2. Re:Very Cool Experiment by QuantumFTL · · Score: 3, Interesting
      Wow, nice to see an anon-post that's insightful for once!

      Bold is me, italics is parent.

      LATOR is capable of testing string theory, an exciting but so far merely theoretical development in high energy physics.

      Or rather, it might conceivably be capable of testing some rather speculative models within string theory; there are plenty of other string theory models that LATOR can't test, and no good reason to believe in one over the other. That's one of the problems with string theory: it's too flexible. People can cook up all sorts of artificial string models, but that doesn't mean that any of those models are likely to be true, even if string theory itself is true.

      It will test some of the most reasonable/popular models, which is a big step up from having never been tested at all.

      LATOR also seems to be much more accurate,

      It is, but it's also a test of something that we've already measured extensively (albeit much more sensitively). Our existing measurements of frame-dragging are extremely crude.

      Quoting this page:
      Abstract: LATOR is a space-based experiment to accurately measure the gravitational deflectional deflection of light. The experiment uses two laser bearing spacecraft at the opposite side of the Sun and a very long baseline heterodyne interferometer to measure the angle at an accuracy of 0.2 uas. Combining this measurement with laser ranging from Earth to both spacecraft, gravitational deflection can be made with an accuracy 5000 times better than previously done and will allow measurements of the second order and frame dragging effects. !10


      As you can see, you were mistaken.

      and less likely to receive interference.

      Why? And, so what? (Unless you're suggesting that GPB will receive so much interference that it won't work.) All it takes is a little bit of interference and the whole thing doesn't work at all, it's so darn sensitive. LATOR is less mechnically intensive.

      I do hope that this experiment works out, however as other posters have mentioned, there only has to be one unexpected source of error to totally screw this up.

      The same is true of LATOR or of any other experiment, especially highly sensitive ones.

      LATOR's architecture is much different, and I believe by using a long baseline etc, it makes it difficult for interference at one end to screw up the entire experiment. Also remember that it's something that's fairly time invarient, whereas precession is not. The architecture of LATOR seems more likely to deal with sources of interference than something that's based primarily on mechnical components.

      But I haven't done the actual math for either, so what do I know? :)

      Cheers,
      Justin
  11. Re:Lets hope it works! by 09za+ · · Score: 2, Interesting

    What is the difference if NASA sells the rights to companies to produce products WE, the taxpayer, funded the research for? I would rather keep the taxes I paid because the cost of these products is not reduced anyway. These companies get free R/D and then charge us top dollar anyway...Let them fund the R/D and let the demand for these products determine what gets made and for how much. If it is the products that justify the taxpayer expense, shouldn't WE, the taxpayer, have the rights to profits from the products? How did NASA become a technology pimp?

  12. Re:Gravity dragging? by whovian · · Score: 3, Interesting

    Couldn't gravitational lensing be a possible means for testing frame dragging?

    Assume frame dragging exists. If you can find a body that does the gravitationaly lensing and if that body rotates, then the light rays you see coming from the multiple lensed images might produce an interference pattern.

    --
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  13. The is already good evidence of frame draggin... by Genda · · Score: 3, Interesting

    Hubble has had a pretty good look at the spectra of supermassive black holes at the ceters of local galaxies. With a nice close look at those centers, there is turbulences, physical discontinuities in the acretion disks around the supermassive black holes, and the only good candidate for the phenomena is frame dragging...

    I mean it'll be cool to see if the numbers and the phenomena match, but it's not like there's going to be wild surprise.

    Genda