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Space Science

NASA Probe Validates Einstein Within 1% 188

Posted by kdawson
from the kind-of-a-drag dept.
An anonymous reader writes "Gravity Probe B uses four ultra-precise gyroscopes to measure two effects of Einstein's general relativity theory — the geodetic effect and frame dragging. According to the mission's principal investigator, the data from Gravity Probe B's gyroscopes confirm the Einstein theory's value for the geodetic effect to better than 1%. In a common analogy, the geodetic effect is similar to the shape of the dip created when the ball is placed on to a rubber sheet. If the ball is then rotated, it will start to drag the rubber sheet around with it. In a similar way, the Earth drags local space and time around with it — ever so slightly — as it rotates. Over time, these effects cause the angle of spin of the satellite's gyroscopes to shift by tiny amounts." The investigators will be doing further data analysis over the coming months and expect to release final results late this year.
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NASA Probe Validates Einstein Within 1%

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  • by Animats (122034) on Monday April 16, 2007 @11:52PM (#18762597) Homepage

    That project took way too long. I remember people working on it when I went through Stanford in the mid-1980s. It was something of a boondoggle; it mostly produced students, not flight hardware. I'm glad to hear it finally worked, though.

    • by schwartzg (1089259) on Monday April 16, 2007 @11:59PM (#18762675)
      True, it did take a while. But I'd like to think it was worth the wait. Also, for those who care, here is a link to the Stanford page http://einstein.stanford.edu/ [stanford.edu] it has the same info as the article along with more stuff about the project.
    • by A beautiful mind (821714) on Tuesday April 17, 2007 @12:01AM (#18762693)
      Actually people have been preparing this experiment since the 1960s.

      There was a great lecture about this on this year's hungarian skeptics conference, spiced with the real life experience that Hungary was part of the soviet influence sphere at that time, so when one physicist was allowed to go to the USA for a year to do research. When he came back, his colleagues were flocking him, discussing the news and that the americans are setting up this experiment. The lecturer, now an old man, can finally see the result of the experiment they were discussing more than 40 years ago.
    • Re: (Score:2, Funny)

      by Anonymous Coward
      This seems like a waste of money and resources. As any creationist will stress to you - gravity is only a THEORY.
    • by Zaph0dB (971927) on Tuesday April 17, 2007 @02:12AM (#18763691)
      Glad it worked? I'm horrified it worked.
      Every time someone (re)validates Einstein relativity theories, we actually know we're one step further from FTL (Faster than light - though I'd be surprised if any /. geek wouldn't know the term) than we thought we were before.

      Damm gravity.
      • by Eyeball97 (816684) on Tuesday April 17, 2007 @02:41AM (#18763885)
        FTL? WTF? Everybody knows that FTL drives are a work of fiction.

        No, my friend, what you need is a warp drive.
        • Re: (Score:3, Funny)

          by Lumpy (12016)
          Warp drives are so 1960's you need either slipstream or even better.

          An oscillation overdrive. That would be exactly what you need.

          Now to find that rock and roll physicist that has the prototype.

      • Wormholes count for something don't they? ...now all we need to do is harness the power of the sun...
        • Re: (Score:2, Funny)

          by KinkyClown (574788)
          No! We fold space! Or better yet: we actually build the improbability drive! ... and put the engine to Ludicris speed! ??!?!?
          • But the odds of anyone building an improbability drive are highly improbable! ....WHOA! *Zaps off to another planet*
      • by alienmole (15522)
        What, the Stargates aren't good enough for you?
      • Re: (Score:3, Insightful)

        by drinkypoo (153816)

        1) your sig has a very lame typo 2) take comfort in the 1%.

        First we had the deistic theory of physics - things fall because they fall, big guys hit harder because they're big, and so on.

        Then we moved up to Newtonian physics.

        Then Einsteinian.

        Who's next? Bohr? Someone I've never heard of? Who knows, but it's an interesting question.

    • This may almost sound Trollish, but I am by no mean a Physics major, and it shows in this.
      Could anyone who actually is familiar with this overall project (Not a stats person, I'm sure they'll say it's insignificant) tell us if the margin of error is truly acceptable?
      I understand that there is always a margin of error due to minimum measurable differences, but can physicists now go "Phew, we are now FULLY sure this is right, and not that there has been a measuring fluke" or is there still some doubt? I
      • Re: (Score:3, Interesting)

        by Tickletaint (1088359)
        I don't think anyone's concerned about proving Einstein absolutely right or absolutely wrong—if you look at it in those terms, any theory is bound to be proved "wrong," eventually, in that it'll fail for some ever-increasing standard of precision. What's news here is that we can now trust Einstein's equations to predict our measured reality within that cited "1%," confirming that general relativity is a pretty damn useful model. But that doesn't mean it won't be supplanted next year by something even
      • by LilGuy (150110)
        An experiment only validates or invalidates a single hypothesis. The results will only create more hypotheses to test. The second you begin to believe you know exactly how and why something happens you begin to err and surely nature will find a way to make an ass out of you.

        I guess my answer to your question is nothing is ever sure nor can it ever be.
    • because nobody was waiting for the result? Any doubt concerning the theory will focus on other areas.
    • During the 40 years it took to implement this experiment several other observations of interplanetary probes already proved it.
    • I think the award for longest project ever should go to this project.

      The Pitch Drop Experiment [uq.edu.au]

      I can't wait for the tenth drop! WooHoo!
  • by gardyloo (512791) on Monday April 16, 2007 @11:55PM (#18762641)
    ... balls on rubber sheets. Seriously.
  • Thomas Edison said that genius is 1% and perspiration is 99% [phrases.org.uk]. It's nice to see scientists proving him right.
    • by RandomPrecision (911416) on Tuesday April 17, 2007 @12:27AM (#18762913)
      While I don't believe Tesla actually said it, I've often seen him credited with the phrase "If only Mr. Edison would a bit smarter, he wouldn't need sweat so much."
    • by Anne_Nonymous (313852) on Tuesday April 17, 2007 @12:29AM (#18762931) Homepage Journal
      >> genius is 1% and perspiration is 99%.

      My sweaty Uncle Phil must have a 198 IQ.
    • Slashdot's quote machine at the bottom of the page just displayed (I kid you not!):

      Genius is one percent inspiration and ninety-nine percent perspiration. -- Thomas Alva Edison

    • Actually... (Score:5, Interesting)

      by Moraelin (679338) on Tuesday April 17, 2007 @04:53AM (#18764665) Journal
      Actually, considering that Edison is famous for:

      - taking credit for his employees' inventions as if he personally and singlehandedly came up with them. (There are at least 28 inventors that Edison ripped off this way, including for example taking credit for inventing the motion picture camera. Actually, it was invented by W.K. Dickson.)

      - patented stuff he didn't actually have yet, and/or wasn't even original

      E.g., he applied for a lightbulb patent a full year before actually having a filament that was commercially viable: and Edison's, or shall we say, his teams, _only_ contribution there was a commercially viable filament. The light bulb as such had already been discovered, it just didn't last long enough to be worth buying. But wait, even the carbon filament wasn't new: Edison't patent application itself had come a whole 1 year after Joseph Swan had patented a working model in England (and was working at it since 1850, 28 years earlier). So basically it took Edison and his team two years to copycat someone else's invention and claim credit.

      - bogus patents, e.g., a number of patents on ornamental designs

      - using PR and bad science to win public support: see the "war of the currents", where Edison (who wanted to sell direct current) paid people to roam the country and conduct demonstrations of killing cats, dogs, and once even an elephant with alternating current. Just, you know, to show people that alternating current kills. (While supposedly his direct current at the same 110V doesn't. Yeah, right.) He's also the author of the electric chair, as part of the same campaign to prove that AC kills. The first execution had the guy pretty much fried alive over a time of more than a minute (he certainly was still alive and struggling after the first 17 second jolt), in a show that sickened spectators and was described by the New York Times as, "an awful spectacle, far worse than hanging." That's the kind of PR that served Edison's purposes.

      - shafting the employees. E.g., Tesla was promised a (huge for that time) bonus of $50,000 if he succeeds in making an improvement to the DC generators. When he actually succeeded, Edison didn't pay him, and in fact told him, "When you become a full-fledged American you will appreciate an American joke." In fact, he even refused to at least give Tesla a raise.

      - mis-treating his employees. They actually spread word of Edison's current mood, so they'd know to duck for cover if he's in a bad mood.

      - speaking of Tesla, here's one thing he said about Edison's dumb trial-and-error methods, a.k.a., 99% perspiration: "His method was inefficient in the extreme, for an immense ground had to be covered to get anything at all unless blind chance intervened and, at first, I was almost a sorry witness of his doings, knowing that just a little theory and calculation would have saved him 90 percent of the labor. But he had a veritable contempt for book learning and mathematical knowledge, trusting himself entirely to his inventor's instinct and practical American sense." (Would explain why most "Edison" inventions were actually from employees who actually understood what they're doing.)

      - various attempts at monopoly, including the infamous "Motion Picture Patents Company", a.k.a., the Edison Trust. You know, if you thought that MPAA is bad, the MPPC meant you couldn't even make independent films without Edison's blessing.

      - showing more contempt to the artists than the RIAA today, and in fact, enough to make the RIAA look like the good guys. Edison refused to even print the artist's name on the label. You're buying Edison music, you peon, not some artist's music. On one occasion he stated, "I would rather quit the business than be a party to the boasting up of undeserved reputations." Yeah, who do you think you _are_ to be getting any reputation for your talent and popularity. Only the great Edison should get a reputation out of it.

      - letting his personal moods and preferences be the only criterio
      • Re: (Score:3, Insightful)

        by Slashamatic (553801)

        To put it into context, Edison's efforts to protect his licenses on Motion Picture technology created Hollywood.

        Yes, there was land and light a plenty in Hollywood but there was elsewhere too. LA was also the other side of the country to his enforcers. We can comfortably postulate that Hollywood was therefore created by a bunch of patent pirates.

      • by hackstraw (262471)
        taking credit for his employees' inventions as if he personally and singlehandedly came up with them.

        Sure, geeks like to bust on Edison. Real geeks prefer Tesla over Edison anyday. But either implicitly or explictly taking credit for people that work for you is common.

        Someone that lives in a custom home says they built it, but odds are they did not drive a single nail. The owner of a construction company can show you all of the building he "built", but again, odds are he did none of the physical construc
        • by Moraelin (679338)
          Such is life indeed. I only have trouble with seeing people quote the "genius is 1% inspiration and 99% perspiration" quote all the time, as if it were some kind of gospel and enlightenment from The Great Wizard himself. When in practice Tesla's quote there pretty much spelled it out that it was only lack of technical skill that made so much perspiration necessary in the first place.
          • by hackstraw (262471)
            I only have trouble with seeing people quote the "genius is 1% inspiration and 99% perspiration" quote all the time, as if it were some kind of gospel and enlightenment from The Great Wizard himself. When in practice Tesla's quote there pretty much spelled it out that it was only lack of technical skill that made so much perspiration necessary in the first place.

            AFAIK, the Edison quote is real (see http://en.wikiquote.org/wiki/Thomas_Alva_Edison [wikiquote.org]), and Tesla, Edison's arch rival, said something like "If Edis
  • by priestx (822223) on Tuesday April 17, 2007 @12:11AM (#18762795) Homepage
    I spent a week watching all the Nova PBS episodes, learning about this and string theory. Even though I'm not a mathematician or physicist, it certainly caught my attention.

    http://www.pbs.org/wgbh/nova/elegant/ [pbs.org]
    • by alienmole (15522) on Tuesday April 17, 2007 @10:13AM (#18766859)
      Brian Greene has certainly mastered the trick of appealing to lay audiences, with an almost new age message about the beauty of physics. Unfortunately, the string theory he's pushing is unverified, essentially untestable, incomplete, and nowhere near as elegant as he makes out. In many respects, it's the opposite of elegant: introduce enough degrees of freedom into the equations so that you can solve any problem by tweaking the parameters.

      String theorists will take these sort of statements as an attack, but they're just a blunt assessment of the situation. GR and QM are well-tested theories. String theory doesn't rise to the same level. It's possible that some version of it will one day -- it's certainly morphed into enough varieties -- but today, it's primarily mathematical speculation.
      • Science Friday had interviewed a person that had written about these problems of string theory. It's been decades since the idea has been introduced and instead of reducing the number of possibilities, it's getting more complex and there has yet to be an experiment that validates string theory predictions.
  • Spinning Weights (Score:4, Insightful)

    by Doc Ruby (173196) on Tuesday April 17, 2007 @12:23AM (#18762871) Homepage Journal
    If I put three gyroscopes, each spinning in a different axis at right angles to each other, into a box, wouldn't its increased inertia make it just seem more massive? How does the momentum of all those electrons and other subatomic particles spinning around contribute to its apparent mass?
    • Re:Spinning Weights (Score:4, Informative)

      by slazar (527381) on Tuesday April 17, 2007 @01:23AM (#18763307)
      Gyroscopes resist changes in angular momentum, not linear momentum. So it only has increased rotational intertia. If you were measuring the box's mass by trying to spin it rather than push it, then yes, it would appear more massive. But if you just pushed it in a straight line, then it would behave the same as if your gyroscopes were still.

      On your second question, electrons and subatomic particles don't really spin, they have orbitals. Electron orbitals are the probability distribution of an electron in a atom or molecule. Take a look: http://www.orbitals.com/orb/ [orbitals.com] So it's not really like a gyroscope. But that is an interesting question, i.e. Do electron orbits effect the angular momentum of atoms? How would you measure that experimentally? Does Newtonian Physics operate on that level?
      • by evanbd (210358)

        Actually, you missed on both counts.

        Putting more than one gyro in a box is the same as putting one in with a different angular momentum. Angular momentum is a vector quantity; two gyros add together and act like one with the corresponding angular momentum. So when you try to move the box it will act like a box with a gyro in it, and you won't be able to tell how many gyros there are.

        Electrons orbit in orbitals, but they also spin, like how the Earth both orbits and rotates. See Quantum spin [wikipedia.org] for detai

        • Quantum spin is one of those things [xkcd.com] you just have to accept in Physics without asking too many questions. (because if you don't understand Quantum Spin yet, you probably won't understand the answers to those questions --- Physics is fun like that)

          Particles have angular momentum, even though they're not necessarily rotating in the classical sense of the word (as a wheel does). Confusing? Yes. Useful? HELL YES. For one, MRI imaging relies entirely on quantum spin to work.
        • Re: (Score:3, Informative)

          by wanerious (712877)
          One fascinating experiment demonstrates the Einstein-de Haas effect. The electron spins are randomly oriented in a non-magetized cylinder of iron, say, so the total angular momentum is 0. Now turn on an external magnetic field to align all the spins (enclose the cylinder in a solenoid) and, since the iron's total angular momentum now has a preferred direction, the cylinder will *spin* in the opposite sense. An amazing demonstration of "macroscopic" quantum stuff.
      • by imsabbel (611519)
        Well, if electron orbits didnt affect angular momentums, we wouldnt have spin-orbit coupling in quantum mechanics, would we?
        Of course your orbital carries an angular momentum (i.e. the electron "spins around the core") if l>0, i.e. for most electrons. Its just very small.
    • Yes, since the constituents of the object have more kinetic energy. In the same way that a hot potato weighs more than a cold potato. Relativistically speaking, the total "apparent" (energy, momentum) 4-vector of the object is equal to the sum of the 4-vectors of the individual particles, so while the momentum can add up to zero, the energy component of the 4-vector is increased. From there, E^2 = m^2* tells you that energy ~ mass. In your example of the atom or subatomic particle, you also have to take int
    • Re: (Score:2, Informative)

      This isn't quite what you are asking but most of the mass of an atom comes from the motion of the constituents of the protons and neutrons. In other words most (80%-90% IIRC) of what we perceive as the rest mass of an atom is actually not rest mass at all but relativistic mass attributable to the motion of quarks.
  • by scubamage (727538) on Tuesday April 17, 2007 @12:24AM (#18762887)
    This was not a NASA experiment per se, it was a Stanford experiment. The original press release can be found here [stanford.edu]. The official stanford website also lists preliminary findings here [stanford.edu].
    • by mbone (558574)
      Uh, no, it was a NASA experiement. They funded it. Lots of people from all over worked on it - the CFA (Harvard) group was essential to its success, for example.
  • links (Score:4, Informative)

    by SaberTaylor (150915) on Tuesday April 17, 2007 @12:52AM (#18763067) Homepage Journal
    sciency details:
    http://cosmicvariance.com/2007/04/15/dragging-on/ [cosmicvariance.com] (4:33 p.m.)

    Also of interest if you're into this sort of thing, what Beyond Einstein programs will be cut?
    http://scienceblogs.com/catdynamics/2007/04/beyond _einstein_iv_showdown_in.php [scienceblogs.com] (April 4)
    sad if you compare sticker prices to the $10 billion per month on the Iraq adventure.
  • by zappepcs (820751) on Tuesday April 17, 2007 @12:52AM (#18763069) Journal
    with regard to this. This isn't someone claiming ID causes the universe to act as it does, this is FSCKING Einstein. That he is proved correct is more about man understanding the universe, and relying less on the theory that it is too complicated to understand and must have been created by an imaginary being. This *IS* news, and should be heralded appropriately.

    While some might think me a troll, think about it, Einstein was right. That means that we are that much closer to understanding how the universe works. Even 100 years ago such progression could only be imagined, not proven. In the time that we live in, science books have to be revised every year not because of a need to spend government money, but to actually keep them up to date!

    So much change and investigation. People have become numb to the actual changes.
    • I think the apathy in this case is due more to the fact that pretty much everyone expected this result.
    • I think the apathy comes from disappointment as much as anything. We all wanted FTL and Hyperspace and Warp drives. Phooey on that now, eh? Looks like stargate is our only remaining option for interstellar travel and exploration. That, or put our consciousnesses in robot bodies and suffer through thousands or millions of years of boredom / deactivation in transit ("Are we there yet?")

      In essence, this is an experiment that strongly suggests your car can't get you to MegaCon, and you'll probably die alon

  • by Anonymous Coward on Tuesday April 17, 2007 @12:57AM (#18763093)
    I assume this is the project: http://en.wikipedia.org/wiki/Gravity_Probe_B [wikipedia.org]

    And the probe itself is just astounding: http://en.wikipedia.org/wiki/Image:Einstein_gyro_g ravity_probe_b.jpg [wikipedia.org]
  • Gravity is such a Drag.
    • Oh for the good old days when Gravity was a Downer, Friction was a Drag, and physics could be understood without needing about three lifetimes worth of math degrees.
  • Gotta love xkcd : )
    http://www.xkcd.com/c54.html [xkcd.com]
  • See, Einstein was a genius. Yet, He struggled with Math. He is my hero.
     
  • But Lisa should help scientists understand how the theory works in "high field" gravitational regimes such as pairs of massive black holes.
    I think she will definitely be able to do that if she has a tattoo on her lower back. Just saying..
  • More info (Score:4, Informative)

    by onx (956508) on Tuesday April 17, 2007 @02:47AM (#18763929)
    For some reason the article and summary only mention that Gravity Probe B was trying to measure was "minuscule" however, I at least find the actual quantity to be FAR more impressive than some journalist calling it small. Anyway want to know the precession?

    Frame Dragging Effect (has NEVER before been measured): 1.1x10^-5 degrees per YEAR
    Geodetic Effect: 1.8x10^-3 degrees per YEAR

    Clearly then, these were not merely "minuscule" shifts...the potential for error is great.

    More information can be found at http://www.nasa.gov/mission_pages/gpb/index.html [nasa.gov]
    • by autophile (640621)

      Speaking of the potential for error, here's something funky. Einstein's equations are real-number equations. That is, they describe computations performed using infinite-precision numbers. But any operation involving infinite-precision numbers must involve infinite operations from an information-theoretic point of view -- think bits, the number of, required to represent an infinite-precision number, and now think of the computations required to process such numbers. Since the universe obviously hasn't graun

  • oops (Score:5, Insightful)

    by Tom Womack (8005) <tom@womack.net> on Tuesday April 17, 2007 @06:34AM (#18765123) Homepage
    Basically, the mission hasn't yet succeeded, and it doesn't seem to be completely certain that it will.

    The goal was to measure the frame-dragging effect of the Earth, which is of the order of 40 milli-arcseconds per year; the current calibration (http://einstein.stanford.edu/content/aps_posters/ ExperimentError.pdf) has a one-sigma error of 100 milli-arcseconds per year, significantly larger than the relativistic effect and significantly larger than the effect from the motion of the target star through space. The initial expectation was for an error budget of less than 0.5 mas per year, so there was a lot of work done on measuring the proper motion of the star to that precision.

    The problems turn out to be really crazily subtle issues in solid-state physics -- the deposited metal films on the gyroscope and on its housing retain charge in patches large enough that they have to be modelled rather than averaged out -- plus an annoying issue from classical mechanics where the motion of a rigid body around three axes XYZ depends on the ratio of the differences of the moments of inertia X-Z and Y-Z. Whilst the gyroscopes are absurdly precisely made, so the moments of inertia are very close, the ratio of the differences of the moments of inertia is a macroscopic number; this is the same effect, and even a similar cause, to some of the oddities with low-precision floating-point arithmetic.

    They'll probably be sorted out, sigma might be reduced by a factor ten after another year's modelling effort, but it seems unlikely that they'll get it down by the factor 200 they were hoping for.

    The frame-dragging has already been measured indirectly by looking at the flickers of X-ray sources caused by frame-dragging-induced precession of the accretion discs around black holes, and most of the theories that suggest relativity is wrong would suggest that any oddities would be more pronounced in the huge gravitomagnetic fields near black holes than in the tiny fields near a mass as small, as non-dense and as slowly rotating as Earth.
    • Re:oops (Score:4, Informative)

      by jpflip (670957) on Tuesday April 17, 2007 @09:15AM (#18766129)
      I was at the announcement at the APS April meeting a couple of days ago. My impression and that of the other physicists I've talked to was that this was darn impressive, but in the end disappointing.

      This is a project that has been rolling along for four decades. Over that time, many of the things this experiment was designed to test have been indirectly tested using observations about binary pulsars. Now they're getting hit by incredibly subtle systematics in their apparatus (note that the apparatus was not misconstructed or anything, there are just some surprises that were too subtle to measure until the thing actually reached space). The worry is that the experiment is now not so interesting, even if they managed to beat down their error bars through blood, sweat and tears. If they confirm the predictions of GR everyone will say "gee, great". If they don't, people will be concerned about how well they really understand their error bars. Either way, they don't make the splash one might have hoped all those years ago.
      • Re: (Score:3, Interesting)

        by mbone (558574)
        This disappointment was actually predicted over a decade ago.

        The snarky joke was that this was truly a null experiment : if it agreed with General Relativity, it would be believed, but it would change nothing. If it did
        not agree with General Relativity, it would be viewed as being in error until it could be confirmed, which would likely take more decades. So, no matter what the result, it wouldn't change fundamental physics, which was the whole point.
      • by Raenex (947668)
        I'm not a physicist, but what I find disturbing is that they are trying to measure a tiny value, and then when they don't get the value predicted, they knock the number down by accounting for unexpected results. Then they keep on doing this until they get the number close to what they were looking for. So even if they finally get their number, has it really provided convincing evidence?
    • Re:oops - Bingo (Score:3, Informative)

      by mbone (558574)
      Bingo !

      I was going to post this myself. The goal was to measure frame dragging. The geodetic effect has been measured before (LLR and binary pulsars),
      and is not nearly as interesting (i.e., its hard
      to see why you wouldn't have it). It's the frame dragging that motivated the decades of effort and expenditure.

      If they can't do frame dragging, the experiment will be deemed a failure.
  • Late to work. (Score:3, Informative)

    by pyro_peter_911 (447333) on Tuesday April 17, 2007 @07:57AM (#18765491) Homepage Journal
    Boss, I was late to work this morning because of frame dragging. I would have been here earlier if spacetime hadn't been warped and then twisted by my car.

    Peter
  • by PhotoGuy (189467)
    Can someone explain to us layman, how being within 1% of a prediction is impressive for this particular area? (For example, if newtonian physics only provided 99% accuracy for localalized physics on earth, it would be a joke.) I'm sure this "within 1%" is impressive, if the experts in the field are saying so; but explain to us layman, why?
    • by Goaway (82658)
      Because that's how accurate the measurements are, not the theory.

      "99% accuracy" does not mean "1% error". It simply means that's how sure we can be that it's correct. The remaining 1% is unknown. If there was a known, repeatable 1% error, that would be big news because the theory would then be known to be wrong. To find said error would, however, require a measurement that was more like 99.9% accurate.
    • Ptolemy said the planets circled the Earth in epicycles, and mathematically "proved" it to the accuracy of available instruments. This was good enough for about a 1000 years. Together, Newton and Galileo proved heliocentricity, but calculated ellipitical orbits, also wrong, and also within the accuracy of available instruments. Brahe and others eventually measured things so precisely that they were able to find that Newton had an error, but they didn't understand it. Later, someone (I forget who) was ab
    • by mbone (558574)
      General relativity is tough because the effects are so small. Basically, special relativity starts to come in (have an influence) at a scale of v (velocity) over c (the speed of light). For an example, a 777 might go at 600 mph or 300 meters per second or v/c of 300 / 300,000,000, or one part in a million. One part per million is not so hard now-a-days, and so a 777 has to take into account special relativity, for example when using GPS.

      Now, for General Relativity (GR), effects start to come in at (v/c) squ
  • Please, nobody tell the autodynamics [autodynamics.org] people about this -- they'll get really depressed.

A bug in the code is worth two in the documentation.

Working...