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Proving General Relativity with Crystal Balls

Posted by Hemos on from the schmatlzy-name dept.

Gonzo, the Pirate King of the Underworld writes "It sounds like something out of one of those magazines that you might find at a grocery story checkout stand, but as is typical with news sensationalism, it is a play on words for what is really going on. Researchers at Stanford University, in cooperation with NASA, are preparing an experiment consisting of four extremely precise gyroscopes in the form of quartz crystal spheres. The Relativity Mission will last a year in an attept to measure the effects of frame-dragging and geodetic precession, and give scientists a means of testing General Relativity. "

65 comments

  1. NASA?? by gee308 · · Score: 1

    It seems like NASA has a lot of projects these days. When was the last time they completed a mission sucessfully? Linux DVD HOWTO

    1. Re:NASA?? by HeghmoH · · Score: 2

      Two days ago.

      Jerk.

      --
      Mod down posts with a "Free Mac Mini/iPod" sig, they're spam!
  2. Why does Einstein look so bummed? by seldolivaw · · Score: 3

    Why can't we have a picture of a smiling Einstein as the icon? He looks like he's just spent five hours installing NT and it's just flashed up a bluescreen.

    1. Re:Why does Einstein look so bummed? by WolfWithoutAClause · · Score: 1

      Hey, give him a break! He is, like, DEAD you know. I mean you can't get much more of a downer... Or maybe he already knows what the result is going to be, being dead and all... Uh oh. Its an omen.

      --

      -WolfWithoutAClause

      "Gravity is only a theory, not a fact!"
    2. Re:Why does Einstein look so bummed? by esme · · Score: 4

      If I'm not mistaken, it's from the famous photograph of Einstein taken by W. Eugene Smith. Smith and Einstein were discussing the ramifications of relativity and the nuclear bomb, and Einstein fell into something of a stupor as he pondered the horrible things that his science had made possible. It was then that Smith took this photo.

      I think it would be hard to find a better icon of science: at once brilliant discovery and sobering consequences.

      -Esme

    3. Re:Why does Einstein look so bummed? by gad_zuki! · · Score: 2

      He's still angry about quantum mechanics. Nice guy, but can sure hold a grudge.

    4. Re:Why does Einstein look so bummed? by MrCreosote · · Score: 1

      you mean something more like this?
      or maybe this?

      --
      MrCreosote Meow!Thump!Meow!Thump!Meow!Thump! "You're right! There isn't enough room to swing a cat in here!"
    5. Re:Why does Einstein look so bummed? by Old+Wolf · · Score: 1

      I tried emailing .me@.seldo..com, but it didn't work.

    6. Re:Why does Einstein look so bummed? by Old+Wolf · · Score: 1

      Can anyone say karmawhore.

  3. Wow! by Money__ · · Score: 1
    From the article:Each gyro is made of a special kind of glass - fused quartz, made when quartz crystals are melted-- machined to a diameter of 3.81 cm (1.5 in), and then polished to within 40 atoms - less than a millionth of an inch - of a perfect sphere. That's equivalent to the Earth's surface being polished so round that mountain peaks and ocean trenches are within 5 meters (16 ft) of the same level. Only neutron stars are thought to be smoother, because gravity flattens everything on the surface.

    Wow! fabrication of these spheres alone is worth applause regardless of the outcome of the mission. I can't imagine what process they employ to achieve such tolerances. This type of nanoscale acuracy on something so large is truly amazing.
    ___

    1. Re:Wow! by Money__ · · Score: 3
      Re:The manufacturing process of atomic bombs has required a similar degree of accuracy for decades.

      40 Atoms? There was nothing in existance in the 40s or 50s to measure such deviations. While I would agree that perhaps 1 or 2 tenths would have been achievable, I doubt very much that +-20 atoms was achievable on anything 30 years ago.
      ___

    2. Re:Wow! by Anonymous Coward · · Score: 1

      Hmm... you're right. Instrumentation such as air-cushioned and computer/laser interferometry guided milling machines (accuracy: few nanometers) did not became widely available until the 1980s.

    3. Re:Wow! by ClickWir · · Score: 1
      The governmet and NASA have some of the most intelligent people in the world working for them, I'm sure that they have technology now, that we see as being viable in 10 years. I wouldn't be suprized if they had a device that could make it even more precise.

      What we see now as being avaliable in 10-15years, they already have that and things that are better.

      I think it was very possible that they had that kind of technology 30 years ago.

    4. Re:Wow! by ca1v1n · · Score: 1

      It's not just "The Government and NASA" working on this. A lot of this is being done by private sector contractors. Also note that the gyroscopes themselves are shown being polished by Stanford people, implicating the educational community for providing invaluable scientific insight. Sure, the government has great stuff, but the talent is spread around quite nicely.

      --
      WARNING: there is a trojan on your
    5. Re:Wow! by tenter · · Score: 1

      Bzzt. Don't forget optical techniques. Lenses have been made +- 1/4 wave (around 7 microinches) for many decades.

      Also making something spherical is easier than arbitrary shapes. Standard ball bearing balls are +- 25 microinches, and have been for years. Think lapping.

  4. Been long time in development by naasking · · Score: 1

    I remember reading about this project a few years ago. It's been in development for something like 30 years. They've been experimenting and working on the idea of testing relativity's frame-dragging hypothesis since then, but couldn't build gyros that were good enough. Until now. I'm eager to see the outcome.

    -----
    "I will be as a fly on the wall... I shall slip amongst them like a great ... invisible ... THING ... !"

    --
    Higher Logics: where programming meets science.
  5. This one is guaranteed to succeed by Brento · · Score: 2

    Here's an overview of the mission: Nasa is putting four gyroscopes up in orbit for a year. If, after a year, they end up pointing in a slightly different direction, then they believe they've proven the theory of relativity. (Omitting a lot of the details here.)

    Here's the catch: this relies on Nasa designing four absolutely perfect gyroscopes. A quote from the site:

    "We've tried very hard to design an absolutely perfect gyroscope," said Dr. Francis Everitt, the Principal Investigator at Stanford University. Even in an age of exquisite measurements, nothing is perfect. The GP-B gyros, though, are about as close as humans can get. The gyros and their support system are so precise that non-relativity effects will cause them to drift by no more than 1/3 milli-arc-second during a year.

    So basically, if the gyros were NOT made perfectly, they will drift. Nasa making something that isn't perfect is pretty well a guaranteed bet these days. That leads me to predict that in 2003, when the year is over, Nasa will be celebrating jubilantly that they've "proven" the theory of relativity. Whoop-dee-doo.

    --
    What's your damage, Heather?
    1. Re:This one is guaranteed to succeed by ZanshinWedge · · Score: 2

      It doesn't work that way. The gyros are supposed to drift. They will be pulled by a very very slight effect called frame dragging (which occurs due to the rotation of a massive body). The precise amount of the drift of the gyros from frame dragging has been calculated and if the end result fits that amount within the expected error margin, then it will be another confirmation that Einstein's theory of relativity (and, for example, not some other forumulation of relativity that is very close) is most likely correct. If the data shows something else, then it means we gots some old fashioned new science on our hands.

    2. Re:This one is guaranteed to succeed by QuantumET · · Score: 2

      I worked on this project last summer (granted, it wasn't exactly at the high levels) but I picked up a decent amount of background information.

      First, the gyros are tested extensively, for smoothness and consistency. They're not that hard to test, really. The hard part was making the darn things. If you blew up one of the gyros to be the size of the earth, the largest height difference would be around 16 feet. They're smooth.

      Besides, NASA didn't make these. Stanford's laboratories did, if that makes any difference. The whole project is an effort between Stanford and Lockheed (with NASA funding, to be sure).

      And 4 gyroscopes is for redundancy. They only really need two, I believe, and the gyros are not measured off each other. Instead, they are all referenced to a guide star which is tracked by a telescope on satellite.

    3. Re:This one is guaranteed to succeed by ca1v1n · · Score: 1

      I am extremely sceptical of your logic, and here's why:

      If they get an external error, due to improper fabrication, or improper assembly, or the thing getting bumoed by a meteor, or something like that, the drift they will get will be FAR beyond what relativity would do, and likely by several orders of magnitude. Everything has been manufacured to miniscule tolerances, so that should have only a minimal effect. If there is anything more than that, it would likely be due to some other force, which would probably not be so subtle.

      They know what kinds of results to expect. They know that even if the theory is disproven, they will still get results of a certain magnitude, far below the minimum effect of any unpredicted mechanical error source.

      --
      WARNING: there is a trojan on your
    4. Re:This one is guaranteed to succeed by Old+Wolf · · Score: 1
      This is a deviation of about four metres, by the way.

      Also, it won't prove anything if the result comes out as expected.

  6. The Project That Ate Stanford by gilroy · · Score: 5
    I was at Stanford for grad school back in the early nineties, and GPB occupied a special place in grad student lore. On the one hand, it's sounds really cool and obviously pushes the edge of the envelope on a host of technologies. (Something not mentioned in the article: They had to invent a way to screen magnetic fields, so someone came up with inflatable superconducting "balloons", since superconductors exclude the field within them. After twelve or so layers of balloons, the magnetic field was lower in the test chamber than the field in the great voids between superclusters...)

    On the other hand, it seemed that they got a large share of resources for a project that had been in place for thirty (and now nearly forty) years. There are whole dynasties of physicists who have worked on essentially nothing else during that time. I'm not saying it is wrong, exactly, but it was odd to talk to GPB people while struggling to get a grant to keep your lab going for just one more year.

    The article fails to mention the extended time that this experiment has been going on. After all, although 13 months sounds like a lot, it's really only 2.5% of the total project time -- well below most probes, I think. We used to joke that the launch date -- which I distinctly remember being announced as 1994 -- slips at a rate of slightly more than one year per year.

    It'll be nice when they start getting the results they've been working towards for so long.

    --
    The Mongrel Dogs Who Teach
    1. Re:The Project That Ate Stanford by Money__ · · Score: 1
      Re:We used to joke that the launch date -- which I distinctly remember being announced as 1994 -- slips at a rate of slightly more than one year per year.

      Not unlike micros~1 vaporware projections. ;)

      gilroy, I do have one question that I'm hoping you might be able to shed some light on. You mentioned many of the other strugles the project had to overcome, was the fabrication of the spheres to such a tight tolerance among these challanges?
      ___

    2. Re:The Project That Ate Stanford by Animats · · Score: 2
      Yeah. I remember GPB from the mid-80s. A friend of mine did some of their machine shop work. Some of the GPB people were talking about using genetic algorithms as part of the data reduction process, because the signal to noise ratio of their data is so low. That bothered me; if they're working that close to the noise, the validity of the results is iffy.

      I notice that NASA still hasn't announced a launch date.

    3. Re:The Project That Ate Stanford by Anonymous Coward · · Score: 1

      I was a physics undergrad at Stanford and worked with GPB for my honors thesis. I actually measured the sphericity of the gyros and plugged the numbers through some complicated math to figure out how the electrostatic suspension system (there are still residual forces) would torque the gyro.

      I can tell you that the gyros really were as round as they say - at least the fused silica core was. after they put on a niobium thin film coating they weren't quite as perfect any more.

      The process of making them involved a great deal of finnesse. The final polishing process, which is where the real magic happens, involved four rotating polishing heads that surrounded the ball in a tetrahedral pattern. All the heads rotated in different directions, and would periodically switch their relative rotation. This sum of all their torques also caused the ball to rotate under them. Basically, it just did a massive amount of averaging to get the sphericity it acheived. Of course, the old guy who ran the machine spent a long time trying different polishing compounds, grinding heads, and wetting techniques to get it to work perfectly. I forget his name - he was a really nice old italian guy who just played with these machines all day. It's more craftsmanship than high-tech.

      They also experimented with making pure crystal silicon spheres, bu they could never avoid the asphericity due to the underlying cubic lattice. Those spheres looked really cool, though.

    4. Re:The Project That Ate Stanford by gilroy · · Score: 2
      Quoth the poster:
      You mentioned many of the other strugles the project had to overcome, was the fabrication of the spheres to such a tight tolerance among these challanges?
      Disclaimer: I never worked on GPB, I just knew grads in my department who did. And I sat through a handful of colloquia on the subject.

      Making the gyros to the right tolerance was definitely one of the big challenges. I think they did some pioneering work in computer aided design and fabrication because they needed such precision. Making quartz pure enough was a big problem for the chemists on the project. Designing a bus vehicle that would cushion the gyros enough so that the launch didn't damage them consumed a lot of effort, too, I think. They also advanced the state of the art in cryonics, because they needed a stable, light, small system.

      My earlier comment might have sounded like I didn't like GPB. Actually, I've generally been impressed with them. If you ever want to see how "basic research" can benefit the larger economy, look at the diverse areas of research needed for GPB to fly. They have "spin-off" written all over them.

      --
      The Mongrel Dogs Who Teach
  7. You're right by Chuck+Chunder · · Score: 1

    It's closer to ten! Seriously though, installing an NT box can take ages, install the OS, then an option pack, then a service pack, then something else, then the service pack again, etc, etc....

    --
    Boffoonery - downloadable Comedy Benefit for Bletchley Park
  8. Unclear on the scientific method are you? by tilly · · Score: 2

    They have a clear estimate of the actual error tolerances they believe that they are achieving. They likewise have a clear estimate of the exact drift they expect to see.

    If they mess up on the first the odds of their accidentally getting a measurement because of that agrees with the second is miniscule (to say the least).

    So while right now the best bet is indeed that they will confirm Einstein, this is by no means a sign of incompetence or a foregone conclusion.

    Sincerely,
    Ben

    --
    My usual seat in the cluetrain is at A HREF="http://pub4.ezboard.com/biwethey.ht
    1. Re:Unclear on the scientific method are you? by Brento · · Score: 1

      Maybe, but you have to agree that any incompetence involved with fabricating the gyros will be a sign in their favor, unlike the other missions. If the gyros are junk, they still win. When the other missions suffered from incompetence, they failed. Ironically, this one can only fail if we are competent - but incorrect.

      --
      What's your damage, Heather?
    2. Re:Unclear on the scientific method are you? by gilroy · · Score: 2
      Quoth the poster:
      You have to agree that any incompetence involved with fabricating the gyros will be a sign in their favor, unlike the other missions
      Um, no, you don't have to agree to that at all. You see, there's this little process called "calibration", which will allow the mission scientists to quantify how precise and how stable the gyros are. I'm not sure what the procedure will be, but you can bet they'll check these things in a way that minimizes or negates any real signal. Then, if there's drift, they'll know it comes from fabrication error or other noise.

      I don't know if the poster is a scientist or not, but that kind of misconception is very common. Nothing is made perfectly, so if science depended on that, we'd all be in trouble. Science is not about what you know -- it's about quantifying what you don't know. The important thing is never the number by itself but the number with its error bars.

      Indeed, one complaint levelled at GPB over the years is that their signal-to-noise ratio is so low, it'll be hard to believe anything that comes out. Personally I believe they've got a handle but honest opinion, for now, can easily differ.

      --
      The Mongrel Dogs Who Teach
    3. Re:Unclear on the scientific method are you? by Brento · · Score: 1

      "There's a process called calibration..."

      Would that be anything like the process called Quality Assurance? The process that did such a great job of catching the metric conversion on the Mars misson? Oh, same kind of thing, eh? Thanks for pointing that out to me. All clear now.

      --
      What's your damage, Heather?
  9. Those gyroscopes are cool by Randy+Rathbun · · Score: 4

    There was a thing around the first of the year in one of the astronomy magazines talking about the gyroscopes this thing will be using. Apparently they are so precise that once they are spinning if you cut the power the things will continue to spin for the next 4000 years.

    To me that is mind blowing....

  10. About time. by Xerithane · · Score: 1

    This has been under the view of a lot of people at NASA for a while now.
    I was working out at Ames RC (Moffett Field, about 30 minutes away from Stanford) and received an email newsletter stating a lot of information about this, and they had a series of satellites that descibed this effect without scientific measure.
    I have been dying to see this thing actually start happening - this has quite a significant impact on Einstein's work, as this is one of the few remaining testable theories. So if this comes back positive, looks like relativity is right. However I am disappointed about the universe destroying faster than light travel..

    --
    Dacels Jewelers can't be trusted.
  11. Don't they already have a way? by z-man · · Score: 1

    I've probably misunderstood this, but didn't they test General Relativity about 80 years ago, during a solar eclipse were everyone was measuring a predicted result (with classic physics), but got the relativ result?

    1. Re:Don't they already have a way? by hellmo · · Score: 1

      This is true. I think they may have also tested the time dialation effects with two atomic clocks in two planes (although it is possible that my physics lecturer made that up).

    2. Re:Don't they already have a way? by Skinwalker · · Score: 1

      I think you're referring to the eclipse of Mercury in 1917 (1918?). IANAP, but I think the apehelion of Mercury's orbit was at (slight) variance with the value predicted by classical mechanics. Einstein was able to accurately predict the value observed during the eclipse using the general relativistic assumption of gravitational light-bending. Frame-dragging and geodesic precession are different facets of general relativity than what was proved 80 years ago.

    3. Re:Don't they already have a way? by gilroy · · Score: 2
      No, actually, that was true.

      Of course, I am a physics teacher , too, so you might lump me in on the conspiracy. :)

      --
      The Mongrel Dogs Who Teach
    4. Re:Don't they already have a way? by Cardbox · · Score: 1
      The stars-during-an-eclipse test actually gave a wide range of results, including ones that disproved as well as proved General Relativity. Sir Arthur Eddington then wrote an article that dismissed the anti-GR results as being due to experimental error of various kinds, while saying that the pro-GR results had no errors).

      Everyone believed him and no-one really minded because they all believed GR by then anyway. Later results have been even more confusing.

      For a fuller story, see The Golem : What You Should Know About Science by Collins & Pinch, which I read a couple of days ago for the second time and found riveting.

  12. Old story. Again. by Bowie+J.+Poag · · Score: 1



    Old story. Someone have a link to the original?

    (Well, at least it was Hemos who fucked up,and not Timothy. You'd be surprised how much more liveable Slashdot is when you turn off articles from everyone BUT Rob and Hemos.)



    Bowie J. Poag

    --
    Bowie J. Poag

    1. Re:Old story. Again. by linuxmop · · Score: 1

      Why does it matter? That's what I have yet to understand. I know I didn't see this last time, so it's still news to me, and probably many others as well. You're not forced to look at this article again if you realized you've already seen it. And if your time is so important, why did you waste time posting this message?

      I'll never understand it, I suppose.

  13. Gyroscope Design by Detritus · · Score: 2
    Does anyone have any information on the design of the gyroscopes? They are crystal spheres, spinning in a vacuum. How do they spin them up, keep them from floating into the side of the enclosure, measure the rotation rate and direction of the rotational axis?

    The Stanford web site appears to be broken.

    --
    Mea navis aericumbens anguillis abundat
    1. Re:Gyroscope Design by Boli · · Score: 2
      Way back in high school (summer 1986), I was fortunate enough to tour some of the GPB labs and talk to a grad student or two. One of them wore a rugby outfit ('cause he just got back from practice) and explained how his PhD was based on solving this problem: When a perfectly spherical metal-plated ball is spinning at a few 1000 rpm in a vacuum, static electricity between the chamber & ball will pit the surfaces. Thus the perfect gyroscope is damaged and the whole experiment is trashed. How can you prevent the static discharges?
      He mentioned that they rev-up the gyros using bursts of nitrogen gas. The rest of the satellite is designed to follow the gyro in orbit. So whereever the gyro wants to travel, the satellite moves to keep the zero-particle/zero-EM field centered around the gyro. Thus eliminating all forces except gravity. One of us asked if the gravity of the satellite would affect the gyro. "Yes" was the answer. "The gyro must remain at the center-of-mass of the satellite..."
      I think the measurements were performed by bouncing lasers off the gyros.

      - boli

    2. Re:Gyroscope Design by Anonymous Coward · · Score: 3

      I worked for Lockheed, subcontracting to Stanford
      on GPB.

      As I recall, the gyros are spun up with streams
      of compressed gas.

      A couple of methods are used to keep the gyro from touching the walls:
      - Charged plates establish an electric field
      around the gyro and induce a charge on the gyro.
      The E-field is modulated to induce a force on the
      charge that serves to move the gyro around.

      - The gyro positions are sensed and the spacecraft
      actually maneuvers around to avoid hitting the
      gyro.

      Rotation rate is determined by bouncing light
      off of the polished gyros and doing FFT's on
      the reflected intensity.

      The orientation of the gyros are determined by
      measuring the dipole moment of the magnetic field
      that comes from the spinning coated gyro. The
      magnetic field is measured with SQUID's (Super
      Conducting Quantum Interference Devices).

      The part I worked on was the temperature
      control system for the SQUID brackets; they had
      to be stable to about 1uK over DC- 15mHz!

      mks@pobox.com (the new user feature is broke!)

    3. Re:Gyroscope Design by eallison · · Score: 1

      Here's the official site for the project: einstein.stanford.edu. It has a complete description of the all the parts of the experiment, including the design and manufacture of the gyros.

    4. Re:Gyroscope Design by QuantumET · · Score: 2

      Worked at GPB last summer, wrote some code for the systems that keep the gyros levitated.

      The gyros are free-floating quarz spheres, coated with a layer of niobium. They are surrounded by four electrode plates, which keep the gyros centered in their housing in case of micrometeorite, etc impacts. (they can handle up to about 1 kg*m/s of impulse)

      The gyros are spun up by running high-velocity helium gas by them (helium because there's a lot of it onboard, the whole assembly is cooled with liquid helium) to a speed of around 10,000 rpm. This is a one-time thing, they can't respeed them up (would ruin the data)

      Because of the liquid helium cooling, the niobium will superconduct, and a spinning superconductor creates a magnetic field precisely aligned with its spin axis. This is measured by a SQUID (Superconducting Quantum Interference Device)

      I don't know if they measure the spin rate or not.

      The satellite follows a free-floating proof mass in its center to maintain a pure gravitational orbit, so the gyros won't drift offcenter much, unless there are micrometeorite impacts or other forces.

  14. Gravity telescopes by ptbrown · · Score: 1

    So once we directly measure Earth's gravity, what do we do with these gravity probes? Why, turn them towards the stars, of course.

    Well, okay, so this first batch isn't likely to be sensitive enough to make any kind of measurements, and AS3 isn't really designed for that. But certainly the knowledge gained from GPB can be used to create a new generation of probes for the purpose of measuring gravity from outside sources. This "gravity telescope" could be used to detect black holes, planets orbiting other stars, or finding the source of Pluto's wobble.

    So here's to crumbling the walls of ignorance and the pursuit of science for the sake of science itself.

    --
    Any sufficiently advanced civilization is indistinguishable from Gods.
    1. Re:Gravity telescopes by hellmo · · Score: 1

      I don't know if this is the same thing but a couple of universities in the UK are working on 'gravity wave' telescopes at the moment. This page contains some information on the group at Birmingham University and gravity waves but does not mention the telescope. However when I was there last autum they showed me the preliminary ideas for one.

  15. Old news - here is a reference from about Dec 99. by z-man · · Score: 1

    The gravity probe mission idea, to test relativity has been around for a while. I remember reading the article in Science Illustrated back in early 99. Anyways, I also found a link to official site for Gravity Probe mission.

  16. Don't get yourself too excited by AintTooProudToBeg · · Score: 1

    I wouldn't call that headline sensational because nobody actually thought magic was being used to prove the theory (except for maybe a few 250lb QVC old lady regulars).

  17. I could have sworn a similar expirement has al... by tcd004 · · Score: 2
    ready been done with atomic clocks.

    tcd004

    Here's my Microsoft Parody, where's yours?

  18. Re:I could have sworn a similar expirement has al. by ZanshinWedge · · Score: 1

    Various aspects of relativity have been confirmed by many experiments. However, this particular experiment aims to confirm (and measure) "frame dragging" which is a very subtle effect (except around black holes and such) that has been measured only very crudely so far.

  19. the subtle world of gyroscopes... by Mad+Hughagi · · Score: 1

    From the article:"Although the scientists will know within a couple of months of launch whether the experiment is working properly, they will be very cautious and scrupulous before making definitive claims about the result. Even after the main data-taking is over, the team will gently tweak the spacecraft and change settings for another two or three months to see how those variations affect the readings from the gyroscopes." Although I believe that the science they are employing to test this aspect of general relativity is concrete, I am not too sure if the actual satellite will function as well as they believe. Any forces acting on the satellite will measure up on these gyro's - even to a small degree - and space isn't as 'empty' as we think. Solar flux will provide a torque on the satellite, and impacts with micro-meteors can seriously damage components as well as provide momentum transfer. With a satellite so dependant on maintaining a stable platform for these gyros, it will truly be a wonder if they get the data they are hoping for - the errors involved might shadow what they are actually trying to see.

    --
    UBU
    1. Re:the subtle world of gyroscopes... by eallison · · Score: 1

      I'm a grad student at Stanford and work in a different satellite lab. GPB is what is called a "drag-free" satellite. What this means is that it has a VERY good control system that monitors the position of the gyros with respect to the body of the satellite. The control system keeps the position of the satellite relative to the gyro constant, basically letting the gyro move in its own frame, with gravity being the only disturbance acting on it. This doesn't help with micrometeorite strikes, but that's a risk inherent to all satellites. The first us of drag-free control was the Navy's Triad transit navigation satellite, in 1972. The controller was was developed in Stanford's Aero/Astro Department as a spin-off of GPB. Drag-free control is now standard on all transit satellites. This is just one of many examples where a requirement for GPB drove development of a technology that is now widely used. For another good GPB site, check out the Navy's site http://www.onr.navy.mil/02/c0241e/GPB.htm .

  20. "Proving Einstein" is a little misleading by Ledskof · · Score: 2

    The experiment will give reasonable proof whether Einstein's general relativity elements of space time distortion and so on exist, but it does not prove all of general relativity the way that everyone including that space news site are talking about. This experiment will not disprove a current belief among many scientists that Einstein is wrong in the areas of his physics that the math blows up and creates black holes, infinite masses, and so on. Einstein puts a speed limit on the universe, but he doesn't put a limit on his physics. Here's a good article to read: http://mist.npl.washington.edu/AV/altvw100.html this article talks about a modified version of GR. I think it was posted on slashdot recently. Also, this modified version of GR is quantizable, which Einsteins GR is not.

    --
    This is my sig. The post is over.
  21. C'mon, Bowie... chill out already. by synaptik · · Score: 1


    (I know I'm gonna burn some karma with this post, but it needs to be said.)

    Who pee'd in your Cheerios today, Poag? I mean, c'mon; if you think it's important enough to bitch about this being an old story, then at the least YOU should go through the trouble of hunting down the URL of the previous post.

    I sure as hell don't remember seeing this story before. Rob, Hemos, and the others have to wade through 100x more submissions then they actually end up posting. I agree slashdot has just about become unreadable but... you're straining gnats here.

    When you've proven that you can do it better, then (and only then) you've earned the right to bitch.


    --synaptik
    If you want to flame me, do so here.

    --
    HSJ$$*&#^!#+++ATH0
    NO CARRIER
  22. Tardis by SWroclawski · · Score: 1

    Crystal Ball huh?

    Didn't I see one of those in Dr. Who's Tardis?

    Millions of US taxpayer's money spent to build a policebox...

    - Serge Wroclawski

  23. gyroscopes to generate electricity by Uberminky · · Score: 1
    Kind of a nifty idea, but if you're getting power from it, you're taking energy away from it one way or another. And we aren't talking about letting it spin in a frictionless, ideal environment. Whatever means you use of getting energy from it, it's gonna run out pretty quickly (especially if you try powering something like a coffee machine, let alone a city). But I bet a quarter-pound gyroscope could power a watch for a few years... if only that were worthwile... ;-)

    Who knows... might already be able to be used to genetrate masive amounts of electricy,

    Electricity, sure. "Massive amounts" of electricity.. I dunno. You need massive amounts of some form of energy to make massive amounts of electricity, or at least fairly non-massive (hm, wrong word..) amounts of matter to convert into energy. Anyhoo. My $0.02 (had to get rid of it somehow.. I hate change).

    --

    The streets shall flow with the blood of the Guberminky.

  24. Sorta :-) by tilly · · Score: 3

    There are 3 classic tests of GR. One is the precession of the orbit of Mercury. One is the redshift of light coming out of a gravity well. And the last is how much gravity bends light.

    Unfortunately the first and third effects are derivable to first-order as a necessary consequence if gravity moves at the speed of light. A German schoolteacher had come up with the first prior to Einstein. (A fact that the Nazis made an unfortunate amount of hay from.) The third was not shown until decades after. But neither of those is therefore a good test since pretty much any realistic theory would be likely to have the same first-order effects.

    The second effect is derivable to first order from QM and potential energy. (Particles coming out of a gravity well lose energy, therefore lengthening their wavelength. Voila, red-shift. And it works out right to first order.) So that effect is again not a particularly amazing prediction in retrospect, even though it was when Einstein made it.

    Unfortunately we cannot easily test the second-order correction for any of these effects from GR.

    So all 3 classic tests actually didn't test as much as was thought at the time.

    Cheers,
    Ben

    --
    My usual seat in the cluetrain is at A HREF="http://pub4.ezboard.com/biwethey.ht
    1. Re:Sorta :-) by KjetilK · · Score: 1
      The possibility that a massive object could bend light rays was discussed by Newton as early as 1704, and the Munich astronomer Soldner predicted in 1804 that a light ray passing near the limb of the sun would be deflected by 0.875". It was never attempted to observe the predicted deflection.

      The third was not shown until decades after. But neither of those is therefore a good test since pretty much any realistic theory would be likely to have the same first-order effects.

      Einstein predicted in 1915 that a ray of light would be bent when close to the limb of the sun by an angle 1.75", this was confirmed in 1919, which is hardly decades.

      AFAIK, Presently, the result is confirmed to precision better than 0.1% by VLBI measurements, see D. E. Lebach et al., Physical Review Letters, vol 75, 1995.

      Anyway, the Relativity Mission is a nice project, it has been a dream for a few people for a long time, and there are certinaly great stuff involved, even though GR is pretty strong as it is.

      --
      Employee of Inrupt, Project Release Manager and Community Manager for Solid
  25. Re:I could have sworn a similar expirement has al. by coyote-san · · Score: 2

    IIRC, the atomic clock experiments demonstrated that time passes slower on the surface of the earth than in orbit, and by the factor predicted by GR. This theory, taken to extremes, is why black holes are "black" -- the time dilation is so severe that that *all* wavelengths are red-shifted into oblivion.

    "Frame dragging" is a far more subtle effect that says that a rotating mass will actually "drag" spacetime around with it. That means that a full circle is less than 360 degrees if you go in the same direction as the rotation. This effect is far more subtle than time dilation, and far harder to measure.

    To test for this effect, you set something pointing at a known distant point, let it orbit once, then measure the angle it's been deflected. A gyroscope will keep pointing in the same direction, but only if you remove all other influences. Even in orbit that's not easy - there's the earth's magnetic field and its interaction with the solar wind, the thin atmosphere, gravitational anomolies, tidal forces from the moon and sun, etc. You can't stay too close to the earth, yet if you go out too far the "frame dragging" effect becomes immeasurable. And if you make the gyroscrope *totally* immune from outside influences, how do you determine how it's spinning?

    One of the pop science magazines, possibly Discover, had an in-depth article on this mission a year or so ago.

    --
    For every complex problem there is an answer that is clear, simple, and wrong. -- H L Mencken
  26. slightly OT by kaiynne · · Score: 1

    i remeber my physics teacher told our class one time about how when he was at uni they made a few very very accurate gyroscopes and they thought it would be fun to place a stream of air under one to keep it stationary and floating then to put a very high powered stream over air over the top of it to get it spinning and they kept it going for about a minute or two and it was spinning extremly fast i cannot remeber exactly how fast, but the puchline is that someone tripped over the power chord (Go Australian universities) and the gyroscope suddenly not help up any more by the stream of air hit the ground bounced twice and punched a hole through about a foot of concrete. They never found that gyroscope by the way ;)

  27. Wrong URL by trey · · Score: 1

    The url for the experiment is actually here. IMHO machining a perfect sphere is very difficult. This experiment will be all about how clean that sphere really is. Good luck guys!

    --

    he who has the fastest cart always has the best lie.
  28. Re:ANYTHING will spin forever in space! by SciBoy · · Score: 1

    Regardless of popular belief there is no abolute vacuum anywhere, not even in space. There IS friction in space. But though "spinning for 4000 years" sounds incredible, it's really hard to make anything of it since we don't know the air pressure inside the gyroscope or the electromagnetic fields that encompass it (though they said those where really miniscule).

    --
    "War is God's way of teaching Americans geography." - Ambrose Bierce (1842-1914)
  29. "Prove" Relativity? by Old+Wolf · · Score: 1

    All that this experiment could possibly achieve is to find more instances (or perhaps a counterexample) of Einstein's theory.

    This is not a proof and goes no way whatsoever towards constituting a proof, or even providing confirmation of the theory, as any philosphy student will know.

    No doubt it will be very interesting to see the measured effects of the experiment though.

  30. Re:And quantum mech still can't deal with gravity. by madprof · · Score: 1

    They're both incomplete descriptions of nature, that is for sure.
    Who is to say in 50 years time we will not see an entirely different method of thinking about physics and we'll look back and laugh at what we now consider accepted ideas?