Proving General Relativity with Crystal Balls 65
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.
"
NASA?? (Score:1)
Why does Einstein look so bummed? (Score:3)
Re:Why does Einstein look so bummed? (Score:1)
Wow! (Score:1)
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.
___
Been long time in development (Score:1)
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"I will be as a fly on the wall... I shall slip amongst them like a great
Re:Why does Einstein look so bummed? (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
This one is guaranteed to succeed (Score:2)
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.
Re:Wow! (Score:3)
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.
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The Project That Ate Stanford (Score:5)
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.
You're right (Score:1)
Re:Wow! (Score:1)
Unclear on the scientific method are you? (Score:2)
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
Re:The Project That Ate Stanford (Score:1)
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?
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Those gyroscopes are cool (Score:4)
To me that is mind blowing....
About time. (Score:1)
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..
Don't they already have a way? (Score:1)
Old story. Again. (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
Gyroscope Design (Score:2)
The Stanford web site appears to be broken.
Gravity telescopes (Score:1)
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.
Old news - here is a reference from about Dec 99. (Score:1)
Re:Old story. Again. (Score:1)
I'll never understand it, I suppose.
Re:Don't they already have a way? (Score:1)
Re:Gyroscope Design (Score:2)
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
Re:NASA?? (Score:2)
Jerk.
Re:Gravity telescopes (Score:1)
Re:Why does Einstein look so bummed? (Score:2)
Don't get yourself too excited (Score:1)
I could have sworn a similar expirement has al... (Score:2)
tcd004
Here's my Microsoft Parody, where's yours? [lostbrain.com]
Re:Unclear on the scientific method are you? (Score:1)
Re:I could have sworn a similar expirement has al. (Score:1)
Re:This one is guaranteed to succeed (Score:2)
Re:Gyroscope Design (Score:3)
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!)
Re:The Project That Ate Stanford (Score:2)
I notice that NASA still hasn't announced a launch date.
Re:Don't they already have a way? (Score:1)
the subtle world of gyroscopes... (Score:1)
"Proving Einstein" is a little misleading (Score:2)
Re:The Project That Ate Stanford (Score:1)
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.
Re:The Project That Ate Stanford (Score:2)
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.
Re:Don't they already have a way? (Score:2)
Of course, I am a physics teacher , too, so you might lump me in on the conspiracy. :)
Re:Unclear on the scientific method are you? (Score:2)
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.
Re:Don't they already have a way? (Score:1)
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 [amazon.com] by Collins & Pinch, which I read a couple of days ago for the second time and found riveting.
Re:Wow! (Score:1)
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.
C'mon, Bowie... chill out already. (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 [slashdot.org].
Tardis (Score:1)
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
gyroscopes to generate electricity (Score:1)
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).
Sorta :-) (Score:3)
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
Re:Gyroscope Design (Score:1)
Re:I could have sworn a similar expirement has al. (Score:2)
"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.
Re:This one is guaranteed to succeed (Score:2)
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.
Re:the subtle world of gyroscopes... (Score:1)
Re:Gyroscope Design (Score:2)
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.
Re:Unclear on the scientific method are you? (Score:1)
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.
slightly OT (Score:1)
Re:Why does Einstein look so bummed? (Score:1)
or maybe this [uni-frankfurt.de]?
Wrong URL (Score:1)
Re:ANYTHING will spin forever in space! (Score:1)
Re:Wow! (Score:1)
Re:This one is guaranteed to succeed (Score:1)
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.
"Prove" Relativity? (Score:1)
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.
Re:Why does Einstein look so bummed? (Score:1)
Re:Why does Einstein look so bummed? (Score:1)
Re:This one is guaranteed to succeed (Score:1)
Also [slashdot.org], it won't prove anything if the result comes out as expected.
Re:And quantum mech still can't deal with gravity. (Score:1)
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?
Re:Sorta :-) (Score:1)
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.
Re:Wow! (Score:1)
Also making something spherical is easier than arbitrary shapes. Standard ball bearing balls are +- 25 microinches, and have been for years. Think lapping.