NASA Gravity Probe Launched

Perfect Quartz Spheres by RobertB-DC · 2004-04-20 09:46 · Score: 5, Interesting

The most facinating tidbit from the NASA article is the absoutely beyond perfect Niobium-coated Quartz spheres at the heart of the ultra-precise gyroscopes.

A quick Google found this link with more cool details, including:

* The 1.5-inch diameter rotors are within 40 atomic layers (0.3 millionths of an inch) of a perfect sphere.

* "Electrical sphericity" must be held to parts in ten million.

* Each rotor spins inside a quartz housing with clearances to the rotor of barely one thousandth of an inch.

* To lift the rotor on earth takes 1,000V. In space, only a fraction of a volt is needed.

* In 1,000 years the gyroscope should barely lose 1% of its starting speed.

* To isolate the gyroscope from the Earth's magnetic field, it will be shrouded in four layers of lead balloons, plus an outer shield of iron.

Plus these cool facts (and a ton more), there are steampunk-styled drawings of the manufacturing process.

Seems like NASA could make some money selling the rejects (you know there are plenty) as the ultimate shooters!

--
Stressed? Me? Of course not. Stress is what a rubber band feels before it breaks, silly.

Re:Perfect Quartz Spheres by Pi_0's+don't+shower · 2004-04-20 09:53 · Score: 3, Interesting

One complaint I have about this is, although the engineering is incredibly fancy, and advances were probably made on many fronts, this was shelved for 45 years for a reason -- a ridiculously small effect is expected to be observed.

Compare the expected General Relativistic correction to the Newtonian contribution and you'll see why, the GR contribution is about 3-4 orders of magnitude smaller.

Case in point, it took hundreds of years of observations of mercury to determine its orbit precessed by 5599 arcsec/century. Newtonian Mechanics accounts for 5556 of those, and GR accounts for the other 43. I have serious reservations about whether a 16 month experiment will observe what it's designed to observe.

The question is who funded it? by foidulus · 2004-04-20 09:48 · Score: 1, Interesting

Was this at all offset by any other governments? Seems kind of pricy for research that will freely be shared worldwide, though from the representations Americans get in the news, you have to wonder if they can really trust the data gathered from something built by products of one of the supposedly worst education systems in the world :P

Re:The question is who funded it? by king-manic · 2004-04-20 09:57 · Score: 2, Interesting

There's always the issue of prestige and technological supremacy. When you can do somethign no one else can technologically, it's more likly other governments/researchers will defer to you on the subject. Your influence increases and your ability to make certain claims increases. It's like civilization, achievement = prestige = influence.

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"There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy."

Einstein... by PeaceTank · 2004-04-20 09:52 · Score: 4, Interesting

I think that Einstein would turn over in his grave if he knew that we were spending 700 million dollars to test one of his theories. Remember, this was the man that came up with some of the most complicated theories in modern physics, and he did it in his head. He used 'geddonken' experiments, and however useful it may be to 'prove' his theories, one has to wonder what he would think...

Re:Einstein... by forgotmypassword · 2004-04-20 17:34 · Score: 2, Interesting

... except that he plagiarized Dirac's works...

Many people had a mathematical understanding of Special Relativity waay before Einstein. You take the rules for Electricity and Magnetism and you immediately see that they don't work right when you add velocities like with Newtonian Mechanics. Newtonian Mechanics has Gallilean relativity. That's right, there was relativity before Einstein.

It is a straight forward exercise to see that Maxwell's Equations (for E&M) have Lorentzian relativity. That's right they have Lorentz symmetry and NOT Einsteinian symmetry. Other people had already figured this out.

It was Einstein that put his foot down and said look here, Maxwell's equations are right and Newton is wrong. He explained the Lorentz transformations as being a very physical thing. This in and of itself wasn't mega-incredibly important, and Einstein never got a Nobel for it.

But he then knew that he had to fix gravity to work with special relativity. And he did that with the new fangled geometry of Riemmann, which was the more generalized form of Poisson's earlier work. Einstien let the metric be dynamic and the rest was just a matter of elbow grease. That is what made him uber. Dirac did not do that.

This is not to say that Dirac wasn't a good physicist or even an equal to Einstein. Dirac was obviously much better at quantum mechanics than Einstein. (Einstein fell behind the times really bad) Dirac did give us the relativistic, quantum theory of the electron and positron.

Dirac probably was an equal to Einstein. But Dirac didn't have a very good personality. He was anti-social to say the least. If you were a student at Florida State and said hi to him, chances were good that he wouldn't respond at all.

You can say that Dirac is underrated by the public, though not by physicists. You can say that Einstien didn't invent but 10% of special relativity. But to say that Einstein stole his work from Dirac is just BS and your link does not justify that statement.

--
A Usenet Troll Triumphs on Slashdot

Re:Yay! Hoorah for science, wooo!! by hacksoncode · 2004-04-20 10:26 · Score: 2, Interesting

Well... disproving this one aspect of the theory would not invalidate the remainder of the theory, which has been verified experiementally numerous times.

Newton's Laws of Motion didn't become "bunk" all of a sudden when Einstein (and later QM) discovered holes in it.

The speed of light bit is actually really well tested. It really does take lots more energy to continue speeding things up near light speed, and the trend of that is completely consistent with it taking an infinite amount of energy to get a non-massless object all the way up to c.

Additionally, time dilation is well demonstrated, and it definitely would allow the creation of time machines (something I morally object to :-) if faster than light travel were possible.

Don't get your hopes up.

Re:Yay! Hoorah for science, wooo!! by JRIsidore · 2004-04-20 10:34 · Score: 2, Interesting

General relativity may surely be proven wrong by the probe's results, but this will not turn it to be "nothing but bunk". So far it successfully passed all tests, which makes it at least a very good approximation (within our current measurement limits).

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:w!q

Re:That's a lot of money to spend by Anonymous Coward · 2004-04-20 11:08 · Score: 5, Interesting

Wouldn't our understanding of something as fundamental as general relativity far out weigh any kind of understanding we could gain from Mars? Not necessarily. More has been learned from putting this experiment together than will be learned from its results - it is a fine-scale test of one of the most successful theories of all time. Going to Mars, though expensive and such, could be a big deal if only as a proof of concept. Look at how much was learned going to the Moon. Going to Mars is orders of magnitude more complex - interplanetary radiation, the technological and social advances that will let a crew live together for months, getting people there and back ... if we can get to Mars and back we can go anywhere in our Solar System with trivial amounts of scaling. And, if we do find life on Mars (or elsewhere), that is potentially the most important discovery, um, ever. It tells us things about the fundamental nature of the universe too - and, short of an experiment either detecting gravity waves or detecting an overall curvature to spacetime, there isn't that much experiments will tell us about gravity right at the moment.

Re:We already have a better understanding of gravi by Bifurcati · 2004-04-20 11:15 · Score: 2, Interesting

In what sense would you claim that relativity is "wrong"? Just to clarify (and for other readers :), is it that you believe there is a bigger picture theory that encompasses GR AND quantum mechanics, etc? (In the same way that GR encompasses Newtonian mechanics) This is sort of theory (quantum gravity!) is needed to explain the inner workings of a black hole, for example, and the beginning of the universe, earlier that 10^{-43} seconds.

But the purpose of this project is to determine whether all the predictions of general relativity are correct - something which we don't know yet. If the experiment gives a positive result, general rel is completely confirmed as a correct theory, within its limits of applicability. A null result probably doesn't prove anything, as other posters have pointed out; it may simply be too hard an experiment to perform. So I think this IS a useful experiment, even if only from a dot your i's and cross your t's perspective.

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Physicist, consultant, science communicator

Re:That's a lot of money to spend by mog007 · 2004-04-20 11:34 · Score: 2, Interesting

Insightful? That's like the classic Seinfeld bit about the bio-engineers that design seedless watermelon instead of using their time to come up with cures for cancer or AIDS. It's about interests. Sure, the fundamentals of the Universe is a very interesting topic, and I'd love to see String Theory proven as much as the next guy, but one person's value of importance may differ from another person. Neither person is wrong, they're simply different.

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Learn something new.

Re:Not always hard by twostar · 2004-04-20 11:42 · Score: 2, Interesting

Even a sheild will let some thermal radiation past, even if just from radiation from the sheild its self. Plus if it's anywhere near another body (Earth, Moon, Jupiter, etc) it'll get some reflection from that source also.

Re:That's a lot of money to spend by Anonymous Coward · 2004-04-20 11:55 · Score: 2, Interesting

But considering that this equipment is the most sensitive made yet and still might not be sensitive enough to detect what it's measuring. Why do you think a GPS satellite is going to care?

It turns out that gravity's second-order effects on time are much easier to measure than its second-order effects on motion. Gravitational redshift makes clocks on the Earth's surface run slow compared to clocks far away, to the tune of about 40 microseconds a day. GPS relies on timing differences between signals from different satellites--40 microseconds turns into a 12 kilometer error accumulation per day.

One reason that time is so easy to measure is that the distances are so large. A GPS receiver is thousands of kilometers away from the satellites, which gives a lot of opportunity for effects to accumulate. The rotors in Gravity Probe B are a few centimeters wide. Time only runs a tiny amount slower over that distance. Ditto for effects like gravitomagnetism.

No, this is more interesting by eclectro · 2004-04-20 12:19 · Score: 2, Interesting

From this link;

I worked as a consultant for the company that was awarded the contract for working on the zerodur glass block that made up the housing for the gyros. They brought us in to try and teach machinists optical fabrication. The tolerances needed for this thing were unbelievable, extremely tough even for a master optician. They manufactured 3 housing blocks, one of them was destroyed during the rough machining process, and an optician trainee who was attempting to polish one of the precision lands with a weighted polishing lap by hand fractured the second. They trusted the same company with the second block to complete the polishing process. They had limited experience with any sort of optical fabrication, and the specs they were looking for were way, way beyond the capabilities of this shop. I felt really bad for the guy, who was absolutely sick with himself after the accident, and perturbed with Stanford University with giving the polishing operation to this shop with very little expertise in optical fabrication. This block had a million plus in material and man hours prior to the polishing operation, wiped out with one bad stroke

Heh. Stuff you don't hear about on NASA's website.

--
Take the cheese to sickbay, the doctor should see it as soon as possible - B'Elanna Torres, "Learning Curve"

Re:That's a lot of money to spend by LnxAddct · 2004-04-20 12:43 · Score: 2, Interesting

Well that test proved that time is warped, this test is to test frame dragging, which I guess in simple terms is testing to see if the space/gravity/time is spun around like a tornado or whirlpool, except the visual those two things give is somewhat inaccurate. Frame dragging involves too many dimensions for most to visualize it, but hopefully you get the idea.

Regards,
Steve

Re:Why has it been in the making for so long? by SEE · 2004-04-20 13:53 · Score: 2, Interesting

Practically every serious physicist knows that GR as currently stated and QM as currently stated are mutually contradictory in certain domains, and that thus one or both are in correct in the same sense Newton's laws were.

Me, I'm hoping we find a divergence with the GR expectation. Some inexplicable data will hopefully inspire a future Nobel Prize winner into making sense of the contradictions and get us a unified theory that can be tested.

We read too much sci-fi by ogma · 2004-04-20 22:20 · Score: 2, Interesting

From the article A Near-Perfect Gyroscope provided by another poster:

"Mechanically, the 1.5-inch diameter rotors are within 40 atomic layers (0.3 millionths of an inch) of a perfect sphere, rounder than anything within many light-years distance from us....Only neutron stars are rounder."

Now I know that here on slashdot such things as neutron stars are always only a synapse or two away from our collective consciousness, but I have to say that reading those words sent a shiver up my spine. A sentence that would feel right at home in an Iain M. Banks novel is being used to describe something happening right now.

Cool.

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