Posted
by
michael
on Saturday April 03, 2004 @01:35PM
from the weighty-concepts dept.

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

But the subatomic world does matter to us, as we are making ultra-mega-supercolliders to probe those length scales. We are in fact "loading the dice" by forcibly sampling the "hardly going to happen" region of the distribution curve of probable events.

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

Anyway, while we do have astrophysical tests of frame-dragging, they're not direct. There's a big difference between trying to infer the effect by observing the orbits of matter outside a black hole, and actually putting a gyroscope into a frame-dragging field and seeing what happens to it. In particular, direct measurement is much more sensitive. Astrophysical tests can merely suggest the existence of frame dragging. GPB can quantitative

Just about all of the engineering that's gone into the project is to eliminate interference from everything else; those gyros are going to be just about the best-isolated objects we've ever made.

Yes, they need to account for solar wind, as well as atmospheric drag, as small as it is at that height. This is done by flying the satellite drag-free; one of the gyros free-floats inside its housing, and if it starts to drift off-center, the satellite fires its thrusters to reposition _the satellite_ so that the free-floating gyro is again in the center of its cavity.

This way, any external force on the satellite can be removed, since the gyro is shielded from them by the bulk of the satellite, and the satellite then follows the gyro on a perfect gravitational orbit.

Magnetic fields are filtered out to some ungodly factor; the leftover fields inside the science probe are on the of 10^-17 gauss.

They also account for micrometeorites, electric noise, and many other error sources. There's a reason this has taken 40 years.

But it looks like to me that LATOR is a very-high precision test of what's already been tested several times: the exact amount of curvature of spacetime that heavy objects create.

GP-B tests the effects of frame dragging, which is a completely separate effect.

As to SUMO, I wouldn't be able to say what kind of effect a Lorentz-transform symmetry breaking would cause, and whether GP-B's results could be affected by that. But the tests seem to be fundamentally about clock rates at various moving frames, which is more of a special relativity test (as the Loretz transform comes from special relativity). GP-B is about general relativity, and specifically about spin, which seems to be relatively untested ground.

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

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

Polar orbit, with satellite roll axis fixed on a guide star for a good reference frame. I think it's about as circular as they can make it.

And yeah, it's superfluid helium, enough for about 18 months given the boil-off rate (it boils off continually to maintain dewar temperature; the boiled-off gas is actually used in the precision manouvering thrusters)

And the suspension system is a rather scary system... it has to ramp from barely touching the gyros to making sure they don't impact the cavity walls when a micrometeorite hits almost instantaneously. And there's only about a millimeter of clearance there. And the gyros spin at 10,000 rpm. You don't want them touching the walls.

Actually working in the civilian aviation I ahd Fluight Engineer swear to me that this is only a problem on OLDER model aircraft, but that the new boing and Airbus do not come with that problem or solved it (how ? Maybe they shield the instrument from the inside too).

Airlines still hold onto the "no cell phone inside" because this is far easier than differenciate old and new aircraft models, and I suppose this is far easier than convince insurance or the other passenger.

Airlines still hold onto the "no cell phone inside" because this is far easier than differenciate old and new aircraft models, and I suppose this is far easier than convince insurance or the other passenger.

The tin-foil hat part of my brain wonders if airlines are afraid that someone'll be on the phone when, say, an engine falls off or the pilot commits some tragic error. The bad PR could cost millions...

I thought this was debunked by the 9/11 commission several months ago. [washingtonpost.com] The boxcutter meme spread like wildfire, and everyone "knew" before the day was out that this was done with boxcutters. But it turns out that only one plane had a boxcutter sighting (relayed via cellphone). They actually used Mace, knives, and bomb threats. I suppose it's possible that "knives" might have been a reference to boxcutters, but we have no further evidence to support i

large body was rotating it would create a drag effect on space-time known as frame dragging.

I think we're all familiar with time dialation (if you haven't read "The Elegent Universe", you're missing the best explanation of *why* time dislation occurs that I have ever heard), but what is frame dragging? What kind of effects does it have on the observer?

The earth is a mass-energy. According to General Relativity, as a mass-energy, it should create a little dimple in the local space-time fabric. It is also theorized that the daily rotation of the earth causes a twisting of the local space-time fabric.
This effect is known as frame dragging and it should manifest itself as a force that pushes a gyroscope's axis out of alignment as it orbits the Earth. [GP-B will be using four small, incredibly precise gyroscopes as its main tool for detection of relativistic effects on the local space-time fabric.] Gravity Probe B will attempt to measure the force, gravitomagnetism, giving scientists an important insight into how it might affect objects that are much larger than ping pong balls, such as black holes. At the same time, the gyroscopes will experience a much bigger force - the geodetic effect - which is a result of the warping of space-time predicted by Einstein. This force will tend to push their axes in a direction perpendicular to the frame-dragging effect which allow it to be measured separately. The geodetic effect is hundreds of times bigger than frame dragging and the experiment should measure its size with an accuracy of 0.01 per cent the most severe test of general relativity ever undertaken.

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

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

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

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

Theoretically, yes [sciencedirect.com].... there's a recent paper [harvard.edu] that works out the numbers for lensing from a spiral galaxy, and it's roughly on the order of a few micro-acroseconds. Possibly detectable by SIM [nasa.gov] or GAIA [estec.esa.nl].

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

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

Einstein discovered that gravity can work much the same way. Moving gravitational charges (i.e. masses) generate an extra force on other moving masses. This extra force is sometimes refered to a gravito-magnetism and is usually v

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

will [GPB] allow and or test for [braneworld] theory or is the device antiquated before deployment?

No, it won't serve as a test of string theory braneworld scenarios, and no, that doesn't make it "antiquated", either. There are lots of reasons to do the experiment, other than its ability to verify somebody's speculative pet theory. (Heck, string theory doesn't even predict that our universe is confined to a brane; it's just a possibility within string theory.)

The point of GPB is merely to test the accuracy of general relativity's predictions. If GR is wrong, there are many ways it could be wrong, and thus GPB might be able to tell us which way is correct, or rule out alternative theories that predict effects that aren't measured.

Well, as I understand it, string theory is incomplete and does not yet necessarily replace relativity, even though it aims to do that, since it's still untested/the math hasn't been worked out/something like that. So the device probably isn't antiquated. Yet, anyway.

From what little I understand of string theory, it's the other way around: the math works out perfectly, but there's no testable hypotheses, thus it isn't going to displace current theories among the majority of physicists until some such test can be devised.

Einstein predicted that the gravity created by a large body warped space-time, but he also predicted that if the large body was rotating it would create a drag effect on space-time known as frame dragging.

NASA announced yesterday that its longest running program, Wooden Block B, was ready and scheduled for dropping off the Empire State Building on April 17th. The project has taken 44 years to complete, at a cost of approximately $700 million. The reason for the high cost is that the probe contains the most expensive wood ever created, which will be used to test Newton's theory of gravity. Newton predicted that an attractive force known as 'gravity' will act between any two bodies. Wooden Block B will be able to test Newton's theory using Earth's gravitational field, and a very tall building.

Inefficent military bureaucracy? I don't know where you heard this from, but in the military if something needs to get done, it gets done.

The main problem with NASA is lack of funding. The military has a similar problem (think about how many people they employ and what they have to buy before you flame that), but they still change when a better system is invented.

Maybe if we got rid of welfare and medicare/medicaid we could fully fund NASA.

Inefficent military bureaucracy? I don't know where you heard this from, but in the military if something needs to get done, it gets done.

Hmmm. When World War II broke out, the US had discovered that, while its tactics with torpedos were more or less sound, they came to naught -- because the actual torpedos had this nasty habit of breaking apart on impact, rather than (say) exploding. It took two years (and who knows how many lives) to get that problem fixed.

The general rule seems, to my reading of history, to be that the military tends to be effective but not necessarily cost-efficient. Or put another way: Throw enough money at any technological problem and it will be solved. People tend to be freer with the gobs of money if they think it's related to national security.

Yep. At the start of World War II for the US, in December 1941, it was amongst the weakest military-wise in the world. By August, 1945, less than four years later, it had nuked Japan. Nuked. In 1945. Look at the cars in 1945. Some military dude said "Let's make a bomb" and they built it.

But it cost a few billion bucks. GDP-wise, it was probably the largest project in US history. But such a pretty cloud!

That project has been kicking around Stanford for decades. I saw that satellite under construction almost twenty years ago. It's basically a subsidy program for PhD students, not a satellite program. If that job had been outsourced to Hughes or Loral, it would have launched decades ago.

General Relativity is one of the pillars of physics (ther other being the Quantum Theory).

The impact on science is quite straightforward. as this is science. Science is about testing theories. Without that, science is just a religion.

GR predicted that Newtonian mechanics are too simplistic. This is one of the tests that verifies this. Anyway, any applications of this test are another 50 or 500 years away. Just like the applications of discovery of electrons (typing away on my electron machine).

According to this BBC article [bbc.co.uk], the mission completion is supposed to be in 16 months.

I found the following quote especially interesting:

Francis Everitt, the principal investigator of the project, said: "Aren't Einstein's theories all established and confirmed? After all it was 50 years ago that Einstein himself died and it's 100 years next year when he developed his first theory of relativity. Don't we already know it all? The answer is no."

I wonder what other theories that are generally accepted throughout the scientific community have not been completely tested and/or verified. And, quite frankly, I'm surprised that there isn't much more VC and grant money available to go and do research on stuff like this. Afterall, these projects are quite prestigious.

"Aren't Einstein's theories all established and confirmed? After all it was 50 years ago that Einstein himself died and it's 100 years next year when he developed his first theory of relativity. Don't we already know it all? The answer is no."

I wonder what other theories that are generally accepted throughout the scientific community have not been completely tested and/or verified.

All of them. It's not possible to perform every test of a theory that can be performed, nor is it possible to perform any given test to an arbitrarily high precision. There are tests of quantum electrodynamics that are accurate to 11 decimal places, but people still test QED, because we never know whether it goes wrong at the 12th place, or whether there's some new phenomenon that QED doesn't predict. Likewise, there are many tests of general relativity, many of which are very accurate, and nobody doubt's the theory's general validity --- but that doesn't mean that there might not be small deviations out there that point the way to an even better theory.

And, quite frankly, I'm surprised that there isn't much more VC and grant money available to go and do research on stuff like this. Afterall, these projects are quite prestigious.

If it takes $100 million to find mistakes in the theory, there is very little practical incentive to research it, since more than likely it will take many times $100 million to exploit any of those newly discovered differences for practical gain. Put another way, if existing theories are good enough for all but the most precise

Interesting opinion, but you are just shuffling the cost off to later generations. Say for example gravity control comes out of discovering a error in relativity. Is that worth it?

I don't think that's what he was talking about. Instead, I think he was trying to explain why there aren't any venture capital funds to fund scientific research. Well, duh. If it's called "venture capital" that means it's used in "capitalistic ventures", and science is not a capitalistic venture.

Einstein's theories have been heavily tested and IIRC, so far hasn't been found to be invalid. There are other theories that explain the way things are. Einstein's theories I think are most accepted because of how well it tested so far.

VC money is much more about return on investment than prestige. Funding science projects doesn't normally bring much money or prestige, IMO.

I wonder what other theories that are generally accepted throughout the scientific community have not been completely tested and/or verified.

All of them.

It is not possible to completely test and verify anything. That's the nature of reality. A theory is defined as an explanation that has been thorougly tested and is widely accepted by people knowledgable in that field, but it's an essential part of science that nothing is ever proved beyond all doubt; there is always room for change if additional data comes to light, or a better explanation for existing data is devised.

One of my pet peeves is the common misuse of "theory" to mean "hypothesis" -- an untested conjecture. This popular misconception then leads to scientific knowledge being dismissed as "it's only a theory" by people who don't understand what a theory actually is, and assume that the Theory of (fill in the blank) is a mere hypothesis.

Someone setup an experiment about 10 years ago with 2 highly percise clocks one was set up on the top of a tall build and the other was set at the bottom...they ticked and stoped at the same exact and the clock on top of the building was very slightly behind the clock on the bottom...so I guess that should say something about his theory of relativaty.

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

So what? It's usually possible to construct a bunch of theories that all describe one particular phenomena (though they don't agree on all phenomena). Should we stop observing phenomena? [...] Well, we should always ask whether a given experiment is worth its cost. But we don't do experiments merely to judge between competing hypotheses. If GPB measured frame-dragging whose magnitude was incontroveribly different from that predicted by GR, then we'd know we'd have to develop a "decent alternative hypothesis

When was the last time you dug in your yard to see whether there was a buried treasure there? I bet you haven't: you make the reasonable assumption that there is no treasure buried there and digging costs valuable time. Until you receive additional information, the cost is simply not worth the expected benefit.

Well, if some renowned physicist showed up with some excellent math demonstrating that there must be buried treasure in my yard, it's worth a day's work to dig it up and test his hypothesis. Wouldn

Since the project was conceived by three scientists after a naked midday swim at Stanford University's pool, more than 1,000 people have worked on the satellite. Two of its founders are dead. More than 90 people have earned their doctorates working on the project.

Naked physicists... wow... with the current administration in charge, this project would have never been approved.

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

And probably not much more expensive.

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

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

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

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

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

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

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

LATOR also seems to be much more accurate,

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

Quoting this page:

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

As you can see, you were mistaken.

and less likely to receive interference.

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

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

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

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

When I was a grad student there, we had a running joke that nobody could get an astrophysics degree without selling at least a piece of their soul to Francis Everett, the chief booster for this project.

I was there when a rogue group suggested that, in the intervening four decades, technology had advanced enough to do the frame-dragging experiment with a laser-coordinated satellite net for half the cost.

We also circulated the "fact" that the GP-B launch date slipped by about 1.05 days per day. A friend defined it as a new universal constant for project overruns...:)

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

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

From the ESA website [esa.int] LISA
LISA is an ESA-NASA mission involving three spacecraft flying approximately 5 million kilometres apart in an equilateral triangle formation. Together, they act as a Michelson interferometer to measure the distortion of space caused by passing gravitational waves. Lasers in each spacecraft will be used to measure minute changes in the separation distances of free-floating masses within each spacecraft.
The LISA mission is designed to search for and detect gravitational radiation

First, I would not call it all of a sudden. Testing theories with experiments is one of the building blocks of science.

So much as Einsten's theories are concerned, since the very day he published his theories, other scientists have analyzed and thought of ways to test them. They have done so where possible, as technology has permitted. One example is the atomic clock and moving bodies experiments that have been done in the past.

I'm more worried about paranoid dumb people dragging the world in another dark age because they fear what they don't understand.
If you're worried about quantum fysics, go and read some books on the subject.

Exploding the Earth would guarantee Bush would not be re-elected so I'm really not that worried.

Seriously, though, I'm more worried that some cave dwelling foul-smelling individual will blow up an observatory in protest encouraging all the other cave-dwelling foul-smelling individuals to blow whatever it is they think is destroying the society they are not even members of.

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

Duke Nukem Forever was originally first described in a Bell Labs whitepaper personally written by Ken Thompson and Dennis Ritchie in early 1970, just over 34 years ago. The whitepaper said that Duke Nukem Forever would run on Bell Labs' new UNIX system, and would be available "sometime before the end of the year". Bell started taking orders the next week, and the historic first order for DNF, by the U.S. patent office, was placed on that day. Eight months later, despite not yet being finished, Duke Nukem Fo

Humm, methinks you may well have the black hole physics part of it backwards. One thing we get damned little out of a black hole is information about its characteristics. We can get a general, plus or minus 20% guess on its mass by measuring the orbital velocities and distances to all the other stars in the locality.

The only other tidbit of info we can eek out of the observations is the miss-match between expected velocities of the really nearby s