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NASA Gravity Probe Set for Launch
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."
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?
Javascript + Nintendo DSi = DSiCade
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.
Gravity Probe A was the launch of an atomic clock on a suborbital rocket, designed to measure time dilation as it passed into weaker areas of gravity.
I believe it was done in 1976
If you look on the web site, you'll see they have already contributed to the technology sector. http://einstein.stanford.edu/content/spinoffs/tech nology.html
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.
See article
Professional Wild-Eyed Visionary
Sorry to follow-up on my own post. Caught a link error. I stated:
That should instead read:
Only Women Bleed (Sex, Sharia remix)
Your 1997 NASA link actually goes to the previous 1995 statement.
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 quantitatively measure it to 1% accuracy.
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.
You can see from the link you cite that LAGEOS only measured the Lense-Thirring effect to about 20% accuracy. GPB can measure it to 1% or better. It's both a refinement and an alternative method (using gyroscopes instead of laser ranging, good for a sanity check).
This comment is offtopic and stolen from here. Bloody trolls!
//Blessed are they that run around in circles, for they shall be known as wheels.
Having worked on GP-B for a bit...
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.
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).
Well, I'm not a physicist; I just played around on the hardware.
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.
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.
This guys post is taken from another discussion and another Slashdot user. Verbatim.
He's a troll relegated to 0 karma land, and desperate for anyway out.
See UID's comment on his post: here
Don't let this guy walk off with 5 mod points for such a stupid trick.
-Malakai
A Dragon Lives in my Garage
Kinda like how you can't hijack a plane with a boxknife?
I thought this was debunked by the 9/11 commission several months ago. 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 it.
Only cosmology and black hole physics can really test GR.
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 stars, and the predicted velocity at that distance based on the above SWAG on its mass from averageing the orbits of the more distant stars.
From that we can deduce the direction and speed of the hole rotation as directly evidenced by the orbital errors of these nearby stars caused by what may well be frame dragging from the rotation of the black hole.
However, the closest such black hole isn't easily observable (IIRC it's Saggitarious B) due to all the dirt and dust from previous supernova's surrounding the center of our own galaxy, the thing you know as the Milky Way. Our far infrared capabilities that can see better thru all that junk will come online with the James Webb telescope and hopefully give us a better view.
In the meantime we have to look to other, much more distant galaxies, where the sheer distances preclude making truely accurate measurements on any one object. I think we do more by doppler effects causeing line spreading, and statistical analysis of that spreading, than by any direct observations of any individual stars in those distant galaxies. Statistics tend to be fuzzy as we all know.
This device, by giving us a very good signal to noise ratio calibration point, will let us analyse those distant objects with considerably more precision than we currently can do. It has the potential of tightening up our "guesses" by at least 2 orders of magnitude, maybe more. Thats worthwhile science, and will narrow the field of candidates for the TOE considerably.
Cheers, Gene
From the ESA website
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 from astronomical sources. In the process, LISA can test some of the fundamental tenets of the theory of gravitation.
The most predictable sources
The most predictable sources of gravitational waves are binary star systems in our galaxy. LISA's observations of these systems would be of interest both for fundamental physics and for astrophysics. The LISA design is such that both the amplitude and also the polarization of gravitational waves can be measured. If gravitational radiation from known binary systems is not detected, or is detected with amplitudes or polarizations not predicted by general relativity, then general relativity must be wrong. If the sources are detected then the polarization measurement reveals the angle of inclination of the orbit of the binary system. This is a crucial missing factor from many optical observations of these systems, and is necessary in order to infer the mass of the stars in the binary pair.
Why so much emphasis on Einstein's Theory all of a sudden??
SBD