This describes a nifty test ofone of the predictions of the theory of general relativity. What is neat is that it worked and did show theexpected vortex generated by earth. Itappears that the tools invented were even niftier.
General relativity is one of thegreatest intellectual achievements of physics. It stalled only because it could not readily work with small measures. Recall that the black hole is nicelypredicted by the theory except that it can say nothing at the eventhorizon. The recent consensus acceptanceof the idea itself is a bad mistake and reflects this lack of understanding.
Quantum tries to work backwardinto structure from macro observations and throws a Ptolemaic blanket over itall.
The introduction of a new generalizedcyclic function as a metric ends this problem (published by myself in PhysicsEssays June 2010)
NASA Announces Results of Epic Space-Time Experiment
May 4, 2011: Einstein was right again. There is aspace-time vortex around Earth, and its shape precisely matches the predictionsof Einstein's theory of gravity.
Researchers confirmed these points at a press conference today at NASAheadquarters where they announced the long-awaited results of Gravity Probe B(GP-B).
"The space-time around Earth appears to be distorted just asgeneral relativity predicts," says Stanford University
An artist's concept of GP-B measuring the curved spacetime aroundEarth.
"This is an epic result," adds Clifford Will of Washington University in St. Louis
Time and space, according to Einstein's theories of relativity, arewoven together, forming a four-dimensional fabric called"space-time." The mass of Earth dimples this fabric, much like aheavy person sitting in the middle of a trampoline. Gravity, says Einstein, issimply the motion of objects following the curvaceous lines of the dimple.
If Earth were stationary, that would be the end of the story. But Earthis not stationary. Our planet spins, and the spin should twist the dimple,slightly, pulling it around into a 4-dimensional swirl. This is what GP-B wentto space in 2004 to check.
The idea behind the experiment is simple:
Put a spinning gyroscope into orbit around the Earth, with the spinaxis pointed toward some distant star as a fixed reference point. Free fromexternal forces, the gyroscope's axis should continue pointing at thestar--forever. But if space is twisted, the direction of the gyroscope's axisshould drift over time. By noting this change in direction relative to thestar, the twists of space-time could be measured.
In practice, the experiment is tremendously difficult.
One of the super-spherical gyroscopes of Gravity Probe B.
The four gyroscopes in GP-B are the most perfect spheres ever made byhumans. These ping pong-sized balls of fused quartz and silicon are 1.5 inches acrossand never vary from a perfect sphere by more than 40 atomic layers. If thegyroscopes weren't so spherical, their spin axes would wobble even without theeffects of relativity.
According to calculations, the twisted space-time around Earth shouldcause the axes of the gyros to drift merely 0.041 arcseconds over a year. Anarcsecond is 1/3600th of a degree. To measure this angle reasonably well, GP-Bneeded a fantastic precision of 0.0005 arcseconds. It's like measuring thethickness of a sheet of paper held edge-on 100 miles away.
"GP-B researchers had to invent whole new technologies to makethis possible," notes Will.
They developed a "drag free" satellite that could brushagainst the outer layers of Earth's atmosphere without disturbing the gyros. Theyfigured out how to keep Earth's magnetic field from penetrating the spacecraft.And they created a device to measure the spin of a gyro--without touching thegyro. More information about these technologies may be found in theScience@NASA story "APocket of Near-Perfection."
Pulling off the experiment was an exceptional challenge. But after ayear of data-taking and nearly five years of analysis, the GP-B scientists appearto have done it.
"We measured a geodetic precession of 6.600 plus or minus 0.017arcseconds and a frame dragging effect of 0.039 plus or minus 0.007arcseconds," says Everitt.
For readers who are not experts in relativity: Geodetic precession isthe amount of wobble caused by the static mass of the Earth (the dimple inspacetime) and the frame dragging effect is the amount of wobblecaused by the spin of the Earth (the twist in spacetime). Both values are inprecise accord with Einstein's predictions.
"In the opinion of the committee that I chair, this effort wastruly heroic. We were just blown away," says Will.
An artist's concept of twisted spacetime around a black hole. Credit:Joe Bergeron of Sky & Telescope magazine.
The results of Gravity Probe B give physicists renewed confidence thatthe strange predictions of Einstein's theory are indeed correct, and that thesepredictions may be applied elsewhere. The type of spacetime vortex that existsaround Earth is duplicated and magnified elsewhere in the cosmos--aroundmassive neutron stars, black holes, and active galactic nuclei.
"If you tried to spin a gyroscope in the severely twistedspace-time around a black hole," says Will, "it wouldn't just gentlyprecess by a fraction of a degree. It would wobble crazily and possibly evenflip over."
In binary black hole systems--that is, where one black hole orbitsanother black hole--the black holes themselves are spinning and thus behavelike gyroscopes. Imagine a system of orbiting, spinning, wobbling, flippingblack holes! That's the sort of thing general relativity predicts and whichGP-B tells us can really be true.
The scientific legacy of GP-B isn't limited to general relativity. Theproject also touched the lives of hundreds of young scientists:
"Because it was based at a university many students were able towork on the project," says Everitt. "More than 86 PhD theses atStanford plus 14 more at other Universities were granted to students working onGP-B. Several hundred undergraduates and 55 high-school students alsoparticipated, including astronaut Sally Ride and eventual Nobel Laureate EricCornell."
NASA funding for Gravity Probe B began in the fall of 1963. That meansEveritt and some colleagues have been planning, promoting, building, operating,and analyzing data from the experiment for more than 47 years—truly, an epiceffort.
What's next?
Everitt recalls some advice given to him by his thesis advisor andNobel Laureate Patrick M.S. Blackett: "If you can't think of what physicsto do next, invent some new technology, and it will lead to new physics."
"Well," says Everitt, "we invented 13 new technologiesfor Gravity Probe B. Who knows where they will take us?"
This epic might just be getting started, after all….
No comments:
Post a Comment