This describes a nifty test of
one of the predictions of the theory of general relativity. What is neat is that it worked and did show the
expected vortex generated by earth. It
appears that the tools invented were even niftier.
General relativity is one of the
greatest intellectual achievements of physics.
It stalled only because it could not readily work with small measures. Recall that the black hole is nicely
predicted by the theory except that it can say nothing at the event
horizon. The recent consensus acceptance
of the idea itself is a bad mistake and reflects this lack of understanding.
Quantum tries to work backward
into structure from macro observations and throws a Ptolemaic blanket over it
all.
The introduction of a new generalized
cyclic function as a metric ends this problem (published by myself in Physics
Essays June 2010)
NASA Announces Results of Epic Space-Time Experiment
May 4, 2011: Einstein was right again. There is a
space-time vortex around Earth, and its shape precisely matches the predictions
of Einstein's theory of gravity.
Researchers confirmed these points at a press conference today at NASA
headquarters where they announced the long-awaited results of Gravity Probe B
(GP-B).
"The space-time around Earth appears to be distorted just as
general relativity predicts," says Stanford University
An artist's concept of GP-B measuring the curved spacetime around
Earth.
"This is an epic result," adds Clifford Will of Washington University
in St. Louis
Time and space, according to Einstein's theories of relativity, are
woven together, forming a four-dimensional fabric called
"space-time." The mass of Earth dimples this fabric, much like a
heavy person sitting in the middle of a trampoline. Gravity, says Einstein, is
simply the motion of objects following the curvaceous lines of the dimple.
If Earth were stationary, that would be the end of the story. But Earth
is 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 went
to space in 2004 to check.
The idea behind the experiment is simple:
Put a spinning gyroscope into orbit around the Earth, with the spin
axis pointed toward some distant star as a fixed reference point. Free from
external forces, the gyroscope's axis should continue pointing at the
star--forever. But if space is twisted, the direction of the gyroscope's axis
should drift over time. By noting this change in direction relative to the
star, 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 by
humans. These ping pong-sized balls of fused quartz and silicon are 1.5 inches across
and never vary from a perfect sphere by more than 40 atomic layers. If the
gyroscopes weren't so spherical, their spin axes would wobble even without the
effects of relativity.
According to calculations, the twisted space-time around Earth should
cause the axes of the gyros to drift merely 0.041 arcseconds over a year. An
arcsecond is 1/3600th of a degree. To measure this angle reasonably well, GP-B
needed a fantastic precision of 0.0005 arcseconds. It's like measuring the
thickness of a sheet of paper held edge-on 100 miles away.
"GP-B researchers had to invent whole new technologies to make
this possible," notes Will.
They developed a "drag free" satellite that could brush
against the outer layers of Earth's atmosphere without disturbing the gyros. They
figured 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 the
gyro. More information about these technologies may be found in the
Science@NASA story "A
Pocket of Near-Perfection."
Pulling off the experiment was an exceptional challenge. But after a
year of data-taking and nearly five years of analysis, the GP-B scientists appear
to have done it.
"We measured a geodetic precession of 6.600 plus or minus 0.017
arcseconds and a frame dragging effect of 0.039 plus or minus 0.007
arcseconds," says Everitt.
For readers who are not experts in relativity: Geodetic precession is
the amount of wobble caused by the static mass of the Earth (the dimple in
spacetime) and the frame dragging effect is the amount of wobble
caused by the spin of the Earth (the twist in spacetime). Both values are in
precise accord with Einstein's predictions.
"In the opinion of the committee that I chair, this effort was
truly 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 that
the strange predictions of Einstein's theory are indeed correct, and that these
predictions may be applied elsewhere. The type of spacetime vortex that exists
around Earth is duplicated and magnified elsewhere in the cosmos--around
massive neutron stars, black holes, and active galactic nuclei.
"If you tried to spin a gyroscope in the severely twisted
space-time around a black hole," says Will, "it wouldn't just gently
precess by a fraction of a degree. It would wobble crazily and possibly even
flip over."
In binary black hole systems--that is, where one black hole orbits
another black hole--the black holes themselves are spinning and thus behave
like gyroscopes. Imagine a system of orbiting, spinning, wobbling, flipping
black holes! That's the sort of thing general relativity predicts and which
GP-B tells us can really be true.
The scientific legacy of GP-B isn't limited to general relativity. The
project also touched the lives of hundreds of young scientists:
"Because it was based at a university many students were able to
work on the project," says Everitt. "More than 86 PhD theses at
Stanford plus 14 more at other Universities were granted to students working on
GP-B. Several hundred undergraduates and 55 high-school students also
participated, including astronaut Sally Ride and eventual Nobel Laureate Eric
Cornell."
NASA funding for Gravity Probe B began in the fall of 1963. That means
Everitt and some colleagues have been planning, promoting, building, operating,
and analyzing data from the experiment for more than 47 years—truly, an epic
effort.
What's next?
Everitt recalls some advice given to him by his thesis advisor and
Nobel Laureate Patrick M.S. Blackett: "If you can't think of what physics
to do next, invent some new technology, and it will lead to new physics."
"Well," says Everitt, "we invented 13 new technologies
for Gravity Probe B. Who knows where they will take us?"
This epic might just be getting started, after all….
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