Is Earth caught in a vortex---of spacetime?

We'll soon know the answer: An NASA/Stanford physics experiment called
Gravity Probe B recently finished a year of gathering science data in
Earth orbit. The results, which will take another year to analyze, are
expected to reveal a subtle space-time vortex around Earth.

Time and space, according to Einstein's theories of gravity, are woven
together as a four dimensional fabric. The tremendous 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 dimpled lines of space-time.

If Earth were stationary, that would be the end of the story. But Earth
is not stationary. It spins. If Einstein's equations are correct, the
spin of our planet should twist the dimple, pulling it around into a
shallow 4-dimensional vortex. This is what GP-B went to space 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 the region of space through which the gyroscope
orbits is slightly twisted, as Einstein\'s theory predicts, the
direction of the gyroscope\'s axis would drift ever-so-slightly over
time. By noting this change in direction relative to the star, the
subtle twists of spacetime could be measured.

In practice, it was tremendously difficult.

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---a minuscule amount, but still enough to ruin the
experiment.

According to calculations, the twisted spacetime around Earth should
cause the axes of the gyros to drift 0.042 arcseconds over a year. An
arcsecond is only 1/3600th of a degree. To measure this angle reasonably
well, GP-B had to have a fantastic precision of 0.0005 arcseconds.

GP-B researchers invented whole new technologies to make this possible.
They developed a "drag free" satellite that could brush against the
outer layers of Earth's atmosphere without disturbing the gyros. And
they concocted a device to measure the spin of a gyro---without touching
the gyro. \[Learn more: A Pocket of Near-Perfection\]

Pulling off this experiment was an exceptional challenge. A lot of time
and money was on the line. But the GP-B scientists appear to have done
it.

\"There were not any major surprises\" in the experiment\'s
performance, says physics professor Francis Everitt, the Principal
Investigator for GP-B at Stanford University. With this major milestone
behind them, he says the mood among the GP-B scientists is \"a lot of
enthusiasm, and a realization also that a lot of grinding hard work is
ahead of us.\"

A careful, thorough analysis of the data is underway. The
scientists will do it in three stages, Everitt explains. First, they
will look at the data from each day of the year-long experiment,
checking for irregularities. Next they\'ll break the data into roughly
month-long chunks, and finally they\'ll look at the whole year. By doing
it this way, the scientists should be able to find any problems that a
more simple analysis might not catch.

Eventually scientists around the world will scrutinize the data. Says
Everitt, carefully, "we want our sternest critics to be us."

If they detect the vortex, precisely as expected, it simply means that
Einstein was right, again. But what if they don't? There might be a flaw
in Einstein's theory, a tiny discrepancy that heralds a revolution in
physics.

First, though, there's a lot of data to analyze. Stay tuned.