Friday, May 6, 2011

Space-Time is Epic

When NASA posts a story about the results of an "epic space-time experiment" I just have to read it.

The story can be boiled down into four words: Einstein was right again.

Space-time is a mathematical model that combines space and time into a single continuum. If you look at the history in the formation of this model you'll find that it steps through the theories/rules of some well known mathematicians. The explanation of space-time didn't start with them all put together and hyphenated, it started with simple geometry and the Pythagorean Rule (you remember that from 8th grade geometry class right? a2 + b2 = c2). When that wasn't enough a Euclidean model for space was was used (he was the one that built the coordinate system). The Euclidean model explained space in terms of dimensions, with the universe consisting of three dimensions of space and one dimension of time. By Newton's time, people were getting pretty good at explaining space using a Euclidean distance function but it did not work when gravity becomes strong. Newtonian physics took the model a further but still had some problems including dealing with the speed of light and gravity. Then Einstein came up with the concept of special relativity. It explained observations like that the speed of light is constant everywhere and in every direction. Einstein's theory of gravity provided a geometric understanding of gravitation.

According to Einstein, space and time are woven together,  forming a four-dimensional fabric called space-time. The mass of a large object causes that fabric to curve or dimple. Think of it like a big rubber sheet that has a heavy ball set on top of it. That is how space-time curves around a planet or star. Now let's add gravity to the mix. Einstein explained gravity as the motion of objects following the curvaceous lines of the dimple. Think of it like a very large funnel that you spin a small ball around, starting at the edge it will slowly spin around to the bottom/center of the funnel. Alright, now lets make the object, the Earth, move. As the planet spins the dimple twists, pulling it around into a four dimensional swirl. That's the theory at least.

NASA went to test this theory with its Gravity Probe B (GP-B). The experiment is actually pretty simple. Put a spinning gyroscope into orbit around the Earth, with the axis pointed at a distant star as a reference point. If the gyroscope is free of external forces the axis should continue pointing at the star for forever. If it not free of external forces, if space is twisted, then the direction of the axis will drift over time. Note the direction of the dirft and you can measure the twists of space-time. The twisted space-time around the Earth should cause the axis of the gyroscope to drift about 0.041 arcseconds (1/3600 of a degree) over a year.

Admittedly, that is a pretty simple concept, but the actual conducting of the experiment is not so simple. GP-B has four gyroscopes. These gyroscopes are about the size of ping pong balls and contained the most perfect spheres ever created by humans. They are made of fused quartz and silicon that never vary from a perfect sphere by more than 40 atomic layers. And because the drift of the gyroscopes would be so small the instruments had to have a precision of 0.0005 arcseconds. Whoa. But we're not done yet. The satellite the gyroscopes were one needed to be drag free so that when it brushed against the outer layers of the atmosphere the gyroscopes would not be disturbed. The satellite also had to keep the Earth's magnetic field from penetrating the spacecraft. And then they created a device that measured the spin of the gyroscope without touching the gyro. Is your jaw on the floor yet because I know mine is.

After a year of taking data and five years of analysis the results are in: 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.

Uh. Ok. Well, let's break that down. Geodetic precession is the amount of wobble caused by the static mass of the Earth (the dimple in space-time) and the frame dragging effect is the amount of wobble caused by the spin of the Earth (the twist in space-time). These results are in precise accord with Einstein's predictions. It is evidence that the predictions in Einstein's theory are correct and that it can be applied to other objects in the universe.

Yep, Einstein was the man. Epic.

Here's the news report from NASA:

The Gravity Probe B mission homepage:

Learn more at Spacetime 101:

And finally, here are a few more NASA stories on this topic you may find interesting:
A Pocket of Near Perfection -
Was Einstein a SpaceAlien? -
In Search of Gravitomagnetism -

(images from the NASA story linked above)
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