Gravity Probe B: It Goes ‘Ding’ When There’s Stuff

I know I am not alone among the nerd community in envisioning the following when imagining a space-time vortex:

Of course, a brilliantly colored wormhole is not what NASA has so enthusiastically been chattering about for the last two days. No, what we’re talking here is a real, non-Time Lordy space-time vortex.

In fact, the idea of a space-time vortex can be traced to Einstein and his theory of relativity.

To discuss a vortex in space-time, it would be helpful to do a quick refresher on what space-time actually entails. The common analogy is to imagine the fabric of space-time as a two-dimensional rubber sheet (though space-time is actually four-dimensional). You drop a bowling ball into the middle of that sheet. What’s going to happen?

The rubber sheet will warp, with the bowling ball sinking down and creating an indentation in the sheet. This is analogous to what gravity does to space-time. It warps the four-dimensional fabric, creating indentations that allow for things like planetary orbits.

I wish I could also import the Feynman-related mouse-over text for this comic... alas.

You’ll remember, though, that our bowling ball is a stationary object. The indentation around it, therefore, is static. But the Earth rotates. Einstein’s theory said that this meant the indentation in the fabric of space-time surrounding the Earth should actually twist in a four-dimensional swirl around the Earth’s axis.

This has proven impossible to measure.

Until now.

Gravity Probe B (GPB) was a NASA experiment that spent years in meticulous study. And when I say meticulous, I mean…

Let’s start from the beginning.

In order to measure whether or not Earth’s space-time indentation is “twisted,” we needed to put a spinning gyroscope into Earth’s orbit. The axis of this gyroscope would be pointed at some distant star, using the star as a fixed reference point. If there wasn’t a vortex around Earth, that little gyroscope would remain pointed at that star forever. However, if there was a vortex, the direction of the gyroscope’s axis should drift over time. And by using this change in direction relative to our reference star, the twists of space-time could even be measured.

Of course, when I say “over time,” I’m talking about an axis change of about 0.041 arcseconds over a year. In order to even measure a change this small, NASA needed a precision of 0.0005 arcseconds. In order to accomplish that, they actually had to invent whole new technologies like a “drag free” satellite and a device to measure the spin of a gyro that never actually touches the gyro.

Oh, and speaking of those gyroscopes… The four 1.5 inch gyros in GPB are the most perfect spheres ever made by humans. They never vary from a perfect sphere by more than 40 atomic layers. Which is a necessity in this experiment- imperfect spheres would have spin axes that wobbled without the effects of a vortex.

And what were the results of GPB’s excursion in space?

“The space-time around Earth appears to be distorted just as general relativity predicts,” says Stanford University physicist Francis Everitt.

Which doesn’t seem like terribly big news, and certainly not worthy of Clifford Will’s comment that the GPB experiment, “will be written up in textbooks as one of the classic experiments in the history of physics.” …Right?

Any experimental verification of a scientific theory is important. And this verification of another aspect of one of the biggest theories in physics is definitely news. After all the time I spend prattling on about unverified potential scientific breakthroughs, isn’t it nice to see a theory actually being backed up by real evidence?


You know what? I just remembered “Goes Ding When There’s Stuff” was the former title of this blog…

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