Is the Earth in a Vortex of Space-Time?

da6d writes "Apparently, we'll soon know for sure.... NASA has announced in an article that 'A NASA/Stanford physics experiment called Gravity Probe B (GP-B) recently finished a year of gathering science data in Earth orbit. The results, which will take another year to analyze, should reveal the shape of space-time around Earth--and, possibly, the vortex.'" More from the article: "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 to check."

Comments

Neat

[Starker_Kull]

I think it's interesting - general relativity makes some very hard to verify but specific predictions. Many competing theories to it over the last 50 years have made predicitions that have, one by one, turned out to be false. Rotational frame dragging is (I think?) one of the last unverified ones. According to Newtonian gravitation & mechanics, the rotation or non-rotation of the earth should not affect an orbiting satellite a whit (ignoring "complications" like variable atmospheric drag based on rotation rate, different shape of earth at different rotation rates, etc.), or put more abstractly, the rotation of an axially symmetric mass distribution should not have anything to do with its gravitational field. General relatitivity does not agree with Newtonian mechanics here, which brings up yet another interesting question:

Is there a difference between rotating reference frames and non-rotating reference frames because of the universe of matter around them, or is it self-generated? In other words, if we "removed" the entire universe except the rotating Earth, would rotation still have meaning? Could we still do an experiment and detect its rotation, or is that an artifact of the universe of matter around it that would vanish when it did? As far as I understand general relativity (and IANAP), it does not make a hypothesis one way or the other. Is the question meta-physical? Or is there some clever way to set up an experiment to actually tell?

Sigh - sometimes, I wish I was a physicist!

Re:uhh

[KylePflug]

Seriously, though. What the hell does "stationary" mean in space?

Nothing, that's what. If anything's stationary. it's the observer. So yes, Earth is as stationary as a planet can be, and the universe revolves in a really complicated way around us.

Re:It's all relative

[meringuoid]

I see they found that universal frame of reference they were looking for.

Doesn't really apply to rotation.

If you're sealed inside a spaceship moving at constant velocity and cannot refer to the outside in any experiment, you have no way to determine what its velocity might be. There's no physical difference between 'stationary' and '0.999c', until you interact with something outside. Even then, you can still declare that you're stationary and that it is moving and the physics works out the same.

If, however, you're sealed inside a spaceship rotating with constant angular velocity, that's quite another matter. You'll know about the rotation, either by reference to gyroscopes if it's spinning very slowly, or by the fact that you seem to be stuck to the wall if it's spinning very quickly...