Is the Earth in a Vortex of Space-Time?

Is the Earth in a Vortex of Space-Time?


Re:uhh
(Score:5, Insightful)
by LionMan (18384) Alter Relationship on Saturday November 19, @05:00AM (#14069848)
(http://l.caltech.edu/ | Last Journal: Sunday December 09, @05:54PM)
What is meant is the following:
One of the exact solutions to the Einstein field equations is a decent assumption for the Earth's (or anything approximately spherical which is not moving relativistically) gravitational field. The curvature of space-time is greater the closer to the center of the massive body. A light ray travelling some distance from the massive body will be deflected from a "straight line" (which is hard to define in curved space).
If you are taking the view that you start rotating the rest of the universe around us, then it is equivalent to having your coordinate system spin around the massive body (well, there is nothing besides the massive body in the universe I am imagining). Physically, light will follow the same path as it did before, since all you have done is redefine the coordinate system, which does not change physics!
Now instead, consider spinning the Earth, instead of the coordinate system. The matter making up the earth now has more energy-momentum (the magnitude of which is a physical quantity which can be measured independent of reference frame, if your frame is freely-falling). Energy-momentum is what causes space-time to curve, so a light ray travelling the same distance from the earth will be deflected by a larger amount, since space will be more curved.
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-Leo
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Re:uhh
(Score:5, Funny)
by ObsessiveMathsFreak (773371) Alter Relationship on Saturday November 19, @07:52AM (#14070199)
(Last Journal: Wednesday March 30, @10:38AM)
No, it's flat because it's stationery, duh!

No. The Earth is too complex to have just ended up flat with the sun spinning around it. A higher power must have had a guiding hand. So we should instruct kids on the Intelligent Flat Earth Design Theory over the Newtonian-Einstienian theories of gravity, which are after all, completely unprovable.

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May the Maths Be with you!
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Re:It's all relative
(Score:5, Informative)
by Starker_Kull (896770) Alter Relationship on Saturday November 19, @01:33AM (#14069438)
Actually, it doesn't have to do with universal reference frames in the sense you mean. In Newtonian mechanics, there is a limited set of preferred reference frames within which Newtonian physics is valid - the inertial reference frames, or, casually speaking, the ones moving at a constant velocity - none of which is a "Universal" or better reference frame than any other. But even in Einstein's model, which incorporates accelerated reference frames in the same framework as inertial, there are still "preferred" reference frames; non-rotating ones. ROTATING reference frames lead to unambigious differences, both in Newtonian and Einsteinian models. While sloppily written, the article means that it is the ROTATION of the Earth's reference frame that leads to different predicted results, not the TRANSLATIONAL motion. Not all reference frames are created equal.
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Re:It's all relative
(Score:5, Interesting)
by meringuoid (568297) Alter Relationship on Saturday November 19, @04:41AM (#14069796)
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...
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Real Daleks don't climb stairs - they level the building.
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Whoa!
(Score:5, Funny)
by memeplex (910698) Alter Relationship on Saturday November 19, @01:21AM (#14069416)
My Cortex is in Gore-Tex contemplating the Vortex. I'm getting a complex! I need a cold compress! I need to undress. I'm relatively impressed. Er... where's Eminem when you need him? Am I off-topic here?
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This statement is false.
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Purple Nurple Probe
(Score:5, Funny)
by Helpadingoatemybaby (629248) Alter Relationship on Saturday November 19, @01:35AM (#14069445)
So if I'm to understand this correctly, the spin of the Earth twists the nipples of spacetime?

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The baby's fine -- please stop sending business cards.
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The engineering story

(Score:5, Informative)

by dracken (453199) on Saturday November 19, @01:40AM (#14069462)
(http://slashdot.org/)

Behind the Gravity Probe B is here [stanford.edu] and here [edn.com]. It is a fascinating read, esp. about the gyroscopes.

"The four gyro rotors are made of fused quartz, fabricated to an extreme level of material homogeneity and then ground to the near-absolute sphericity (Figure 1). The spheres are round to within 40 atomic layers, which is proportionally equivalent to an Earth-sized sphere with surface height variations of only 16 feet...."

"It's one thing to have a virtually perfect gyro rotor, but that alone does not provide the necessary performance for this experiment......The electric fields center the rotors to a few millionths of an inch. They did not perform the spinning up electrically, however. Instead, they directed a precise stream of helium gas, traveling at nearly Mach 1, at the rotors. It takes about half an hour for the rotor to reach full speed, and it loses less than 1% of this speed over 1000 years in the super-vacuum of the cavity."

T
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Neat
(Score:5, Interesting)
by Starker_Kull (896770) Alter Relationship on Saturday November 19, @01:52AM (#14069488)
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!