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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."
Honestly, this is a cool thing, so i don't mean to demean it. But it's the sort of thing only a geek with more than a passing familarity of physics would get excited for.
I'm sure they thought that 75 years ago about Quantum Theory. This is a relatively big deal even if it isn't sexy. I mean, we have to test these things. How many chances do we get to observe major space-time dilation? I mean, minor stuff with satellites, right? But it's hard to get tests of theories involving planets.
So, your problem with the story is that it's too geeky? Which part of "News for Nerds" is opaque to you?
f -External-Forces Greek chap, but humanity has learned the lack of wisdom of that approach several times over.
Proving things that are suspected to be true is the meat-and-bones of science. After all, they might turn out to not be true. Idle speculation may have been good enough for Aristotle the Things-Will-Stop-Moving-Without-the-Application-o
My other body is also not wearing any.
Only once the data is analyzed will the vortex phenomona considered proven (or disproven, obviously).
Not so obvious. The word 'inconclusive' comes to mind.
Mod down people who tell people how to mod in their sigs
It seems to me that confirming (or refuting) a key prediction of relativity is a moderately good story, at least.
And the brethren went away edified.
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.
-Leo
Curiously enough Rudolf Steiner once stated that the laws of physics aren't the same everywhere. According to him they gradually change the further you get away from a certain point in space. He said something like:"Very much like the gravity influence of an object declines the further away you get from it, so do the laws of physics change."
This could be the proof of his statement.
We suffer more in our imagination than in reality. - Seneca
"Energy-momentum is what causes space-time to curve,..."
Just for clarification: So, gravity by itself doesn't cause space-time to curve?
A couple of other things:
1) Since the Earth is traveling so fast around the Sun itself, the spin of the Earth isn't like a basketball on Meadowlark Lemon's finger, as one might imagine it spinning on it's own axis, but is traveling in a linear fashion as it goes around the Sun; meaning, no point on the Earth is ever, relative to Space itself (and assuming Space has an exact center, if not, then, at least, the Milkyway having an exact center), to occupy the same 'space' twice.
Assuming the Milkyway is moving, as a galaxy, in some direction, perhaps even rotating around something, and that the Sun is assumed to be rotating around the center of the Milkyway, and the the Earth is rotating around the Sun... Doesn't that really mean that "spinning" is a perceived phenomena and not a reality? Instead, since the Milkyway (presumably) is traveling relative to Space itself, and the Sun is traveling around the center of the Milkyway, and then the Earth around the Sun, the best we can come to spinning is some form of zig-zagging through "Absolute Space" (assuming such a thing exists, if not then we can define it as "the center of all Space"). And,
2) If a ray of light is traveling through Space and is then deflected by an object, does the light ray, in any way, know that it has been deflected? If it were us and we were looking forward, we would 'see' our destination (who really knows what we would 'see' while traveling the speed of light) and light traveling from that destination would have also been deflected by an object that we, as a ray of light, would also be deflected by. Thus, wouldn't we seem to continue in the same path we were traveling in in the first place? Would a ray of light even notice it was being deflected?
So, finally, I think spinning is a poor choice of words for describing gravitational fields since it precludes the assumption that either the Sun is stationary relative to 'all Space' or 'the center of all Space' or the Earth is stationary. But, we know the answer to the later. Or, better yet, that we have sufficient knowledge about the Universe to know that our frame of reference, from Earth and this Solar System, is enough to preclude that we know that which is stationary. Which we can't know that because we likely do not really know the rotational period of the Sun about the Milkyway nor the movement of the Milkyway itself.
No it won't. GR is derived from several axioms - in particular, the assumption that the laws of physics are the same everywhere that they are meaningful. If G Probe B get expected results, then it would back up this assumption, and do disprove Steiner.