Reflected Gravitational Waves 329
WSOGMM sends in an arXiv blog post about reflecting gravity waves. The speculation is that reflected gravity could go some ways toward explaining the odd readings being returned by Gravity Probe B. "In the couple of weeks since he introduced the idea that superconducting sheets can reflect gravity waves, Raymond Chiao from the University of California, Merced, has been busy with a couple of buddies working out how big this effect is... Chiao and co. ask how big the effect of a gravitational wave on a thin superconducting sheet is compared to the effect on an ordinary conducting sheet. The answer? 42 orders of magnitude bigger."
Re:So... (Score:5, Informative)
Nine thousand and one
Re:So... (Score:5, Informative)
Re:Cue the Douglas Adams references! (Score:2, Informative)
Re:So... (Score:5, Informative)
Gravity is (from one point of view) just the curvature of spacetime. Its the large sagging indentation in the rubber sheet of spacetime that a massive body creates. Gravitational waves are fluctuations in this curvature, not gravity itself.
The distinction is somewhat akin to acceleration and velocity - consider a car (hurrah!) travelling with a very high velocity, which accelerates very slightly for a short period. If you could reflect the velocity, it would turn around instantly. Reflecting the acceleration however, causes no immediately obvious change. The car's still travelling bloody fast, in the same direction.
The gravitational waves caused by the earth's motion & rotation are so minute that gravity probe b's measurements, taken over a whole year, still took many months of processing before they could even be detected. Gravity waves are far too weak to have any practical purposes, and certainly not in "anti gravity".
Re:Possible correlation? (Score:5, Informative)
You know what's too bad? The anomalous effects in GPB have been explained, peer reviewed, etc, in the final report http://einstein.stanford.edu/content/final_report/GPB_Final_NASA_Report-020509-web.pdf [stanford.edu]
And, AFAIK, it was "expected" from build imperfections in the spheres, and has nothing to do with gravity waves. Maybe there's something hidden there, but it's probably a very small signal not the huge (compared to the target) wobbling due to the process described there.
Re:This is a-posteriori explanation of GP-B issue (Score:5, Informative)
http://arxiv.org/abs/0707.3806 [arxiv.org]
/Joss
Re:This is a-posteriori explanation of GP-B issue (Score:1, Informative)
And yet every gravity wave detector picks up nothing. I don't buy it.
Re:This is a-posteriori explanation of GP-B issue (Score:4, Informative)
Re:Gravity wave detectors. (Score:2, Informative)
Re:"Indentation in rubber sheet" (Score:5, Informative)
"Indentation in rubber sheet" I never got that, nor did my physics teacher (who started out as a real physicist.) If we imagine gravity as a deflection in a rubber sheet, why does the object "fall" into it?
The answer is, it doesn't fall onto it. It's called an analogy.
You are thinking of this rubber sheet as existing in our 3 dimensions, when it would better work as a dimension of its own.
If analogies don't work for you, then the technical answer is the objects mass causes the indentation or the 'falling into it' as you say. This mass causes a warp in spacetime, and the warping itself is what we SEE as gravity, not what gravity is however, since that is a force of nature that results from mass (or so it seems) which we can't directly observe yet, we can only observe its effect on things with mass.
Now, WHY mass causes gravity (or the indentation on the sheet, or for the body to 'fall' into said sheet), to give us an effect we can see, we don't know yet. Hopefully this discovery can help us get closer to that understanding.
But the biggest mistake is to think of the object 'falling into' a sheet, since that description itself uses gravity as both the description of the event, and the event itself. They are not at all the same, so there is no magic 2nd gravity field. That 2nd field you are thinking of results 100% from the poor analogy and of course doesn't exist, it just helps some people wrap their mind around the effect in a visual way.
Basically, the falling on a sheet visual seems more helpful to right-brained people, while the maths itself is more helpful to the left brained people.
Neither representation (visual or the maths in the theory) is complete or correct at this point, so both are bound to cause confusion if you are looking for the end-answer.
Re:So... (Score:1, Informative)
I understand the difference (the wave is simply a fluctuation of the medium), but are we really sure that gravity is only a curvature? the speed of gravity is not infinite, (IANAP, but from what I have read from various articles) it is the speed of light, so could it be that gravity is a sort of a particle, undetected so far, with properties similar to a photon? i.e. no rest mass, with only kinetic energy.
That is pretty much what it looks like (humanity still doesn't know for sure yet), and what a lot of scientists assume is the case.
It's also possible however that gravity itself is not bound by the speed of light at all, however the information resulting from the effect of gravity Would be limited to the speed of light.
If that was the case, while gravity wouldn't fit nicely in with our other standard model particles, it would appear to function at the speed of light since that is as fast as gravities effects can reach us.
Re:Truly Amazing (Score:2, Informative)
This theory has implications that could revolutionize scientific thought across numerous fields. It may even provide some direction for the unified theory people to look in that isn't horribly complex and require inventing 1700 dimensions to make the math work.
Nassim Haramein has put forth a unified field theory which doesn't rely on made up science: http://theresonanceproject.org/ [theresonanceproject.org]
Re:So... (Score:2, Informative)
Yes, as with all classical field theories, when you quantize it you get a gauge boson. In this case it's called the graviton and current (incomplete) quantum gravity formulations have it pop out as spin-2 and massless. Remember kits fields are classical, gauge bosons are quantum mechanical.
Re:Is arxiv actually legit? (Score:1, Informative)
Its not peer reviewed. Salt as required. I'm using a 40kg bag for this one.
Re:Is arxiv actually legit? (Score:5, Informative)
It's legitimate, but it's also not peer-reviewed.
The cells on the grid. (Score:5, Informative)
Disclaimer : IANAP, IAAMD. And we doctors aren't very renown for our skill in physics...
the analogy requires it to change path so as to lose potential energy and gain kinetic energy as a result of the perpendicular field. So the thought experiment seems to gravity as a deflected rubber sheet into which things fall because of another gravity in an external dimension. To make things worse, the rubber sheet is effectively 2D in a 3D universe.
Well, that's a way to interpret the rubber sheet metaphor and as you point out, it requires a sheet in a higher dimensional space and an additional perpendicular force. As it is enough to have a mental image of beads making turns on a sheet, it seem to be enough when taught in school.
From what I understand, the importance isn't the higher dimensional shape, it's the shapes of the cells on the grid that represent the rubber sheet on the illustration.
Physical bodies aren't bead rolling *on* the sheet. The sheet is the space-time itself. Physical bodies are travelling inside the sheet, crossing cells of the grid.
In the absence of that field the object would presumably travel through the space time deflection with unchanged velocity
And that's what happens. An object is simply going straight ahead, moving from one grid's cell to the next one.
But the 2D universe grid isn't regular as on a flat sheet. Big masses "wrap" the space around them and cells have strange deformed shapes.
It's just handy to paint those deformed cells as a bump.
And the object is simply following the same path as before, but as the cells it "crosses" are weirdly shaped, the point where the object leaves one cell isn't in line with the points where the object left the previous cells.
It follows a straight path, but as the terrain isn't even, the net result is a curve.
In our 3D universe, what form does the curvature take?
It's still a grid. It's now a 3D grid. Composed of small cubic cells. Except that, around big masses, the cells all of sudden aren't perfectly cubic anymore.
Thus if an object was following a subjectively straight path from on cell to the next, seen from the "outside" the path will be curved, because the cells have non-cubic shapes.
I've actually seen one exposition (for 100th anniversary of Einstein's annus mirrabilis) where it was indeed shown that way.
This model is nice because it helps understanding why massless thing such as light still recieve an effect (gravitational lensing) from big masses :
- on the high dimensional rubber sheet it won't work as they won be affected by the perpendicular "extra-gravity".
- but on the grid, they just run straight ahead in the cells and the cells happen to have been shaped into a curve. Thus "seen from far away", the resulting path is a curve. Massless light particle just happen not to make any curve around them on their own.
Re:We now know the question to the answer... (Score:3, Informative)
I can't tell if you are somehow trying to be funny or not. Either way, epic fail.
Please hand in your geek card on your way out.
Re:We now know the question to the answer... (Score:2, Informative)
Re:"Indentation in rubber sheet" (Score:1, Informative)
I'm pretty sure we can observe the effects of gravity on things without mass as well.