Posted on 10/29/2002 10:42:41 AM PST by RightWhale
For some reason, FReepers have opinions on this.
Also because such trips should theoretically require an infinite input of energy.
Gravity waves travel at "c", i.e., light speed.
Some people, notably Tom Van Flandern and cohorts have advanced the position that gravity must propagate at infinite velocity. Their arguments are based on straightforward--and unfortunately incorrect--interpretations of classical dynamics. These arguments produce the conclusion that if gravity travelled at any finite velocity, the Solar System would be unstable and all of the planets would be accelerated out of the system by the "couple" (of forces) resulting from finite gravity propagation.
This position has been refuted by appeal to both special and general relativity. These theories show that gravity waves will radiate any "excess energy" and hence excess angular momentum, in precisely the correct amounts to keep the planets in their appointed orbits.
--Boris
If they can detect gravity waves at several separated sites around earth, and if gravity waves propagate at a finite speed, they should be able to see where the gravity wave came from in a general sense. If they detect the gravity wave at 4 sites not coplanar they should be able to narrow down the direction in spherical space. I don't know what angular resolution they expect.
The Enterprise discovered the existence of The Guardian time portal device mainly because of extremely intense gravity waves emmanating from a distant planet.
Another case of life imitating art.
This might be hard to believe, especially in the case of Harlan Ellison, but gravity scientists might see something entirely unsuspected. It could happen, and seems to happen often when new instruments of new design are used for the first time to examine things never seen before. Scientists live for this.
The next step is to arrange detectors and use the differences in signal at different ones to map out what waves you are receiving, where and when. But it is obviously much harder to get a good picture of a one-off, transient phenomenon that way, than a picture of a steady source.
Strong gravitational waves are easier to imagine getting produced in a transient rather than a continual source. Gravity tends to rapidly smush things into symmetric shapes that thereafter produce uniform gravity, and only changes in gravity produce gravitational waves. A gravity wave is a propogating "ripple" in space-time itself.
The wildcard is that we know that our theory of gravity probably leaves something out, in details. There is no consistent quantum theory of gravity. We only know our gravity theory checks out for large scale phenomenon. But wave -propagation- may depend in some respects on small scale phenomenon.
Mathematically, they integrate a bunch of infinitessimals without really knowing how the infinitessimal scale looks. For large scale and continuous enough properties, that has always worked so far. But supposedly sensitive gravity wave detectors have been around for a while now, and nobody has actually seen one with them, to date.
The detection schemes are getting better, and obviously as the article shows they have high hopes. We shall see, and that is always fun...
Basically it says something might be detected someday. I beleive the title is overstating the real situation a bit. Interesting though.
And that in itself is rather amazing to me; because doesn't a star collapse into a neutron star or a black hole at least once a day somewhere out there in the universe? Or two black holes merge, say?
Well, I'm looking forward to it, whatever "it" is. I'm sure there will be some surprises; there always are. :-)
Thanks, RW! Makes perfect sense.
I can explain the scheme of the new detector ideas, which are pretty clever. They are looking for tiny changes in space-time that propogate through the whole detector. They need a combination of a minute sensitivity with a large scale to gather a wide portion of a gradual effect. Something small would have the former, but not the latter, and thus fail. Something large would have the latter, not the former, and thus fail. They need to span as many orders of magnitude as possible between the small and the large.
Their solution is three spacecraft millions of miles apart pointing laser rangefinders at each other, able to detect changes in their distance apart down to a billioneth of a centimeter, based on changes in the interference of the laser light with split portions of itself. The scheme thus spans 24 orders of magnitude.
They need to use three in order to use a "base" pair to correct for changes in distance between each other pair due to other causes. (Otherwise put, with just two they would "drift" farther and closer due to random collisions with interstellar particles, etc, and so generate false signals).
More details on the scheme here -
http://lisa.jpl.nasa.gov/whatis.html
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