Skip to comments.Gravity waves analysis opens 'completely new sense'
Posted on 10/29/2002 10:42:41 AM PST by RightWhale
Gravity waves analysis opens 'completely new sense'
Washington University in St. Louis
St. Louis, MO. -- Sometime within the next two years, researchers will detect the first signals of gravity waves -- those weak blips from the far edges of the universe passing through our bodies every second. Predicted by Einstein's theory of general relativity, gravity waves are expected to reveal, ultimately, previously unattainable mysteries of the universe.
Wai-Mo Suen, Ph.D., professor of physics at Washington University in St. Louis is collaborating with researchers nationwide to develop waveform templates to comprehend the signals to be analyzed. In this manner, researchers will be able to determine what the data represent -- a neutron star collapsing, for instance, or black holes colliding.
"In the past, whenever we expanded our band width to a different wavelength region of electromagnetic waves, we found a very different universe," said Suen. "But now we have a completely new kind of wave. It's like we have been used to experiencing the world with our eyes and ears and now we are opening up a completely new sense."
Suen discussed the observational and theoretical efforts behind this new branch of astronomy at the 40th annual New Horizons in Science Briefing, Oct. 27, 2002, at Washington University in St. Louis. The gathering of national and international science writers is a function of the Council for the Advancement of Science Writing.
Gravity waves will provide information about our universe that is either difficult or impossible to obtain by traditional means. Our present understanding of the cosmos is based on the observations of electromagnetic radiation, emitted by individual electrons, atoms, or molecules, and are easily absorbed, scattered, and dispersed. Gravitational waves are produced by the coherent bulk motion of matter, traveling nearly unscathed through space and time, and carrying the information of the strong field space-time regions where they were originally generated, be it the birth of a black hole or the universe as a whole.
This new branch of astronomy was born this year. The Laser Interferometer Gravitational Wave Observatory (LIGO) at Livingston, Louisiana, was on air for the first time last March. LIGO, together with its European counterparts, VIRGO and GEO600, and the outer-space gravitational wave observatories, LISA and LAGOS, will open in the next few years a completely new window to the universe.
Supercomputer runs Einstein equation to get templates
Suen and his collaborators are using supercomputing power from the National Center for Supercomputing Applications at the University of Illinois, Urbana-Champaign, to do numerical simulations of Einstein's equations to simulate what happens when, say, a neutron star plunges into a black hole. From these simulations, they get waveform templates. The templates can be superimposed on actual gravity wave signals to see if the signal has coincidences with the waveform.
"When we get a signal, we want to know what is generating that signal," Suen explained. "To determine that, we do a numerical simulation of a system, perhaps a neutron star collapsing, in a certain configuration, get the waveform and compare it to what we observe. If it's not a match, we change the configuration a little bit, do the comparison again and repeat the process until we can identify which configuration is responsible for the signal that we observe."
Suen said that intrigue about gravity waves is sky-high in the astronomy community.
"Think of it: Gravity waves come to us from the edge of the universe, from the beginning of time, unchanged," he said. "They carry completely different information than electromagnetic waves. Perhaps the most exciting thing about them is that we may well not know what it is we're going to observe. We think black holes, for sure. But who knows what else we might find?"
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.
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 -
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