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What's up with gravity wave detection?
I found an old PBS documentary on VHS from 1991 called _The Astronomers_
at the local public library. One of the programs in the series was "Waves of the Future" about gravitational waves. In the program Kip Thorne was shown making a bet with one of his collaborators on gravity wave theory that these waves would positively be detected by 2000. I found this both humorous and a touch sad. The program described some of the early planning for LIGO (Laser Interferometer Gravitational Wave Observatory). Curious, I went to the LIGO web site to see what was going on. I found nothing of substance there -- just a lot of slick PR. So my question is, what are the prospects that gravity waves will be detected anytime soon? Is LIGO still having technical problems or what? It is now 2004, after all. Other detection labs are being built around the world. Are these labs going to have any better luck? Also, what are people's opinions about gravity waves? Is it possible that these are a scientific dead end like the decay of the proton turned out to be? If gravity waves are never detected, what are the implications for the general theory of relativity? |
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dkomo wrote:
I found an old PBS documentary on VHS from 1991 called _The Astronomers_ at the local public library. One of the programs in the series was "Waves of the Future" about gravitational waves. In the program Kip Thorne was shown making a bet with one of his collaborators on gravity wave theory that these waves would positively be detected by 2000. I found this both humorous and a touch sad. The program described some of the early planning for LIGO (Laser Interferometer Gravitational Wave Observatory). Curious, I went to the LIGO web site to see what was going on. I found nothing of substance there -- just a lot of slick PR. So my question is, what are the prospects that gravity waves will be detected anytime soon? Is LIGO still having technical problems or what? It is now 2004, after all. Other detection labs are being built around the world. Are these labs going to have any better luck? Most likely LIGO will detect gravitational waves. See: http://www.ligo.caltech.edu/ http:/www.edu-observatory.org/eo/cosmology.html PHYSICS NEWS UPDATE The American Institute of Physics Bulletin of Physics News Number 632 April 9, 2003 by Phillip F. Schewe, Ben Stein, and James Riordon FIRST LIGO SCIENTIFIC RESULTS. With two controlling partners, MIT and Caltech, and two branch offices (two completely independent detectors) located in Washington State and Louisiana, the Laser Interferometer Gravitational-Wave Observatory (LIGO) is essentially a giant strain gauge. In the LIGO setup laser light reflects repeatedly in each of two perpendicularly oriented 4-km-long pipes. A passing gravity wave will distort the local spacetime, stretching very slightly one of the paths while shrinking the other, causing the interference pattern of the two merging laser light beams to shift in a characteristic way. LIGO does not measure static gravitational fields, such as those from the sun or the Earth itself. Rather it strives to see ripples in spacetime radiated by such events as the inspiral of two neutron stars toward each other, a phenomenon which would typically produce a strain in the LIGO apparatus as large as one part in 10^20. That is, a passing gravity wave is expected to change the distance between mirrors some 4 km apart by about 10^-18 meters, a displacement 1000 times smaller than a proton. Such a measurement represents a physics and engineering feat of great delicacy. But at long last the LIGO team has prepared its instrument and at this week's APS meeting, reported its first official results from the initial "science" run conducted over 17 days in September 2002. In this first run no gravitational wave events were observed, but palpable knowledge was gained as to what the sky should look like when viewed in the form of gravity waves. So great is LIGO's sensitivity that it has been able to set the best upper limit on the output of gravitational waves from three of the four prime source categories. These four expected waveforms are as follows: bursts from sources such as supernovas or gamma bursters; chirps from inspiraling objects such as coalescing binary stars; periodic signals, perhaps from sources like spherically asymmetric pulsars; and a stochastic background source arising from gravity waves originating from the big bang itself. LIGO deputy director Gary Sanders (Caltech, ) said that in three of these four categories, had set new upper limits on the rate at which gravitational waves were being produced. In the coalescing binary category, for instance, LIGO has established an upper limit of 164 per year from the Milky Way, a factor of 26 better than the previous limit. Erik Katsavounidis (MIT, ) said that LIGO could establish an upper limit on periodic signals from bright pulsars with a sensitivity of about 10^-22. Sheila Rowan (Stanford Univ and Univ Glasgow) spoke of future operations at LIGO. First of all, the second scientific run currently underway will be some ten times more sensitive than the first run, the one being reported at the meeting. If in the first science run LIGO was essentially sensitive to gravity waves from the whole of the Milky Way, then in the second science run (conducted Feb-Apr 2003), featuring a ten-times improvement in sensitivity, the region of space patrolled would effectively reach out to about 15 million light years, a realm that includes the nearby Andromeda galaxy. (For more information about LIGO and a complete collaboration list, see www.ligo.caltech.edu ) In its search for gravity waves, LIGO (which with about 440 scientists is as big as the large particle physics experiments underway at accelerators) is also collaborating with other interferometer devices such as GEO (in Germany, www.geo600.uni-hannover.de ) and TAMA (Japan). |
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"dkomo" wrote in message news I found an old PBS documentary on VHS from 1991 called _The Astronomers_ at the local public library. One of the programs in the series was "Waves of the Future" about gravitational waves. In the program Kip Thorne was shown making a bet with one of his collaborators on gravity wave theory that these waves would positively be detected by 2000. I found this both humorous and a touch sad. The program described some of the early planning for LIGO (Laser Interferometer Gravitational Wave Observatory). Curious, I went to the LIGO web site to see what was going on. I found nothing of substance there -- just a lot of slick PR. So my question is, what are the prospects that gravity waves will be detected anytime soon? Is LIGO still having technical problems or what? It is now 2004, after all. Other detection labs are being built around the world. Are these labs going to have any better luck? Yep. And the AI folks had predicted machine intelligence by now, too. We do have Fritz8... Also, what are people's opinions about gravity waves? Is it possible that these are a scientific dead end like the decay of the proton turned out to be? If gravity waves are never detected, what are the implications for the general theory of relativity? The implications of conservation of baryon number as you allude to when you say proton decay detection represents a dead end has not yet been truly absorbed in the greater schema of thought. Something very wrong is occuring and we are just now obtaining proof that the last 30 years of thought is wrong. The first run of gravity wave detection has determined a baseline for event detection that can only get larger (read worse) the longer they run the interferometers..... if no gravity waves are detected out to theoretical limits - as has happened with proton decay- then there will be none but the blind who will say our interpretation of the universe is dead wrong and is wrong in such a way that theoreticians will not be able to fix, or modify, current theory to make it even seem to work on a bad day. There are already rumblings coming from unnamed sources that the first run should have found *something*.... believe me, there are many careers at stake on the result of this project, as well as many fingers crossed... We may even have to rip the "Big Black Book" in half and throw it, along with substantial portions of geometrodynamics in the trash can on this one if it should go wrong. Greysky www.allocations.cc Learn how to build FTL radio. |
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Most likely LIGO will detect gravitational waves.
See: http://www.ligo.caltech.edu/ http:/www.edu-observatory.org/eo/cosmology.html It is very interesting how institutions would spend millions of dollars trying to detect something that has not been thoroughly understood. As I read in Scientific American a year or two ago, LIGO was chosen to be built in places where noise generated by human activities are at near maximum. This means LIGO's detection of gravitational waves is subjected to broad and creative interpretations of data which can easily be explained by something else. |
#5
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"dkomo" wrote in message news | I found an old PBS documentary on VHS from 1991 called _The Astronomers_ | at the local public library. One of the programs in the series was | "Waves of the Future" about gravitational waves. In the program Kip | Thorne was shown making a bet with one of his collaborators on gravity | wave theory that these waves would positively be detected by 2000. | | I found this both humorous and a touch sad. The program described some | of the early planning for LIGO (Laser Interferometer Gravitational Wave | Observatory). Curious, I went to the LIGO web site to see what was | going on. I found nothing of substance there -- just a lot of slick PR. | | So my question is, what are the prospects that gravity waves will be | detected anytime soon? Why not consider the biggest "wave" or pulse in our galaxy imaginable? That would correspond to ALL the mass of a star entirely disappearing, as could just conceivably happen if the star were converted to entirely to energy in one enormous supernova. We'd see a brilliant flash of EM radiation, brighter than daylight, but the entire gravity would be gone. This would correspond to a negative going pulse radiating outward, which for the sake of argument we'll allow to be at velocity c (although we have no evidence of that), and ask if we could detect it. Next, we ask if this cataclysm were to occur at the nearest star (other than the sun, of course), since that would provide the strongest negative pulse obtainable to any instrument capable of detecting it. So... how much gravity do we at present detect from Proxima Centauri that would disappear? In reality, even a supernova leaves a considerable remnant, so at best we could expect 1/10th of a full pulse. There is a gravity 'wave' we can detect. As our planet turns upon its axis, it passes through the lunar gravity and causes the tide to rise and fall, which is clearly detectable as a sinusoidal wave. Take the moon away, and this would vanish. Also, a lesser tide is produced by our own sun, and this is superimposed on the oceans. We have spring and neap tides depending on the relative positions of the moon and sun with respect to the earth. Take the sun away and this too would vanish, but so would we. The highest tides we know of are in the Bay of Fundy, "Every 12 hours 25 minutes 100 billion tonnes of water surges out of the NE Atlantic and slams into a 70 mile wide funnel between Nova Scotia and New Brunswick. When it reaches this point, 100 miles in, the channel narrows and divides into two narrow prongs. The bottom one, Minas Channel, is only 10-15 miles wide. All that lunar-driven water has nowhere to go but up. Near Wolfville in the Minas Channel high tide is about 16 metres above low tide, the highest on earth." - http://www.tvnature.com/obh/bald-eagle.htm and that channel tells we could artificially duplicate our own miniature Bay of Fundy anywhere in the world, passing the water through a narrow tube and measure it's velocity and volume as the Earth turns with considerable precision, since we can measure the height of the water in the tube with great precision using the wavelength of light. So... how much does the tide rise and fall as a result of Proxima Centauri being nearby? I'll leave you to do the trigonometry of Earth, Moon, Sun and Proxima Centauri and the numbers, you'll have more luck detecting the pull of Jupiter, Mars, Venus and Saturn, and you'll be looking for the effect of something far less than the miniscule tug of Phobos or Deimos. I'm going to say LIGO was doomed to failure at the outset, and it will not detect a darned thing. That is not the same as saying there is nothing to detect, just that the effect is so miniscule it cannot be measured. The inverse square law totally precludes any possiblity of detecting anything with a source of gravity as far away as Proxima Centauri. So the answer to your question is... zilch. Androcles. Is LIGO still having technical problems or what? | It is now 2004, after all. Other detection labs are being built around | the world. Are these labs going to have any better luck? | | Also, what are people's opinions about gravity waves? Is it possible | that these are a scientific dead end like the decay of the proton turned | out to be? If gravity waves are never detected, what are the | implications for the general theory of relativity? | | | |
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On Mon, 16 Aug 2004 07:05:56 GMT, "Androcles"
wrote: "dkomo" wrote in message news | I found an old PBS documentary on VHS from 1991 called _The Astronomers_ | at the local public library. One of the programs in the series was | "Waves of the Future" about gravitational waves. In the program Kip | Thorne was shown making a bet with one of his collaborators on gravity | wave theory that these waves would positively be detected by 2000. | | I found this both humorous and a touch sad. The program described some | of the early planning for LIGO (Laser Interferometer Gravitational Wave | Observatory). Curious, I went to the LIGO web site to see what was | going on. I found nothing of substance there -- just a lot of slick PR. | | So my question is, what are the prospects that gravity waves will be | detected anytime soon? Why not consider the biggest "wave" or pulse in our galaxy imaginable? That would correspond to ALL the mass of a star entirely disappearing, as could just conceivably happen if the star were converted to entirely to energy in one enormous supernova. We'd see a brilliant flash of EM radiation, brighter than daylight, but the entire gravity would be gone. [snip] No, EM radiation gravitates too. Do you know what the stress-energy tensor is? How about the theoretical construct called a geon? |
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"Australopithecus Afarensis" wrote in message news:zQXTc.100010$sh.86278@fed1read06...
Most likely LIGO will detect gravitational waves. See: http://www.ligo.caltech.edu/ http:/www.edu-observatory.org/eo/cosmology.html It is very interesting how institutions would spend millions of dollars trying to detect something that has not been thoroughly understood. The theory of gravitational radiation has been well established for several decades. Details can usually be found in any GR textbook. Weinberg's book is probably the best in this regard. As I read in Scientific American a year or two ago, LIGO was chosen to be built in places where noise generated by human activities are at near maximum. This means LIGO's detection of gravitational waves is subjected to broad and creative interpretations of data which can easily be explained by something else. Why do you think they built two of them in entirely separate locations? |
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"d" == dkomo writes:
d I found an old PBS documentary on VHS from 1991 called _The d Astronomers_ at the local public library. One of the programs in d the series was "Waves of the Future" about gravitational waves. In d the program Kip Thorne was shown making a bet with one of his d collaborators on gravity wave theory that these waves would d positively be detected by 2000. d I found this both humorous and a touch sad. The program described d some of the early planning for LIGO (Laser Interferometer d Gravitational Wave Observatory). Curious, I went to the LIGO web d site to see what was going on. I found nothing of substance there d -- just a lot of slick PR. You don't define "slick PR" but I see links for "Observational Results," "Publications," "Research Bulletin Boards," "LIGO Email Archives," .... At least some of these strike me as more than PR. Of course, you've hit upon a problem not unique to LIGO. If the Web site isn't slick and flashy, then it's derided as boring and useless. If it is slick and flashy, then it's derided as just PR. d So my question is, what are the prospects that gravity waves will d be detected anytime soon? Is LIGO still having technical problems d or what? It is now 2004, after all. Other detection labs are being d built around the world. Are these labs going to have any better d luck? There are a host of other gravitational wave laboratories around the world. The LIGO site has links to VIRGO, GEO600, TAMA300, ACIGA, LISA, and IGEC. As for prospects of detection, that's probably a good question to post on sci.astro.research. In part that depends upon how kind Nature is to us. I think if a supernova went off in our part of the Galaxy tomorrow, LIGO would (or should!) detect it. Right now, of course, it has not detected anything, so the best that one can do is say that the density of fill in your favorite gravitational wave source is no larger than some upper limit. Some will, of course, decry this as adjusting the theory. However, getting a handle on potential gravitational wave sources is tough. For instance, just last year the binary pulsar PSR J0737-3019 was discovered. It's (probably) less than 2000 light years away from us and yet had gone undetected for the first 35 years of pulsar searching. Binary neutron star systems are thought to be a prime candidate for gravitational wave sources as they spiral together. Finding a binary neutron star system so close to us immediately boosted the expected signal strength for gravitational waves from binary neutron star systems. d Also, what are people's opinions about gravity waves? Is it d possible that these are a scientific dead end like the decay of the d proton turned out to be? If gravity waves are never detected, what d are the implications for the general theory of relativity? What about PSR B1913+16? This is a binary neutron star system in which one of the neutron stars is seen as a pulsar. The orbit is decaying at a rate exactly consistent with that predicted by general relativity, if gravitational waves are carrying away energy. In a few years (if not sooner), the orbital decay of PSR J0737-3019 should also be measurable. (PSR J0737-3019 is a much tighter system, a 2.4-hr orbit, as compared to PSR B1913+16, an 8-hr orbit, so the rate of orbital decay should be higher.) The decay of the orbit of PSR B1913+16 is only an indirect measurement, of course, but it is a powerful indicator that gravitational waves do exist. -- Lt. Lazio, HTML police | e-mail: No means no, stop rape. | http://patriot.net/%7Ejlazio/ sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html |
#10
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Dear Australopithecus Afarensis:
"Australopithecus Afarensis" wrote in message news:zQXTc.100010$sh.86278@fed1read06... Most likely LIGO will detect gravitational waves. See: http://www.ligo.caltech.edu/ http:/www.edu-observatory.org/eo/cosmology.html It is very interesting how institutions would spend millions of dollars trying to detect something that has not been thoroughly understood. Like AIDS? Money is spent to find out about things that are not yet known. That is what research is for. That is what theories are about, predict and test. David A. Smith |
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