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Sure, the planets would have a big gravity wave signal, in the same
way that jupiter appears brighter than P Centauri in the night sky. But surely LIGO can tell what direction a wave is coming from - that's the whole point, isn't it? Dave "Androcles" wrote in message ... ....snip... 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. |
#12
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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? 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? For the LIGO weekly report, see: http://www.ligo.caltech.edu/~weekly/weekly.htm For a "LIGO-in_space", see: http://lisa.nasa.gov/ For the Louisiana LIGO as seen from space, see: http://www.terraserver-usa.com/image...=1056&z=15&w=1 -- Clive Tooth http://www.clivetooth.dk |
#13
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"Dave Houseman" wrote in message om... | Sure, the planets would have a big gravity wave signal, in the same | way that jupiter appears brighter than P Centauri in the night sky. No comparison whatosever. Jupiter is reflecting sunlight. You cannot observe any planets in orbit about Proxima Centauri. You are comparing soldier ants to eleph ants. | But surely LIGO can tell what direction a wave is coming from - that's | the whole point, isn't it? | Dave Can it? I don't think so. As dkomo said, all he's seen is PR hype, not results. Androcles. | "Androcles" wrote in message ... | ...snip... | 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. | |
#14
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On Sun, 15 Aug 2004 23:58:58 -0800, Eric Gisse
wrote: No, EM radiation gravitates too. No, that's just an error in the practice of current models -- which themselves don't require such gravitation, which has never been observed. Note this is a separate issue from travelling along null geodesics. Do you know what the stress-energy tensor is? How about the theoretical construct called a geon? Not relevant to observation. |
#15
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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. 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. They will detect nothing but thermal noise and geo vibrations. Signal to noise ratio will be too low to make anything out of that. Any signal processing applied will open the room to subjectivity. Another one bites the dust. Gravity will always stay a mystery. Mike |
#16
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In sci.astro Eric Flesch wrote:
On Sun, 15 Aug 2004 23:58:58 -0800, Eric Gisse wrote: No, EM radiation gravitates too. No, that's just an error in the practice of current models -- which themselves don't require such gravitation Certainly they do. In general relativity, the right-hand side of the field equations must include the stress-energy tensor for all matter. Otherwise, the vanishing covariant divergence of the left-hand side is inconsistent. More generally, electromagnetic radiation observably responds to gravitational fields. If it does not itself gravitate, you get an immediate violation of basic Newtonian physics. Just trap a bunch of radiation in a mirrored box and glue it next to a mass. The radiation will be attracted toward the mass, but if the radiation doesn't gravitate, the mass won't have an equal attraction toward the radiation. So the whole system will self-accelerate. which has never been observed. That's true. It *has* been observed that electrostatic energy, specifically the electrostatic binding energy of nuclei, gravitates, but there's been no such observation for electromagnetic radiation. (Gravity is weak, and it's hard to trap enough radiation in one place.) Steve Carlip |
#17
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On Mon, 16 Aug 2004 07:07:28 -0700, "N:dlzc D:aol T:com \(dlzc\)" N:
dlzc1 D:cox wrote: Like AIDS? Money is spent to find out about things that are not yet known. Or which are well known but denied by an advocacy group? |
#18
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#19
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#20
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"A" == Androcles writes:
A "Dave Houseman" wrote in message A om... Sure, the planets would have a big gravity wave signal, in the same way that jupiter appears brighter than P Centauri in the night sky. A No comparison whatosever. Jupiter is reflecting sunlight. You A cannot observe any planets in orbit about Proxima Centauri. You are A comparing soldier ants to eleph ants. Actually, the planets do not produce a gravitational wave signature (or if they do, it is incredibly small). But surely LIGO can tell what direction a wave is coming from - that's the whole point, isn't it? Dave A Can it? I don't think so. As dkomo said, all he's seen is PR hype, A not results. In principle it can, crudely. There are two of them. So by timing when the signal gets to one versus when it gets to the other, one gets a rough sense of the direction from which the signal came. -- 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 |
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