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Measuring Distance, Light and Curved Space-Time
On Sep 1, 7:14 pm, wrote in
sci.physics.relativity: jeffp wrote: A quick question (or series of related questions) thats been bugging me for years for the physics gurus out there. Given that space-time warps based on its proximity to massive objects (including unobservable black holes, and theoretically, unobserved-to- date dark matter) and that light travels over that warped medium, how do scientists know whether or not light from a distant object has been significantly bent/slowed down for some part of the journey on the way to earth? In general, the effect of bending is quite small. A light ray grazing the Sun, for example, is deflected less than two arcseconds, about 1/1000 of the angle subtended by the Moon. A light ray passing even slightly farther from the Sun is deflected less -- the deflection angle is inversely proportional to the "impact parameter," the distance of closest passage. Bigger masses can give bigger deflections, but only if the light happens to pass very close to their centers. There is, in fact, a major effort to measure this deflection, since it can be used to map the matter in the Universe, including dark matter. The measurements are possible because gravitational lensing, in addition to deflecting light, also distorts images. If you look at http://www.cita.utoronto.ca/~hoekstra/lensing.html you'll see some nice illustrations and photos. The deflection is almost always small enough, though, that it takes a huge amount of data to extract it from random noise. (This will be one of the main missions of the LSST, the Large Synoptic Survey Telescope.) Astronomers also look for deflection by black holes and other forms of concentrated matter. This is possible, in part, because light deflected by a gravitational field is also focused, so an image becomes brighter. Since a black hole, say, is unlikely to be exactly at rest relative to a background star, we can look for sudden brightening -- in a particular, predictable pattern -- to search for a black hole (or a planet, or a brown dwarf, or a lump of dark matter) passing in front of a star. This search for "microlensing" events was pioneered by the MACHO project, http://wwwmacho.mcmaster.ca/. (A MACHO is a "massive compact halo object," a possible form of dark matter; a competing form is a WIMP, a "weakly interacting massive particle.") Looking at 18 million stars, they've found 53 likely microlensing events -- it is, again, not a very common event. There is also a time delay (the Shapiro time delay) from gravitational fields, but this is again small. For example, there was a famous supernova, SN1987A -- I guess "famous" depends on the circles you travel in -- in 1987, and physicists did a reasonable careful calculation of the time delay (see Longo, Phys. Rev. Lett. 60 (1988) 173. The total time delay comes out to about five months. This seems large, but it's over a travel time of some 160,000 years. So again it's a very small error -- astronomers would be thrilled if they could measure distances to anywhere near that accuracy. Steve Carlip The last active teacher in Einsteiniana, Steve Carlip, stopping short, as though by instinct, at the threshold of the dangerous thought: "Arthur Eddington was simply unable to measure the deflection, let alone to discriminate between the prediction given by Newton's emission theory of light and that given by Einstein's "theory", and therefore the 1919 experiment "catapulting Einstein into fame" was a complete fraud": http://www.liferesearchuniversal.com...html#seventeen George Orwell: "Crimestop means the faculty of stopping short, as though by instinct, at the threshold of any dangerous thought. It includes the power of not grasping analogies, of failing to perceive logical errors, of misunderstanding the simplest arguments if they are inimical to Ingsoc, and of being bored or repelled by any train of thought which is capable of leading in a heretical direction. Crimestop, in short, means protective stupidity." http://vaghelasv.com/Documents/Steph...ry.Of.Time.pdf Stephen Hawking: "Einsteins prediction of light deflection could not be tested immediately in 1915, because the First World War was in progress, and it was not until 1919 that a British expedition, observing an eclipse from West Africa, showed that light was indeed deflected by the sun, just as predicted by the theory. This proof of a German theory by British scientists was hailed as a great act of reconciliation between the two countries after the war. It is ionic, therefore, that later examination of the photographs taken on that expedition showed the errors were as great as the effect they were trying to measure. Their measurement had been sheer luck, or a case of knowing the result they wanted to get, not an uncommon occurrence in science." http://www.cieletespace.fr/evenement...taient-fausses "Relativité: les preuves étaient fausses.....Le monde entier a cru pendant plus de cinquante ans à une théorie non vérifiée. Car, nous le savons aujourdhui, les premières preuves, issues notamment dune célèbre éclipse de 1919, nen étaient pas. Elles reposaient en partie sur des manipulations peu avouables visant à obtenir un résultat connu à lavance, et sur des mesures entachées dincertitudes, quand il ne sagissait pas de fraudes caractérisées." http://www.cieletespaceradio.fr/inde...-la-relativite "Au début du XXème siècle, des scientifiques comme le Britannique Arthur Eddington avaient tant à coeur de vérifier la théorie de la relativité qu'ils ont tout mis en oeuvre pour que leurs expériences soient probantes." (ECOUTEZ!) http://discovermagazine.com/2008/mar...out-relativity "The eclipse experiment finally happened in 1919 (youre looking at it on this very page). Eminent British physicist Arthur Eddington declared general relativity a success, catapulting Einstein into fame and onto coffee mugs. In retrospect, it seems that Eddington fudged the results, throwing out photos that showed the wrong outcome. No wonder nobody noticed: At the time of Einsteins death in 1955, scientists still had almost no evidence of general relativity in action." http://www.newscientist.com/article/...to-albert.html New Scientist: Ode to Albert "Enter another piece of luck for Einstein. We now know that the light- bending effect was actually too small for Eddington to have discerned at that time. Had Eddington not been so receptive to Einstein's theory, he might not have reached such strong conclusions so soon, and the world would have had to wait for more accurate eclipse measurements to confirm general relativity." Pentcho Valev |
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Measuring Distance, Light and Curved Space-Time
On Sep 4 Steve Carlip wrote in sci.physics.relativity:
There have been efforts to see whether high energy gamma rays from supernovae travel at a different speed than lower energy gamma rays -- if so, this would indicate a violation of special relativity, and perhaps give us clues about quantum gravity -- but no real effect has been seen. Honest Carlip your brothers Einsteinians (Lee Smolin etc.) have extracted a lot of career and money from this so you should not be so hostile. Instead of waiting for a "real effect", just analize the Pound-Rebka experiment: does it confirm variable speed of light, or does it confirm constant speed of light? Remember this: http://math.ucr.edu/home/baez/physic..._of_light.html Steve Carlip: "Einstein went on to discover a more general theory of relativity which explained gravity in terms of curved spacetime, and he talked about the speed of light changing in this new theory. In the 1920 book "Relativity: the special and general theory" he wrote: ". . . according to the general theory of relativity, the law of the constancy of the velocity of light in vacuo, which constitutes one of the two fundamental assumptions in the special theory of relativity [. . .] cannot claim any unlimited validity. A curvature of rays of light can only take place when the velocity of propagation of light varies with position." Since Einstein talks of velocity (a vector quantity: speed with direction) rather than speed alone, it is not clear that he meant the speed will change, but the reference to special relativity suggests that he did mean so. (...) In this passage, Einstein is not talking about a freely falling frame, but rather about a frame at rest relative to a source of gravity. In such a frame, the speed of light can differ from c..." Which situation are we in now? I don't know; but I don't think anyone else does, either. Steve Carlip Bryan Wallace did know, Honest Carlip, but he died in oblivion while you and your brothers Einsteinians were fiercely exploiting the money- spinner called "theory of relativity": http://www.ekkehard-friebe.de/wallace.htm Bryan Wallace: "Einstein's special relativity theory with his second postulate that the speed of light in space is constant is the linchpin that holds the whole range of modern physics theories together. Shatter this postulate, and modern physics becomes an elaborate farce!....The speed of light is c+v." Pentcho Valev |
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