🚀 go-pugleaf

On Sep 2, 9:31 pm, Pentcho Valev <pva...@yahoo.com> wrote:
> On Sep 1, 7:14 pm, carlip-nos...@physics.ucdavis.edu wrote in
> sci.physics.relativity:
>
>
>
>
>
> > jeffp <j...@brilliantwebsites.com.au> 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/1984-17.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/Stephen.Hawking.A.Brief.History.Of.Tim...
> 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/relativit-les-preuves-taient-fau...
> "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/index.php/2008/05/26/390-histoire-des...
> "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/20-things-you-didn.t-know-about-...
> "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/mg16321935.300-ode-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
> pva...@yahoo.com- Hide quoted text -
>
> - Show quoted text -

Light takes a parabolic curve in time in gravity.

Mitch Raemsch