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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.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/relativit-les-preuves-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/index.php/2008/05/26/390-histoire-des-sciences-les-preuves-de-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/20-things-you-didn.t-know-about-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/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
pvalev@yahoo.com