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The Deflection of Light by the Sun's Gravitational Field:
An Analysis of the 1919 Solar Eclipse Expeditions.
INTRODUCTION -
According to Einstein's general theory of relativity published
in 1916, light coming from a star far away from the Earth and
passing near the Sun will be deviated by the Sun’s gravitational
field by an amount that is inversely proportional to the star’s
radial distance from the Sun (1.745'' at the Sun's limb). This
amount (dubbed the full deflection) is twice the one predicted
by Einstein in 1911, using Newton's gravitational law (half
deflection). In order to test which theory is right (if any), an
expedition led by Eddington was sent to Sobral and Principe for
the eclipse of May 29, 1919 [1]. The
purpose was to determine whether or not there is a deflection of
light by the Sun's gravitational field and if there is, which of
the two theories mentioned above it follows.
The
expedition was claimed to be successful in proving Einstein's
full deflection [1,2]. This test was
crucial to the general approval that Einstein's general theory
of relativity enjoys nowadays.
However, this experimental result is obviously not in accordance
with the result found in chapter ten. This is not a problem, as
we will show that the deflection was certainly not measurable.
We will see that the effect of the atmospheric turbulence was
larger than the full deflection, just like the Airy disk. We
will also see how the instruments could not give such a precise
measurement and how the stars distribution was not good enough
for such a measurement to be convincing. Finally, we will
discuss how Eddington's influence worked for Einstein's full
displacement and against any other possible result.
ABOUT THE EXPERIMENTAL RESULTS -
Atmospheric turbulence is a phenomenon due to the atmosphere
which causes images of stars as seen by an observer on Earth to
jump, quiver, wobble or simply be fuzzy. This is a well-known
phenomenon to any astronomer, amateur or professional. In fact [3] (page 40),
Rare is the night (at most sites) when any telescope, no matter how large its aperture or perfect its optics, can resolve details finer than 1 arc second. More typical at ordinary locations is 2- or 3-arc-second seeing, or worse.The problem becomes even worse during the afternoon due to the heat of the ground. Tentative solutions to this seeing problem have only recently been experimented [4].
"when the [astrographic] object glass is mounted in a steel tube, the change of scale over a range of temperature of 10° F. should be insignificant, and the definition should be very good".During the team’s stay at Sobral, the temperature ranged from 75°F during the night to 97°F in the afternoon. This change in temperature must have affected the astrograph, but what about the the mirrors and the 4-inch telescope?
"If we had not the prejudice of Einstein’s theory we should not say that the figures strongly indicated a radial law of displacement."This brings us to our next point, which is to what degree social circumstances influenced the acceptation of Einstein's theory.
ABOUT EDDINGTON’S INFLUENCE -
The
results from the 1919 expedition were quickly accepted by the
scientific community. When preliminary results were announced,
Joseph Thomson (from the Chair) said [2]
(page 394):
"It is difficult for the audience to weigh fully the meaning of the figures that have been put before us, but the Astronomer Royal [Dyson] and Prof. Eddington have studied the material carefully, and they regard the evidence as decisively in favor of the larger value for the displacement."Thomson makes it look like only Eddington and Dyson are able to understand the results. It seems that they have such a reputation that the general and the scientific public should blindly believe them.
"I do not think that it would be possible to measure so small a quantity."We clearly see that Dyson contradicted himself.
"Although the material was very meager compared with what had been hoped for, the writer (who it must be admitted was not altogether unbiased) believed it convincing."Moreover, according to Chandrasekhar [8] (page 25),
"had he been left to himself, he would not have planned the expeditions since he was fully convinced of the truth of the general theory of relativity!"Eddington was a Quaker and like other Quakers, he did not want to go to war (WWI). In England, Quakers were sent to camps during the war, but because of Dyson's intervention [8] (page 25),
"Eddington was deferred with the express stipulation that if the war should end by May 1919, then Eddington should undertake to lead an expedition for the purpose of verifying Einstein’s predictions! "The circumstances of the war forced Eddington to do an experiment that he would have never done had he had a choice because he was so convinced of its outcome.
http://munshi.sonoma.edu/jamal/physicsmath.html:
Dr. F. Schmeidler of the Munich University Observatory has published a paper [49] titled "The Einstein Shift An Unsettled Problem," and a plot of shifts for 92 stars for the 1922 eclipse shows shifts going in all directions, many of them going the wrong way by as large a deflection as those shifted in the predicted direction! Further examination of the 1919 and 1922 data originally interpreted as confirming relativity, tended to favor a larger shift, the results depended very strongly on the manner for reducing the measurements and the effect of omitting individual stars. So now we find that the legend of Albert Einstein as the world's greatest scientist was based on the Mathematical Magic of Trimming and Cooking of the eclipse data to present the illusion that Einstein's general relativity theory was correct in order to prevent Cambridge University from being disgraced because one of its distinguished members was close to being declared a "conscientious objector"!CONCLUSION -
REFERENCES
[1] Dyson, F. W., A. S.
Eddington and C. Davidson, A Determination of the Deflection
of Light by the Sun's Gravitational Field, from Observations
Made at the Total Eclipse of May 29, 1919, in Philosophical
Transactions of the Royal Society of London, series A, 220,
p. 291-333, 1920. (See also: Annual Report of the Board of
Regents of the Smithsonian Institution Showing the Operations,
Expenditures, and Conditions of the Institution for the Year
Ending June 30 1919, Government Printing Office,
Washington, p. 133-176, 1921.
[2] Joint Eclipse
Meeting of the Royal Society and the Royal Astronomical
Society, 1919, November 6, The Observatory, 42,
545, p. 389-398, 1919.
[3] MacRobert, Alan M., Beating
the Seeing, Sky & Telescope, 89, 4, p.
40-43, 1995.
[4] Fischer, Daniel, Optical
Interferometry: Breaking the Barriers, Sky &
Telescope, 92, 5, p. 36-41, 1996.
[5] von Klüber, H., The
Determination of Einstein's Light-Deflection in the
Gravitational Field of the Sun, Vistas in Astronomy,
Pergamon Press, London, 3, p. 47-77, 1960.
[6] Meeting of the
Royal Astronomical Society, Friday, 1919, December 12, in
The Observatory, 43, 548, p. 33-45, Jan. 1920.
[7] Eddington, A., Space,
Time
and Gravitation: An Outline of the General Relativity Theory,
Cambridge University Press, Cambridge, 218 pages, 1959.
[8] Chandrasekhar, S., Eddington:
The
Most
Distinguished
Astrophysicist
of
His
Time, Cambridge University Press, Cambridge, 64 pages,
1983.
[9] Earman, J. and C.
Glymour, Relativity and Eclipses: The British Eclipse
Expeditions of 1919 and Their Predecessors, in Historical
Studies in the Physical Sciences, 11, p. 49-85,
1980.
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