Centennial: Einstein's General Theory of Relativity

Amateur Astronomers Association of Pittsburgh (AAAP) Co-Founder
Leo J. Scanlon (left), who would later become one of the first Buhl
Planetarium lecturers, thanks Albert Einstein (right) for visiting the
AAAP booth at the 1934 convention of the American Association for
the Advancement of Science in Pittsburgh.
More Information: Link >>> http://old.3ap.org/features/leo/leoScanlonBio6.shtml
(Sources: AAAP, Scanlon Family Collection; Photo Reproduction:
© Copyright David Smith)

By Glenn A. Walsh

Reporting for SpaceWatchtower

One hundred years ago today, Physicist Albert Einstein completely unveiled his General Theory of Relativity before the Prussian Academy of Sciences in Berlin. It was on 1915 November 25, the fourth of a series of lectures over four consecutive Thursdays, where he detailed the mathematical field equations that explained and supported his General Theory of Relativity.

Dr. Einstein's General Theory of Relativity continues today as the best explanation of gravity in modern Physics.

Interestingly, Dr. Einstein made revisions in his field equations, from one lecture to the next, during the four lectures in November of 1915. Throughout this month, he continued conferring with academic colleagues, regarding these equations.

Until this time, scientists had relied on Isaac Newton's Law of Universal Gravitation, which said that gravity was a “force” that attracted two objects of mass to each other. Hence, by this theory, the “force” of gravity, caused by the large mass of the Planet Earth, strongly attracted all objects found on the Earth (including us) to the Earth.

In the General Theory, Dr. Einstein explained gravity as a warp in space-time, caused by the mass of matter. Hence, the large mass of the Planet Earth caused such a large warp in space-time that other objects near the Earth would simply follow the warp, “falling” toward the Earth. By this explanation, we (and every other object on the Earth) are simply following the warp toward the Earth.

In the General Theory of Relativity, no gravitational force deflects objects from their natural, straight pathways. Rather, gravity corresponds to changes in space and time, which changes the straightest-possible path of an object to a possibly curved path.

With the General Theory, Dr. Einstein also recognized that gravity and motion were equivalent. To an observer, the pull of gravity from a planet was no different than the pull felt by a moving rocket or a moving elevator.

The General Theory implies the existence of Black Holes, the end of life of some of the most massive stars. Black Holes are considered “black” because these are regions of space where space and time are distorted to such an extent that nothing, not even light, can escape.

The General Theory of Relativity predicts the existence of gravity waves, which have since been indirectly observed. As of mid-September, scientists are trying to directly detect gravity waves, using a Laser Interferometer Gravitational-Wave Observatory (LIGO), which uses a laser to detect the slight changes caused by gravity waves.

Also predicted by the General Theory, the path of light is bent, as it passes through a gravitational field from a body of great mass, known today as gravitational lensing. To test this prediction required great precision, as the deflection of light would be very slight. However, no experiment on Earth would provide the accuracy necessary to confirm the prediction.

Sir Frank Watson Dyson, Astronomer Royal of Great Britain, proposed confirming this prediction by using a Total Eclipse of the Sun which would occur in 1919. The May 29 eclipse would allow the observation of stars from the bright Hyades Star Cluster, as the light from these stars passed close to the fully eclipsed Sun. With this star light passing so close to the Sun, the Sun's gravitational field would deflect the star light, and accurate measurements of this deflection could be performed.

English Astronomer Sir Arthur Eddington agreed to make the observations necessary to confirm this prediction. He first measured the “true” positions of the stars in January and February of 1919. In May, he observed the eclipse from the remote island of Principe, in the Gulf of Guinea off of the west coast of Africa. He also sent a second expedition to observe the eclipse from Sobral, Brazil, in case the African site was clouded-out during the eclipse.

Good observations of the eclipse were made from both locations. Sir Eddington announced his findings, confirming Dr. Einstein's General Theory of Relativity, on 1919 November 6. Until then, a young, fairly unknown physicist, the next day Albert Einstein was on the front page of newspapers around the world!

An often told story is when a student of Dr. Einstein asked about the possibility the solar eclipse would not confirm the General Theory. Dr. Einstein, who often was convinced of a theory without experimental evidence, was reported by the student to have said, “Then I would have been sorry for the dear Lord. The theory is correct.”

However, University of Winnipeg History Professor David R. Topper, in his 2007 book, Quirky Sides of Scientists, reports that this quote is probably a myth. Dr. Topper writes, “In a meticulously researched study of the story, Klaus Hentschel has convinced me the event never happened, and that it was a reconstruction by the student much later than the event (in the 1950s) to support her view that Einstein shared her philosophical (neo-Kantian) viewpoint (which he did not).” Klaus Hentschel is a German physicist and the head of the History of Science and Technology section of the History Department of the University of Stuttgart.

Just ten years before the presentation of the General Theory, Albert Einstein had unveiled his Special Theory of Relativity, which is now an experimentally well-confirmed physical theory regarding the relationship between space and time. The two postulates of the Special Theory of Relativity are:

1. The laws of physics are invariant in all inertial systems;
2. The speed of light in a vacuum is the same for all observers, no matter the motion of the light source.

Even today, the Special Theory of Relativity is the most accurate model of motion at any speed. And, from the Special Theory arose the idea of mass—energy equivalence, better known by the general public as the famous equation E = mc2.

More on the General Theory of Relativity: Link >>> https://en.wikipedia.org/wiki/General_relativity

More on the Special Theory of Relativity: Link >>> https://en.wikipedia.org/wiki/Special_relativity

More about Albert Einstein: Link >>> https://en.wikipedia.org/wiki/Albert_Einstein

More on Albert Einstein's speaking engagement at the 1934 convention of the American Association for the Advancement of Science in Pittsburgh and his meeting with the Amateur Astronomers Association of Pittsburgh: Link >>> http://old.3ap.org/features/leo/leoScanlonBio6.shtml

Photograph of Albert Einstein's desk the day before he passed-away:
Link >>> http://buhlplanetarium.tripod.com/bio/einstein/pix/Einsteindesk.jpg

Related Blog Post ---

"Laser Observatory May Directly Detect Gravity Waves." 2015 Oct. 7.

Link >>> http://spacewatchtower.blogspot.com/2015/10/laser-observatory-may-directly-detect.html 

Source: Glenn A. Walsh Reporting for SpaceWatchtower, a project of Friends of the Zeiss.

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