Einstein’s General Theory of Relativity and how it was finally proved on the 1922 solar eclipse expedition

Albert Einstein 1921 by F Schmutzer Public DomainFerdinand Schmutzer ,  http://web.archive.org/web/20071026151415/http://www.anzenbergergallery.com/en/article/134.html

In late August 1922 a group of astronomers, naval men, and Aboriginal stockmen began the arduous task of unloading their complicated scientific equipment and stores from boats onto a deserted beach on the coast of Western Australia. The shallow nature of the approach meant the boats were anchored three or four miles from the high-water line and the stores, after being brought to shore, were then transported by donkey wagons to the observation site at Wollal. This was no ordinary expedition and its members knew the eyes of the world were on them waiting to see if they would be the ones to finally prove Einstein’s controversial ‘Theory of General Relativity‘.

To do this they would have to photograph the light from stars bending around the sun and then measure their placement extremely accurately. At stake was the whole concept of universe as envisaged by Sir Isaac Newton over 250 years before. Everyone involved in the project was well aware of how difficult this task was and that they were only one of eight other astronomical expeditions who were also setting up their equipment at sites across Australia. The largest group of observers, based near the Wollal post and telegraph station consisted of three international parties, the Lick Observatory party, under the direction of W. W. Campbell, a group from the University of Toronto, under C. A. Chant and the Indian expedition supervised by J. Evershed. In addition Australia provided a fourth group from the Perth Observatory. They were directed Mr. Nossiter and included Mr. Nunn, Mr. Matthews, Mr. Dwyer and Mr. Yates. On top of this were four others set up on the east coast under the direction of the Sydney Observatory and W. E.Cooke.

All this preparation was for the solar eclipse predicted on 22 September 1922 and the hope they would be the ones to resolve the scientific problem Einstein had set in train 17 years previously. In 1905 Einstein (then an unknown patent clerk) had published four groundbreaking scientific papers in what is commonly referred to as his ‘miracle year’. While these included his famous equation E=Mc2 which determined how energy became matter and matter in turn became energy, it also included a mind-blowing paper describing how the fabric of space and time are woven together; this paper he titled ‘The Special Theory of Relativity’.

This radical new concept had come to him in Berne while he was riding in a bus and looking back at the local town clock. As he describes it a ‘storm broke in my mind’ as he imagined what would happen if the bus was travelling at the speed of light. If this was the case then the light from the clock couldn’t catch up with the bus and thus time would appear to stop. For Einstein this implied that space and time were one and the same and were in fact a flexible fabric he labelled space/time.

There was no instant acclaim for his theories but he did have an important supporter, Max Planck, one of the foremost physicists of the day. As a result of discussions with other scientists Einstein started to write a new article on special relativity in 1907 but realised his original concept was limited as it only dealt with objects moving in one direction and at one speed. Clearly this was not the way things work in the real world and so he rewrote his paper taking into account gravity calling this one the Theory of General Relativity.

The problem Einstein was addressing was this, if an apple falls we traditionally say a mysterious force, which Newton called gravity, is pulling it down. But Einstein knew from his working with physics that objects usually moved if they were pushed and instead he posited the idea that there was no such thing as gravitational pull. Instead he suggested that the earth has curved space around it and it is this that is keeping our feet firmly planted on the ground by pushing on the atmosphere and all the objects on the earth. In the case of the earth going around the sun most people would say it was the gravitational force of the sun pulling the earth around it. Instead Einstein suggested it was the gravitation of the sun distorting the space around the earth and that this was the force pushing the earth around the sun.

But while Einstein could propose this new theory of the universe and of gravity using maths and physics it was another thing to prove it by experiment. Thus his ‘General Theory of Relativity’, unlike his photon, energy and mass equations, remained an interesting but unproven theory in the eyes of the scientific community. He needed to find a way to measure the effects of gravity on the straight beams thrown from a light source. If he could show this he could also prove his theory that space/time was flexible. But where could he possibly find something with enough gravity to bend light.

It was then that he came up with a great idea, what about using light from distant stars and the sun which has around 300,000 times more mass than the earth. Einstein hypothesised that if his theory was correct light from a star would bend as it passed through the sun’s gravitational field. The problem was that the sun was too bright to see this happen – UNLESS THERE WERE A SOLAR ECLIPSE!

When the sun’s rays are blocked out by the moon during a solar eclipse we can see the stars around it. And if his theory was correct these should appear to be slightly out of place from their actual positions as measured in the night sky because the light they emitted was bent as it went past the sun.

Of course to do this Einstein needed someone to photograph the event. So in 1912 he published his thoughts on this experiment and appealed to astrophysicists to take up his challenge. Instead of a chorus of willing voices his challenge was initially met with silence. Except for an assistant astronomer at the Berlin Observatory Erwin Finlay-Freundlich who although still in his early 20s saw Einstein’s call as an opportunity to make his name. A total solar eclipse is only visible over a small area of the earth and the next one was on the 21 of August 1914, and would be best seen from the Crimea in Russia.

After being refused by his boss Freundlich wrote to William Wallace Campbell, a pioneer in solar eclipse photography, at the Lick Observatory in USA. He asked him to come to Russia and prove or disprove Einstein’s theory. As a result Freundlich and Campbell both made their way to Russia in 1914 with Freundlich setting up his instruments in the Crimea while Campbell sets his up near to Kiev. Unfortunately for everyone major political events unfolding in the background and bad weather destroyed their chances for capturing the event.

On June 28 1914 Archduke Franz Ferdinand of Austria is assassinated and Germany declared war on Russia. As a result Russian officers seize Freundlich’s equipment, (in fact he and his assistants are held as POWs for a number of months afterwards). Campbell as an American is allowed to continue his project but unfortunately clouds obscure the eclipse and he not able to good photographs of the event.

Einstein is initially devastated by the failure but it turns out that these particular clouds had a silver lining. In the wake of the eclipse fiasco and while locked down in Germany by the war Einstein begins going over his initial calculations and finds he has made some fundamental errors. He now recognises that if the 1914 eclipse expedition had been a success they would have used these calculations, and they would have been wrong and discredited his theory. So Einstein sets about redoing his calculations and finally on 25 November 1915 he presents his General Theory of Relativity to the Prussian Academy of Sciences. In 1916 he finally submits his paper, with correct calculations, and a completely different view of the universe. But while many accept to work the scientific community remains divided, particularly given the theory had yet to be proven.

Help came in the form of an Englishman, Arthur Stanley Eddington. He was not only an astronomer at Cambridge University, he was also a conscientious objector and saw in Einstein a fellow scientist opposed to the war. In February 1916 he received a package from a friend in Holland which contained a copy of Einstein’s theory translated into English. Eddington was astounded, and decided to see if they could prove, or disprove, Einstein’s theory by making observations at the next solar eclipse, on 8 June, 1918.

The limited viewing window for this eclipse made the United States a prime site for setting up his equipment but unfortunately the war made it difficult for Eddington to travel there. Instead he also decided to contact Campbell at the Lick Observatory and ask if he would be able to try one more time to photograph the eclipse. Campbell agrees but his equipment had been confiscated by the Russians in 1914 and this forced him to improvise from existing equipment lying around at the Lick Observatory. Thus it turned out that although Campbell had the solar eclipse observations all to himself he was forced to take his photographs using sub-standard equipment, and this was to have some serious implications for this story.

On Saturday June the 8 the clouds parted in time to allow Campbell to take some photographic plates which he gave to Heber Curtis to make the measurements from. So after doing his measurements Curtis gives Campbell the news that he believes the stars are actually in the same position and thus Einstein is wrong. However this is a momentous decision and Campbell, realising his reputation could be at stake holds off announcing the results as he is worried his sub-standard equipment may have affected the results. Instead he asks Curtis to re-do his measurements.

On the 11 November 1918 World War One ended. This took away the restrictions on travel which had been holding back astronomers and as a result tEddington was free to travel to observe the next solar eclipse. The event happened on May 29 1919 and this time Eddington carved his way through the jungle of island of Principe (off the west coast of Africa) to set up his equipment. He spent a month there building the telescope but as luck would have it on the day clouds affected the view forcing Eddington to take his photographs in quick succession hoping all the time they caught the moment of full eclipse when the stars would be most visible.

Eddington was so concerned about the results that he started measuring the plates then and there while still in the middle of the jungle. Many proved worthless but a few showed enough stars visible for him to make some preliminary results. And unlike Campbell’s his confirmed Einstein’s theory.

In a strange twist of fate Eddington’s cable confirming Einstein’s theory arrives in London at the same time as Campbell physically arrives to present his results, disproving the theory. As a result Campbell gets nervous again about the quality of the equipment and Curtis’s measurements and decides to again delay the presentation of his negative results to London’sRoyal Astronomical Society. Instead it is Eddington who on 6 November 1919 presents his positive results and word of this momentous decision spreads quickly spreads around the world. Very quickly Einstein becomes the face of genius and a world renown scientist – BUT still there many sceptics in the scientific community who questioned Eddington’s results and a backlash began, helped in part by anti-German sentiment in the wake of War.

It quickly becomes clear that another expedition needed to be organised to settle the issue once and for all. The next scheduled solar eclipse was on the 21 September 1922, and would be visible over the continent of Australia. By now Einstein was 42 years old, a household name, and yet his theory of relativity published eight years previously had yet be confirmed to the satisfaction of the scientific community. It seemed that Australia would be the place where the controversy would be settled once and for all and so it is no surprise to find the event generated huge media and scientific interest.

 Document from the Powerhouse Museum Collection

So we come full circle back to the astronomers loading their donkeys on a remote beach in Western Australia with the world’s gaze upon them as they prepared their equipment to photograph the solar eclipse.

Document from the Powerhouse Museum Collection

This time the weather and the equipment would provide optimal conditions for Campbell and his group at Wollal. In this photograph we can see the polar axis set up to hold the spectrographs, the Floyd telescope and the two short focus camera. The woman on the left is probably the wife of W. W. Campbell as during the eclipse she was responsible for the exposures of the solar corona by means of the Floyd camera.

 nal was a specially made 1.52 metre (5 foot) solar telescope camera named fittingly the ‘Einstein camera’. campbell himself directed this camera but looking after the changing of the glass plates was left to two Australian naval men, Messers. Rhoades and Kenny, under Commander Quick. It is quite possible that these are the two men seen here.
Finally amongst the Lick Observatory’s 35 tons of stores and equipment was a forty foot coronal camera which required supporting towers 36 feet high. This photograph of the eclipse during total phase was taken by Dr. Adams using this astrograph and it was the measurements from these plates that finally led to H. Spencer Jones of Greenwich Observatory announcing in May 1923, … as a result of the observations secured last September, together with the two previous confirmations from the 1919 eclipse, leave little room for doubting that the deflection deduced from Einstein’s theory is the correct one.

After years of controversy, a World War, and several failed eclipse expeditions, Einstein’s Theory of General relativity was finally proved, and science’s understanding of how the world around us worked was completely overturned.

Post by Geoff Barker, 2012

References
Campbell, W. W., ‘The Total Eclipse of the Sun, September 21, 1922′, Astronomical Society of the Pacific, provided by the NASA Astrophysics Data Sy
stem, May 2008
Evershed, J., ‘Report of the Indian Eclipse Expedition to Wollal, West Australia’, Kodaikanal Observatory, Bulletin, number LXI
Spencer Jones, H., ‘The Total Solar Eclipse of 1922 September 21′, The Observatory, May 1923
Thomas Levenson, Einstein in Berlin
Walter Isaacson, Einstein; his life and his Universe 
Amir D Aczel, God’s Equation 
Michio Kaku, Physics of the Impossible

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