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The race to test relativity

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Deborah Valkenburg
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« on: May 04, 2008, 11:05:20 pm »

The race to test relativity
Oct 09, 2005 01:00 AM
Jeffrey Crelinsten
Albert Einstein published his theory of special relativity in 1905 but it wasn’t until 1919, after British astronomers announced that they had verified a prediction from his generalized theory that the sun’s gravity bends light, that he became a superstar, hounded by reporters, admirers and detractors. This three-part series by Jeffrey Crelinsten examines how astronomers around the world debated and tested Einstein’s theory of relativity right into the 1930s.

Part 1. Astronomers Encounter Einstein

Erwin Freundlich, junior assistant at the Berlin Observatory, was frustrated.

Freundlich had studied mathematics and astronomy at Göttingen University from 1905 to 1910 under brilliant teachers, including mathematician Felix Klein. When he graduated in 1910, Klein got him a job at the observatory in Berlin.

But Freundlich wanted to explore new and exciting ideas in theoretical physics and astrophysics. When he complained to Klein that he knew little practical astronomy, his professor was firm. "You did not come to university in order to learn everything, but in order to learn how to learn everything. You are to go to Berlin."

Freundlich's new boss, Hermann Struve, was conservative and autocratic. He didn't share Freundlich's interest in modern physics theories. Struve assigned him menial observing duties and the arduous task of compiling a star catalogue.

One of Freundlich's jobs was to show visitors around the observatory. In August 1911, Leo W. Pollack, a young physicist from the German-speaking university in Prague, paid a visit.

Pollack told Freundlich about a new professor who had recently joined the faculty: Albert Einstein. Freundlich remembered that one of his professors had startled the scientific world in 1908 with a lecture on a new theory of space and time — relativity — developed by Einstein.

Pollack excitedly told the young astronomer about Einstein's latest paper on his relativity theory. Einstein predicted that the gravitational field of the sun would bend light and slow down clocks so that the frequency of light from the sun would change. Best of all, he had figured out a way for astronomers to test his predictions. Pollack urged Freundlich to write Einstein and offer to collaborate.

Freundlich jumped at the chance, and soon he and Einstein were corresponding. Einstein figured that during a solar eclipse the apparent position of stars near the sun should change due to the bending of starlight in the sun's gravity. By comparing photos of stars around the eclipsed sun with photos of the same stars taken when the sun was in a different part of the sky, he hoped Freundlich would be able to measure the difference.

Another visitor to Berlin provided a possible line of attack. Charles Dillon Perrine, director of the Cordoba Observatory in Argentina, had worked for several years at the Lick Observatory in southern California.

Perrine had gone on three Lick expeditions to photograph the sun during a solar eclipse in search of a planet inside the orbit of Mercury. Precise observations of Mercury's orbit over hundreds of years had revealed that its elliptical orbit rotated a bit faster than Newton's theory of gravitation predicted.

The discrepancy was minuscule: 43 seconds of arc per century. The French mathematician Urbain Jean Joseph Leverrier had calculated that a hypothetical planet, Vulcan, close to the sun could account for this extra movement.

When astronomical photography came into wide use toward the end of the 19th century, William Wallace Campbell, director of Lick Observatory, put the observatory on the leading edge of eclipse photography. Perrine's photos showed that the elusive Vulcan did not exist.

Perrine suggested that Freundlich ask Campbell and other astronomers for their old eclipse plates and use them to measure star positions near the eclipsed sun to test Einstein's theories.

Freundlich wrote to several astronomers, including Campbell, who sent him copies of several plates. Unfortunately, the star images weren't precise enough to measure accurately because the telescopes had tracked the sun, not the stars.

But Campbell became intrigued with the "Einstein problem." In 1912, he sent his equipment to Perrine in Argentina to try the Einstein test at an eclipse visible from the southern hemisphere. Perrine cabled from the eclipse camp: "RAIN." Campbell and Freundlich then set their sights on an eclipse that would be visible from Russia in 1914.

By then Einstein had become famous among German-speaking scientists. He was in Prague for less than a year before several universities tried to lure him away with better offers. The Zurich Polytechnic won him largely because one of Einstein's old school chums, Marcel Grossmann, was the dean of mathematics there. Einstein was trying to generalize his relativity theory and he needed to work with a mathematician; Grossmann fit the bill.

Zurich managed to keep Einstein for two years. In 1913, several of the most influential scientists in Germany enticed him to move to Berlin, then the leading centre of scientific research in the world. They made him an offer he couldn't refuse: membership (the youngest ever appointed) in the prestigious Prussian Academy of Science, with an honorarium of 900 marks; the maximum professor's salary of 12,000 marks; a professorship at the University of Berlin with the right, but no obligation, to teach; and directorship of a new physics institute to be created under the auspices of the Kaiser-Wilhelm-Gesellschaft (which later became the Max Planck Society).

All Einstein had to do was live in Berlin and attend meetings of the Prussian Academy. He felt the Germans were "betting on me like a prized hen." He wondered if he could lay another golden egg.

Einstein used his newfound influence to help Freundlich raise funds for his eclipse expedition to Russia, even though Freundlich's boss refused to contribute. Campbell sent his own party, and the two groups met at the eclipse site.

Before the eclipse occurred, however, the Russians arrested Freundlich. World War I had broken out, and the Russians wanted to exchange him and his colleagues for Russians caught in Germany. Then thick, grey clouds ruined Campbell's plans. The Lick party beat a hasty retreat under threat of German U-boats, leaving their valuable equipment behind.

"I never knew before how keenly an eclipse astronomer feels his disappointment through clouds," Campbell wrote the astronomer George Ellery Hale. "One wishes that he could come home by the back door and see nobody."

Hale was an internationally renowned solar astronomer and founder of the Mt. Wilson Observatory in southern California. He had received a letter from Einstein before the war asking if it might be possible to measure star positions near the sun during daylight using an infrared camera. Hale had ruled out the idea, encouraging Einstein to contact Campbell about the eclipse method.

While Campbell wrestled with the light-bending test, Hale and his colleagues began to tackle Einstein's other prediction: that clocks slow down in a gravitational field. If time runs more slowly in the sun's gravity than here on Earth's surface, then light emitted at the sun would appear to be slightly redder than light emitted here on Earth.

Astronomers had already noticed that light from the sun tends to shift to the red end of the spectrum, but the shifts were complicated. The generally accepted explanation came from Mt. Wilson, where Hale had built the largest solar telescope in the world.

Its unique design put the optics at the top of an 18-metre tower far above the disturbances of heated air near the ground, projecting the solar image straight down into a subterranean, temperature-controlled chamber. There the sunlight was spread into an enormous spectrum that made it easy to measure. Astronomers used this leading-edge instrument to measure the solar spectrum very precisely. In 1910, they concluded that pressure in the sun's atmosphere was the main cause for the redshifts.

John Evershed, a British solar astronomer who was director of Kodaikanal Observatory in southern India, challenged the Mt. Wilson interpretation. He argued that pressure in the solar atmosphere was at most one-tenth of what astronomers generally thought it to be, and hence could not be a factor.

By 1912, astronomers began to consider Einstein's relativity theory as a possible explanation, but most found redshifts that were smaller than the relativity prediction.

The outbreak of war isolated Einstein and Freundlich in Germany from the international astronomical community that was trying to test Einstein's predictions. Einstein deplored the ascendancy of the military. A convinced pacifist, he tried to counter the insanity around him. He plunged into his work on generalizing his theory of relativity to see if he could indeed lay another golden egg.

Jeffrey Crelinsten is a science writer and historian based in Toronto. His book, "Einstein's Jury: The Race to Test Relativity" (Princeton University Press), will be released in spring 2006.
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Deborah Valkenburg
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« Reply #1 on: May 04, 2008, 11:10:44 pm »

The race to test relativity   

Oct 16, 2005 01:00 AM
Jeffrey Crelinsten
Albert Einstein published his theory of special relativity in 1905, but it wasn’t until 1919, after British astronomers announced that they had verified a prediction from his generalized theory that the sun’s gravity bends light, that he became a superstar, hounded by reporters, admirers and detractors. This three-part series by Jeffrey Crelinsten examines how astronomers around the world debated and tested Einstein’s theory of relativity right into the 1930s.

Part 2. Men of Science Agog

While young men killed each other on European battlefields, Einstein wrestled with his own adversary — mathematics. His 1905 theory of relativity rested on the idea that the laws of physics are the same for everyone. Restricting himself to uniform motion in a straight line, Einstein stated that no experiment you perform could tell you whether you're moving or stationary. That simple requirement led to a revolution in our conception of space and time. Observers moving past each other disagree about length and time measurements; about whether or not two events occur at the same moment; about mass. Absolute space — the container in which we live — no longer exists. Absolute time — which inexorably charts our existence — is a fiction.

In 1907, Einstein had the "happiest thought of my life" — a falling person has the sensation that gravity has disappeared. Put a closed box around a person in free fall and let the box fall freely. Since all objects fall at the same rate, the person floats inside the box. It's as if the box is not moving and gravity is turned off. Accelerated motion (falling) is undetectable. Einstein made a generalization that gravity and acceleration are equivalent. In principle, you can't tell the difference.

Einstein's "equivalence principle" revealed that light bends in a gravitational field. If you accelerate upwards in a rocket ship and shine a light beam from one wall to the other, the light will hit the opposite wall slightly lower, because your spacecraft is moving upwards as the light crosses the ship. So, inside a stationary spacecraft in a gravitational field, the light from one wall will also hit the opposite wall slightly lower. Light bends in the direction of gravity.

In 1912, Einstein's mathematician friend Marcel Grossmann introduced him to a powerful form of mathematics. Called differential geometry, its equations could describe the shape of a surface independently of any observer. Einstein and Grossmann developed equations relating space and time to matter and energy. Gravity turned out to be a geometrical entity — a curvature in space-time. The equations elegantly described the physics.

Alone in Germany during the war, Einstein continued his work. By 1915 he had found equations for the gravitational field that were independent of the observer's motion or position. He sat down to calculate the motion of Mercury's orbit. Newton's theory of gravity was off by 43 seconds of arc per century. Crunching the numbers was a painstaking task, taking days. When Einstein finished, his heart started to palpitate. The resulting motion was precisely the observed amount. He had outdone Newton!

Einstein published a comprehensive paper on his general theory of relativity and new theory of gravitation. The momentous news might have stayed inside war-torn Germany, except that two of Einstein's closest friends lived in neutral Holland. Hendrik Antoon Lorentz and Paul Ehrenfest received proofs of Einstein's paper and shared it with their astronomy colleague, Willem de Sitter.

Knowing that German periodicals were not reaching England, de Sitter sent Einstein's paper to Arthur Stanley Eddington, secretary of the Royal Astronomical Society. Eddington was flabbergasted. "Hitherto I had only heard vague rumours of Einstein's new work," he replied. "I do not think anyone in England knows the details of his paper."

Unable to publish a German paper, Eddington asked de Sitter to write a series of articles. In this way, the English-speaking astronomy community heard about Einstein's breakthrough during the darkest years of the war.

The exact accounting for Mercury's orbital motion impressed astronomers. Einstein's new theory also retained his earlier light-bending prediction, but the amount of bending is doubled. The slowing of clocks also remained, causing light emitted in the sun to be slightly redder than light emitted here on Earth.

At Mt. Wilson Observatory in Pasadena, Charles St. John tried to determine the cause of light reddening in the sun. Most astronomers believed that pressure in the solar atmosphere was six to seven times greater than on Earth. Lab experiments showed that pressure tends to shift light toward the red end of the spectrum; so astronomers generally believed that the observed solar redshifts were due to pressure.

John Evershed in India argued that pressure in the sun is much lower and could not cause the redshifts. For some parts of the spectrum, he measured the amount predicted by relativity. For others, he got different amounts.

St. John used the superior equipment at Mt. Wilson to observe areas of the solar spectrum caused by cyanogen gas in the solar atmosphere. Lab experiments showed that the wavelengths of light from cyanogen are independent of the gas pressure, so St. John could eliminate any pressure effects. He published preliminary results in 1917. There was no appreciable redshift. Relativity could not be correct.

`I am confident that there is no Einstein effect whatsoever.'

Heber Curtis
U.S. astronomer


Eddington was horrified. He had studied Einstein's new theory and decided that it was beautiful, elegant, powerful — and most likely correct. "St. John's latest paper has been giving me sleepless nights," he complained, "chasing mare's nests to reconcile the relativity theory with the results, or vice versa. I cannot make any headway."

Many astronomers were delighted that the prestigious Mt. Wilson astronomers had found Einstein wrong. They felt his theory was too complicated. At Lick Observatory near San Jose, Calif., astronomer Heber Curtis admitted in a publication that Einstein's theory was attractive for many reasons but added, "Many will feel that the idea of a four-dimensional time-space is fully as difficult of comprehension as was the mystery of gravitation, all-pervading, inexplicable, in our classical physical theories." Curtis would later become an outspoken critic of the theory.

In 1918, a total solar eclipse was visible from the United States. Lick Director William Wallace Campbell and Curtis went to nearby Goldendale, Wash., but they had left their good equipment in Russia when war broke out. Curtis cobbled together an Einstein program using borrowed equipment, but clouds threatened to repeat the failure in Russia. At the last minute, a break in the clouds allowed him to get photographs. Soon after the eclipse party returned, Curtis went off to Washington to do war work, and the plates lay unmeasured.

In Britain, Astronomer Royal Frank Dyson initiated plans to observe an eclipse in May 1919 — if the war ended in time. He wanted Eddington to lead one of two expeditions. The War Office tried to draft Eddington, but he objected on religious grounds.

Dyson appealed to national pride, arguing that Eddington was the only man who could determine whether or not a German theory would supplant the great Sir Isaac Newton. The War Office gave Eddington a reprieve on the condition that he observe this important eclipse and settle the matter.

Campbell got wind of the British plans and the race was on. When the war ended, he urged Curtis to return immediately and start measuring his plates. Meanwhile, Eddington and colleagues set sail to observe the eclipse.

Campbell headed an American delegation to Europe to help establish the International Astronomy Union — the first healing of international relations since the war. Days before he left Washington, he received word from Curtis: "I am confident that there is no Einstein effect whatsoever... you can make it as strong as you like."

Campbell announced Curtis's results at a special meeting of the Royal Astronomical Society. He cautioned that probable errors were large, but he felt Einstein's double value was ruled out, though the smaller value might exist. At the same meeting, Dyson read a cable from Eddington — he had poor results, but one plate seemed to indicate the full Einstein deflection.

Campbell suppressed publication of Curtis's results until the plates could be remeasured. The British had three sets of data. Eddington threw out one, because heating of the mirror had blurred the star images. The average of the other two agreed with Einstein.

A special meeting of the Royal Society and the Royal Astronomical Society announced the results in November 1919. Here was one of the most surprising turns of history. A combination of war weariness, fascination with the universe, and intrigue that British scientists had verified a German theory just after the war catapulted Einstein to world fame.

In London, the Times pronounced a "Revolution in Science" and "Newton Overthrown." The New York Times declared "Lights Askew in the Heavens" and "Men of Science Agog."

Dyson admitted to George Hale, the astronomer and founder of Mt. Wilson observatory, that he had initially been a skeptic. "Now I am trying to understand the principle of relativity and am gradually getting to think I do."

Hale confessed: "The complications of the theory of relativity are altogether too much for my comprehension. If I were a good mathematician I might have some hope of forming a feeble conception of the principle, but as it is I fear it will always remain beyond my grasp."

Hale was not alone among American astronomers in having difficulty with Einstein's new theory. Their inability to master the details of general relativity bolstered their resistance to it for another decade.

Jeffrey Crelinsten is a science writer and historian based in Toronto. His book, "Einstein's Jury: The Race to Test Relativity" (Princeton University Press), will be released in spring 2006.
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Deborah Valkenburg
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« Reply #2 on: May 04, 2008, 11:12:35 pm »

The race to test relativity

Oct 23, 2005 01:00 AM
Jeffrey Crelinsten
Albert Einstein published his theory of special relativity in 1905, but it wasn’t until 1919, after British astronomers announced that they had verified a prediction from his generalized theory that the sun’s gravity bends light, that he became a superstar, hounded by reporters, admirers and detractors. This three-part series by Jeffrey Crelinsten examines how astronomers around the world debated and tested Einstein’s theory of relativity into the 1930s.

Part 3. Einstein Triumphs

Einstein's vindication by British astronomers made international headlines. Lead astronomer Arthur Eddington was dumbfounded at the enormous public response. "All England has been talking about your theory," he wrote Einstein. "It has made a tremendous sensation."

Although Einstein's colleague, Erwin Freundlich, had been "first in the field," as a pacifist and science internationalist Eddington was delighted that the British had been the ones to prove Einstein correct. "It is the best possible thing that could have happened ... in giving this object-lesson of the solidarity of German and British science even in time of war."

Einstein, too, was thrilled that the British had taken the trouble to do the test. Now he wanted astronomers to verify his gravitational redshift in the solar spectrum. "If it were proved that this effect does not exist in nature," he insisted, "then the whole theory would have to be abandoned."

Indeed, while relativity had passed two tests — explaining the motion of Mercury's orbit and now light-bending due to gravity — the explanation for the redshift of the solar spectrum was still unclear. Many scientists refused to accept relativity until this third test could be verified. Einstein received several nominations for the 1919 Nobel Prize in physics, but the committee decided to pass him over until the redshift problem could be clarified.

Most astronomers were not as keen as Eddington on relativity and did not accept his eclipse results. Many believed they would be able to explain the light-bending as a refraction effect in the sun's atmosphere. William Wallace Campbell and Heber Curtis at Lick Observatory had obtained photographs at an eclipse in 1918. Curtis thought his plates proved that Einstein was wrong, but his probable errors were very large and Campbell chose not to publish his results. Campbell also questioned Eddington's decision to throw out one set of British data, which, if averaged with the others, would not have confirmed Einstein.

Curtis was convinced that he had disproved Einstein and was furious when Campbell refused to publish his negative results. Campbell insisted that Curtis rework his measurements of the 1918 plates. He also wanted to take new night observations of the eclipse star field in order to improve accuracy when comparing them with the eclipse photographs. Curtis left Lick Observatory before the work was finished to become director of Allegheny Observatory in Pittsburgh. He missed the clear California skies and the large telescopes but preferred to be his own boss.

Campbell replaced Curtis with a young, Swiss-born astronomer, Robert Trumpler. Trumpler was a top-notch observer but, having been trained in Europe, he was also conversant with theoretical physics, including relativity. This talent for theory would come in handy during the acrimonious debates that were to follow.

Campbell spent over a year redoing the 1918 eclipse results. He discovered that instrument problems had caused blurring of the star images. His improved measuring techniques yielded a light-bending less than Einstein's prediction. Though he never published, he announced his results at several scientific meetings, and everyone knew that Campbell disagreed with the British conclusions.

At Mt. Wilson Observatory, Charles St. John undertook a systematic study to sort out the various mechanisms at play in shifting the solar spectrum. He was still getting a zero shift in wavelengths due to cyanogen gas, which is unaffected by pressure. He expanded his search to other elements to crack the riddle. John Evershed at Kodaikanal Observatory in India had found evidence for a strange "Earth effect," where the Earth repels solar gases, causing a redshift due to movement away from Earth (Doppler shift). He began observations of the planet Venus to study the spectrum of sunlight reflected from its surface, hence coming from the "back side" of the sun, and compare it with the spectrum of direct sunlight. If his "Earth effect" was real, then the reflected light should show a violet shift.

Others joined the hunt for the "Einstein effect" in the sun, including two young German spectroscopists, Leonhard Grebe and Albert Bachem. They received funding from Einstein's new physics institute, which the German government had promised him in 1913 as part of their package to lure him to Berlin.

The war had intervened, but Einstein's post-war fame made him a major cultural asset for the new government, which quickly funded his institute. In 1920, Grebe and Bachem claimed they had found the "Einstein effect" in the sun. The British journal Nature quoted Einstein giving uncritical, enthusiastic praise to the German duo for finally resolving the issue. The New York Times trumpeted "Einstein's Third Victory."

St. John threw cold water on the German results, however, describing the inherent complexities and questioning their procedures. Evershed agreed. The issue remained unresolved. That year Einstein received more than a dozen nominations for the 1921 Nobel Prize for physics, most of them for his work on relativity. The committee decided not to give any physics prize that year because relativity was still too controversial.

Seven expeditions set up camp in Australia to test Einstein again at the 1922 eclipse. Campbell designed completely new equipment: two "Einstein cameras" and two shorter focal length cameras using a new lens from Eastman Kodak to allow photographs of a large area around the sun without distortion. With many more star images, they could test how the light-bending reduces with distance from the sun.

Campbell arranged for the Australian Navy to transport his party to Wallal, a dry, isolated site where the eclipse would last the longest and the weather was promising. Others had rejected this site, thinking it was inaccessible. Evershed from India and Clarence Augustus Chant from Canada, the first director of the David Dunlap Observatory in Toronto, joined Campbell at Wallal.

The British went to Christmas Island to vindicate their 1919 results. Freundlich co-located there with a joint German-Dutch expedition — his first chance since 1914. Two Australian groups from Adelaide and Sydney tried their luck elsewhere.

Campbell had perfect weather. Instrumental problems plagued Evershed, who returned home empty-handed and exasperated. The British and Freundlich faced disappointment from clouds. The Australians had excellent weather, but within a few weeks Sydney astronomers announced that their plates were unusable. Their equipment was not up to scratch. Expedition leader William Ernest Cooke predicted "the first satisfactory results would be those of Dr. Campbell, of the Lick Observatory." The public would probably have to wait several years, he said, "because the most minute calculations and measurements would require to be carried out before any announcement on the subject could be accepted as being correct."

It was almost a year before Campbell felt ready to announce preliminary results. An early announcement from the Canadians supporting Einstein prodded him to act. Trumpler and Campbell had completely measured three out of four plates, so Campbell decided to release preliminary results in order not to be scooped by the Canadians. For years, Lick astronomers had been saying that Einstein was wrong. Now, perhaps to their own surprise, they announced Einstein was right. The impact on astronomers around the world was enormous.

By now Evershed had discovered systematic errors in his earlier observations that ruled out his strange "Earth effect." Further tests verified the "Einstein effect" in the sun. However, almost everyone waited for an opinion from Mt. Wilson. When Charles St. John finally announced results consistent with Einstein's prediction, most astronomers were convinced.

Despite the powerful support from Lick and Mt. Wilson, the 1920s saw continued debate about Einstein's theory of gravitation. Charles Perrine, a former associate of Campbell, complained: "The whole relativity business has seemed to me unreal and so purely philosophical that to accept it is to upset our previously carefully constructed and very material systems."

Curtis confided to Chant: "There may be a deflection, but I do not feel that I shall be ready to swallow the Einstein theory for a long time to come, if ever. I'm a heretic."

Curtis teamed up with a discontented theoretical astronomer, Charles Lane Poor from Columbia University, who mounted a systematic campaign against Einstein's theory and the Lick eclipse results. Poor focused on the complicated mathematics and "metaphysical" nature of Einstein's theory. Trumpler's facility in modern physics was an effective counter to attacks by Poor and others. As the decade progressed, George Hale, the founder of Mt. Wilson Observatory, and other Americans invited European theorists to give lectures on relativity. The Americans' understanding improved.

By the end of the decade, Mt. Wilson astronomer Edwin Powell Hubble had found that the more distant a galaxy is, the faster it recedes from us. This startling discovery meant that the universe is expanding — a prediction that Dutch astronomer Willem de Sitter had made using Einstein's field equations in 1916. General relativity quickly became useful for astronomers interested in the large-scale structure of the universe. Einstein's theory moved from being a controversial speculation to a working tool for astronomers.

Astronomers' early debates about relativity and its astronomical tests entrenched the theory's acceptance, yet reinforced the belief that it violates common sense and is incomprehensible — a belief that exists to this day.


Jeffrey Crelinsten is a science writer and historian based in Toronto. His book, "Einstein's Jury: The Race to Test Relativity" (Princeton University Press), will be released in spring 2006.
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