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Charles Tracy L P S / y a a w s n e v a R n a v v e l t e D connections

Last year we celebrated the International Year of Physics — time and light. In particular, it described how space also known as Einstein Year. In the century since Einstein’s becomes distorted near a massive object such as a star, so that light follows a curved path rather than annus mirabilis (see CATALYST Vol. 16, No. 1) there has travelling in a straight line (Figure 1). been a revolution in the study of physics. This article explores Its publication in wartime and the fact that it was the links between some of the architects of this revolution. written in German meant that few people read it. However, one person who did read it was the British astronomer Arthur Eddington. The story goes that it was Eddington who brought Einstein to the world’s attention — though Einstein might have disagreed. instein did not become instantly famous in Eddington was a conscientious objector. As such, GCSE key words 1905; it took several years before he became a he should have spent the war in jail. Instead, he got Gravity Eglobal icon. In 1915, while Europe was caught official permission to prepare for a trip to observe a scattering up in the First World War, Einstein broadened his total eclipse of the Sun — a rare event. His intention special theory of relativity. His general theory of was to verify Einstein’s general theory of relativity. relativity predicted the effects of gravity on space, Einstein felt that no such verification was needed, but

14 Catalyst Figure 2 An electron Distant star, Apparent has spin. In a magnetic hidden position behind Sun of star field, it can either spin clockwise (spin up) or anti-clockwise (spin down) Magnetic field line

and black body radiation. The theory came from a mistake he made in a lecture: while trying to show Photons are the that theory could not predict the behaviour of particles which carry photons, he accidentally showed that it could. the energy of After some correspondence with Einstein, Bose electromagnetic developed a new type of statistics that described the radiation. Einstein behaviour of photons and similar particles. These used the idea of photons to explain the particles, which have whole-number values (0, 1, 2 photoelectric effect. etc.) of a property called spin, are now known as bosons after Satyendra Bose. Particles that are not bosons are called fermions. 1 1 1 They have a spin of 2⁄ , 1 2⁄ , 2 2⁄ and so on. This family Sun Starlight bent by Sun's gravity of particles includes protons, neutrons and electrons (Figure 2), and takes its name from Enrico Fermi, the Italian American who built the first nuclear chain reactor in a Chicago squash court in 1942. This was 4 years after he had escaped from In his annus mirabilis, the fascists at the time of his Nobel prize ceremony. Einstein published three Figure 1 One of the After collecting his prize — for work on creating papers. Their contents initiated modern implications of the radioactive isotopes through neutron bombardment cosmology and general theory of — Fermi slipped out of the Stockholm Institute and made good his escape. quantum mechanics — relativity is that space the foundations of is distorted by large modern physics. masses like the Sun. Physics and facism Moon Even light will alter its Another scientist who fled the fascists was . course. So stars appear Bohr stayed in his native Denmark for 3 years of the out of position, Nazi occupation. But, in 1942, he escaped via Sweden something we can only to England in the empty bomb rack of a British plane. He made his way to America and joined Fermi and Earth see when the Sun’s light is blocked by the Moon others in the Manhattan Project, building America’s during a solar eclipse atomic bomb. Before he left, Bohr had had a secret meeting with Classical mechanics, his former pupil, the German physicist Werner developed by Newton Eddington went ahead as planned in 1919. During Heisenberg. In the 1920s, Heisenberg had developed and others, is used to the eclipse, Eddington measured the apparent shift in a mathematical method to describe the behaviour of describe large-scale the positions of stars that were beyond the Sun, as . This was one of the foundations of quantum phenomena. It does not their light rays were curved by its gravity. His results mechanics, the basis of much of today’s physics. work on the scale of atoms — quantum were in close agreement with Einstein’s predictions. Later, during the Second World War, he was a mechanics must be used The international press were captivated. One member of the Uranium Club — the German group instead. It is the basis of reporter suggested to Eddington that he was one of trying to develop a fission weapon. In 1941, he semiconductors and only three men who understood Einstein’s theory. travelled to Copenhagen to meet his old friend Bohr therefore much of our Eddington replied, possibly ironically: ‘I am trying to and they went for a stroll after dinner. Their discussion technological world. think who the third person is.’ remains a mystery. Did Heisenberg pass information to Bohr, or did he try to enlist Bohr’s help with the Predicting particles Uranium Club? We may never know for sure. That person could well have been Satyendra Bose, The Uranium Club also included the German the Indian physicist who translated Einstein’s paper physicist Hans Geiger. During the Second World War, on the general theory of relativity from German into Geiger was an enthusiastic Nazi. This was totally at English. In 1924, Bose devised a theory for photons odds with the vehemently anti-fascist views of his

April 2006 15 Right: Computer graphic of the interior of the Sun. Scientists now know that the Sun is a massive nuclear fusion reactor L P S / k y l u K u a h e M

The Hot Big Bang former tutor, , for whom he had is best remembered for developing a theory, generally performed the famous alpha particle scattering exper- theory that describes the nuclear processes inside the accepted by scientists iments during 1908. In 1933, Rutherford had set up Sun. His theory explained, at last, how the Sun could today, says that the the Academic Assistance Club to help Jewish scholars stay so hot and have lasted so long — 4.5 billion universe exploded into escape the rising hatred in . years, long enough for life to evolve on Earth. Only existence, emerging Another of Rutherford’s students, , 50 years earlier, William Thomson (Lord Kelvin) had from a single point, could have used some help in the previous war. Chad- estimated the age of the Sun as about 20 million about 14 billion years ago. wick left Manchester in 1914 to work with Geiger in years — 200 times too small. Berlin. Unfortunately for him, the assassination of Kelvin had described the Sun as an incandescent Archduke Ferdinand on 28 June 1914 led to the out- rock that had gained all its energy from ancient break of the First World War. He was trapped in meteor impacts. Somewhat boldly, in 1900 he had Germany and spent 4 years interned in the stables of a stated that: ‘There is nothing new to be discovered in German racecourse. On his return home, he joined physics now. All that remains is more and more Rutherford at the Cavendish Laboratory in Cambridge precise measurement.’ Had Kelvin waited 5 years — where his work led to the in for Einstein’s influential papers — he might have been 1932. more cautious. The age of the Sun Physics, past and future The following year, the Russian physicist, George Hans Bethe died in 2005, the year in which we Gamow, escaped a different tyranny by defecting celebrated 100 years of astute, committed and often

G Visit www.physics.org/ from Stalin’s to America. Gamow brave people who made the century of physics. Their evolution/evolution.asp worked on many things (including the genetic code), stories are as much about human endeavour, strength for an animated history but is renowned for his description of the Hot Big and frailty as of laboratories and brassware. The of physics. Bang. The paper, which he wrote with his student physics they have developed would be unrecognisable Ralph Alpher, was published in 1948. When he heard to Kelvin. Physics is still changing. Who knows what that Hans Bethe was in town, Gamow could not resist will happen in the next 100 years? a little radiation joke: he asked Bethe to add his name to the paper which became the Alpher, Bethe, Gamow Charles Tracy is a schools adviser in Hertfordshire and develops (α,β,γ) paper. physics teaching resources.

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