by Mike Bennett
At the end of the 1920s, Bohr, Heisenberg and Pauli had worked out what was called the Copenhagen interpretation of quantum mechanics, but it was rejected by Planck, and by Schrödinger, Laue and Einstein as well. Planck expected that wave mechanics would soon render quantum theory (his own child) unnecessary. This was not to be the case, however. Further work only cemented the concept of quantum theory.
When the Nazis seized power in 1933, Planck was seventy-four. He witnessed many Jewish friends and colleagues expelled from their positions and humiliated, and hundreds of scientists wanted to emigrate from Germany. Planck tried to persuade them to stay and continue working. He hoped the crisis would abate soon and the political situation would improve.
The next great physicist and chemist of this era was Ernest Rutherford. He was a New Zealand-born Canadian/British physicist who became known as the father of nuclear physics. He was born in 1871 in Brightwater, New Zealand, and died in 1937 in Cambridge, UK. He was knighted in 1914, and is also a Nobel Laureate.
Early in his career he discovered the concept of radioactive half-life, and proved that radioactivity involved the transmutation of one chemical element into another. He also differentiated and named alpha and beta radiation. This work was done at McGill University in Canada. It was the basis for the Nobel Prize in Chemistry he was awarded in 1908.
Rutherford moved in 1907 to the University of Manchester (a great seat of physics) in the UK, where he and Thomas Royds proved that alpha radiation is created by helium ions. Rutherford performed his most famous work after he became a Nobel Laureate. In 1911, although he could not prove whether it was positive or negative, he theorised that atoms have their charge concentrated in a very small nucleus, and thereby pioneered the Rutherford model of the atom.
This was brought about through his discovery and interpretation of Rutherford scattering in his gold foil experiment. He is also credited as the first scientist to split the atom. He achieved this breakthrough at Manchester University in 1917 in a nuclear reaction between nitrogen and alpha particles, in which he also discovered and named the proton. He was then promptly poached by Cambridge University.
Rutherford became Director of the Cavendish Laboratory at Cambridge University in 1919. Under his leadership the neutron was discovered by James Chadwick in 1932. In the same year, the first experiment to split the atomic nucleus in a fully controlled manner was performed by his students John Cockcroft and Ernest Walton working under his supervision. After his death in 1937, he was honoured by being interred with the greatest scientists of the United Kingdom, near Sir Isaac Newton’s tomb in Westminster Abbey. The chemical element Rutherfordium was named after him in 1997.
At Cambridge, Rutherford started to work with J.J. Thomson on the conductive effects of X-rays on gases. This made advancements based on the work which led to the discovery of the electron by Thomson in 1897. Hearing of Becquerel’s experience with uranium, Rutherford started to explore its radioactivity, discovering two types that differed from X-rays in their penetrating power. Continuing his research in Canada, he coined the terms alpha ray and beta ray in 1899 to describe the two distinct types of radiation.
He then discovered that thorium gave off a gas, which produced an emanation which was itself radioactive and would coat other substances. He found that a sample of this radioactive material of any size invariably took the same amount of time for half of the sample to decay, known as its “half-life” (eleven-and-a-half minutes in this case).
From 1900 to 1903, he was joined at McGill by the young chemist Frederick Soddy (Nobel Prize in Chemistry, 1921), for whom he set the problem of identifying the thorium emanations. Once he had eliminated all the normal chemical reactions, Soddy suggested that it must be one of the inert gases, which they named thoron (later found to be an isotope of radon). They also found another type of thorium that they called Thorium X, and kept on finding traces of helium. They also worked with samples of “Uranium X” from William Crookes, and radium from Marie Curie.
In 1902, they produced a “Theory of Atomic Disintegration” to account for all their experiments. Up until then atoms were assumed to be the indestructible basis of all matter, and although Curie had suggested that radioactivity was an atomic phenomenon, the idea of the atoms of radioactive substances breaking up was a radically new idea. Rutherford and Soddy demonstrated that radioactivity involved the spontaneous disintegration of atoms into other types of atoms (one element spontaneously being changed into another).
In 1903, Rutherford considered a type of radiation discovered, but not yet named, by French chemist Paul Villard in 1900, as an emission from radium. He realised that this observation must represent something different from his own alpha and beta rays, due to its very much greater penetrating power. Rutherford therefore gave this third type of radiation the name of gamma rays. All three of Rutherford’s terms are in standard use today. Other types of radioactive decay have since been discovered, but Rutherford’s three types are the most common.
In Manchester, he continued to work with alpha radiation. In conjunction with Hans Geiger, he developed zinc sulphide scintillation screens and ionisation chambers to count alphas. By dividing the total charge they produced by the number counted, Rutherford decided that the charge on the alpha was two. In late 1907, Ernest Rutherford and Thomas Royds allowed alphas to penetrate a very thin window into an evacuated tube. As they sparked the tube into discharge, the spectrum obtained from it changed as the alphas accumulated in the tube. Eventually, the clear spectrum of helium gas appeared, proving that alphas were at least ionised helium atoms, and probably helium nuclei.
Before leaving Manchester in 1919 to take over the Cavendish laboratory in Cambridge, Rutherford became the first person to deliberately transmute one element into another. In this experiment, he had discovered peculiar radiations when alphas were projected into air, and narrowed the effect down to the nitrogen, not the oxygen in the air. Using pure nitrogen, Rutherford used alpha radiation to convert nitrogen into oxygen through the nuclear reaction 14N + α → 17O + proton.
A construction of nuclei where a single element could have different atomic weights, and therefore contain other matter, had been inferred for many years. It was also found that the different atomic weights all varied as whole numbers (that of the weight of hydrogen). Hydrogen was known to be the lightest element, and its nuclei presumably the lightest nuclei. Because of all of this evidence, Rutherford decided that a hydrogen nucleus was possibly a fundamental building block of all nuclei, and also possibly a new fundamental particle as well. Thus Rutherford postulated the hydrogen nuclei to be a new particle in 1920, which he called the proton.
In 1921, while working with Niels Bohr, Rutherford theorised about the existence of neutrons, which could somehow compensate for the repelling effect of the positive charges of protons. This could occur by causing an attractive nuclear force, and thus keep the nuclei from flying apart from the repulsion between the protons. The only alternative to neutrons was the existence of “nuclear electrons” which would counteract some of the proton charges in the nucleus, since by then it was known that nuclei had about twice the mass that could be accounted for if they were simply assembled from hydrogen nuclei (protons). But how these nuclear electrons could be trapped in the nucleus was a mystery.
Rutherford’s theory of neutrons was proved in 1932 by his associate James Chadwick, who recognised neutrons immediately when they were produced by other scientists and later by himself, in bombarding beryllium with alpha particles. In 1935, Chadwick was awarded the Nobel Prize in Physics for this discovery.
Rutherford’s research, and the work done under him as laboratory director, established the nuclear structure of the atom and the essential nature of radioactive decay as a nuclear process. Rutherford’s team, using natural alpha particles, demonstrated nuclear transmutation. He is known as the father of nuclear physics. Rutherford died too early to see Leó Szilárd’s idea of controlled nuclear chain reactions come into bein
g.
Eight years after the birth of Rutherford, another true icon of modern theoretical physics, Albert Einstein, was born in Ulm, Germany. Einstein developed the general theory of relativity, one of the two pillars of modern physics. He is best known for his mass-energy equivalence formula E = mc2. He is also a Nobel Physics Laureate.
Albert Einstein started his career as a patent clerk. While working, Einstein evaluated patent applications for electromagnetic devices. He quickly mastered the job, leaving him time to ponder on the transmission of electrical signals and electrical-mechanical synchronisation, an interest he had been cultivating for several years. While at the polytechnic school he had studied Scottish physicist James Maxwell’s electromagnetic theories which describe the nature of light, and discovered a fact unknown to Maxwell himself: that the speed of light remained constant. However, this violated Isaac Newton’s laws of motion because there is no absolute velocity in Newton’s theory. This insight led Einstein to formulate the principle of relativity.
In 1905 (often called Einstein’s “miracle year”) he submitted a paper for his doctorate and had four papers published in the Annalen der Physik, one of the best-known physics journals. The four papers (the photoelectric effect, Brownian motion, special relativity, and the equivalence of matter and energy) would alter the course of modern physics and bring him to the attention of the academic world. In his paper on matter and energy, Einstein deduced the well-known equation E = mc2, suggesting that tiny particles of matter could be converted into huge amounts of energy, foreshadowing the development of nuclear power. There have been claims that Einstein and his wife, Mileva Marić, collaborated on his celebrated 1905 papers, but historians of physics who have studied the issue find no evidence that she made any substantive contributions. In fact, in the papers, Einstein only credits his conversations with Michele Besso in developing relativity.
At first Einstein’s 1905 papers were ignored by the physics community. This began to change when he received the attention of Max Planck, perhaps the most influential physicist of his generation and founder of quantum theory. With Planck’s complimentary comments and his experiments that confirmed his theories, Einstein was invited to lecture at international meetings, and he rose rapidly in the academic world. He was offered a series of positions at increasingly prestigious institutions, including the University of Zürich, the University of Prague, the Swiss Federal Institute of Technology and finally the University of Berlin, where he served as director of the Kaiser Wilhelm Institute for Physics from 1913 to 1933. As his fame spread, Einstein’s marriage fell apart.
But hey, it can happen to anyone. My own marriage started getting ropey when my wife started accusing me of being sexist. I was very upset by this, but what can you do? It happened when we were watching a TV comedy show featuring Billy Connolly and his wife Pamela Stephenson. They are both world-class comedians and entertainers. After a heated discussion on the difference between the sexes, Billy Connolly asked her why, if women are so good at multitasking, are they unable to have a headache and sex at the same time. I thought that this was hilarious, but my wife considered it to be sexist. Things went downhill from there. I guess that everybody gets fed up with me eventually, as some years later she filed for divorce.
Under the Family Scotland Act (1996), it is irrelevant how poorly either the husband or the wife have behaved. It is sufficient just to say that the marriage had run its course (whatever that means) and a divorce is granted with the couple’s assets being split 50-50.
I remember that at the final divorce hearing my poor sense of humour finally got the better of me. The Sheriff presiding over this hearing was a frosty octogenarian lady, who clearly had no sense of humour at all. After I had been dragged across the coals for over two hours, she asked me if everything had been declared fairly and honestly, to confirm that she was now in a position to make a judgement based on the required 50-50 split.
I had lost the plot by this time, and informed her that she had not taken into account my wife’s breasts. As I had paid for the implants, I suggested that the law required me to take possession of one of her breasts. The sheriff then informed me that if I made any other similar comments, I would be held in contempt of court. I then said that if I could not get custody of one of her breasts, could I have access to one at the weekends. I was held in contempt and taken down to the cells.
OK, back to the science.
Due to Einstein’s constant travel and the intense study required by his work, the arguments about his children and the family’s meagre finances led Einstein to the conclusion that his marriage was over. Einstein began an affair with a cousin, Elsa Löwenthal, whom he later married. He finally divorced his wife Mileva in 1919 and as a settlement agreed to give her the money he might receive if he ever won a Nobel Prize.
In November 1915, Einstein completed the general theory of relativity, which he considered his masterpiece. He was convinced that general relativity was correct because of its mathematical beauty, and because it accurately predicted the perihelion of Mercury’s orbit around the sun, which fell short in Newton’s theory. General relativity theory also predicted a measurable deflection of light around the sun when a planet or another sun oribited near the sun. That prediction was confirmed in observations by British astronomer Sir Arthur Eddington during the solar eclipse of 1919. In 1921, Albert Einstein received word that he had received the Nobel Prize for Physics. Because relativity was still considered controversial, Einstein received the award for his explanation of the photoelectric effect.
In the 1920s, Einstein launched the new science of cosmology. His equations predicted that the universe is dynamic, ever expanding or contracting. This contradicted the prevailing view that the universe was static, a view that Einstein had held earlier, and which was a guiding factor in his development of the general theory of relativity. But his later calculations in the general theory indicated that the universe could be expanding or contracting. In 1929, astronomer Edwin Hubble found that the universe was indeed expanding, thereby confirming Einstein’s work. In 1930, during a visit to the Mount Wilson Observatory near Los Angeles, Einstein met with Hubble and declared the cosmological constant, his original theory of the static size and shape of the universe, to be his “greatest blunder”.
While Einstein was touring much of the world speaking on his theories in the 1920s, the Nazis were rising to power under the leadership of Adolf Hitler. Einstein’s theories on relativity became a convenient target for Nazi propaganda. In 1931, the Nazis enlisted other physicists to denounce Einstein and his theories as Jewish physics. At this time, Einstein learned that the new German government, now fully controlled by the Nazi party, had passed a law barring Jews from holding any official position, including teaching at universities. Einstein also learned that his name was on a list of assassination targets, and a Nazi organisation published a magazine with Einstein’s picture and the caption Not Yet Hanged on the cover.
In December 1932, Einstein decided to leave Germany forever. He took a position at the newly formed Institute for Advanced Study at Princeton, New Jersey, which soon became a Mecca for physicists from around the world. It was here that he would spend the rest of his career trying to develop a unified field theory, an all-embracing theory that would unify the forces of the universe, and thereby the laws of physics, into one framework. This would refute the accepted interpretation of quantum physics. Other European scientists also fled various countries threatened by Nazi takeover and came to the United States. Some of these scientists knew of Nazi plans to develop an atomic weapon. For a time, their warnings to Washington went unheeded.
In the summer of 1939, Einstein, along with another scientist, Leó Szilárd, was persuaded to write a letter to President Franklin D. Roosevelt to alert him of the possibility of a Nazi atomic bomb. President Roosevelt could not risk the possibility that Germany might develop an atomic bomb first. The letter is believed to be the key factor that motivated the United States to investigate th
e development of nuclear weapons. Roosevelt invited Einstein to meet with him and soon after the United States initiated the Manhattan Project.
Not long after he began his career at the Institute in New Jersey, Albert Einstein expressed an appreciation for the “meritocracy” of the United States and the right people had to think what they pleased, which was something he didn’t enjoy as a young man in Europe. In 1935, Albert Einstein was granted permanent residency in the United States and became an American citizen in 1940. As the Manhattan Project moved from the drawing board to testing and development at Los Alamos, New Mexico, many of his colleagues were asked to develop the first atomic bomb, but Einstein was not one of them.
According to several researchers who examined FBI files over the years, the reason was that the US government didn’t trust Einstein’s lifelong association with peace and socialist organisations. FBI director J. Edgar Hoover went so far as to recommend that Einstein be kept out of America by the Alien Exclusion Act, but he was overruled by the US State Department. Instead, during the war, Einstein helped the US Navy evaluate designs for future weapons systems and contributed to the war effort by auctioning off priceless personal manuscripts. He sold a handwritten copy of his paper on special relativity for $6.5 million, and it is now in the Library of Congress.
On 6th August 1945, while on vacation, Einstein heard the news that an atomic bomb had been dropped on Hiroshima, Japan. He soon became involved in an international effort to try to bring the atomic bomb under control, and in 1946, he formed the Emergency Committee of Atomic Scientists with physicist Leó Szilárd. In 1947, in an article that he wrote for The Atlantic Monthly, Einstein argued that the United States should not try to monopolise the atomic bomb, but instead should supply the United Nations with nuclear weapons for the sole purpose of maintaining a deterrent. At this time, Einstein also became a member of the National Association for the Advancement of Coloured People. He corresponded with civil rights activist W. E. B. Du Bois and actively campaigned for the rights of African-Americans.
