Physics Evolution - Text Only Version
1890 to 1920
The optimism of a new century spread into science. Many believed that all that was needed was to tidy up loose ends and refine measurements. This confidence was shattered by the discovery of radioactivity, the publication of Relativity and the First World War in Europe.
Hendrik Lorentz, physicist – He showed how fast objects contract (1853-1928)
Dutch born in Arnhem.
As well as being a great and influential theoretical physicist, Hendrick Lorentz was a modest man who was generous with his time and interested in other people.
Lorentz, like most 19th century physicists, was shocked by the discovery of radioactivity and had his confidence shaken by its implications for Physics. Yet, like Maxwell, whose work he developed, he contributed to the development of new strands of Physics – in his case, Special Relativity.
He developed theories of the production, propagation and reflection of light based on Maxwell’s equations and proposed the existence of electrons. He helped devise (and gave his name to) a set of mathematical transformations that calculate the contraction of a fast-moving object. Published in 1904, these form the basis of Einstein’s special theory of relativity.
In later life, he chaired the committee that analysed the expected movements of sea water when the Zuyderzee on the Dutch coast was drained and reclaimed from the sea.
- Lorentz’s developed his transforms to work with * Hertz’s wave equation.
- Lorentz developed transforms to work with Maxwell’s equations.
- Einstein used Lorentz’s transforms in his Special Theory of Relativity.
Marie Curie née Maria Sklodowska, physicist – Lasting legacy from a tragic life (1867-1934)
French physicist born in Warsaw, Poland
Marie Curie was the first woman to win the Nobel Prize and the first person to win it twice. As well as her pioneering work in science, she was very active in the First World War, setting up mobile X-ray units with her daughter Eve Curie.
Marie Curie was working on magnetic effects. However, following Becquerel’s discovery of radiation, she switched her field of study. Given the strangeness of this new field, few men were studying it so it was easier for her, as a woman, to get backing.
She observed that the mineral pitchblende was more active than expected (given its uranium content). She concluded that there was a previously unknown chemical element in the pitchblende.
She worked tirelessly with her husband, Pierre, to chemically reduce the pitchblende and concentrate the unknown component. In the end, from tons of uranium ore, they obtained a few hundredths of a gram containing the source of the radiation. In it were two highly radioactive new chemical elements. They named them polonium, after Marie Curie’s homeland and radium.
When Pierre Curie was killed in a road accident, Marie Curie took over Pierre’s chair at the Sorbonne, becoming the first woman to teach there.
Because of a lack of knowledge about the dangers of radioactivity, she had been exposed to massive doses of radiation and she eventually died from leukemia.
- Although this was a new branch of physics, Curie relied on the elements and gaps in Mendeleev’s table
- Rutherford used Curie’s discoveries to probe the atom
Sir Joseph John Thomson, physicist – Clumsy but accomplished experimenter (1856-1940)
Physicist born near Manchester, England.
Joseph John (J. J.) Thomson was going to be an engineer. However, after the death of his father (when Thomson was 16), his mother couldn’t afford the large apprenticeship fee. So he stayed at College in Manchester and, some years later, won a scholarship to Cambridge where he worked for the rest of his life.
At the age of 28, he was given the senior post at the Cavendish Laboratory despite, as his assistant put it “being very awkward with his fingers” and being discouraged from handling the instruments. He was, however, inspired with his designs for apparatus and interpretations of experimental results.
His work on gas discharges and cathode rays led, in 1897, to his discovery of the electron – his interpretation of the results of deflecting cathode rays.
A theorist as well as an experimenter, Thomson described the plum-pudding model of atomic structure, in which electrons were like negative ‘plums’ embedded in a ‘pudding’ of positive matter. This was the first step on the road to our current model of the atom.
- Thomson’s discovery of the electron developed and helped explain Hallwachs’ experiment
- Thomson worked with Rutherford
- Einstein later explained the photoelectric effect using the electron
- Bohr developed Thomson’s model of the atom.
Max Planck, physicist – Almost a musician (1858-1947)
Physicist, born in Kiel, Germany
Max Planck was amongst the physicists who, at the end of the 19th century, felt there were a few loose ends to be tied up. He then became one of the founders of quantum physics in the 20th century. At school, he was as talented in music as he was in mathematics and considered taking up a career in music.
After advice from a musician – “if you need to ask advice, study something else” – he studied Physics and Mathematics at university. He went on to teach (at first for no salary) at a number of Universities before becoming professor of Theoretical Physics at Berlin University in 1888.
As a younger man, Planck had worked on thermodynamics – the classical physics of the late 19th century. In trying to solve the problem of the spectrum of black body radiation, he proposed that radiation was not given out in a continuous flow. He introduced the planck constant, h, to relate the energy to the frequency of radiation.
This theory revolutionised physics; Einstein used his ideas in his treatment of the photoelectric effect, saying that the radiation travels in discrete packets – or quanta – with an amount of energy E = hf. This was the beginning of quantum mechanics.
- Planck built on Maxwell’s ideas of thermodynamics.
- Along with Michelson, Planck’s work led to a rethink on the behaviour of light.
- Einstein used Planck’s idea of packets of radiation to explain the photoelectric effect.
- Bohr’s model of the atom used quantised levels based on Planck’s ideas of packets of radiation.
Baron, Sir Ernest Rutherford, physicist – Why was he called “The Crocodile”? (1871-1937)
Physicist born in Nelson, New Zealand
Ernest Rutherford was born and grew up in rural New Zealand but worked in England and Canada. During his life, he founded nuclear physics, was the first successful alchemist and set up the Academic Assistance Council to help scientists flee Nazi Germany.
Rutherford left new Zealand at the age of 23, with three degrees and a scholarship to Cambridge, where he joined J. J. Thomson’s group at the Cavendish. He proposed that radioactivity was the spontaneous disintegration of atoms and conceived the idea of half life.
Working with Geiger, he showed that alpha particles were ionised helium and used them to probe inside gold atoms in his thin foil experiment. He was astonished by the results of this experiment saying it “was like firing an artillery shell at tissue paper and seeing it bounce back”. From this, he deduced that atoms must contain a dense nucleus.
He was a hugely popular and motivational team leader and was known as the ‘crocodile’ either because he wouldn’t let go of a problem or because he only ever looked forward or maybe because his booming voice signalled his approach like the ticking clock in Captain Hook’s favourite crocodile.
He went on to find proof of the proton, predict the neutron and transmute nitrogen into oxygen. He later achieved the alchemists’ goal of creating gold from another metal; unfortunately, the other metal was platinum, which is even more expensive than gold!
- Rutherford used Marie Curie’s work on radioactivity to probe the atom.
- Rutherford and Thomson worked together .
- Geiger worked under Rutherford in Manchester and helped carry out the alpha scattering experiments.
- Bohr’s model of the atom developed Rutherford’s idea of a nucleus.
- Chadwick worked with Rutherford in Manchester and Cambridge.
Hans Geiger, nuclear physicist – A member of the “Uranium Club” (1882-1945)
Nuclear physicist born in Neustadt-an-der-Haardt.
Hans Geiger was born, educated and lived most of his life in Germany, spending 5 years at Manchester working with Ernest Rutherford.
He was a reluctant, conscript in the First World War and a member of the Uranium Club in the Second. He was a member of the Nazi party and was unsympathetic (at the least) to Jewish colleagues who lost their academic jobs after Hitler’s first race law in 1933. There is still debate whether the Uranium Club – the German Physicists charged with developing an atomic bomb – deliberately prevented Hitler getting the weapon.
Whilst with Rutherford in Manchester, he helped develop the techniques that led to the conception of a nucleus and, when he returned to Germany, developed the Geiger Mueller tube with Walther Mueller.
Geiger survived the Second World War but lost his home when it was occupied in 1945; he just lived to learn of the atomic bombs in Japan
- Geiger was a student with Rutherford before the Second World War.
- Geiger’s work helped lead towards Bohr’s model of the atom; but they were very much on opposite sides in the War.
Albert Einstein, theoretical physicist – A great man who never wore socks (1879-1955)
Theoretical physicist born in Ulm, Germany.
Albert Einstein is, perhaps, the most famous physicist of all time. And his equation, E=mc2, the best known equation. He was a citizen of three countries, was married twice, never wore socks and didn’t talk until he was six.
In 1896, whilst living in Switzerland, Einstein renounced his German citizenship to avoid national service. He trained as a teacher but got a job in a patent office in 1902. He said this suited his desire to pursue Physics without the constrictions of an academic career.
In 1905, he published three papers that shook the world of Physics. The first explained Brownian motion and was the first direct evidence of molecules in motion; the second discussed the quantum nature of light and explained the photoelectric effect (based on Planck’s theory); the third introduced the Special Theory of Relativity. This gave a physical basis and interpretation to the Lorentz transformations and led to new and astonishing predictions.
He said that he started to get the ideas of Special Relativity when, at the age of 16, he imagined what it would be like to ride on a photon.
Einstein soon took up academic posts in Zurich, Prague, Berlin and (in 1933) Princeton where he remained (renouncing his German citizenship for a second time). In 1915, he published his General Theory of Relativity which tackled some of the problems of the Special Theory and included gravity. Its ideas about curved space and time were verified during a solar eclipse in 1919, turning Einstein into a world celebrity.
His last effort, a Unified Field Theory, which attempted to account for electromagnetic force and gravitational force using one set of laws was not entirely successful.
In 1939, prompted by other physicists, Einstein wrote a letter to President Roosevelt about the likelihood that the German government was making an atomic bomb. The letter helped lend urgency to efforts in the United States to build its own bomb but Einstein himself played no role in the work and knew nothing about it at the time.
- Einstein brought about the biggest shift in ideas since Isaac Newton 250 years earlier
- Einstein’s theories of Relativity didn’t rely on an ether – thanks to Michelson’s experiment
- His theories showed how Maxwell’s equations could work in all situations
- One of Einstein’s 1905 papers explained the photoelectric effect – discovered by Hallwachs
- Einstein included the Lorentz transformations in his Special Theory of Relativity.
- Einstein based his explanation of the photoelectric effect on Planck’s idea of packets of radiation.
- Thomson’s work on the electron helped to explain the photoelectric effect.
- Einstein thought it unnecessary, Eddington led an expedition in 1919 that confirmed the predictions of General Relativity
- Einstein supported Bose’s theory and added his name to the statistics of bosons.
- Bohr picked up on the idea of packets of radiation and developed it into the beginnings of quantum mechanics.
Niels Bohr, physicist – Why did he have to flee from Denmark? (1885-1962)
Physicist born in Copenhagen
Niels Bohr was one of the founders of quantum mechanics. He worked on an atomic model and on the atomic bomb and, in 1942, escaped from Nazi occupied Denmark with his son.
As an undergraduate, he studied nuclear physics under J. J. Thomson at Cambridge before moving to Manchester to work with Ernest Rutherford. Bohr’s work drew on Rutherford’s nuclear model of the atom and made use of Planck’s quantum theory. It suggested that the electrons in an atom exist in shells around the nucleus. This model contributed enormously to future developments of theoretical atomic physics and chemistry.
During the Second World War, he had a secret meeting with the German Physicist Heisenberg. The meeting is the subject of some fascinating speculation because the men were friends but on opposing sides (Denmark was occupied by the Germans). And America and Germany were both trying to develop nuclear weapons.
Bohr escaped from Denmark and made his way to America where he and his son joined in the effort at Los Alamos to develop the first atomic bomb. He opposed the complete secrecy of the project and after 1945 worked to develop peaceful uses for atomic energy.
- Bohr developed a more complicated and successful model of the atom than Thomson’s.
- Bohr used Rutherford’s idea of an atomic nucleus to develop his model of the atom.
- Bohr included Planck’s theory on packets of radiation in his model of the atom.
- Heisenberg worked closely with Bohr and helped develop the new theory of quantum mechanics.
Edwin Hubble, astronomer – A lawyer or a liar? (1889-1953)
Astronomer born in Marshfield, Missouri.
Edwin Hubble, the privileged and talented son of an insurance manager, is now best known for the space telescope that carries his name.
Hubble was a handsome athlete, a gifted scholar and a story-teller – some would say a liar. Having had a charmed school career, he went to University in Chicago and Oxford (to study Law – his father objected to him being an astronomer).
When he returned to America, he spent some time as a school teacher (though he said he had been a lawyer) before, at the age of 25, he went back to astronomy.
He was an extremely gifted observer and showed that nebulae were in fact large star systems, or galaxies, several hundred light years outside the Milky Way.
In 1929, he observed that these galaxies were moving away from us and that their speed increased with their distance. This substantiated the theory of an expanding Universe and was one way of resolving Olber’s paradox. Much later, it led to the theory of the Big Bang.
- Hubble’s observations and suggestion of receding galaxies helped explain Olber’s paradox.
- Arthur Eddington was the next famous astronomer.
- Gamow used Hubble’s results to develop the idea of The Big Bang.
Werner Heisenberg, physicist – Did he work on the bomb? It’s uncertain! (1901-1976)
Physicist born in Wurzburg.
Werner Heisenberg grew up with the First World War as his backdrop. One of the effects was to disrupt his formal education. However, he studied freely and became an accomplished mathematician, physicist and pianist.
At University in Munich, he was exposed to some of the problems of describing the structure of atoms. Whilst recovering from a bout of hay fever on a volcanic atoll, he is said to have come up with a novel (to him) method of multiplying variables. It turned out that he had developed matrices (though he had never seen a matrix before). This method of matrix mechanics is one way of solving problems in quantum mechanics.
From 1924 to 1927 he worked with the Danish physicist Niels Bohr and, in 1926, he came up with his famous principle of uncertainty. This states that, for a microscopic particle like an electron, it is impossible to precisely determine both its position and momentum at the same time. The act of measuring one of them makes the other one uncertain.
This principle has important philosophical and physical consequences because it means the difference between a Universe that is certain and predictable and one that is based on probability. It is one way of seeing that a clockwork Universe can never have a known starting position.
During the war, he had a secret meeting with Neils Bohr in occupied Denmark. There is much speculation and debate about this meeting and about Heisenberg’s involvement in the German atomic bomb project.
- Heisenberg took Planck’s idea of packets of radiation and included it in the new field of quantum mechanics
- Heisenberg worked closely with Bohr on his theories
- Heisenberg wasn’t close to Schrödinger, who developed an alternative formulation of quantum mechanics
Erwin Schrödinger, physicist – What does his cat have to do with physics? (1887-1961)
Erwin Schrödinger was an accomplished physicist by the time he turned his mind to quantum mechanics. He had a particular interest and skill with waves and wave equations. Spurred on by the limited power of the Bohr model of the atom and de Broglie’s matter waves, Schrödinger took a holiday in the Alps to contemplate the hydrogen atom. (The story goes that he took his mistress, not his wife, for company).
What he developed was his wave equation and the beginnings of wave mechanics. The equation describes the probability of where we would find an electron in a given system such as a hydrogen atom.
The interpretation of the equation is key to our attempt to understand quantum mechanics. It predicts possible states and positions for particles. Not where they are but where they might be if you were to observe them.
He illustrates his ideas about probability in a famous thought experiment in which a hypothetical cat is put in a box with a devious device that links the microscopic world of probabilities to the life of the poor cat.
Schrödinger fled to Dublin during the Second World War because he strongly opposed the persecution of Jews. He became very disillusioned with the bomb project and wrote What is life? which prompted a number of Physicist to turn to molecular biology and hastened the discovery of DNA.
- Schrödinger built on Planck’s idea of packets of radiation and included them in his wave equation.
- Schrödinger developed some of Bohr’s ideas on waves to create a version of quantum mechanics.
- Schrödinger wasn’t close to Heisenberg but between them they created quantum mechanics.
- Dirac developed a relativistic version of Schrödinger’s wave equation.
- Murray Gell-Mann took forward many of Schrödinger’s ideas of quantum mechanics into his theories of particles.
Paul Dirac, physicist – Where can you find his equation? (1902-1984)
Theoretical physicist born in Bristol, England.
Paul Dirac, like Newton and Rutherford before him, is buried in Westminster Abbey. However, he has the distinction of being under the only tombstone with an equation on it – the Dirac equation – a relativistic quantum equation for the electron.
His equation predicted the existence of the positron, or anti-electron – a particle with the same mass as an electron but opposite charge (and some other opposites).
Dirac’s theory was confirmed in 1932 when the American physicist Carl Anderson discovered the positron. In 1933 Dirac shared the Nobel Prize for Physics with the Austrian physicist Erwin Schrödinger.
In 1950, Dirac proposed string theory, a version of atomic theory which replaces the idea of elementary particles as points with the idea that they are loops or vibrating strands of energy.
- Dirac developed a relativistic version of Schrödinger’s wave equation
- Dirac used Einstein’s relativity in his wave equation.
- Murray Gell-Mann took forward many of Dirac’s ideas on quantum mechanics into his theories of particles.
- Yukawa developed Dirac’s ideas in quantum mechanics in the 1930s.
Enrico Fermi, physicist – Where did he go after getting his Nobel prize? (1901-1954)
Italian/American physicist, born in Rome.
Enrico Fermi, the man who remarked “If I could remember the names of all these particles, I’d be a botanist” was a particle physicist. When he started out, there were very few particles: electrons, protons and neutrons; later the number of particles and their names became harder to handle!
Fermi was born and educated in Italy, which he left for America in 1938 (he fled to Chicago from Sweden where he had just received the Nobel Prize). This was partly because his wife had Jewish descent and partly because he was more likely to get funding there. Italy was a poor country as well as a Fascist one at the time.
Fermi was an expert on particle behaviour and on neutrons. When fission was discovered in 1939, he realised that the spare neutrons could be used to start a chain reaction.
In 1942, in a squash court at the University of Chicago, his team created the first nuclear fission chain reaction. For the rest of World War II he worked at the Los Alamos Scientific Laboratory on the atomic bomb project.
He later opposed the development of the hydrogen bomb on ethical grounds.
- Fermi’s work relied on – and proved – Einstein’s most famous equation.
- Fermi used Rutherford’s theories of the nucleus.
- Fermi relied on Chadwick’s neutrons to create chain reactions.
- Fermi developed Marie Curie’s work on radioactivity and contributed to understanding it better.
Sir James Chadwick, physicist – A shy man, accidental physicist and internee of The Third Reich (1891-1974)
Physicist, born in Manchester, England.
James Chadwick was well known for his modesty and shyness and, the story goes, became a Physicist because of it. He applied to do Mathematics at Manchester, was interviewed for Physics by mistake and was too self conscious to mention it.
In 1909 he began working with Ernest Rutherford and teamed up with him again 9 years later in Cambridge. Between times, he spent four years interned in Germany where he had gone to work with Geiger and failed to leave before World War II broke out.
After the war years in prison, Chadwick returned to England and worked at the Cavendish with Rutherford. After ten years of experiments, he managed to find (or prove the existence of) the neutron in 1932. This led directly to the possibility of nuclear fission and, in 1943, Chadwick joined Fermi’s team at Los Alamos to work on the atomic bomb
- Chadwick worked with Rutherford.
- Chadwick’s discovery of the neutron helped Fermi during the war.
- Gell-Mann later described the structure of neutrons and protons in terms of quarks.
Arthur Eddington, astrophysicist – How did he escape prison? (1882 – 1944 )
Astrophysicist born in Kendal, Cumbria.
Through his article, Report on the relativity theory of gravitation, Arthur Eddington introduced General Relativity to the English speaking world – the First World War had meant that this theory, published in German in 1915, was not well known.
Eddington also claimed he confirmed the predictions of General Relativity during the solar eclipse of 1919, turning Einstein into a world figure – even superstar! However, there is a bit more to this story.
Eddington was a conscientious objector during the First World War. This meant he should have been imprisoned. However, in 1918 the Astronomer Royal, for whom he worked, spoke up for him. He suggested that Eddington should prepare an expedition to an island off the African coast to measure the apparent shift in the position of stars as they were viewed from behind the Sun (a measurement that can only be made during an eclipse).
Einstein felt the trip was unnecessary but, by now, Eddington had too much invested in it to call it off – or to fail. Despite the fact that it rained throughout the eclipse, Eddington managed to get one photograph from which he claimed to prove General Relativity.
He is also known for his jocular (and immodest) response to a reporter who asked if it was true that only three people understood General Relativity. His answer: “I am trying to think who the third person is.”
George Gamow, physicist – Third in the Greek alphabet (1904-1968)
Theoretical physicist born in Odessa, Ukraine.
George Gamow (‘Geo’ to his friends) was an accomplished physicist, author, science populariser and eccentric. He is best known for his description of the Hot Big Bang.
He was born in Russia and gradually made his way westwards through European Universities and defected to America in 1933.
In the 1920s, he developed quantum explanations of radioactivity and showed how low energy alpha particles could escape from the nucleus through quantum tunnelling. This prompted research that led to particle accelerators and chain reactions.
In the 1940s, he wrote a paper with his student Ralph Alpher which included a description of the Hot Big Bang. Hearing that the young Hans Bethe was in town, he invited him (on a whim) to add his name to the paper, which became the Alpher-Bethe-Gamow (alpha, beta, gamma) paper.
He predicted that the Big Bang would leave behind cosmic background radiation in the form of microwaves. This radiation was identified by Arno Penzias and Robert Wilson in 1965.
- Gamow used Hubble’s results in his theory of the Big Bang
- Hoyle invented the term Big Bang to deride Gamow’s theory; Hawking further developed the theory.
- Starobinsky refined some of Gamow’s ideas of the early Universe.
Satyendra Nath Bose, physicist – Made his discovery from a mistake (1894-1974)
Satyendra Nath Bose
Physicist born in Calcutta, India
Satyendra Bose was the son of a railway engineer and a highly successful student. He was lecturing by the time he was 22 and, later, translated The General Theory of Relativity from German to English. He worked at Calcutta and Dacca, and studied X-ray diffraction.
During a lecture on the photoelectric effect (in which he was trying to show that theory did not predict the experimental results), he made a simple statistical error that did lead to the measured results. He used this accident to devise a different statistical approach to dealing with photons. His papers on the subject were rejected until he enlisted Einstein’s support.
So, in 1924, Satyendra Bose did publish his paper on black-body radiation which founded Bose-Einstein statistics; these treat photons as being indistinguishable from each other. The class of particles that behave in the same way are called bosons after him.
- Bose convinced Einstein of the validity of his statistics and they cowrote a paper on them.
- Bose developed a set of statistics that work in situations where Maxwell’s does not work.
- Hoyle and Hawking relied on Bose’s translation of Einstein’s General Relativity.