Isaac Newton (1642-1727)

Figure 1.6 Isaac Newton Click here for larger image (16.24kb)

Isaac Newton was born on Christmas Day 1642 at Woolsthorp in Lincolnshire, England. His father had died a few months before the birth and Newton himself was born so prematurely that it was thought he might not survive. Newton was partly brought up by his grandmother, and seems not to have had a close relationship with his mother. He exhibited no great talent at school, but managed to avoid the task of managing his mother's farmlands and became instead an undergraduate at Trinity College in the University of Cambridge.

Figure 1.7 Woolsthorp Manor - Newton's birthplace. Click here for larger image (23.27kb)

As a student Newton read the works of Aristotle and was taught mathematics, as was customary, but he also taught himself physics and thus became acquainted with the works of Galileo and Kepler, amongst others. He graduated in 1665, by which time he had already started to break new ground in mathematics. Due to an outbreak of plague, the University of Cambridge was closed for much of the next two years and Newton spent most of his time back at Woolsthorp. It was during this period that he made many of his greatest breakthroughs, or at least laid their foundations. Over an eighteen month period he:
made fundamental advances in mathematics (essentially creating the subject of calculus, which has become a major part of the language of physics);

used a glass prism to demonstrate that white light is actually a mixture of colours;

began to consider the possibility that gravity, which obviously influenced bodies close to the Earth, might be a universal phenomenon holding the Moon in its orbit around the Earth and the Earth in its orbit around the Sun.

Following the reopening of the University, Newton returned to Trinity College where he became a Fellow in 1667. Two years later, still only 26, he was appointed Lucasian Professor of Mathematics on the recommendation of his predecessor, Isaac Barrow.

In addition to combining mathematical genius and profound physical insight, Newton also possessed practical skills. He built the furnaces in his own small laboratory in Trinity College, where he personally carried out alchemical experiments. He also constructed a novel kind of reflecting telescope, for which he was elected a Fellow of the Royal Society. However, Newton was a solitary and difficult person who has often been described as neurotic.

Figure 1.8 Trinity College, Cambridge around 1690 Click here for larger image (24.38kb)

He reacted badly to criticism and expected to get full credit for his discoveries even though he often did little to publicize them. He became involved in a number of bitter disputes over priority. Newton also harboured unconventional religious views (he was essentially a Unitarian) which prevented him from becoming the Master of his college. In 1678 he apparently suffered a nervous breakdown and for several years thereafter concentrated on alchemy and scriptural studies.

Newton was recalled to natural philosophy in 1684 by the young astronomer Edmond Halley who asked how a planet would move if it was attracted towards the Sun by a force that weakened in proportion to the inverse square of its distance from the Sun: in symbols,
.
(This means, for example, that increasing the distance by a factor of three decreases the force by a factor of nine.)
Newton is said to have immediately told Halley the answer (an ellipse) having worked it out during the plague years. Halley persuaded Newton to recreate his calculations and publish them. The result, in 1686, was what is widely regarded as the most influential book in the history of science, Newton's Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy), a work usually referred to simply as Principia. In the opening pages of this book, Newton presented his definitions of force and mass, and his three laws of motion. He then went on to demonstrate that a body attracted towards a fixed point by a force that varied in proportion to the inverse square of its distance from that point would, in many circumstances, follow

Figure 1.9 Principia - Newton's masterpiece Click here for larger image (25.45kb)

an elliptical path. After establishing many other results Newton presented, in Part 3 of the book, his System of the World in which he proposed that gravity was a universal force, acting between any two particles of matter, with a magnitude that is proportional to the product of their masses and the inverse square of their separation - just the kind of inverse square law that Halley had asked about. Thus Newton was able to explain the observed motion of the planets. He went on to consider the Moon's motion in detail (taking account of the gravitational influence of both the Earth and the Sun), the behaviour of comets, and the gravitational origin of the Earth's oceanic tides. The scope and power of Principia caused a sensation, and made Newton the foremost scientist of his time, or perhaps any time.

Newton suffered another breakdown in 1693 and subsequently quit Cambridge and the academic life in favour of London and the world of affairs. He became Warden of the Mint in 1696 and successfully oversaw the introduction of a new coinage. As a consequence he was appointed to a lucrative position as Master of the Mint and devoted much of his remaining time to theology and biblical chronology. He was elected President of the Royal Society in 1703, published his last great scientific work Opticks in 1704 (based on work performed many years earlier), and was knighted in 1705. He died, in London in 1727, and is buried in Westminster Abbey.

Ludwig Boltzmann (1844-1906)

Entropy and disorder

The statistical interpretation of thermodynamics was pioneered by James Clerk Maxwell (1831-1879) and brought to fruition by the Austrian physicist Ludwig Boltzmann.

Figure 1.15 Ludwig Boltzmann (1844-1906) Click here for larger image (16.95kb)

In 1877 Boltzmann used statistical ideas to gain valuable insight into the meaning of entropy. He realized that entropy could be thought of as a measure of disorder, and that the second law of thermodynamics expressed the fact that disorder tends to increase. You have probably noticed this tendency in everyday life! However, you might also think that you have the power to step in, rearrange things a bit, and restore order. For example, you might decide to tidy up your wardrobe. Would this lead to a decrease in disorder, and hence a decrease in entropy? Actually, it would not. This is because there are inevitable side-effects: whilst sorting out your clothes, you will be breathing, metabolizing and warming your surroundings. When everything has been taken into account, the total disorder (as measured by the entropy) will have increased, in spite of the admirable state of order in your wardrobe. The second law of thermodynamics is relentless. The total entropy and the total disorder are overwhelmingly unlikely to decrease.

Boltzmann's contribution was vital, but had a tragic outcome. Towards the end of the nineteenth century several puzzling facts (which eventually led to quantum theory), triggered a reaction against 'materialist' science, and some people even questioned whether atoms exist. Boltzmann, whose work was based on the concept of atoms, found himself cast as their chief defender and the debates became increasingly bitter. Always prone to bouts of depression, Boltzmann came to believe that his life's work had been rejected by the scientific community, although this was far from being true. In 1906, he committed suicide. If despair over rejection, or frustration over being unable to prove his point, were contributing factors the irony would be great indeed. Soon after Boltzmann's death, clinching evidence was found for atoms, and few would ever doubt their existence again.

Michael Faraday (1791-1867)

Michael Faraday was the son of a blacksmith. Apprenticed to a bookbinder at 14, he read about science, became enthralled with the subject, secured a job as a laboratory assistant at the Royal Institution in London, and eventually rose to be the Institution's Director and one of the most accomplished experimental researchers of all time.

Figure 1.17 Michael Faraday (1791-1867) Click here for larger image (16.99kb)

Amongst his many achievements, he is credited with the construction of the first electric motor and the discovery of both the principle and the method whereby a rotating magnet can be used to create an electric current in a coil of wire (still the basis of modern electricity generating plants). Faraday never became a very able mathematician, and it was his profoundly physical way of viewing the world that led him to create the concept of a field.

Figure 1.18 Faraday's apparatus demonstrating the principle of the electric motor. The upper end of a stiff wire is suspended in such a way that it is free to rotate. The lower end of the wire is immersed in the liquid metal mercury, and is free to move. The wire and its suspension form part of an electrical circuit that can be supplied with electric current from a battery. In the middle of the pool of mercury, next to the wire, is a short cylindrical magnet. When an electric current is passed through the wire it moves around the magnet. The use of mercury allows the current to continue flowing even though the wire is moving. Click here for larger image (15.03kb)

James Clerk Maxwell (1831-1879)

James Clerk Maxwell was the son of a Scottish laird. He studied at the Universities of Edinburgh and Cambridge and was appointed Professor of Natural Philosophy at Aberdeen at the age of 27.

Figure 1.19 James Clerk Maxwell Click here for larger image (11.51kb)

Four years later he moved to King's College, London, where he spent his most productive period. In 1865 he resigned his post in London but continued to work privately on his family estate in Scotland. In 1871 he agreed, somewhat reluctantly, to become the first Professor of Experimental Physics in the University of Cambridge. He died, from cancer, at the early age of 47, but by that time he had already made fundamental contributions to the theory of gases, the study of heat and thermodynamics, and, above all, to electromagnetism. He recast the discoveries of Faraday and others in mathematical form, added an important principle of his own and thus produced what are usually referred to as Maxwell's equations - the fundamental laws of electromagnetism (Figure 1.20). Much of his work on field theory was published in his masterpiece, A Treatise on Electricity and Magnetism (1873).

Albert Einstein (1879-1955)

Figure 1.25 Albert Einstein Click here for larger image (14.25kb)

Albert Einstein was born in Ulm, Germany on 14 March 1879. The following year he and his family moved to Munich where he had a successful, though not brilliant, school career. In 1896 Einstein renounced his German citizenship and started to study for a high-school teaching diploma at the prestigious Eidgenössische Technische Hochschule (ETH) in Zurich, Switzerland. Amongst his fellow students at ETH was Mileva Maric, who became his first wife. Einstein graduated in 1900 and in December of that year submitted his first paper to a scientific journal. However, he failed to get any of the university positions that he applied for, and after some temporary school teaching he became, in 1902, a technical expert (third-class) at the patent office in Bern. He continued to pursue his interest in physics while at the patent office, and worked on a doctoral thesis during his spare time.

1905 was an extraordinary year in Einstein's life and in the progress of science. During that year he produced four of his most important papers. In the first he explained Brownian motion - the apparently random motion exhibited by pollen grains and other small particles when they are suspended in a fluid. According to Einstein, the motion is a result of the incessant bombardment of the suspended particles by molecules of the fluid. The quantitative success of this explanation established beyond reasonable doubt the existence of molecules, which until then had been questioned by many physicists. In his second 1905 paper, Einstein formulated a theory of the photoelectric effect - the liberation of electrons from a metal exposed to electromagnetic radiation. His explanation was one of the earliest applications of quantum physics and was an important step in the development of that subject. It was mainly for this piece of work that Einstein was awarded the Nobel Prize for Physics in 1921. His third and fourth 1905 papers concerned the special theory of relativity. He laid out the foundations of the subject in the third paper and in the fourth he provided a brief but eloquent justification of his famous equation E = mc², which uses c, the speed of light in a vacuum, to relate the mass m of a body to its total energy content E.

Figure 1.26 Einstein's 1905 paper On the Electrodynamics of Moving Bodies. This was his first paper on special relativity. Click here for larger image (10.28kb)

Although these brilliantly original papers eventually established Einstein as a physicist of the first rank, three more years were to elapse before he obtained his first academic post. During that time he worked on a variety of topics and did pioneering work on the quantum physics of solids. In 1909 he was finally appointed to a lecturing post at the University of Bern, in 1911 he became a professor at the University of Prague and in 1912 he returned to Zurich, as Professor of Theoretical Physics at ETH. By this time his attention was focused on the search for a general theory of relativity that would extend his earlier work on the special theory. The principle of equivalence which he formulated in 1907 had convinced Einstein that a general theory of relativity would also be a new theory of gravity, and it was from the gravitational point of view that the problem of general relativity was attacked.

In 1914 Einstein moved to Berlin, the main centre of scientific research in the German-speaking world, to take up a research professorship that would free him from teaching duties. He and his wife separated soon after the move, and were eventually divorced. Einstein continued to work on general relativity and in 1916 produced the first systematic treatment of the subject in a long paper entitled Die Grundlage der allgemeinen Relativätstheorie ('The foundations of general relativity theory'). The creation of general relativity was one of the greatest intellectual achievements of the twentieth century: it led on to the study of black holes and the prediction of gravitational waves, and it provided a firm basis for future investigations in cosmology - the study of the Universe as a whole. Observations carried out in 1919, during a total eclipse of the Sun, confirmed one of the key predictions of general relativity: the gravitational deflection of starlight passing close to the edge of the Sun. This quantitative success of Einstein's theory was widely reported, and did more than any other event to make Einstein into an instantly recognized icon of scientific genius.

Figure 1.27 The article from the Times of November 7, 1919. Copyright Times Newspapers Limited, 1919. Click here for larger image (25.46kb)

Soon after completing the general theory, Einstein turned his attention to the quantum theory of electromagnetic radiation and postulated the existence of stimulated emission - the process that now underpins the operation of lasers. However, in 1917 he became seriously ill. He was nursed back to health by his cousin Elsa, whom he married in 1919. His second marriage seems to have been reasonably happy, but he was not, by his own admission, a good husband.

By the early 1920s Einstein's best scientific work was done: he wrote in 1921 'Discovery in the grand manner is for young people... and hence for me is a thing of the past'. He was none the less extremely influential in the physics community and he did much to prepare the ground for many later developments. He travelled a lot, and became increasingly active in social and political causes, particularly in support of Zionism. (Many years later he was offered the presidency of Israel, which he declined.) In 1932, Einstein and his wife left Germany for good, mainly in response to growing anti-Semitism, and moved to the USA where Einstein settled as a professor at the Institute for Advanced Study in Princeton, New Jersey. Einstein eventually became an American citizen, though he also retained the Swiss citizenship he had held since his twenties. Although Einstein was a believer in peace and harmony, and eventually argued for a world government, he also recognized the dangers of Nazism and the potential power of atomic science. As a result, in 1939, he was persuaded to co-sign a letter to the American President, Franklin D. Roosevelt, warning of the possibility of atomic weapons. This is widely thought to have had a decisive effect in prompting the US government to undertake the development of the atomic bomb, though Einstein himself played no part in the project.

Although Einstein had been deeply involved in the birth of quantum physics, he became increasingly dissatisfied with the way the subject developed after the mid-1920s. He did not believe that it gave a truly fundamental account of natural phenomena. His last major contribution to the field was the development of Bose-Einstein statistics in 1925. However his name is also recalled in the Einstein-Podolsky-Rosen experiment, a 'thought experiment' proposed in 1935 in an attempt to show that quantum physics was seriously flawed. The attempt was unconvincing, but it did emphasize the gulf that separated quantum physics from the classical physics that preceded it. The other project of Einstein's later years that continues to be remembered is his search for a unified field theory that would bring together gravity and electromagnetism. He continued to work on this up to the time of his death, often with great ingenuity, but little of that work is regarded as being of enduring value. He died in Princeton in 1955.

Paul Adrien Maurice Dirac (1902-1984)

Paul Adrien Maurice Dirac was born in Bristol, England, in 1902. His father was a Swiss-born teacher of French, his mother a librarian. Dirac's first degree, obtained at the Merchant Venturer's Technical College, was in electrical engineering, but he had no real interest in the subject and after graduating spent two years studying mathematics at the University of Bristol. In 1923 he left Bristol for Cambridge where he remained for most of his working life.

Figure 1.31 Paul Dirac Click here for larger image (13.62kb)

Dirac's achievements in Cambridge were prodigious. In 1925, while working for his doctorate, he became one of the founders of quantum mechanics when he produced an elegant extension of Heisenberg's work. A little over a year later he presented a very general formulation of quantum mechanics that has remained the basis of the subject ever since. During the next year he essentially founded quantum electrodynamics. In 1928 Dirac took an important step towards bringing quantum physics into conformity with Einstein's special theory of relativity by devising an equation (now called the Dirac equation) that could describe the behaviour of electrons at any speed up to the speed of light. This equation provided a natural explanation of one of the electron's intrinsic properties - its spin. Taking the mathematical form of his equation seriously, and searching for a way of interpreting it, Dirac was led, in 1931, to propose that there should exist a class of 'anti-electrons', particles with the same mass and spin as the electron but with the opposite electrical charge (Figure 1.32). By correctly predicting the existence of these antiparticles, now called positrons, Dirac became recognized as the 'discoverer' of antimatter - one of the most important discoveries of the century.

Figure 1.32 Tracks left by fundamental particles. Click here for larger images (20.99kb Combined total)

(a) An electron and a positron (a particle-antiparticle pair) reveal their opposite charges by spiralling in different directions in a magnetic field.

(b) A variety of particles created from the energy released when an electron and a positron collide at high speed and annihilate.

From 1932 to 1969 Dirac held the Lucasian Chair of Mathematics in Cambridge, the post that Newton himself had once occupied. During this period Dirac worked on a variety of topics including magnetic monopoles (hypothetical magnetic charges) and the speculation that the fundamental constants of physics might be gradually changing in a co-ordinated way. However he became disenchanted with some of the detailed developments that occurred in quantum field theory and became increasingly distanced from what others regarded as the scientific mainstream.

In 1971, following his retirement from Cambridge, Dirac moved to the USA where he became a professor of physics at Florida State University. He died there in 1984. Throughout his life Dirac was renowned for his economy of speech and lack of social awareness. His book Principles of Quantum Mechanics (1930) is regarded as a classic of clear and elegant exposition. When a correspondent asked him to clarify a certain result in the text, Dirac is said to have replied that he knew of no clearer way of expressing the point. No rudeness would have been intended, just an honest statement of fact. Dirac preferred to work by himself, and had few collaborators or research students.

Richard P.Feynman (1918-1988)

Richard Phillips Feynman was one of the most colourful and celebrated of US physicists. He was born in New York in 1918 and educated at the Massachusetts Institute of Technology (MIT) and Princeton. From 1942 to 1945 he was involved in the atomic bomb project at Los Alamos, where he gave ample evidence of his enormous technical virtuosity as well as earning himself a reputation as a practical joker.

Figure 1.34 Richard P. Feynman Click here for larger image (15.38kb)

After the Second World War Feynman went to Cornell University where he became one of the major figures in the development of quantum electrodynamics (QED). During this period he also devised his own approach to quantum mechanics called the 'path integral' or 'sum over histories' approach. This has since been applied to quantum field theory and is now the standard formalism in many areas of the subject.

In 1950 Feynman moved to the California Institute of Technology (Caltech) where he remained for the rest of his life. While there, he worked on many topics, including the theory of fundamental particles, the theory of superfluidity and the nature of the forces and interactions within the atomic nucleus. He became renowned as a teacher of physics, combining profound physical insight with a very down-to-earth style. Towards the end of his life, when already ill with cancer, he was invited to join the commission investigating the in-flight explosion of the space shuttle Challenger. As part of that work he memorably demonstrated, in front of a massive TV audience, the disastrous effect of low temperature on the booster rocket's O-ring seals by dropping one of them into a glass of iced water.

Feynman will long be remembered as one of the twentieth century's greatest exponents of intuitive - yet highly rigorous - physics. The three volumes of Feynman Lectures on Physics from his Caltech years, and Feynman's autobiographical works 'Surely You're Joking Mr Feynman!' and 'What Do You Care What Other People Think?' also ensure that he will be remembered as a character of extraordinary insight, wit and charm. In 1965 Feynman shared the Nobel Prize for Physics with Julian Schwinger and Sin-itiro Tomonaga.