Month: September 2021

John Wheeler

John Wheeler was an eminent American theoretical physicist, perhaps best known for having initially coined the terms “black hole,” “wormhole” and several other colorful phrases. In the 1930s, he developed the important “S-matrix” in particle physics and worked with Niels Bohr to explain nuclear fission in terms of quantum physics. Later, he developed the equation of state for cold, dead stars, helped popularize the study of general relativity in the mainstream of theoretical physics, and to firm up the theory and evidence for black holes. He also collaborated with Albert Einstein in his search for a Grand Unified Theory of physics.

Education and Influences

John Archibald Wheeler was born on 9 July 1911 in Jacksonville, Florida, USA, the oldest child in a family of librarians. The family moved around a lot, and over the years they lived in Florida, California, Ohio, Washington D.C., Maryland and Vermont. He attended the Baltimore City College high school, graduating in 1926, and went on to study physics under the supervision of Karl Herzfeld at Johns Hopkins University. He received his doctorate in 1933, with a dissertation on the theory of the dispersion and absorption of helium. Soon after graduating, he traveled to Copenhagen, where he worked for a time with Niels Bohr, the godfather of the quantum theory revolution. He married Janette Hegner in 1935, and they were to have two daughters (Alison Letitia) and a son (James) and were to stay together for the whole of their long lives.

Contributions and Impact

He became a professor of physics at Princeton University in 1938, where he remained, with an interruption during World War II, for 38 years until 1976. During his very early years at Princeton, he introduced the scattering-matrix (or “S-matrix”), which relates the initial state and the final state for an interaction of particles, and which was to become an indispensable tool in particle physics.

Wheeler knew Einstein well and sometimes used to hold seminars with his students in Einstein’s home. When Bohr visited the United States in 1939, with news of the achievement of nuclear fission in Germany, he and Wheeler collaborated on the development of the influential “liquid drop” model of the atom, first proposed by George Gamow, in an attempt to explain the theoretical basis of nuclear fission.

Together with many other leading physicists, Wheeler interrupted his academic career during World War II to participate in the development of the U.S. atomic bomb as part of the Manhattan Project at the Hanford Site in Washington state. Among other things, he correctly anticipated that the accumulation of “fission product poisons” (particularly an isotope of xenon) would eventually impede the ongoing nuclear chain reaction by absorbing neutrons.

After the war, he returned to Princeton to resume his academic career, and began to teach a course on Einsteinian gravity in the early 1950s, when it was still considered not quite an acceptable field of study, although for many years he resisted the idea that the laws of physics could lead to something as apparently absurd as a singularity. He also continued to do government work, however, and was integrally involved in the development of the American hydrogen bomb in the early 1950s at Los Alamos and at Princeton (where he was responsible for setting up Project Matterhorn). At one point, in 1953, he was he officially reprimanded for apparently losing a classified paper on the hydrogen bomb. His somewhat hawkish views on national defense, the Vietnam War, and missile defense often ran counter to those of his more liberal colleagues.

With his government research finished, Wheeler returned to Princeton, where he collaborated with Albert Einstein in the waning years of his life on a “unified field theory” of the physical forces of nature. In 1956, he helped to determine what types of materials are located inside dead, cold stars with the “Harrison-Wheeler Equation of State for Cold, Dead Matter,” ascertaining that it would be largely iron because the efficient fusion process breaks down when the core reaches that state. In 1957, while working on extensions to general relativity, he introduced the word “wormhole” to describe hypothetical tunnels in space-time.

In the late 1950s, he formulated the theory of geometrodynamics, a program of physical and philosophical reduction of all physical phenomena (including gravitation and electromagnetism) to the geometrical properties of curved space-time. However, he later abandoned this theory in the early 1970s, having failed to explain some important physical phenomena, such as the existence of fermions (electrons, muons, etc.) and gravitational singularities.

He always gave a high priority to teaching and continued to teach freshman and sophomore physics even after he had achieved fame, believing that the young minds were the most important. He was known for his high-energy lectures, writing rapidly on chalkboards with both hands, and twirling to make eye contact with his students. Among his graduate students were some important theoreticians of the later 20th Century, including Richard Feynman, Kip Thorne, and Hugh Everett.

He worked extensively on the theory of gravitational collapse, and he is usually credited with coining the term “black hole” during a 1967 talk at the NASA Goddard Institute of Space Studies (although in fact he was prompted to it by a shout from the audience). Along with Dennis Sciama at Cambridge and Yakov Borisovich Zeldovich in Moscow, Wheeler was integral to the so-called “Golden Age of general relativity” of the 1960s and 1970s, a paradigm shift during which the study of general relativity (which had previously been regarded as something of a curiosity) entered into the mainstream of theoretical physics. Under his leadership, Princeton became the leading American center of research into Einsteinian gravity. The comprehensive general relativity textbook “Gravitation,” which he co-wrote with Charles Misner and Kip Thorne, appeared in 1973, and it became the most influential relativity textbook for a generation.

After Einstein’s death, Wheeler continued his pursuit of the role of gravity in a Grand Unified Theory of physics and became something of a pioneer in the field of quantum gravity. This led to his collaboration with Bryce DeWitt and the development of the Wheeler-DeWitt Equation or, as Wheeler preferred to call it, the “wave function of the universe.” Other products of Wheeler’s colourful way with words include the phrase “black holes have no hair” (to describe how black holes should be a perfect, simply definable shape, and not have any sorts of projections out of them), “mass without mass” (to indicate the need to effectively remove any mention of mass from the basic equations of physics), “it from bit” (to describe how information is fundamental to the physics of the universe, just as it is in computing) and “quantum foam” (to describe a space-time churned into a lather of distorted geometry).

In 1976, faced with mandatory retirement at Princeton, Wheeler moved to the University of Texas at Austin, where he held the position as director of the Center for Theoretical Physics from 1976 until his retirement in 1986. It was during this time (specifically in 1978) that he proposed a variation of Thomas Young’s double-slit experiment (and Richard Feynman’s later refinement), often referred to as the “delayed choice” experiment. He posited that the detection of a photon even AFTER passing through a double slit would be sufficient to change the outcome of the experiment and the behavior of the photon. Therefore, if the experimenters know which slit it goes through, the photon will behave as a particle, rather than as a wave with its associated interference behavior. This somewhat counter-intuitive hypothesis was finally verified in a practical experiment in 2007.

Wheeler returned to Princeton as a professor emeritus in 1986, where he remained for the next twenty years. His so-called “Everything Is Fields” phase (in which he viewed the universe and all the particles which make it up as mere manifestations of electrical, magnetic and gravitational fields and space-time itself) gave way to an “Everything Is Information” phase (when he focused on the idea that logic and information is the bedrock of physical theory). He also began to speculate that the laws of physics may be evolving in a manner analogous to evolution by natural selection in biology, and he coined the term “participatory anthropic principle” to describe his version of the anthropic principle, in which observers (i.e., us) are necessary to bring the universe into being.

Wheeler received numerous honors over the years, including the National Medal of Science, the Albert Einstein Prize, the Enrico Fermi Award, the Franklin Medal, the Niels Bohr International Gold Medal and the Wolf Foundation Prize. He was a past president of the American Physical Society, and a member of the American Philosophical Society, the Royal Academy, the Accademia Nazionale dei Lincei, the Royal Academy of Science and the Century Association. He was awarded honorary degrees from 18 institutions.

This essay was written as part of our effort to learn more about the lives of scientists who have shaped our understanding of the world as we know it. We’ve learned what we can from various sources on the web and put it into our own unique “namedat” voice in hopes that we can make it easily-digestible and fun to learn. This essay is original, and if you enjoyed it, please share it with others!

Scientists

Karl Schwarzschild

Karl Schwarzschild was a German physicist, best known for providing the first exact solution to Einstein’s field equations of general relativity in 1915 (the very same year that Einstein first introduced the concept of general relativity). His work generated many original concepts which now bear his name, such as Schwarzschild coordinates, the Schwarzschild metric, the Schwarzschild radius, Schwarzschild black holes and Schwarzschild wormholes.

Education and Influences

Karl Schwarzschild was born on 9 October 1873 in Frankfurt am Main, Germany, the oldest of six children. The family was Jewish and quite well-off, his father being a respected member of the business community in Frankfurt. Schwarzschild attended a Jewish primary school in Frankfurt up to the age of eleven, before entering the Gymnasium there. He was something of a child prodigy, constructing his own telescope and publishing a paper on celestial mechanics (specifically, on the theory of orbits of double stars) when he was only sixteen. He studied at the University of Strasbourg from 1891 to 1893, where he learned a great deal of practical astronomy, and then at the University of Munich where he obtained his doctorate in 1896 with a work on Henri Poincaré’s theories.

Contributions and Impact

From 1896 to 1899, he worked as an assistant at the Kuffner Observatory in Vienna, Austria, and then spent two years lecturing at the University of Munich. From 1901 until 1909, he was a professor at the prestigious University of Göttingen, where he had the opportunity to work with some significant figures, including the mathematicians David Hilbert and Hermann Minkowski, and where he also became director of the Göttingen observatory. In 1909, he married Else Posenbach, and they had three children, Agathe, Martin, and Alfred. His son, Martin, born in 1912, would also become an eminent physicist whose work led to greater understanding in the fields of stellar structure and stellar evolution.

In 1909, Schwarzschild moved to a post as director of the Astrophysical Observatory in Potsdam, the most prestigious post available for an astronomer in Germany at that time, and in 1913 he was elected a member of the Berlin Academy of Science. In 1914, at the outbreak of World War I, he joined the German army, despite being over 40 years old, serving on both the western and eastern fronts, and rising to the rank of lieutenant in the artillery. While serving on the front in Russia in 1915, he began to suffer from a rare and painful skin disease called pemphigus.

Despite serving in the war and suffering this painful debility, Schwarzschild nevertheless managed to write three outstanding papers during in 1915, two on relativity theory and one on quantum theory. His papers on general relativity produced the first exact solutions to Albert Einstein’s field equations, and a minor modification of these results gives the well-known solution that now bears his name, the Schwarzschild metric. Einstein himself was pleasantly surprised to learn that the field equations admitted exact solutions, partly because of their prima facie complexity, but partly because at that time he had only produced an approximate solution. Schwarzschild’s more elegant “polar-like” coordinate system (which has since become known as Schwarzschild coordinates), based on a spherically symmetric space-time, was able to produce an exact solution.

Schwarzschild’s solution identified a radius for any given mass, known as the Schwarzschild radius, where, if that mass could be compressed to fit within that radius, no known force or degeneracy pressure could stop it from continuing to collapse into a gravitational singularity or black hole. Thus, where the radius of the body is less than its Schwarzschild radius, everything, even photons of light, must inevitably fall into the central body. As a corollary, when the mass density of this central body exceeds a particular limit, it triggers a gravitational collapse to what is known as a Schwarzschild black hole, a non-charged, non-rotating black hole. A general acceptance of the possibility of a black hole did not occur until the second half of the 20th Century, and Schwarzschild himself did not believe in the physical reality of black holes, believing his theoretical solution to be physically meaningless.

Although Schwarzschild’s best-known work lies in the area of general relativity, his research interests were broad, including work in celestial mechanics, observational stellar photometry, quantum mechanics, instrumental astronomy, stellar structure, stellar statistics, Halley’s comet and spectroscopy. In particular, earlier in his career, he pioneered the measurement of variable stars using photography and worked on the improvement of optical systems.

Scientists

Erwin Schrödinger

Erwin Schrödinger was an Austrian theoretical physicist who achieved fame for his contributions to quantum mechanics. The philosophical issues raised by his 1935 “Schrödinger’s cat” thought experiment perhaps remains his best-known legacy, but the Schrödinger equation, which he formulated in 1926 to describe the quantum state of a system, is his most enduring achievement at a more technical level. It is celebrated as one of the most significant achievements in 20th Century physics, and it revolutionized quantum mechanics and earned Schrödinger a share in the 1933 Nobel Prize in Physics.

Education and Influences

Erwin Rudolf Josef Alexander Schrödinger was born on 12 August 1887 in Vienna, Austria (Austria-Hungary at that time). His father was an Austrian Catholic, and his mother was an Austrian-English Lutheran, and Schrödinger grew up speaking German and English. He attended the Akademisches Gymnasium high school in Vienna from 1898 to 1905, and then studied at the University of Vienna between 1906 and 1910 under Franz Serafin Exner and Friedrich Hasenöhrl, as well as conducting experimental work with K.W.F. Kohlrausch. From an early age, Schrödinger was strongly influenced by the philosophy and Eastern religion of the Austrian philosopher Arthur Schopenhauer.

In 1911, Schrödinger became an assistant to Exner at the University of Vienna, earning his habilitation in 1914. During World War I, between 1914 and 1918, he participated in war work as a commissioned officer in the Austrian fortress artillery, and after the War, in 1920, he married Annemarie Bertel. The same year, he became the assistant to Max Wien at the University of Jena, and then quickly obtained a series of promotions, working in the universities of Stuttgart, Breslau and finally Zürich in 1921.

Contributions and Impact

In 1926, Schrödinger published a remarkable series of four papers in the prestigious “Annalen der Physik” journal, which marked the central achievement of his career, and which were at once recognized as having great significance by the international physics community:

A paper on wave mechanics, in which he derived what is now known as the Schrödinger equation, an equation that describes how the quantum state of a physical system changes over time, and giving the correct energy eigenvalues for a hydrogen-like atom with one electron. This paper has been universally celebrated as one of the most important achievements of the 20th Century and created a revolution in quantum mechanics.
A paper solving the quantum harmonic oscillator, the rigid rotor, and the diatomic molecule, and giving a new derivation of the Schrödinger equation.
A paper showing the equivalence of his approach to that of Heisenberg, and giving the treatment of the Stark effect (the shifting and splitting of spectral lines of atoms and molecules due to the presence of an external static electric field).
A paper showing how to treat problems in which the system changes with time, as in scattering problems.

In 1927, Schrödinger succeeded Max Planck at the Friedrich Wilhelm University in Berlin, and his career seemed to be flourishing. However, when Adolf Hitler seized power in 1933, Schrödinger decided to leave Germany as a protest against the anti-Semitism of the Nazi regime, and he settled in Oxford, England, becoming a Fellow of Magdalen College at the University of Oxford. Soon after, he received the 1933 Nobel Prize in Physics, shared with Paul Dirac, “for the discovery of new productive forms of atomic theory.”

His position at Oxford, though, did not work out (it is likely that his unconventional personal life – he lived with two women, his wife, Annemarie Bertel, and his pregnant mistress, Hilde March – did not meet with acceptance in the proper Oxford of the 1930s). He was offered a permanent position at Princeton University in the United States in 1934, but he did not accept it, and again his lifestyle may have posed a problem. In the end, he took up a position at the University of Graz in Austria in 1936.

Somewhere in the midst of all these tenure issues, he found time for an extensive correspondence with his personal friend Albert Einstein and, as a result, he proposed in 1935 what has become known as the “Schrödinger’s cat” thought experiment or paradox in order to illustrate the problem of the so-called “Copenhagen interpretation” of quantum mechanics (as propounded by Niels Bohr and Werner Heisenberg). The thought experiment proposed a scenario in which a cat was hidden in a sealed box, where the cat’s life or death was dependent on the state of a particular sub-atomic particle. According to the Copenhagen interpretation, the cat remains both alive and dead until the box is opened, and it is the act of measurement that causes the calculated set of probabilities in the wave function to “collapse” to the value defined by the measurement.

In 1939, after the unification of Austria into Greater Germany, Schrödinger’s known opposition to Nazism and his earlier flight from Germany led to threats and eventually to dismissal from his job at the University of Graz (despite his public recantation, which he later much regretted). He was under orders not to leave the country, but he and his wife managed to escape to Italy, and from there to visiting positions in Oxford University and Ghent University.

In 1940, he accepted an invitation to help establish an Institute for Advanced Studies in Dublin, Ireland, and he became the Director of the School for Theoretical Physics there. He remained in Dublin until his retirement in 1955, during which time he became a naturalized Irish citizen. He continued his scandalous involvements with students, however, fathering at least two children by two different Irish women.

During his time in Dublin, he wrote about 50 further publications on various topics, including his explorations of unified field theory. His influential 1944 book “What is Life?” discussed the idea that life feeds on negative entropy, and introduced the concept of a complex molecule containing the genetic code for living organisms. Schrödinger’s speculations about how genetic information might be stored in molecules gave James Watson and Francis Crick the inspiration to research the gene that led to the discovery of the DNA double-helix structure.

In 1956, Schrödinger returned to Vienna. He continued to court controversy, including his refusal to speak on nuclear energy at a major energy conference due to his skepticism about it (he gave a lecture on philosophy instead), and his turn, late in life, away from the wave-particle duality espoused by mainstream quantum mechanics in favor of the wave idea alone.

Scientists

Andrei Sakharov

Andrei Sakharov was an eminent Soviet Russian nuclear physicist, although he is perhaps better known as a dissident, human rights activist, advocate of civil liberties and reforms in the Soviet Union and Nobel Peace Prize winner. Although much of his early career was spent contributing to the military might of the Soviet Union through the development of the atomic bomb and the hydrogen bomb, he later became one of the program’s fiercest critics. In later life, he devoted his prodigious intellect to fundamental theoretical physics, particle physics and cosmology, contributing essential insights on the matter-antimatter imbalance in the universe, and hypothesizing about singularities linking parallel universes.

Education and Influences

Andrei Dmitrievich Sakharov was born in Moscow, Russia (then the USSR) on 21 May 1921. His father was a physics teacher, an amateur pianist, and a vehement atheist, and, despite his pious mother’s insistence on baptizing him, religion did not play an important role in Sakharov’s life. He entered Moscow State University in 1938, although he was evacuated in 1941 during the Great Patriotic War to Ashgabat (in today’s Turkmenistan), where he completed his studies and graduated.

After graduating, he was assigned laboratory work in Ulyanovsk, during which period he met and married Klavdia Alekseyevna Vikhireva. They married in 1943 and raised together two daughters and a son. He returned to Moscow in 1945 to study at the Theoretical Department of FIAN (the Physical Institute of the Soviet Academy of Sciences), receiving his Ph.D. in 1947.

Contributions and Impact

After the war, Sakharov spent some time researching cosmic rays but gradually became involved in weapons research. In 1948, he participated in the Soviet atomic bomb project under Igor Kurchatov and was present at the testing of the first Soviet nuclear device in 1949. After moving to the “closed” (or restricted) town of Sarov in 1950, Sakharov played a key role in the next stage, the development of the thermonuclear hydrogen bomb, which was first tested in 1953, followed by the first megaton-range Soviet hydrogen bomb, which was tested in 1955.

In 1950, in association with Igor Tamm, he also proposed an idea for a controlled nuclear fusion reactor, the tokamak, which is still the basis for the majority of work in the area, based on the premise of confining extremely hot ionized plasma by torus-shaped magnetic fields in order to control the thermonuclear fusion process. He also worked on generating extremely high-power electromagnetic pulses by compressing magnetic flux using high explosive.

In 1953, Sakharov received his DSc degree, was elected a full member of the Soviet Academy of Sciences and was awarded the first of his three Hero of Socialist Labour titles. By the late 1950s, however, Sakharov had become concerned about the moral and political implications of his nuclear weapons work. He became politically active during the 1960s, warning against nuclear proliferation and pushing for an end to atmospheric tests. He played a prominent role in the Partial Test Ban Treaty, signed in Moscow in 1963. In 1967, when anti-ballistic missile defense became a core issue in US-Soviet relations, he argued for a bilateral rejection of such weapons on the grounds that an arms race in this new technology would only increase the likelihood of nuclear war.

After 1965, Sakharov returned to fundamental science and began working on particle physics and cosmology, particularly the search for an explanation for the “baryon asymmetry” of the universe (the huge preponderance of matter, as opposed to antimatter, in the known universe). He was the first scientist to introduce the concept of two universes called “sheets,” which may have been linked at the time of the Big Bang. The “other” universe would exhibit complete “CPT symmetry” (the inversion of charge, parity and time), having an opposite arrow of time and being mainly populated by antimatter. Sakharov called the singularities, where these two sheets could theoretically interact without being separated by space-time, a “collapse” and an “anticollapse,” similar to the black hole and white hole of wormhole theory. He also proposed the idea of induced gravity (or emergent gravity) as an alternative theory of quantum gravity.

After his continued agitation against the deployment of nuclear weapons, he was banned from all military-related research in 1968 and returned to FIAN in Moscow. In 1970 he founded the Moscow Human Rights Committee, together with Valery Chalidze and Andrei Tverdokhlebov, and came under increasing pressure from the regime. He married a fellow human rights activist, Yelena Bonner, in 1972. He was awarded the Prix Mondial Cino Del Duca in 1974 and the Nobel Peace Prize in 1975, although he was not allowed to leave the Soviet Union to collect it (his wife read his speech at the ceremony in Oslo).

Sakharov was arrested in early 1980 after his public protests against the 1979 Soviet invasion of Afghanistan and was sent to internal exile in the city of Gorky (now Nizhny Novgorod), a closed city inaccessible to foreign observers. He remained under tight Soviet police surveillance, subject to repeated searches and heists, until 1986, when he was allowed to return to Moscow under the perestroika and glasnost policies of Mikhail Gorbachev. There, he helped to initiate the first independent legal political organizations and became prominent in the Soviet Union’s growing political opposition. He was elected to the new parliament in 1989, and briefly co-led the democratic opposition.