Physics | The Canadian Encyclopedia

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# Physics

Physics is the study of matter and radiation, the space-time continuum that contains them, and the forces to which they are subject.

### Physics

Physics is the study of matter and radiation, the space-time continuum that contains them, and the forces to which they are subject. Physics may be experimental, observing the behaviour of matter and radiation under various conditions, using increasingly sophisticated instruments; or it may be theoretical, using mathematical tools to construct models, to formulate laws governing observed behaviour and to indicate (on the basis of these models and laws) promising avenues for further experimentation. The terms macroscopic and microscopic (or, more accurately, submicroscopic), and "classical" and "modern," refer to aspects of physics characterized by different scales in the phenomena studied. Macroscopic or classical physics deals with matter in bulk, as solids, liquids or gases.

The closely interrelated fields of mechanics (based on Newton's laws of motion), heat (ie, thermometry and calorimetry), thermodynamics, classical electricity and magnetism (based on discoveries by Coulomb, Ampère, Faraday and Maxwell), and some aspects of statistical physics, lie in the domain of classical physics. Submicroscopic or modern physics studies the detailed structure of matter: atoms, molecules, electrons, nuclei, nucleons and various so-called "elementary particles," many of which are unstable and very short-lived.

The transition from classical to modern physics involved recognition of the existence in nature of a number of fundamental constants, which have since been measured with ever greater precision. Thus the speed of light in a vacuum is now known to 0.004 parts per million (c = 299 792 458 m/s). Other fundamental constants, such as e (the charge of an electron), m (its mass), M (the proton mass) and h (Planck's constant), have all been measured to a precision of a few parts per million. In classical physics, radiation (eg, visible light, radio waves) is treated as continuous waves characterized by a wavelength and a frequency. Modern physics introduced the concept of discrete bundles of energy, called quanta, associated with the waves and, shortly thereafter, discovered that under certain conditions the subatomic units of matter exhibit a wavelike behaviour. To deal with this behaviour a new mode of mathematical description, known now as quantum mechanics, has been developed.

Finally, the pair of terms basic and applied represents an arbitrary division of physics into 2 broad areas, between which the boundary shifts continually. Michael Faraday's basic studies of the relation between electricity and magnetism have led to the applied field of electrical engineering. The basic studies in nuclear physics by Ernest Rutherford at McGill at the turn of the century eventually resulted in CANDU nuclear power reactors. Basic studies in spectroscopy, such as those of Canada's Nobel laureate Gerhard Herzberg, underlie lasers, atomic clocks, and the National Research Council of Canada's daily time signal on CBC Radio.

GEORGE M. VOLKOFF

### History in Canada

The history of physics in Canada involves the development of undergraduate and graduate studies and research in universities, research in government institutions and in private industry.

### Subfields

Physics has been divided into various subdisciplines unified by the basic laws of mechanics, both Newtonian and relativistic, and of quantum mechanics and thermodynamics. In each of these subdisciplines, work proceeds on both the theoretical and experimental fronts; progress is made by the constant interaction and mutual testing of these 2 aspects of research against each other.

### Space Physics

Space physics deals with the behaviour of matter and the flow of energy in regions beginning about 60 km above the Earth's surface and extending to the far reaches of the solar system. Most of this region is occupied by a tenuous gas of charged particles known as plasma, the behaviour of which is regulated by magnetic and electric fields. The main source of energy is a flow of plasma from the sun known as the solar wind. The solar wind and its embedded solar magnetic field distort the Earth's magnetic field to form a comet-shaped cavity called the magnetosphere. Space scientists attempt to understand the complex interactions that take place between the electric and magnetic fields and the electrons and ions which constitute the space plasma environment. One visible manifestation of these processes is the Northern Lights.

By the end of the first half of the 20th century, it was recognized that navigational compass errors and radio wave communication disruptions were associated with displays of the northern lights. This stimulated intense research activity following auroral studies carried out during the first International Polar Year (1882-83) and the Second International Polar Year (1932-33). The era of modern space research is considered to have commenced with the International Geophysical Year (1957-58), and from that time forward Canadian scientists have been in the forefront of space physics research. A research rocket range was established at Churchill, Man, in 1957, which stimulated the development of a Canadian family of research rockets known as Black Brants, manufactured by Bristol Aerospace. The experience with research rockets led to the development of Canadian satellite payloads, the most notable of which were flown aboard the Alouette 1 and Alouette 2 spacecraft launched in the first half of the 1960s and the ISIS 1 and ISIS 2 spacecraft launched in 1969 and 1971 respectively. These satellites provided definitive information about the structure of the ionosphere and the nature of the energetic electrons and protons responsible for the northern lights.

Canadian space scientists have gained international renown through their contributions to increased understanding of the nature of the space plasma environment and the origin of the northern lights. One of the fathers of Canadian space physics was Balfour Currie at the University of Saskatchewan, who helped create a powerful research group in studies of the aurora and ionospheric radio wave propagation in the period following the International Geophysical Year. Colin Hines of U of T is considered to have pioneered the study of gravity waves, atmospheric disturbances that have a profound effect on regions from the troposphere to the ionosphere. In 1961, together with W. Ian Axford, Hines introduced one of the 2 frameworks accepted by modern space scientists for understanding the transport and dissipation of energy in the magnetosphere-ionosphere system.

Today, Canadian space scientists operate large arrays of ground-based remote sensing equipment (eg, CANOPUS) monitoring the level of the solar-terrestrial interaction and fly payloads aboard foreign satellites (eg, the Swedish Viking and Freja and the Japanese Akebono missions). The Canadian Space Agency was mandated in 1989 to support space science and technology in Canada and is now responsible for the developmental and operational costs of most major space research efforts in the country. Most researchers are employed at Canadian universities and are funded by the Natural Sciences and Engineering Research Council of Canada.

GORDON ROSTOKER

### Earth Physics

Earth physics studies the solid Earth and its atmosphere and oceans. Although land, sea and air are often studied in isolation by separate disciplines (geophysics, oceanography, meteorology), modern investigations are often intensely multidisciplinary. The physics of the solid Earth encompasses both academic and applied aspects. The questions of how and of what Earth was formed and what physical and chemical processes control its evolution remain at the forefront of current research. Perhaps the most important scientific advance in the past century of geophysical inquiry has been the dramatic verification of the hypothesis of continental drift, achieved since 1965. This plate tectonics theory received support from the geophysical methods of seismology and geomagnetism (see geology).

These methods are also employed, with considerable practical success, in exploring the near-surface crustal region of Earth for economically important deposits of petroleum and base metals. Electrical methods, many of which have been developed in Canadian laboratories, have proven to be particularly suited to the discovery of mineral deposits. These methods include electromagnetic induction, induced polarization and direct current resistivity measurements. Other geophysical techniques that are of major industrial significance include both seismic reflection and refraction surveying, and also potential field methods based on the analyses of minute variations in Earth's gravitational and magnetic fields. In all these areas Canada has played a leading role in developing and implementing the new methodology.

The atmospheric sciences, often considered together under meteorology, are also characterized by a multifaceted collection of applied and fundamental concerns, including questions regarding the detailed processes through which precipitation (rain, hail and snow) is formed; the potential negative effects of increases in carbon levels in the atmosphere; the sensitivity of the atmosphere to small changes in insolation and to changes in stratospheric concentrations of ozone and the oxides of nitrogen; and the assessment of air quality, especially relating to the problem of acid rain. Considerable recent progress has also been made in understanding the planetary-scale hydrodynamics of the atmosphere, through the use of detailed mathematical models implemented on the largest digital computers available. Practical byproducts of this fundamental research include the numerical weather prediction models routinely employed to make twice-daily forecasts. Canada's Atmospheric Environment Service has played a leading role in developing and improving such models.

The science of oceanography has many similarities to both solid Earth geophysics and meteorology. Physical oceanographers study the waves and currents of all spatial and temporal scales that characterize the motions of the sea in the major ocean basins. Chemical oceanographers study the composition of the sea and, more recently, have begun to employ measurements of trace-element concentrations to reveal the patterns of oceanic circulation. Biological oceanographers are concerned with the life systems that the oceans sustain.

The necessity for acquiring improved understanding of the oceans has been made particularly clear by recent and unsuccessful United Nations attempts to formulate a Law of the Sea that would control exploitation of the mineral wealth of the ocean floors. This economic incentive and that provided by large-scale offshore programs of drilling for subsurface deposits of hydrocarbons have enhanced traditional concerns about the sea as a source of food.

W.R. PELTIER

### Optics

The Greek word optikes originally meant the study of the eye and vision. Today, optics encompasses the whole spectrum of electromagnetic waves, radio waves, microwaves, infrared, visible light, ultraviolet, X rays and gamma rays. Classical optics dealt mainly with lenses, mirrors, gratings and instruments made with them. Such artifacts can be designed and analysed using the classical (ie, geometrical and wave) theories of light. The main proponents of geometrical theory were Johannes Kepler (German astronomer) and Sir Isaac Newton (English physicist and mathematician). This theory assumes that a light source emits light rays, which propagate rectilinearly in a homogeneous medium. When the medium changes, the rays are reflected, refracted or both. Pinhole cameras and shadows of objects cast by light beams demonstrate the truth of this theory.

The main proponent of wave theory was Christian Huygens (Dutch scientist). It assumes that a light source emits waves that travel out in spheres; at any moment, every point on a wavefront acts as a new secondary source emitting new wavelets. The optical phenomena of interference, diffraction and polarization can be studied by this theory. Optics has always been an extremely important component in spectroscopy, which has played a vital role in the study of atoms and molecules. In Canada, Gerhard Herzberg won a Nobel Prize (1971) for his work in molecular spectroscopy.

Optics was revitalized and revolutionized by the invention of the maser and laser by Charles Townes (American physicist), N.G. Basov and A.M. Prokhorov (Soviet physicists), winners of the 1964 Nobel Prize for physics for their work in this field. The first laser was built by Theodore Maiman (American physicist) in 1960. The main types of lasers are (according to the lasing materials used) solid, liquid, dye, gas and semiconductor. Extreme high-intensity pulses can be produced by transversally excited atmospheric carbon dioxide (TEA-CO2) lasers. The Canadian Defence Research Establishment, Valcartier, Qué, was among the important pioneers and inventors of TEA-CO2 lasers. Canada has a few laser-manufacturing companies, including internationally renowned Lumonics Inc.

Among the latest developments in optics is fibre optics. Optical waves can propagate inside optically transparent fibres by total internal reflection. The diameters of the fibres may be a few micrometres (single mode) to a few hundred micrometres (multimode). Because of their high frequencies, optical waves in the visible and near infrared regimes can carry far more information than electrical currents in metal wires. Canada is one of the leaders in fibre optics. Much research is done at the Communications Research Centre.

Commercially, Bell-Northern Research and Canada Wire and Cable are the leading Canadian companies. The world's first fibre-optic, cable-television, digital super trunk system was installed in London, Ont. Some other early Canadian systems were installed at Department of National Defence headquarters, Ottawa (1976), downtown Montréal (1977), Toronto (1978) and Vancouver (1979). Two recent and very advanced systems were the Calgary-Cheadle (Alta) and the Elie-St Eustache (Man) projects.

JOHN W.Y. LIT

### Atomic and Molecular Physics

Atomic and molecular physics is concerned with understanding the physical nature of atoms and molecules and with observing and understanding processes involving a small number of atoms and molecules which may or may not be electrically charged. The emphasis on the small number of particles distinguishes atomic and molecular physics from solid state physics, statistical mechanics and thermodynamics, and plasma physics. The subject has diffuse borders with many branches of physics, chemistry and astrophysics. The ultimate aim of atomic and molecular physics is to establish the physical laws that govern observed atomic and molecular processes.

At present, it is generally believed that all known phenomena are compatible with the laws of quantum mechanics and quantum electrodynamics. While many elegant verifications of these laws have been obtained for simple physical systems, the quantitative application to more complex systems is limited by mathematical and computational difficulties.

The term electronics was first used to describe the branch of physics that evolved from the discovery of the electron by English physicist J.J. Thomson in 1897. The subject then involved the determination of the fundamental properties of individual electrons (eg, charge, mass, magnetic moment) and the properties of free electrons in vacuum tubes. Today the term has a wider connotation, embracing the study, design and application of devices (eg, electronic tubes, transistors, integrated circuits) the operation of which depends largely on the characteristics and behaviour of electrons. Electronics plays a key role in communications and computers.

Spectroscopy is concerned with the interaction between matter and radiation. Historically the subject started in the visible region of the spectrum and was primarily concerned with the emission and absorption spectra of atoms. Today the subject embraces the complete electromagnetic spectrum and is concerned with atoms, molecules and charged species in the gas, liquid and solid phases. The emission or absorption of radiation by a system accompanies a transition between 2 energy levels or quantum states of the system and gives information on the nature of these quantum states (see Chemistry Subdisciplines). The spectrum of a substance is probably its most characteristic single property; this fact underlies the widespread use of various forms of spectroscopy in both qualitative and quantitative analysis.

D.A. RAMSAY

### Nuclear and Particle Physics

The atomic nucleus is a small, dense object containing nearly the entire mass of the atom. The existence of the nucleus was demonstrated by E. Rutherford in 1911, but an understanding of its composition came only with English physicist James Chadwick's discovery of the neutron in 1932. The existence of the neutron provided the key to understanding the nucleus as a composite body, formed of neutrons and protons. The neutrons and protons (referred to as nucleons) are bound in the tiny nuclear volume by a force that is very strong (ie, much stronger than the energies involved in binding atoms to form a molecule) and of very short range.

The most important manifestations of nuclear energy are found in the processes of nuclear fusion and fission, in which a fraction of the internal nuclear energy is transformed into kinetic energy, which ultimately appears as heat (see Nuclear Power Plants). A chemical element has a characteristic number of nuclear protons but nature permits a certain latitude in the number of neutrons that may bind to the protons under the influence of the strong force. The differing neutron numbers give rise to what are known as isotopes. Several isotopes of a chemical element may be absolutely stable, but the remainder manifest an instability called radioactive decay. Some radioisotopes occur naturally in the heavy elements and many more have been produced artificially. Many radioisotopes are valuable in medicine and industry.

A nucleus may have a number of distinct excited states, differing from one another by discrete amounts of internal nuclear energy. Such states undergo radioactive transformation under the perturbing effects of internal electromagnetic interactions or the very feeble, but significant, weak interaction. These excitations and transformations have been much studied as a means of understanding the complexities of the strong nuclear force. Although the structure of a nucleus is explicable in terms of just 2 particles, scores of other subatomic particles have been observed, studied and classified. These particles are grouped in 3 families: baryons, mesons and leptons.

The lepton family is characterized by its insensitivity to the strong interaction; the most notable attribute of the baryon and meson families is their affinity for the strong interaction. Baryons and mesons appear to have an important internal structure of their own: the baryon family is believed to be formed of different combinations of 3 fundamental constituents, known as u, d and s quarks; the meson family is formed by the binding of 2 constituents, a quark and an antiquark. The quarks are thought to be permanently confined or bound and hence unobservable as free particles. The quark hypothesis received strong support in 1974 and 1977 with the discoveries of massive long-lived mesons, known as psi and upsilon mesons, formed by the binding of heavy quarks, called c and b, with their respective antiquarks.

A very important concept in particle physics is the unified theory of weak and electromagnetic interactions. According to this theory the weak interaction is associated with particles about 100 times more massive than the proton. These particles are expected to be observed in the large electron-positron and proton-antiproton colliding beam machines now in operation or construction in Europe and the US.

D.G. STAIRS

### Condensed Matter Physics

In condensed matter physics, scientists study the fundamental microscopic properties of matter in the solid and liquid phases and investigate their technological uses. They wish to know how the constituent atoms and electrons are spatially organized, how they move, how they are affected by heat and cold, pressure, light, electric and magnetic fields, radiation and particles of all sorts, and how they can be controlled for useful purposes.

Condensed matter physics is an outgrowth of solid state physics, which blossomed in the post-WWII period. Most research in this area has traditionally focused on crystalline materials, in which the atoms are in ordered positions. These fall into 3 broad classes depending on their electron properties: metals, insulators and semiconductors. Metals have good mechanical strength and are electrical and thermal conductors. They can be used to transport electrical currents as in household electrical wires or high tension power cables. Insulators, in contrast, are bad conductors and can be used to safeguard against electrical shock, in wires and cables for instance, or as protection against extremes in temperatures, as in building insulation. Semiconductors are misfits whose electron conduction solid state scientists have learned to tune at growth.

This led to the discovery of the transistor and the semiconductor laser, which have revolutionized electronics and opto-electronics. These are now at the heart of modern communications and space technology, computers, commercial electronic devices and microelectronics. One now mundanely talks of nanostructures whose components have dimensions of a millionth of a millimetre. These high-tech devices have reached the quantum level at which the wave properties of the electrons are manifest. For example, there is ongoing research into single-electron memories for computers, the ultimate in miniaturization.

There is also work going on in 2-dimensional electronphysics. This occurs in sheets of electron constrained at semiconductor surfaces or interfaces. The integer quantum Hall effect (Nobel prize in 1985) and more recently the fractional quantum Hall effect (Nobel prize in 1998) have uncovered novel electron behavior of these sheets in a magnetic field. The former is now used in electrical standards, such as at the Institute for National Measurement Standards of the National Research Council, while the latter has revealed the existence of electronic excitations, called quasiparticles, having a fraction of the charge of an electron. In opto-electronics, one is looking forward to the day when computers will use "light transistors" to achieve the ultimate speed.

Solid state physics evolved into condensed matter physics in the 1970s in Canada. Indeed, there is a strong affinity between the properties of liquids and solids and between the techniques used to investigate them. There are similarities between the disordered (amorphous or glassy) materials and liquids. There is a parallel between superfluids, which flow without friction, and superconductors, in which electrical currents flow without losses, at low temperature. These co-operative phenomena, which implicate all particles in unison, have applications in cyrogenics, computers, electric-power transmission and public transport (superconducting motors and levitation). Liquid-crystals (eg, watch and portable computer screen displays) have properties of both the liquid and solid. P.G. de Gennes, a Nobel Prize winner in 1991, has helped to popularize the term "soft matter" (eg, polymers, colloids) covering activities which bridge the liquid and solid states.

There are yet more unusual states of matter. One can fabricate macroporous materials having regularly spaced voids or pores of the size of the wavelength of visible light. These may one day be utilized as photonic crystals to control light. But the most uncommon photonic crystals are surely the optical lattices obtained by laser cooling atoms to ultra-low temperatures (Nobel Prize in 1997) and using magnetic containment. The atoms are not held together by electronic forces, as in regular crystals, but rather by the light from the lasers. The same technique has been used to finally observe the Bose-Einstein condensation, a special tenuous quantum condensate akin to that of superfluidity predicted long ago by statistical physics but elusive until the mid-1990s.

There are potential or proven applications for materials such as layered solids (eg, graphite) and polymer conductors, used in batteries, organic conductors and ceramic superconductors (Nobel prize, 1987), and new forms of carbon, fullerenes and nanotubes. Fullerene (Nobel prize in 1996) is made up of giant carbon molecules or "bucky balls," having 60 carbon atoms, and is named in honour of the architect who invented the geodesic dome (US pavilion at Expo 67 for example), R. Buckminster Fuller. It can become superconducting when some metal atoms are added. Carbon nanotubes are formed by wrapping single graphite sheets around in a cylinder and capping the ends with half a fullerene "ball." They could be used in molecular size devices. There is active interest in the conversion of light to electricity and the storage of energy (eg, solar heat, hydrogen) in materials. The electron tunneling microscope (Nobel prize, 1986), which allows one to see individual atoms on surfaces, and its sibling, the atomic force microscope, have found varied use in materials science, chemistry, engineering and biology.

The Canadian effort in condensed matter is quite substantial and at the fore in most areas described above. Canada played a pioneering role in development and use of neutrons and positrons to probe condensed matter. The efforts of the Canadian physicist B.N. Brockhouse at the Chalk River Laboratories in the area of neutron spectroscopy were internationally recognized when he was awarded the Nobel Prize in 1994.

LAURENT G. CARON

### Plasma Physics

An ordinary gas undergoes a transition into a new state of matter called plasma when atoms are ionized; ie, they dissociate into positively charged ions and negatively charged electrons. Ionization is caused by an electric discharge, by heating of a neutral gas or by irradiation by short-wavelength electromagnetic waves. Not all ionized gases are called plasmas; they must contain enough charged particles so that the electromagnetic field produced by them affects the movement of each individual electron and ion. The collective behaviour resulting from this self-consistent field constitutes a unique characteristic of plasmas. Plasmas stay, on average, electrically neutral by containing sufficient number of electrons to balance the positive charge of ions. Since the studies of electrical discharges by the American chemist Irving Langmuir in the 1920s, plasma physics has grown into a major research discipline.

Plasmas are common in the universe: stars and interstellar matter are in a plasma state; astrophysical objects such as pulsars, X-ray stars, quasars and supernova remnants display various plasma phenomena. At high altitudes 70-500 km above its surface, the Earth is surrounded by a plasma layer called the ionosphere, which influences short wave radio communication by reflecting electromagnetic signals. The ionosphere is the lower boundary of a larger domain, the magnetosphere, where the plasma is controlled by the Earth's magnetic field. The outer boundary of the magnetosphere is created by the interaction with a flow of plasma ejected from the sun known as the solar wind. The wind confines the Earth's magnetic field and provides an energy source for phenomena such the northern lights. Plasma is produced naturally in lightning, and it appears in devices such as fluorescent lamps, neon tubes, welding torches and gas lasers. Engineering applications of plasmas include surface etching and material processing in the microelectronic industry.

The quest for controlled thermonuclear fusion has stimulated intensive studies of laboratory plasmas since the early 1950s. Controlled thermonuclear reaction is an outstanding physical problem which promises a solution to the world's energy needs by producing power during fusion of light isotopes of hydrogen, such as deuterium (D) and tritium (T) . This reaction might be sustained in a very hot (temperature in excess of 100 million degrees), dense plasma. In the first of 2 primary approaches to fusion research, plasma is trapped in a magnetic field and confined on the time scale of a second at densities of approximately 1014 particles per cm3 (magnetic confinement fusion). The second approach relies on the inertia of small imploding D-T targets reaching a density of 1025 particles per cm3 over a 10-10 sec to provide confinement and conditions for a fusion reaction (inertial confinement fusion). The targets are heated and compressed by focused laser or ion beams. Experiments with laboratory plasmas have led to the discovery of important sources of short wavelength radiation (eg, X-ray sources in laser-produced plasmas and tunable microwave generators such as gyrotrons and free-electron lasers).

W. ROZMUS

### Societies

The Canadian Association of Physicists, the national society of Canadian physicists, has a membership of over 1800 individuals and 30 corporations. CAP was founded in 1945 and incorporated in 1951. It publishes a bimonthly bulletin, Physics in Canada, and holds an annual 3-day congress for discussion of current research.

Since 1945, the Canadian Association of Physicists Medal has been awarded annually for distinguished achievement in physics and, since 1970, the Herzberg Medal for outstanding achievement by a physicist not more than 38 years of age. From time to time, CAP produces special reports on the state of physics in Canada. Canada's national physics journal is the Canadian Journal of Physics. Many physicists are members of the Association canadienne-française pour l'avancement des sciences. ACFAS was established in 1923 for the advancement of science in Québec and in French-speaking communities of North America. With a membership of over 2500, ACFAS holds an annual congress attended by 2000 researchers and students, who gather to hear approximately 1000 scientific papers.

Most Canadian physicists are also active members of the many scientific societies in physics and astronomy that form the American Institute of Physics. Canadian physicists have taken an active part in international organizations; eg, the International Council of Scientific Unions and the International Union of Pure and Applied Physics, which promotes international co-operation in physics, and international agreements on the use of symbols, units, nomenclature and standards. Scientific exchanges have permitted collaboration of many groups in nuclear and particle physics research, making use of the costly accelerators at national laboratories in Europe, the US and Canada (AECL and TRIUMF).

Canadian physicists have been honoured by both national and international bodies. Physicists who have served as presidents of the Royal Society of Canada include G. Herzberg, H.E. Duckworth, J.T. Wilson, J.L. Kerwin and R.E. Bell. In the past decade, a number of Canadian physicists have been made fellows of the Royal Society (of London), including Z.S. Basinski, R.E. Bell, B.N. Brockhouse, A.E. Douglas, G. Herzberg, W.B. Lewis, A.E. Litherland, M.H.L. Pryce, D.A. Ramsay, B.P. Stoicheff, H.L. Welsh and J.T. Wilson.

BORIS P. STOICHEFF

Authors contributing to this article:

### Universities

The first professors of natural philosophy (physics combined with mathematics) were appointed at Dalhousie University in 1838 and at King's College (later University of Toronto) in 1843. Professorships were established at Dalhousie (1879), Toronto (1887) and McGill (1890). The professors were occupied primarily by teaching, doing little original research; however, the European discoveries of the 1890s (X-rays, radioactivity, electrons, etc) inspired Canadian professors to become active in the development of their subject. Especially prominent were Ernest Rutherford (McGill) and J.C. McLennan (U of T). Establishment of graduate programs with research followed.

Until after WWI, U of T and McGill were the only Canadian universities granting PhDs in physics. However, especially after WWII, many universities set up comprehensive graduate study and research programs. Between 1974 and 1985, 1075 PhDs in physics were awarded by 28 universities (about 31% at U of T).

The early slow growth of physics research was largely the result of financial difficulties. Establishment in 1916 of the National Research Council of Canada promoted the development of science through scholarships for graduate students and apparatus grants to professors. Financial assistance from federal and provincial government sources increased, especially after WWII. In 1980 the Natural Sciences and Engineering Research Council (established 1978) took the place of the NRC as the main federal granting agency.

Dalhousie can probably lay claim to the first meaningful research by a physics professor. J.G. MacGregor was appointed in 1879 and, during the next 20 years, published some 50 papers and memoirs. H.L. Bronson, department head from 1910 to 1956, inspired many students, including G.H. Henderson (radioactivity, pleochroic halos) and W.J. Archibald (theoretical physics), to take up careers in physics.

McGill got off to an excellent start with H.L. Callendar and E. Rutherford as Macdonald professors of physics. Important discoveries in radioactivity and nuclear physics were made by Rutherford and numerous assistants, some of whom (eg, H.M. Tory, J.A. Gray, H.L. Bronson, R.W. Boyle) played vital roles in the development of science in other parts of the country. Nuclear physics at McGill culminated in 1949 in establishment of the Radiation Laboratory with the first cyclotron in Canada. This development was due chiefly to J.S. Foster, world-renowned for his work on the Stark effect. The Radiation Laboratory was headed by R.E. Bell for many years, and J.M. Robson, a nuclear physicist, was head of the physics department. In the 1920s, L.V. King did outstanding work in mathematical physics. D.A. Keys and A.S. Eve initiated early work on geophysics and, somewhat later, J.S. Marshall, on atmospheric physics. McGill was the first Canadian university to develop a theoretical physics group and has produced numerous theorists with international reputations.

J.C. McLennan was director of the physics laboratory at U of T from 1906 to 1932. His first researches were on atmospheric conductivity and cathode rays, but he shifted to atomic spectroscopy with the advent of the Bohr atom in 1912. Optics and spectroscopy have continued to be one of the main interests of the department with M.F. Crawford, H.L. Welsh, Elizabeth J. Allin and, since 1965, B.P. Stoicheff as leader of a large laser group. In the 1920s McLennan, G.M. Shrum and others built a helium liquefier, the first in North America, for work on metals and solidified gases at low temperatures; this type of work is still actively pursued. During this early period, E.F. Burton supervised research in colloid physics and, in the late 1930s, he and his students built the first high-resolution electron microscope in North America.

In the late 1920s L. Gilchrist began work in geophysics which later, under J. Tuzo Wilson, became one of the largest research groups in the department. In the 1960s a program in atmospheric physics was inaugurated. Extensive work was begun in high-energy particle physics in the early 1960s with K.G. McNeill and A.E. Litherland, and in medical biophysics with H.E. Johns. Until the 1960s, theoretical physics was chiefly the concern of the department of applied mathematics which included J.L. Synge and L. Infeld. However, with the appointment of J. Van Kranendonk in 1958, a strong theoretical section, embracing most of the branches of modern physics, was set up in the physics department.

UBC and McMaster, founded around the turn of the century, demonstrated a remarkable rise in scientific productivity in the 1940s. At UBC the change resulted from the appointment of G.M. Shrum (head 1938-61) and others (including G.M. Volkoff, M. Bloom, R.D. Russell and J.B. Warren), which made possible a broad spectrum of teaching and research in many branches of physics. In the 1970s, UBC became the site of TRIUMF (the Tri-University Meson Facility), one of the most important nuclear facilities in Canada. McMaster became an important centre of Canadian science following appointment of H.G. Thode in 1939. His work on mass spectroscopy and isotope abundances led to intensive work on various aspects of nuclear physics by M.W. Johns, H.E. Duckworth, B.N. Brockhouse and others. In 1957 a research reactor was set up, the first university reactor in the Commonwealth, followed in the 1970s by a particle-accelerator laboratory with extensive facilities. McMaster has achieved prominence in other research fields; eg, spectroscopy (A.B. McLay), solid state physics, biophysics and theoretical physics (M.H. Preston, J. Carbotte). Research is interdisciplinary (eg, in the Institute for Materials Research with J.A. Morrison as director).

R.W. Boyle became professor of physics at the University of Alberta in 1912 and began extensive research in ultrasonics. Somewhat later, S. Smith and R.J. Lang began important work in optics and spectroscopy. Research has gradually broadened to include geophysics (J.A. Jacobs) and solid state, nuclear, medical and theoretical physics (A.B. Bhatia, W. Israel).

At U Laval, Italian physicist F. Rasetti began a new era in physics teaching and research (1939-47). Rasetti was followed by his friend E. Persico (1947-50) and J.L. Kerwin, P. Marmet, A. Boivin and others. Main areas of research are optics, atomic and molecular physics, nuclear and theoretical physics. Like Laval, Université de Montréal has greatly increased its contributions to Canadian physics in the last 30 years. The 2 main areas of research are nuclear and plasma physics and associated theory, developed by P. Demers, P. Lorrain and others.

The department at Manitoba was begun by F. Allen, who made applications of physics to physiology. After WWII, active work on nuclear physics was begun by R.W. Pringle and expanded rapidly by B.G. Hogg and others. More recently, A.H. Morrish has instituted important work on magnetic materials. The department at Saskatchewan developed during the long headship (1924-56) of E.L. Harrington. Upper atmospheric research, begun by B.W. Currie in 1932, led to the present Institute of Space and Atmospheric Studies with an international reputation. In the period 1935-45, Gerhard Herzberg worked on atomic and molecular structures. In the 1950s the department gained renown with its betatron in photonuclear physics and radiation therapy, including development of a cobalt-60 unit by H.E. Johns and others. Plasma physics is also an important field of study. The younger western universities, Victoria, Simon Fraser and Calgary, have rapidly developing physics departments.

Queen's University, Kingston, and the University of Western Ontario have made notable contributions to physics. Research and graduate work at Queen's was initiated by A.L. Clark in the 1920s. Nuclear physics research was begun by J.A. Gray and continued with B.W. Sargent, A.T. Stewart and others. Other fields of research are optics (initiated early by J.K. Robertson), microwave spectroscopy and solid state physics. At UWO rapid development of research began in the 1940s with a radar program. The work begun by R.C. Dearle, G.A. Woonton and others was continued by P.A. Forsyth, culminating in the Centre for Radio Science (1967), which studies problems in atmospheric and ionospheric physics. Nuclear research has made considerable progress, especially in the scattering of positrons (J.W. McGowan).

The University of Waterloo was established in the late 1950s. The physics department immediately embarked on a program of research in experimental and theoretical solid state physics, with connected areas in laser physics and microwave spectroscopy. Geophysics and biophysics are also studied. York University has a Centre of Research for Experimental Space Sciences with R.W. Nicholls as director. The universities of Ottawa, Windsor, Guelph and Carleton (with its particle physics program initiated by E.P. Hincks) have promising futures. Concordia, L'École Polytechnique de Montréal and the Universities of Sherbrooke, New Brunswick, St Francis Xavier and Memorial conduct advanced studies in physics.

Physics staff members and graduates played an important role in both world wars. In WWI J.C. McLennan became director of experimental research for the British Admiralty and also organized production of helium from Canadian natural-gas wells; R.W. Boyle conducted ultrasonic experiments in the Admiralty antisubmarine division. In WWII university staffs were in danger of being completely depleted by requests for assistance from NRC and other government and national defence organizations. In addition, several universities gave concentrated courses in physics and electronics to enlisted personnel destined to operate radar and signal devices in the army, navy and air force.

### Federal Research

The NRC has played a major role in physics research. In 1928, the NRC established laboratories in Ottawa, including a Division of Physics with R.W. Boyle as director. The division expanded very rapidly after the outbreak of WWII; areas of study important to the war effort included nuclear physics, submarine detection and minesweeping devices, aerial photography and range finders. To implement results in optics and radar, Research Enterprises Ltd was set up as a crown corporation.

A large part of the physics staff dispersed at the end of the war; however, things began to improve with the appointment in 1948 of Herzberg and introduction in 1949 of a program of postdoctoral assistants with one- or 2-year terms. Applied physics became a separate division (1955), under L.E. Howlett. The spectroscopy section of the pure physics division rapidly attained world renown with the work of Herzberg, A.E. Douglas, D.A. Ramsay, T. Oka and others.

In the 1970s the spectroscopy section was incorporated with astronomy and astrophysics in the Herzberg Institute of Astrophysics. The solid state section under D.K.C. MacDonald (1951-63) also attained renown. After establishment of the Herzberg Institute, the divisions of physics and applied physics were reunited. Sections of this division include electric and time standards, high-energy physics and solid state science.

In 1942 a British-Canadian atomic energy project, under NRC administration, was begun in Montréal, leading to the building of NRX, a heavy-water uranium research reactor, which began operation in 1947 at Chalk River (now Laurentian Hills), Ont. In 1952 administration of the project was transferred to Atomic Energy of Canada Ltd. In 1957 a much larger reactor, NRU, came into operation, and an MP Tandem Van de Graaf accelerator was installed. The aim of this program was to develop research reactors for nuclear experimentation and nuclear power reactors for generation of electricity. W.B. LEWIS was in charge of research. Many Canadian physicists have been involved in the project, including G.C. Laurence, B.W. Sargent, J.M. Robson (neutron decay), R.E. Bell, B.N. Brockhouse (neutron scattering), E.P. Hincks (cosmic rays) and A.E. Litherland.

### Provincial Research

Physics-related research is carried out by many of the 8 provincial research organizations, the oldest being the Alberta Research Council (established 1921). The hydroelectric corporations of most provinces have research facilities relating to electric power generation and transmission, the largest of these being that of Hydro-Québec.

### Industrial Research

Compared with other industrialized nations, Canada shows a rather low level of industrial research and development. Many of the better industrial laboratories doing physics-related research have been set up as Canadian subsidiaries of American companies. For example, the Radio Corporation of America maintained for many years the RCA Canadian Research and Development Laboratories Ltd (under M.B. Bachynski from 1958); in 1976 a large part of its work was taken over by MPB Technologies Inc, with Bachynski as president and director. The Xerox Research Centre of Canada Ltd is a recent example of an American firm locating a part of its research in Canada. Bell-Northern Research Ltd is doing excellent work.

H.L. WELSH

### Theoretical Physics

Physics proceeds by the constant interplay between experimentation and observation and the conceptual interpretation of the results. Until late in the 19th century the 2 often went hand in hand; early 19th-century physicists often engaged in both activities. With the development of increasingly sophisticated techniques of experimentation on the one hand and of mathematical analysis on the other, and with a rapid acceleration of the acquisition of knowledge in the 20th century, specialization became more general and theoretical physics, which was leading a revolution in the conceptual structure of physics and exploiting its power, emerged as a more or less distinct discipline.

The division of physicists into the categories "theoretical" and "experimental" has now become almost universal. A distinction should, however, be made between "theoretical physics" and "mathematical physics," the former being preoccupied with concepts and models of the physical world and the latter with development of mathematical technique and rigorous analysis per se. (Thus, Michael Faraday a century and a half ago, though completely unversed in mathematics, made fundamental changes in physical thought, the importance of which is reflected in contemporary physics.)

The modern revolution in physics stems from 3 major developments of the late 19th and early 20th centuries. The first of these was the generalization from the science of thermodynamics by Rudolf Clausius (1822-88) and J. Willard Gibbs (1839-1903) to a general statistical theory which was to become one of the cornerstones of modern physics. The next involved the formulation of the general theory of relativity by Albert Einstein in 1917. This theory laid the basis for the first scientific cosmology by integrating gravity, the principal motor of the cosmos, into the very structure of space and time. The third was the development of an integrated and coherent quantum theory arising out of the work of Max Planck, Einstein, Louis de Broglie, Niels Bohr, Erwin Schrödinger and Werner Heisenberg among others. An elegant general formulation of this theory, as well as its adaptation to the requirements of relativity, were accomplished by P.A.M. Dirac. Quantum theory is essential to the understanding of the subatomic structure of matter; it is also the basis of how the macroscopic world functions - specifically, quantum phenomena as manifested in superconductors, lasers and magneto-optic effects.

The 20th-century developments began in Europe, primarily in Germany and Great Britain. The American continent, with its emphasis on technology and an empirical tradition, contributed only modestly. The rise of European fascism caused a mass emigration from Europe to the US and refugees (eg, Einstein, Fermi, Wigner, Bethe, Peierls and Weisskopf) propelled American physics, in the space of a generation, into a position of world leadership in theoretical physics.

In Canada, where the empirical tradition had been firmly established by Rutherford and others, theoretical physics was almost nonexistent until after WWII and even then most often found its first home in departments of mathematics. Only at U of T had Leopold Infeld, a refugee from Poland working in a new department founded by the Irish theorist J.L. Synge laid the groundwork for a new school. The enhanced prestige of theoretical physics resulting from its dramatic contributions to the winning of the war created the conditions for the rapid expansion of theoretical physics in the universities.

A strong theoretical group in the wartime atomic energy project continued into the postwar years, but those who did not remain, as well as some from other wartime projects, formed nuclei for the expansion of theoretical physics in some of the leading universities (eg, BC, McGill, Toronto, McMaster).

By 1957 a theoretical physics division was created within the Canadian Association of Physicists, and conferences attracting world-famous theorists were organized. This was the beginning of a period of rapid expansion that carried Canada to a strong position on the world scene. An important element in that process was the development of the National Research Council into a strong centre of fundamental research on the initiative of its wartime director, C.J. Mackenzie. Aside from creating its own laboratories, it was responsible for the funding of basic research in the universities, on the basis of enlightened policies due to E.W.R. Steacie and Gerhardt Herzberg, among others.

The balance between theoretical and experimental physics has become much the same as in the US, and internationally recognized work is being done by Canadian theorists in all domains. At the same time, graduates of major Canadian schools, such as McGill, are prominent in leading American universities.

The scope of theoretical physics has expanded in recent years. Fundamental particle or high-energy physics has, despite incursions into astrophysics and cosmology, come to somewhat of a roadblock, leading some of its practitioners to seek out other areas of challenge. Work on the physics of fundamental biological processes has attracted some of the best minds, while the new areas of chaos theory and "complexity theory" (the theory of nonlinear self-organizing systems) have become major foci of attraction. Reductionism seems to have run its course, and conceptions of what is truly fundamental are slowly changing. The euphoric vision of a final theory, an "end to physics" envisaged by Stephen Hawking, seems to be giving way to a revolution of outlook that brings us closer to the realization that there are still vast unexplored areas of human ignorance challenging theorists.

P.R. WALLACE

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