Faraday and Maxwell

The story of Michael Faraday and the development of field theory in the early nineteenth century and his discovery of the magneto-optical effect, which linked the study of optics and light to electromagnetism for the first time, and led to the discovery of the displacement current. The integration of electrostatics and electromagnetism by James Clerk Maxwell and others. How Maxwell discovered his great equations, which predict a constant speed of light and show that light is an electromagnetic wave. How the symmetry which resulted from his displacement current provided an important clue for Einstein’s theory. Maxwell’s current-charge balance apparatus, which allowed him to measure the speed of light by purely electrical means. How Maxwell’s equations were later used in the discovery of radio waves. Maxwell’s life and interests, from poetry to horse riding and guitar. Kelvin and the laying of the Atlantic cable.

James Bradley, Sailing on the Thames

The story of the astronomical observations of James Bradley in the eighteenth century, whose measurements of the small movements of a star throughout the year provided an independent estimate of the speed of the Earth around the Sun relative to the speed of light. His work provided the first experimental evidence in support of Copernicus’s theory that the earth is in motion, and against the idea that it is stationary at the center of the universe. His simple telescope at home, his brilliant idea and perseverance, and his life’s work and influence. The importance of his result for the development of Einstein’s theory of relativity and for theories of the Aether in the following centuries.

Ole Roemer, Who Started It All

The story of the first measurement of the speed of light by Ole Roemer in 1676. Galileo had discovered the moons of Jupiter with his new telescope, and proposed using observations of their eclipse every forty-two hours as a universal clock for our planet, since they could be seen from practically anywhere. This would keep track of the time at home, and so give a traveller his or her local longitude. (The King of Spain had offered a prize for longitude determination to avoid disasterous shipwrecks.) Roemer noticed that the eclipses were sometimes a little late, which he concluded was due to the time it took light to get from Saturn to Earth and the movement of the Earth between eclipses. His estimate of the time for light to travel from the Sun to Earth was quite accurate. Roemer’s remarkable life story and many other achievements are told.

Faster-than-Light Schemes

Developments since Einstein are summarized. Our systems of units and their relationship to the speed of light. Light propagation in vacuum—what stuff is an electric field made of? Quantum field theory ideas. The Casimir force and energy. Olbers’ paradox and the cosmic horizon. Effect of gravity on speed of light. Schemes for messaging at speeds greater than that of light. The Einstein–Rosen–Podolsky paper of 1935 and its interpretation in simple terms. The reality of the quantum world. Hidden variable theories and Bell’s theorem. Interpretation of many-body quantum wavefunctions—Bohm, Born, Schrӧdinger, Heisenberg, de Broglie, their lives and contributions to physics. The Copenhagen interpretation of quantum mechanics and others. The measurement problem and collapse of the wavefunction. Entangled states. The unreasonable effectiveness of mathematics in the natural sciences.

Einstein

The confused state of theoretical physics in 1900 and the great unresolved issues are summarized, one of which led to the birth of quantum mechanics, and the other to relativity. How it seemed impossible to reconcile Bradley’s measurements of the speed of light with Fresnel’s Aether drag hypothesis, which was well supported by Fizeau’s measurements in Paris of the speed of light in a moving medium (flowing water). Maxwell’s equations predicted a constant speed of light, suggesting an absolute frame of reference in the universe, but did not “transform” in the same way as Newton’s equations from one moving observer to another. How Einstein made sense of all these rival theories and experimental results with his unifying theory of relativity, based on two assumptions. His life and work is discussed, and a simple explanation given of his relativity theory. How the failure of this search for an absolute frame of reference in our universe led him inexorably to perhaps the most famous equation in physics E = mc2, giving the energy release from nuclear explosions and the stars.

Early Ideas

Mankind’s early ideas about the speed of light, the Aether (supposed to fill the universe) and the instantaneous “action at a distance” theory, before the speed of light was first measured. Euclid’s work on optics, in which he used his theorems from geometry to explain what is seen, assuming that rays of vision were sent out by the eye. The discovery of refraction, explained by Snell’s law and its implications for the speed of light in the theories of Descartes and Fermat, and its importance in modern physics as a principle of least action. How the study of refraction, as when a light beam from a laser pointer bends on entering water, divided scientists for centuries into two groups, those who believed that light sped up on entering water and was a particle, and those who believed it slowed down and was a wave.

Radio and Telecommunications

The Cassini space probe and its recent voyage to Saturn, and communications system are described. Communication with it at the speed of light takes over an hour to reach Earth. The power and range of its transmitter, how its antenna works, and NASA’s deep space communications global network. Heinrich Hertz and the discovery of radio communication in 1887, after Maxwell’s death. FitzGerald’s publication predicting radio transmission in 1883. His life and apprenticeship under Helmholtz and theoretical and experimental work. His use of a spark gap as a receiver with resonant circuits to set up standing electro-magnetic waves in his laboratory. His discovery that these waves, of much lower frequency than light, travelled at the speed of light. Dipole radiation. Hertz’s visit to London and his life. David Hughes, his life, adventures and inventions, including the carbon microphone and printing telegraph, and his accidental pre-discovery of radio using a carbon microphone as a “coherer” detector.

Introduction

This book tells the human story of one of mankind’s greatest intellectual adventures - how we understood that light travels at a finite speed, so that when we look up at the stars we are looking back in time. And how the search for an absolute frame of reference in the universe led inexorably to Einstein’s famous equation E = mc2 for the energy released by nuclear weapons, which also powers our sun and the stars. From the ancient Greeks measuring the distance to the sun, to today’s satellite navigation and Einstein’s theories, the book takes the reader on a gripping historical journey. How Galileo with his telescope discovered the moons of Jupiter and used their eclipses as a global clock, allowing travellers to find their Longitude. How Roemer, noticing that the eclipses were sometimes late, used this delay to obtain the first measurement of the speed of light, which takes eight minutes to get to us from the Sun. From the international collaborations to observe the Transits of Venus, including Cook’s voyage to Australia, to the extraordinary achievements of Young and Fresnel, whose discoveries eventually taught us that light travels as a wave but arrives as a particle, and the quantum weirdness which follows. In the nineteenth century we find Faraday and Maxwell, struggling to understand how light can propagate through the vacuum of space unless it is filled with a ghostly vortex Aether foam. We follow the brilliantly gifted experimentalists Hertz, discoverer of radio, Michelson with his search for the Aether wind, and Foucault and Fizeau with their spinning mirrors and lightbeams across the rooftops of Paris, competing to be the first to measure the speed of light on earth. The difficulty of sending messages faster than light using quantum entanglement, and the reality of the quantum world conclude this saga.

Albert Michelson and the Aether Wind

The life of the gifted American scientist who devoted his life to detection of the Aether wind which the Earth should be moving through, and to the measurement of the speed of light. The struggle to understand how light could propagate through a complete vacuum. Michelson’s invention of his interferometer. Michelson’s great experiment at Case University showing that the speed of light is the same in all directions, independent of the Earth’s velocity. His communication with Maxwell, Kevin, and Rayleigh, and sense of failure over his inability to detect the Aether wind or to locate the Aether as an absolute frame of reference. The Aether drag theories and their tests. Rayleigh’s work on the difference between phase and group velocity. Heaviside’s life and work. Fitzgerald, Einstein, Lorentz, and Michelson.

The Nineteenth CenturyLight Beams Across the Rooftops of Paris

The history of the discovery that light is a wave by the remarkable scientists Fresnel, Young, and Huygens, and their eventful lives. The discovery of optical interference, and the influence of Newton, who mostly treated light as a particle. Wheatston’s measurement of the speed of electricity, the first use of rotating mirrors. Paris in the nineteenth century, the Siege of Paris and the Commune, and the extraordinarily adventurous life of Francois Arago and his achievements. The first non-astronomical measurements of the speed of light on Earth by Fizeau, Foucault, and Cornu, using spinning toothed wheels and rotating mirrors at the Paris Observatory.