A journey through the lightyears*
Shiva Agarwal**
How the light, that we have around us, was demystified by two
extraordinary minds of the nineteenth century.
Physics is an exciting play-field and there are numerous sculptors of the rules of this game. Many a time (or almost every time) we come across equations, formulations, experiments and works in physics that are being cherished, doubted, loved, hated and taught. Most of the time this physics journey is about the work of some brilliant minds, working day in, day out to produce some of their marvels but what lay hidden are the stories behind those sculptors, stories that are to be read aloud and to be told to everyone. There are story-lines that are beautifully plotted and equally well proposed, some of tragedy, some of triumphs, some showing envy, some of great affection and some inspiring and heartening.
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There have been instances in the lives of many great physicists that could be considered as illuminating and manifesting their true self to the world. One such incident was when two great scientists, Michael Faraday (1791-1867) and James Clarke Maxwell (1831-1879) met each other. For physics-lovers, this association left a symphony of physical equations and a series of fascinating experiments.
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Maxwell laid the foundation of the theoretical formulation of electrodynamics in the 19th century and could explain that light that we see around is nothing but an amalgamation of the electric and magnetic fields. Previously light’s speed was a mystery and physicists could only tell that light travels with finite speed but in 1865 Maxwell proposed that light was an electromagnetic wave, and therefore traveled at the speed c appearing in his theory of electromagnetism. Maxwell showed that speed of light c could be calculated using his famous equations by comparing the second order equations for the electric (E) and the magnetic fields (B) with the three-dimensional general wave equation [1]. As written by David J. Griffiths in his book, 'Introduction to Electrodynamics', “Astonishingly the constants in Coulomb’s law and Biot-Savart law could deduce the velocity of light, the same constants that are measured in experiments involving charges, batteries and wires- experiments having nothing to do with light.” But it wasn’t the sole effort of Maxwell which could explain light so beautifully and artistically; another great and bright physicist of the 19th century was the inspiration of all the mathematics behind. It was Michael Faraday who could first observe in the year 1845 that magnetic field influence polarized light- a phenomenon known as Faraday’s effect.
Michael Faraday (left) and James Clarke Maxwell (right).
Faraday had no formal training in Mathematics and Mathematics troubled him all his life. He left school when he was thirteen and worked at a bookbinding shop which formed the basis for his basic formal education by reading the books he used to bind. His passion for science grew when he read in a book he was binding, Encyclopaedia Britannica, a description of electricity, after which he started experimenting in an improvised laboratory. He later assisted Humphry Davy at the Royal Institution in London. Faraday being a laborious lad, was appointed as Davy’s collaborator in 1813 and then the Director of the Laboratory in 1825 [2]. Faraday left such an impression on Davy that when latter was asked about his greatest discovery, Davy replied, “My greatest discovery was Michael
Faraday” [3]. Faraday was an exceptional experimentalist who could visualize physical systems and phenomena, which led him to demonstrate many physical ideas to scientists and laymen. In 1831, he gave his law of induction which said that changing magnetic field produces an electric field.
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Faraday’s picture of the field of force was indeed the most ingenious work in Physics (a concept that baffled Newton in his later years) and was described by Einstein as 'the great change in Physics'. He was able to define a relationship between electricity and magnetism but his inquisitive mind was not going to stop at that only as he went on to find a relation between light, electricity and magnetism. As mentioned earlier, he could demonstrate this relation but couldn’t convert his ideas into the language of modern physics-precise mathematical equations. (Mathematics was the culprit!). This relation of the trio was not accepted until about 20 years when James Clarke Maxwell entered the picture, one of the greatest mathematicians ever walked the planet Earth.
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Faraday and Maxwell were both celebrated physicists of their time, both contributed a lot to the field of electromagnetism, both born geniuses. They might seem alike yet so contrasting they were, Maxwell born in a rich family and Faraday into a humble one, Maxwell was an exception at handling Mathematics and Faraday knew nothing about Mathematics, Maxwell a great theoretical physicist and Faraday an equally great experimentalist. But it required both of them to uncover the mystery behind the light, Maxwell could find out what Faraday had seen.
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By his early twenties, Maxwell had made his name as a mathematician, while other scientists came to think Faraday as old fashioned, Maxwell knew better. Maxwell spent five years of his life (1860- 1865) at King’s College, London and it was the most productive time of his life. He was awarded the Royal Society’s Rumford medal in 1860 for his work on color and was later elected to the society in 1861. During this period he also developed his ideas of the viscosity of gases and proposed the concept of dimensional analysis for physical quantities. Also during these years, Maxwell used to attend lectures at the Royal Institution, London and thus came into regular contact with Faraday. At that time Faraday was forty years senior to Maxwell but they both maintained respect for each other’s talent and eminence. Maxwell had faith in the ideas of Faraday and was convinced that his field lines were real, he was so impressed by the work of Faraday that being a great mathematician himself, he was still lost in the Physics behind the field lines. He says at the onset of this treatise, "Before I began the study of electricity I resolved to read no mathematics on the subject until I had first read [Faraday]." He set out to give the ideas of
Faraday a precise mathematical formulation and could find out that Faraday’s static field lines were actually waves that travel with the speed of light. Maxwell described this experience by saying: I found that ... Faraday's methods ... begin with the whole and arrive at the parts by analysis, while the ordinary mathematical methods were founded on the principle of beginning with the parts and building up the whole by synthesis.[4]
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Finally, in 1865 the world saw the dawn of the light that we see today- an electromagnetic wave and moving at the finite velocity of 299,792,458 m/s. Faraday had a dream to present the trilogy of electricity, magnetism and light to the world and Maxwell had a dream to help him do so. Was it a dream that came true for Maxwell or a dream that came true for Faraday? Probably it was a dream that came true for millions of physics lovers and will be cherished by many more to come.
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* The article was originally appeared in Physics Bulletin (2017) in Department of Physics, Aligarh Muslim University, India.
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** Shiva Agarwal has completed his MSc in Department of Physics, Aligarh Muslim University, India
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References:
[1]Introduction to electrodynamics by David J. Griffiths
[2]http://www.rigb.org/our-history/people/f/michael-faraday
[3]https://www.bbvaopenmind.com/en/faraday-electromagnetic-theory-light/
[4]http://www.uh.edu/engines/epi905.htm