Why Does E=mc2_ - Brian Cox [8]
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The Speed of Light
Michael Faraday, the son of a Yorkshire blacksmith, was born in south London in 1791. He was self-educated, leaving school at fourteen to become an apprentice bookbinder. He engineered his own lucky break into the world of professional science after attending a lecture in London by the Cornish scientist Sir Humphry Davy in 1811. Faraday sent the notes he had taken at the lecture to Davy, who was so impressed by Faraday’s diligent transcription that he appointed him his scientific assistant. Faraday went on to become a giant of nineteenth-century science, widely acknowledged to have been one of the greatest experimental physicists of all time. Davy is quoted as saying that Faraday was his greatest scientific discovery.
As twenty-first-century scientists, it is easy to look back at the early nineteenth century with envious eyes. Faraday didn’t need to collaborate with 10,000 other scientists and engineers at CERN or launch a double-decker-bus-sized space telescope into high-earth orbit to make profound discoveries. Faraday’s “CERN” fitted comfortably onto his bench, and yet he was able to make observations that led directly to the destruction of the notion of absolute time. The scale of science has certainly changed over the centuries, in part because those areas of nature that do not require technologically advanced apparatus to observe them have already been studied in exquisite detail. That’s not to say there aren’t examples in science today where simple experiments produce important results, just that to push back the frontiers across the board generally requires complicated machines. In early Victorian London, Faraday needed nothing more exotic or expensive than coils of wire, magnets, and a compass to provide the first experimental evidence that time is not what it seems. He gathered this evidence by doing what scientists like to do best. He set up all the paraphernalia associated with the newly discovered electricity, played around, and watched carefully. You can almost smell the darkly varnished bench mottled with shadows of coiled wire shifting in the gaslight, because even though Davy himself had dazzled audiences with demonstrations of electric lights in 1802 at the Royal Institution, the world had to wait until much later in the century for Thomas Edison to perfect a useable electric lightbulb. In the early 1800s, electricity was physics and engineering at the frontier of knowledge.
Faraday discovered that if you push a magnet through a coil of wire, an electric current flows in the wire while the magnet is moving. He also observed that if you send a pulse of electric current along a wire, a nearby compass needle is deflected in time with the pulse. A compass is nothing more than a magnet detector; when no electricity is pulsing through the wire, it will line up with the direction of the earth’s magnetic field and point toward the North Pole. The pulse of electricity must therefore be creating a magnetic field like the earth’s, although more powerful since the compass needle is wrenched away from magnetic north for a brief instant as the pulse moves by. Faraday realized that he was observing some kind of deep connection between magnetism and electricity, two phenomena that at first sight seem to be completely unrelated. What does the