Albert Einstein was born in the village of Ulm near Munich in 1879. Like Newton he didn’t have a particularly distinguished academic career, primarily because, in the words of one of his professors, he would “not let yourself be told anything.” He failed to get a recommendation for graduate school and thus spent three years as a patent clerk. This time, like Newton’s isolation during the Black Plague, allowed Einstein time to ponder basic questions about the world and set the stage for later scientific breakthroughs.
In particular, this time allowed him to solve a puzzle he had propounded to himself as a teenager. Aware of the speed of light, some 300,000 km/sec. (187,500 miles/sec), he wondered “what if I were riding on a beam of light?” He imagined riding a beam of light, holding a mirror in front of his face. If the speed of light was measured relative to the ether (Einstein was unaware of Michelson and Morley’s experiment that disproved the existence of the ether), then, he surmised, as he approached the speed of light his reflection would vanish because the light from his face would never reach the mirror so as to be reflected back.
This conclusion was shocking because it violated Galileo’s theory of relativity of movement. Galileo explained it in this way: Imagine you are shut up below deck on a ship moving in a straight line at a constant speed. Have a fishbowl with fish, a jar with butterflies, a bottle suspended and dripping into a container at a constant rate. There will be nothing to indicate the movement of the ship. The fish will swim the same as if the ship was at rest; the butterflies will flit around undisturbed by the movement; and the water will drop straight down into the container. In short, you have no way of determining whether the ship is at rest or moving from the observations you can make inside the hold of the ship. But in Einstein’s puzzle, he could tell he was moving because as he approached the speed of light he would no longer see his reflection.
Einstein toyed with this idea for the three years he worked as a patent clerk. Finally, he realized that his conclusion that his reflection would vanish was based on the assumption that the universe is filled with ether. Ether provided the absolute reference point against which all motion could be measured. However, if there is no ether, there is no reference point against which to measure the speed of light. Einstein made the intuitive conclusion that the speed of light is relative to the observer. In other words, every observer, regardless of her motion, measures the speed of light to be 300,000 km/second. Thus, if Einstein were riding a beam of light, holding a mirror in front of him, he would seem to be at rest according to Galileo’s theory. Light would leave his face at 300,000 km/second, relative to him, reach the mirror and be reflected back. He would not be able to discern movement based on the mirror. Of course a corollary to this thought experiment is that there is no ether.
Einstein’s and Michelson/Morley’s separate conclusions that the ether doesn’t exist came through separate methods, demonstrating the difference between theoretical and experimental physics. Einstein reached his conclusions based purely upon reasoning, while Michelson and Morley conducted experiments. Both have a place in science. When it comes to the cosmos, theoretical physicists have the upper hand since it’s difficult to re-create the Big Bang in the laboratory.
In 1905, at the age of 26, Einstein published three papers. In the first he made a brilliant theoretical argument to support the observed Brownian movement, which supported the theory that matter is composed of molecules and atoms. The second, which won him a Nobel Prize, showed that another well-observed phenomenon known as the photoelectric effect, could be explained using the new field of quantum mechanics. The third summarized his thinking on the speed of light relative to the observer and created a new paradigm for physics, setting the stage for a deeper study of the universe and how it began. This is called his special theory of relativity. The implications of this theory are mind-boggling. One of them is that time is not absolute as had always been assumed. Instead, like motion, time appears different to different observers.
The special theory of relativity will be the subject of the next few posts.