Albert Einstein was born in Ulm, southern Germany, in 1879. At school, he only seemed interested in mathematics. It is reported that one of his frustrated teachers remarked, “Einstein, you will never amount to anything.” He got into a college in Switzerland and only scraped through his final exams with the help of a friend’s lecture notes and, with the help of the father of the same friend, he found a job as a junior official at the Patent Office in Bern. This undemanding job left him plenty of time to develop his physics so that four years later, in 1905, he had what might be called a ‘purple patch’ – publishing papers on three different topics that were to change the face of physics.
1) The photoelectric effect
When Hertz discovered radio waves, he also accidently came across the photoelectric effect but left it to his student, Philipp Lenard, to investigate the details. In 1902, Lenard noted that the kinetic energy of electrons emitted from a metal surface depended on the frequency of light (x-rays), not its intensity – at odds with classical physics. Einstein solve this problem in 1905 when he modelled light as photons with energy E = hf.
As far as Planck was concerned, blackbody radiation propagated as a wave. It was Einstein who made the bold assumption that light energy could also be delivered as ‘packets’ that we now called ‘photons’, and gave physical meaning to Planck’s constant (i.e. the concept of energy being quantised). We now accept the fact that light behaves in this way but in 1905 it was revolutionary and required a considerable leap of imagination. It took another 10 years of experiments to establish the theory beyond doubt. In the meantime, many scientists were sceptical. In 1921, Einstein was awarded a well-deserved Nobel Prize for his explanation of the photoelectric effect, yet his best work was still ahead of him.
2) Brownian motion
Einstein’s second topic was Brownian motion, named after the Scottish botanist, Robert Brown, who discovered it in 1827. Looking down his microscope, Brown could see small structures within pollen grains jiggling about. He thought they were alive until he observed the same thing happening to particles of dye.
The bombardment takes place from all directions and normally the resulting forces on the particle would cancel out. With a very small particle, the number of molecules hitting it will also be smaller. Exact cancellation of the forces is therefore less likely to occur, making the particle move. Einstein’s contribution was to work out all the mathematical details. Also, even though the atomic theory of matter had already been around for 100 years by this time, there were still a few eminent scientists who thought atoms were merely a convenient fiction. Einstein’s analysis of Brownian motion finally convinced even the last remaining diehards that molecules really did exist.
3) Special relativity
Einstein’s third topic in 1905 shook physics to its very foundations. It was his special theory of relativity – the work for which he is best known for. To find out what relativity is about, we go back to Maxwell and his prediction of electromagnetic waves. There is no medium in Maxwell’s formula for the speed of light. This left physicists with a problem. Against what frame of reference was light supposed to be moving? Einstein’s theory solves this problem immediately by stating that the speed of light is the same to all observers who are in uniform motion relative to each other. While this agrees perfectly with Maxwell’s formula, it leads to other results that appear to contradict common sense: e.g. length contraction, time dilation. However, common sense is based on our limited experience with object of ordinary size moving at ordinary speeds. Looking at things the size of the universe or of an atom and considering speeds comparable to that of light, common sense is not always the best guide.
Einstein was an important contributor to quantum physics. However, he was the sole creator of relativity. No one else was involved, which makes this a stunning accomplishment, ranking easily with the achievements of Newton. Most professional physicists would be more that happy to produce just one peiece of groundbreaking work in their lifetime. To produce three in one year, you have to be just one of the greatest physicists who has ever lived.