At number 4 in *The Guardian’s* list of the ten best physicists is Albert Einstein.

The fact that Einstein is at number 4 in this list of “ten best physicists” leads me to believe that this list is not in any particular order. I can’t imagine there would be anyone who would not place Einstein alongside Newton as being one of the two greatest physicists in history.

Quite simply, Einstein revolutionised our understanding of Physics and of the Universe. He overturned the absoluteness of Newtonian mechanics, replacing it with his theories of relativity. He was also instrumental in our understanding of the World at the atomic scale. His name is now synonymous with genius, we all understand what a phrase like *“he’s not an Einstein”* means.

## Einstein’s brief biography

Albert Einstein was born in Ulm (in present day Germany) in 1879. His father Hermann and his mother Pauline (née Koch) were also both German. In 1880 the family moved to Munich where Einstein’s father and uncle started a company manufacturing electrical equipment running on direct current electricity. In 1894 this company failed, when alternating current became the standard worldwide for distributing electricity. The family moved to Italy, but Einstein stayed in Munich to finish his studies.

In 1896, having obtained top marks in his mathematics and physics exams, Einstein enrolled on a 4-year mathematics and physics teaching diploma course at Zurich Polytechnic. He graduated in 1900. During his time at Zurich Polytechnic he became romantically involved with a classmate, MIleva Mariƈ. They married in 1903, by which time Einstein was working as a patent clark in the Swiss Patent Office.

In 1905 Einstein had his *annus mirablis* (miraculous year). He completed his PhD at the end of April from the University of Zurich, and then proceeded to publish five important papers, four of which are generally recognised as being great works of physics in their own right. I will discuss these five papers below, but by 1908 his work from 1905 had gained enough attention that he was appointed a lecturer at the University of Bern.

Einstein was only at Bern for one year, in 1909 he was offered a lecturing position at the University of Zurich, and then in 1911 was offered a full Professorship at the Charles-Ferdinand University in Prague. In 1914 he was appointed the Director of the Kaiser Wilhelm Institute for Physics and made a Professor at the Humboldt University in Berlin, arguably Germany’s most prestigious university.

In 1919 Einstein became a celebrity when Sir Arthur Eddington verified one of the key predictions of Einstein’s theory of gravity, his *General Theory of Relativity*. Newspaper headlines around the World acclaimed him, and from that year on his life was never the same. In 1921 he was awarded the Nobel Prize in Physics for his work on the photoelectric effect.

In 1933, with Hitler coming to power in Germany, Einstein seized on the opportunity of a visit to the United States to “defect”. He never returned to Germany, and with many academic job offers to choose from he settled at the Institute for Advanced Study at Princeton University in New Jersey, USA. It is there he saw out the rest of his career, dying in 1955.

## Einstein’s contributions to Physics

It is difficult to know where to start in discussing Einstein’s contributions to Physics. As I said above, alongside Newton, Einstein stands as one of the two most important people in Physics. *Time Magazine* decided to make Einstein their *“Person of the Century”*, placing above all the 20th Century’s great statesmen. Why?

Einstein changed our perception of our Universe. He will be best remembered for his two theories of relativity. In 1905, as the third paper in his *annus mirablis*, he published a paper entitled *“On the Electrodynamics of Moving Bodies”*, a fairly innocuous title. But the contents were far from innocuous, it asked us to accept the idea that if two observers are moving relative to each other they will *always measure the speed of light to be the same*. This has far reaching consequences. It means that time passes differently depending on how you are moving, it means that lengths will be measured differently, and it means that the inertial mass of an object will change as its speed increases. Later in the same year, Einstein wrote a paper entitled *“Does the inertia of a body depend upon its energy content?”*, and this paper introduced what has become the most famous equation in Physics, , showing that mass and energy are equivalent. These two papers together describe the ideas of what we now call *Special Relativity*.

Before publishing his paper on the electrodynamics of moving bodies, Einstein published a paper which would win him the 1921 Nobel Prize. This was a paper on the *photoelectric effect*, a phenomenon which had been known about for several decades but for which no-one had a successful explanation. The photoelectric effect is when electrons are released from the surface of certain metals when a light is shone upon the metal’s surface. The experimental results of this phenomenon could not be explained with the accepted “wave theory” of light. Einstein extended the idea of *“light quanta”*, which had first been suggested by Max Planck in 1900 to explain blackbody radiation. Einstein suggested that light could be thought of as individual quanta of energy (what we now called *photons*), with the energy of each photon given by where is Planck’s constant and is the frequency of the light. This simple but revolutionary idea explained the results of the photoelectric effect perfectly, and was the beginnings of having to think of all sub-atomic phenomena as a combination of waves and particles, something which is at the heart of Quantum Mechanics.

In 1905 Einstein also published a paper explaining Brownian motion as the jostling of pollen grains by molecules in the liquid in which the grains are suspended. This was one of the first direct proofs of the existence of atoms. With the five papers Einstein published in 1905 he was destined to be an important physicist. But what propelled him to being considered *the* greatest physicist next to Newton was what came next, his *General Theory of Relativity*.

Einsteins’ General Theory of Relativity is his re-working of Newton’s theory of gravity, which had been around for over two hundred years and which most physicists felt was as correct a theory as any that had been developed. But Einstein realised that Newton’s way of thinking about gravity was incompatible with his earlier Special Theory of Relativity. Over a period of some seven years, from 1908 to 1915, Einstein worked out the mathematical details of his theory, and when it was finally published it was even more revolutionary in some ways than his Special Theory of Relativity. It asked us to think of gravity not as a force, but as a bending of space-time. Masses cause the *space-time continuum* to deform, and in this deformed continuum objects move along the shortest path. I am not going to go into too much detail here, but will explain many of the most important ideas and predictions of General Relativity in series of future blogs. Suffice it to say that, to date, his new way of thinking about gravity has withstood every test to which it has been put, and is considered one of the most important theories in physics, as well as one of the most beautiful.

Einstein made many other contiributions to 20th Century Physics, including the *Einstein coefficients* which enable us to work out how long electrons will spend in different energy levels in atoms, and *Bose-Einstein Statistics*, which is how particles which are indistinguishable from each other behave in a statistical way.

It is difficult to imagine where Physics would be today if it weren’t for Einstein’s contributions. Some people have argued that, whereas his *Special Theory of Relativity* was just waiting to be discovered (indeed, in a talk in 1904 the French mathematician/physicist Henri Poincaré suggested the idea of the relativity of time), his *General Theory* was so revolutionary that it required someone with Einstein’s genius to even think of it, and that no other physicist before or since *could have thought of it*. Einstein’s name towers over Physics like no one else, except of course for Isaac Newton, whom I will talk about in a few weeks’ time.

## Read more

You can read more about Albert Einstein and the other physicists in this “10 best” list in our book *10 Physicists Who Transformed Our Understanding of the Universe*. Click here for more details and to read some reviews.