1879–1955

OF the essays written by Einstein in 1905, arguably the most influential was his enunciation of a “special” theory of relativity, which advanced the idea that the laws of physics are actually identical to different spectators, regardless of their position, as long as they are moving at a constant speed in relation to each other. Above all, the speed of light is constant. It is simply that the classical laws of mechanics appear to be obeyed in our normal lives because the speeds involved are insignificant.

The Speed of Light

But the implications of this principle if the observers are moving at very different speeds are bizarre and normal indicators of velocity such as distance and time become warped. Indeed, absolute space and time do not exist. Therefore, if a person were to theoretically to travel in a vehicle in space close to the speed of light, everything would look normal to them, but another person standing on earth waiting for them to return would notice something very unusual. The space ship would appear to be getting shorter in the direction of travel. Moreover, whilst time would continue as “normal” on earth, a watch telling the time in the ship would be going slower from the earth’s perspective even though it would seem correct to the traveller (because the faster an object is moving the slower time moves). This difference would only become apparent when the vessel returned to earth and clocks were compared.

If the observer on earth were able to measure the mass of the ship as it moved, he would also notice it getting heavier too.

Ultimately, nothing could move faster than or equal to the speed of light because at that point it would have infinite mass, no length, and time would stand still.

A General Theory of Relativity

From 1907 to 1915, Einstein developed his special theory into a “general” theory of relativity which included equating accelerating forces and gravitational forces. Implications of this extension of his special theory suggested light rays would be bent by gravitational attraction and electromagnetic radiation wavelengths would be increased under gravity. Moreover, mass, and the resultant gravity, warps space and time, which would otherwise be “flat”, are turned into curved paths which other masses (for example, the moons of planets) caught within the field of the distortion follow.

Amazingly, Einstein’s predictions for special and general relativity were gradually proven by experimental evidence. The most celebrated of these was the measurement taken during a solar eclipse in 1919 which proved the sun’s gravitational field really did bend the light emitted from stars behind it on its way to earth. It was the verification which led to Einstein’s world fame and wide acceptance of his new definition of physics.

Einstein spent much of the rest of his life trying to create a unified theory of electromagnetic, gravitational and nuclear fields but failed. It was at least in keeping with his own remark of 1921 that “discovery in the grand manner is for young people and hence for me is a thing of the past.”

E=MC²

Fortunately, then, he had completed three other papers in his youth (in 1905) in addition to his one on the special theory of relativity! One of these included the now famous deduction which equated energy to mass in the formula E=mc² [where E=energy, m=mass and c=the speed of light]. This understanding was vital in the development of nuclear energy and weapons, where only a small amount of atomic mass (when released to multiply by a factor of the speed of light squared under appropriate conditions) could unleash huge amounts of energy.

The third paper described Brownian motion, and the final paper made use of Planck’s quantum theory in explaining the phenomenon of the “photoelectric” effect, helping to confirm quantum theory in the process.

Further Achievements

Almost inevitably, Einstein was also drawn into the atomic bomb race. He was asked by fellow scientists in 1939 to warn the US President of the danger of Germany creating an atomic bomb. Einstein himself had been a German citizen, but had renounced his citizenship in favour of Switzerland, and ultimately America, having moved there in 1933 following the elevation of Hitler to power in his home country. Roosevelt’s response to Einstein’s warning was to initiate the Manhattan project to create an American bomb first.

After the war Einstein spent time trying to encourage nuclear disarmament.

In 1922, Albert Einstein was awarded the Nobel Prize for Physics.

. Science Book