Einstein was born in 1879, the year Maxwell died. It was the year when Michelson made the first in the series of his experiments in investigating the velocity of light. Einstein was born in Ulm, the town in which Kepler, his favorite scientist of earlier times, had spent some of the last months of his life, before dying in 1630. In high school the geography teach declared Einstein to be moronic; in the Zurich Polytechnic his physics professor, as Einstein told me, once said to him: In this college the poorest class is of experimental physics, and the poorest pupil are you. Upon graduation he was unable to secure a teaching position and, after years of private tutoring of students deficient in mathematics, he was happy to receive the position of a patent examiner in the Bern Patent Office. There he profited in learning to express himself in short and exact terms. At the age of twenty-six, in 1905, he offered the theory of relativity, later called the special or restricted theory of relativity, in distinction from the theory he offered eight years later, the general theory of relativity.
Should I try to put into one single sentence the gist of the theory in 1905, I would do it thus:
A second is no longer a second for all observers. A second of time is of different duration for observes in motion and at rest; but 186,000 miles per second, whatever miles or whatever seconds, was always true.
A mile-long spaceship travels and overtakes our earth. A light signal is sent in the very middle of the spaceship; for the traveler in the spaceship the light will arrive simultaneously at both of its ends; for the observer on earth (assuming he could observe such small differences) the light will come first to the rudder that travels toward the light and then to the bow that travels away from the light. Thus the very notion of simulataneity was emptied of real content.
The theory of Fitzgerald made the matter shorter when crossing through ether and thus masked the change in velocity of light; Einstein, however, made the velocity of light in a vacuum an immutable quantity, or a constant for all observers in whatever relative motion to the source of light they might be.
This is a sentence that can be expressed mathematically; but it is not easy to visualize it by reason. A light leaves its source and whatever object it meets in motion, toward or away from the source of light, the relative velocity of light and the object is always 186,000 miles per second.
Thus a ray of light speeds from the place of explosion in Coventry with the velocity of 186,000 miles per second to Birmingham and with the same velocity in the opposite direction toward Rugby; but the two photons of light speeding in opposite directions have a relative speed of 186,000 miles per second, not of 392,000 miles per second: nothing can be swifter than 186,000 miles per second, the velocity of light.
In those early years of Einsteins career, he spent often his time in discussions with another mathematical genius, W. Ritz. The latter could not see that the velocity of the source would not add itself to the velocity of light: in mechanics, a stone thrown by a passenger in a train acquires not only the velocity of throw but also the velocity of the train that carries the passenger. Ritz printed a paper to oppose the notion of Einstein. De Sitter answered Ritz and proved his point on an astronomical reasoning. There are double stars so placed in space that one partner eclipses the other at regular intervals. If the velocity of the retreating star would reduce from the speed of light reaching the observer and the velocity of the advancing star would add to the speed of light emitted by it, the system would appear to deviate from Keplerian motions. Such is definitely not the case.(1) the earth would be such that the reduction in the speed of light would let the light of one star of the binary arrive to the earth when the star would appear to be in the same place where its companion would appear at the same time. [phrase better].
The special theory of relativity explained why an ether drift cannot be detected through the experiment with the velocity of light; but it went a step farther and disclaimed any necessity of an ether. This makes a very great differenceprobably the next question after the perennial Is there a God? is Does a medium fill all space or is space between the material masses empty? And not just between material massesether is supposed to fill everything, all space and all matter. Between the electrons and protons of an atom there is comparatively very wide space, as it is between the sun and the planets. Is the space all filled or is it empty?