Tonight at 10:00 P.M. Pacific Time (at least in my frame of reference), the the History Channel will feature the story of Albert Einstein. It was already shown on Nov. 17th, but I didn’t have time to watch it then. If, like me, you missed it, be sure to catch it this time around as will I.
You may recall that in 1905, Einstein had somewhat productive year as per published papers. Five of them in fact. They ranged from introducing the concept of special relativity, to explaining the photoelectric effect and Brownian motion. Of course, special relativity fundamentally changed how we view space and time and how one must take care of how such things are measured. In spite of changing how we view reality at a fundamental level with relativity, he received the Nobel Prize for explaining the photoelectric effect. This merely had the effect of laying some of the foundations for all quantum mechanics.
Of course, the special theory of relativity worked for inertial frames. Frames of reference that moved at a constant velocity relative to each other. Think of a car moving at a constant velocity of 60 mph relative to the ground. An observer on the ground measuring phenomena in the car, and an observer in the car measuring the same phenomena will agree on the laws of physics. If the person in a car throws a ball at 5 mph towards the front of the car, he’ll measure the ball’s speed as 5 mph, but the observer on the ground will measure it as 65 mph. That makes sense. But there are 4 equations called Maxwell’s equations which describe all electromagnetism. Embedded in these equations is the speed of light. The startling implication is that the speed of light in a vacuum is part of “physical law” and so both observers must agree on its value. The resolution of this problem leads to the special theory of relativity.
Interestingly enough, not only must space and time coordinates transform, but carrying this forward leads to equations which describe how velocities, and momenta transform. This leads into how forces transform. Following the force transformation give an interesting result. Two charges at rest with respect to each other have only an electrostatic force between them. But if they are in a reference frame moving with constant velocity respect to another, the other observer sees a modified electric force and another force dependent on the velocity of one of the charges. This turns out to be due to a magnetic field. So relativity provides a link between electricity and magnetism. Following, this one can see how electric and magnetic fields transform into each other in different frames of reference. How exactly this works may be a bit nonintuitive, but I hope to find some time into making that into a posting one of these days. Of course, if you want to jump way ahead, check out the wiki. The stuff on electromagnetism is a bit more mathematically formal than how I intend to discuss later, if I ever get around to it. But I hope the average person can take away something.
Of course, what interested Einstein afterward, was how to extend this to noninertial reference frames. This lead to the general theory of relativity which relates a gravitational field to noninertial frames and shows show space can curve and time dilation effects are observed in the presence of gravitational fields. That’s a can of worms for a completely different post.
Truly one of the greats of the 20th century.