Science Friday: Einstein's Special Relativity 1

One of the things on my bucket list is to understand an equation in quantum physics called Schrödinger's equation before I die.  For anyone who thinks Wikipedia is for lightweights, tell me what you think of this page.

Off and on for years I have tried to find an entry point, but I usually don't even get through the starting point of quantum physics, Max Planck in 1900.  Schrödinger proposed his equation in 1925. I would love to grasp those 25 years in physics, let alone get beyond them. Dare I share one of my novel starts (I've started dozens)--a quantum physicist who has an accident in which his brain damage leads him to struggle to relearn some of what he formerly knew so well, only to achieve the barest of success.

I found a delightful book recently by Alan Lightman called, The Discoveries. Not that I have made much progress in it either. But he has some of the most groundbreaking scientific essays of the twentieth century in it, and he gives nice introductory essays.

I feel almost ready to write one "chapter" in those groundbreaking first 25 years.  In 1905, Einstein published four groundbreaking papers, including one that introduced his idea of special relativity. I thought perhaps I could summarize that paper slowly here.
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"On the Electrodynamics of Moving Bodies," Albert Einstein, 1905.

Introduction
Einstein starts by noticing that the famous theories of James Clerk Maxwell (1831-79) lead to some inconsistencies. Maxwell was a Scottish physicist who seemed to establish that light was a wave and at least established that electricity and magnetism were manifestations of the same basic phenomenon. His "electromagnetic theory" was the greatest achievement in physics since Isaac Newton (1642-1727) and paved the way for the developments of twentieth century physics (not to mention the radio, television, and cell phones).

The first paragraph of Einstein's essay points out some of the problems Maxwell's theory had left. For example, science at that time had two different explanations for the current created in a wire around a magnet, depending on whether you moved the magnet through the wire or the wire over the magnet. If you moved the magnet through the wire, science said that the magnet generated an electric field around it that caused current in the wire. But if you moved the wire over the magnet, science did not say there was an electric field over the magnet. Instead, it said that an electromagnetic force was created in the wire. The current generated, however, was exactly the same.

[Note: I do not really grasp the relevance of this particular example at this point]

In the second paragraph of the introduction, Einstein sees a solution to these sorts of anomalies in the reconciling of two principles that were already accepted but that seemed contradictory.

First, there was the "principle of relativity" that had been established three hundred years earlier by Galileo.  Physical laws operate the same in any "inertial frame of reference," that is, in any collection of items moving together at a constant velocity. The recent laws of electromagnetism set down by Maxwell were no exception: "the same laws of electrodynamics and optics will be valid for all frames of reference for which the equations of mechanics hold good." (72).

The second postulate on which Einstein will base his theory is the "theory of light constancy."  "Light is always propagated in empty space with a definite velocity c which is independent of the state of motion  of the emitting body" (72). In other words, light will move at 300,000,000 meters per second whether it shines from a spaceship moving 100,000 meters per second or from someone with a flashlight in your back yard. Einstein himself was not the first to suggest this constancy.

Einstein was keen to resolve the apparent contradiction between these two postulates. How is it that light does not move faster off a moving truck than it does from someone standing on the side of the road? They are two different inertial frames of reference and so, relative to each other, the velocity of the truck should add on to the velocity of light relative the ground.

Maxwell's equations worked for "stationary bodies." That is to say, they worked within the framework of a single inertial frame of reference. Einstein's goal in this essay is to present a "simple and consistent theory" that will work for bodies moving in relation to each other, to present a theory relating to the "electrodynamics of moving bodies."

As a side benefit, he aims to show that the notion of a "luminiferous ether" is superfluous. Since Maxwell had seemed to show that light was a wave, the question had arisen as to what sort of a medium the wave moved through.  Water waves moved through water.  What did light waves move through?  At the time, physicists assumed there must surely be some sort of invisible medium through which light moved, something they called the "ether."

But experiments had failed to show any ether (e.g., the Michelson-Morley experiments). The ether gave a sense of absolute space--there would be something at rest at every point of the universe. Einstein's theory ends up negating the notion of "absolute stationary space" or absolute rest in space.