Historic Unifications in Physics
Galileo Galilei invented modern science. The way he investigated the world around him shaped how science would be done for centuries. Before him, the greatest minds were largely philosophers and theologians. Before Newton’s time, Galileo sought to investigate the principles of motion. He laid the groundwork for understanding the laws of motion, most importantly by distinguishing one important concept: an object moving with constant velocity is just like a stationary object – it just depends on your frame of reference. It may seem trivial, but it changed the way people thought about motion, and it gave Newton the starting push to discover the laws of motion.
Several hundred years later, Michael Faraday was tampering with currents in wire circuits in his lab when he noticed that when he switched the current off in one of the wires, a nearby one generated a current. What he discovered was induced current, which happens whenever there is change in magnetic fields. Anywhere there is current, there is a magnetic field, and when there is a change in current, thus a change in magnetic field, a new opposing current and magnetic field are generated, called the induced current. Faraday had little formal training, and he wasn’t much of a mathematician, so he described his discoveries visually, often with diagrams.
Decades later, physicist James Clerk Maxwell discovered mathematical expressions for Faraday’s concepts. Using inspiration from Faraday, Maxwell did an experiment measuring the velocity of induced magnetic and electric current fields. His findings showed that both electricity and magnetism propagated as waves at the speed of light, which was no coincidence. Maxwell had discovered for the first time that electricity, magnetism, and visible light were all manifestations of the same electromagnetic wave phenomenon. This is known as the second great unification in physics.
However, it wasn’t until Einstein’s theory of relativity that the important discrepancy between Galileo’s discovery and Maxwell’s discovery were reconciled. Einstein theory of relativity states that velocity is completely determined based off your frame of reference. For example, if you’re sitting in a car going 40 miles per hour, from inside the car it looks like your sitting still. However, an observer on the side of the road sees the car going 40 miles per hour. This ties back into Galileo’s discovery; if you’re going at constant velocity, it is fundamentally impossible to distinguish whether or not you are truly moving unless you have an outside viewer with a different frame of reference. But what if there is no other frame of reference? If you shine a laser pointer out of the front of a car going 99% the speed of light, would an outside observer measure light going almost twice the speed of light? Einstein noted that surely this was not the case, because then Galileo’s idea that there is no way one can tell whether or not they are moving if they are moving at constant velocity would be false, as you would be able to tell based off the speed of light. Einstein was left in a situation where both Galileo and Maxwell were experimentally correct, yet their ideas conflicted with each other. Einstein finally concluded that in order for light to have the same velocity from every possible frame of reference while still having the speed Maxwell measured, time and space had to be variable. This meant that the faster an object moves, the slower it perceives time pass, and the closer to the speed of light an object got, the shorter it became. This notion that time and space, both seemingly static, are actually changing all the time, depending on your velocity.
This relates to IMT because it took the supremely type A characteristics of Einstein to realize that time and space are variable quantities. Part of what made Einstein a great physicist was his ability to remove himself from his physicist silo and think about problems holistically from the top down.
Krauss, Lawrence Maxwell. Fear of Physics: A Guide for the Perplexed. New York, NY: Basic, 1993. Print.