When we hear the name “Einstein” we automatically think the word” genius” and “relativity.” It is that second word which leaves the vast majority of us ordinary mortals totally clueless.
The concepts of relativity are so weird (but true); like astronauts aging slower than the rest ogf us or solid objects changing their shapes at high speed.
One has to be an astrophysicist and a math genius to even have a rudimentary understanding of relativity. What we don’t understand is that Einstein himself thought in much simpler terms.
If you pick up a copy of Einstein’s original paper on relativity from 1905, it’s a straightforward read. His text is plain and clear, and his equations are mostly just algebra—nothing that would bother a typical high-schooler.
That’s because fancy math was never the point for Einstein. He liked to think visually, coming up with experiments in his mind’s eye and working them around in his head until he could see the ideas and physical principles with crystalline clarity.
Einstein’s work emerged from what can be characterized as “thought experiments.”
In 1895 Einstein was thinking about running along side a beam of light.
By this point, Einstein’s ill-disguised contempt for his native Germany’s rigid, authoritarian educational methods had already gotten him kicked out of the equivalent of high school, so he moved to Zurich in hopes of attending the Swiss Federal Institute of Technology.
First, though, Einstein decided to put in a year of preparation at a school in the nearby town of Aarau—a place that stressed avant garde methods like independent thought and visualization of concepts. In that happy environment, he soon he found himself wondering what it would be like to run alongside a light beam.
Einstein had already learned in physics class what a light beam was: a set of oscillating electric and magnetic fields rippling along at 186,000 miles a second, the measured speed of light. If he were to run alongside it at just that speed, Einstein reasoned, he ought to be able to look over and see a set of oscillating electric and magnetic fields hanging right next to him, seemingly stationary in space. After all, if he was traveling at the same speed as the light beam it should appear stationary to him.
Yet that was impossible. For starters, such stationary fields would violate the mathematical laws that codified everything physicists at the time knew about electricity, magnetism and light. The laws were (and are) quite strict: Any ripples in the fields have to move at the speed of light and cannot stand still—no exceptions.
Worse, stationary fields would violate concepts embraced since the time of Galileo and Newton that the laws of physics couldn’t depend on how fast you were moving; all you could measure was the velocity of one object relative to another.
Finally, anything he could see while running beside a light beam should be creatable in a laboratory yet nothing like this had ever been observed.
This problem would bug Einstein for another 10 years, all the way through his university work a and his move to the Swiss capital city of Bern, where he became an examiner in the Swiss patent office. That’s where he resolved to crack the paradox once and for all.
It wasn’t easy. Einstein tried every solution he could think of, and nothing worked. Almost out of desperation, in 1905 he began to consider a notion that was simple but radical.
Maybe, he thought, the speed of light is always constant. When you saw a light beam zip past, in other words, it wouldn’t matter whether its source was moving toward you, away from you, or off to the side, nor would it matter how fast the source was going. You would always measure that beam’s velocity to be 186,000 miles a second. Among other things, that meant Einstein would never see the stationary, oscillating fields, because he could never catch the light beam.
At first, though, this solution seemed to have its own fatal flaw. Einstein later explained the problem with another thought experiment: Imagine firing a light beam along a railroad embankment just as a train roars by in the same direction at, say, 2,000 miles a second.
Someone standing on the embankment would measure the light beam’s speed to be the standard number, 186,000 miles a second. But someone on the train would see it moving past at only 184,000 miles a second. If the speed of light was not constant the basis of physics since Galileo would be violated – that the laws of physics could not depend on how fast you were moving.
Suddenly, while walking in a park with a good friend Michele Besso on a beautiful morning in May 1905, Einstein saw the solution.
Einstein’s revelation was that observers in relative motion experience time differently: it’s perfectly possible for two events to happen simultaneously from the perspective of one observer, yet happen at different times from the perspective of the other. And both observers would be right.
Einstein later illustrated this point with another thought experiment. Imagine that you once again have an observer standing on a railway embankment as a train goes roaring by. But this time, each end of the train is struck by a bolt of lightning just as the train’s midpoint is passing. Because the lightning strikes are the same distance from the observer, their light reaches his eye at the same instant. So he correctly says that they happened simultaneously.
Meanwhile, another observer on the train is sitting at its exact midpoint. From her perspective, the light from the two strikes also has to travel equal distances, and she will likewise measure the speed of light to be the same in either direction. But because the train is moving, the light coming from the lightning in the rear has to travel farther to catch up, so it reaches her a few instants later than the light coming from the front. Since the light pulses arrived at different times, she can only conclude the strikes were not simultaneous—that the one in front actually happened first.
In short, Einstein realized that time and space are relative and that simultaneity doesn’t exist. This would become the corner stone of the General Theory of Relativity. Once you accept that, all the strange effects we now associate with relativity are a matter of simple algebra. Einstein dashed off his ideas in a fever pitch and sent his paper in for publication just a few weeks later. He gave it a title—“On the Electrodynamics of Moving Bodies” and added a thank you to Michele Bosso “for his invaluable suggestions” guaranteeing his friend a touch of immortality.
He urged you magine you are floating in a box, unable to see what’s happening outside of the box. Suddenly, you drop to the floor. So what happened? Is the box being pulled down by gravity? Or is the box being accelerated by a rope yanking it upward?
The fact that these two effects would produce the same results led Einstein to the conclusion that there is no difference between gravity and acceleration — they are the same thing.
Now consider Einstein’s previous assertion that time and space are not absolute. If motion can affect time and space, and gravity and acceleration are the same thing, that means gravity can actually affect time and space. The ability of gravity to warp spacetime is a huge part of Einstein’s general theory of relativity.
That first paper wasn’t the end of it, though. Einstein kept obsessing on relativity all through the summer of 1905, and in September he sent in a second paper as a kind of afterthought.
It was based on yet another thought experiment. Imagine an object that’s sitting at rest, say in space. And now imagine that it spontaneously emits two identical pulses of light in opposite directions. The object will stay put, but because each pulse carries off a certain amount of energy, the object’s energy content will decrease.
Now, said Einstein, what would this process look like to an observer unaware they them selves were moving? From the observer’s perspective, looking out a window, the object would be moving in a straight line while the two pulses flew off. But even though the two pulses’ speed would still be the same—the speed of light—their energies, when measured would be different: The pulse moving forward along the direction of motion would now have a higher energy than the one moving backward.
With a little more algebra, Einstein showed that for all this to be consistent, the object not only had to lose energy when the light pulses departed, it had to lose a bit of mass, as well. Or, to put it another way, mass and energy are interchangeable.
Think of burning a piece of firewood, reducing the mass of the wood to ash for energy – or the atomic bomb, smashing a mass of uranium and producing an atomic explosion.
Einstein wrote down an equation that relates the two. Using today’s notation, which abbreviates the speed of light using the letter c, he produced easily the most famous equation ever written: E = mc2.
And Einstein wrote about it all in plain text that everyone could understand.
The Nazis would denounce relativity as a “Jewish perversion” – the 1930s equivalent of “fake news.” In America J. Edgar Hoover would have a 1,500 page dossier on Einstein by the time of his death, characterizing him as an “extreme radical.”
What did the man Einstein think besides his “thought experiments?”
“Unthinking respect for authority is the greatest enemy of truth.”
Silence in the face of evil, he once said, “would have made me feel guilty of complicity.”
Militant nationalism is “The measles of mankind.”
He questioned capitalism. “I regard class differences as contrary to justice and, in the last resort, based on force.”
“Let every man be respected as an individual and no man idolized.”
He protested racism. In 1937, when African-American singer Marian Anderson was denied a hotel room in Einstein’s new home town of Princeton, New Jersey, he and Elsa invited Anderson to stay in their home—the beginning of a lifelong friendship. He also befriended the African-American singer Paul Robeson, who had been ostracized for being a communist. And in a 1946 address to the historically black Liberty University in Pennsylvania, Einstein declared segregation to be “a disease of white people.”
There was more to Albert Einstein than just relativity.