The Theory of Relativity is huge: the grandest, most world-altering scientific shift in the twentieth century. But it showed that the universe works in counter-intuitive ways. Ways that are helpfully illustrated with carrot-shaped spaceships.
Start with Newtonian Mechanics: the cut and dry explanation of gravity and forces that had been accepted for hundreds of years. These are the laws of physics that you’ve heard since grade school: gravity attracts, an object in motion stays in motion, an object at rest stays at rest. Newtonian physics are useful because they explain most things we see on a daily basis. The speed at which is Earth spins around the sun, and the speed at which coffee flies from your shattering cup can both be determined by this set of laws.
The Newtonian laws are nice because they show the universe to be a sane place. Things stay where you put them, what goes up comes down, time is a straight line. It’s like a giant clock, and if you understand all the pieces well enough, you can know how they will move and where they will be at what time.
A beautiful picture, but not quite right.
In 1915 Albert Einstein proposed his theory, and to this day it makes claims that rattle the brain. The easiest way to explain it is through light, and the way it moves.
A Missile Flies at You
Imagine a spaceship traveling towards you at a nice, slow 30 miles per hour.
Now imagine that spaceship shooting a missile, at a slightly faster 70 miles per hour.
From the spaceship’s perspective, the missile is traveling towards you at 70 miles per hour. But from your perspective, the missile is coming at you at 100 miles per hour, the speed of the missile’s launch plus the speed of the carrot ship itself.
This isn’t a big revelation. People instinctively understand this, if you want to throw something really hard, you run forward a bit before you throw it. But the intuitiveness of this just makes the Theory of Relativity all the stranger.
Some Light Flies at You
Now imagine that the carrot ship turns on its headlights. This seems to be the same problem as before, only now the ship is throwing light at you, instead of a missile. For the sake of the problem, imagine the space ship is traveling at 90% the speed of light. That’s over 600 million miles per hour, which makes jumping out of the way a little tricky. I’ll use ‘c’ to represent the speed of light.