So, here’s the deal: my cousin Bert, who lives on the planet Schnipplefarq, and I have devised an experiment. We have carefully synchronized our watches to Cosmic Mean Time. I will leave Earth at a prearranged time in my spaceship, which travels at exactly one half the speed of light, making a bee-line for Bert’s house, where he will wait with his notebook to write down the results. In my spaceship, I will have two items: a red laser pointer, and a high tech bean shooter capable of shooting a bean, also at exactly one half the speed of light. At a pre-determined time, I will simultaneously point the laser at Bert’s house and press the button, and launch a bean, also at his house.
Since the speed of light is constant, according to Mr. Einstein, and the speed of the bean is relative to the speed of my spaceship, they should arrive at the same time. Bert will have long since given up, of course, forgetting that our carefully synchronized watches will be way off, since time for me and my watch will pass more slowly than for him and his.
What should happen is that my red pointer light will arrive on time, but magically blue. Bert, by that time, having decided that I’m hopelessly forgetful, will have put away his notebook and gone back into the house for a quick shot and a nap. So he won’t notice when the bean also arrives at the same time, having increased to infinite mass due to travelling at the speed of light. Which is just as well, since Bert, his shot glass, his comfy chair, and his planet will be annihilated by the collision.
Now, you might think what I find bothersome about all this is that time slows down for me, or that a bean could acquire infinite mass just by going real, real fast, but no. Oh, it’s true that while I’m zipping along relative to Bert, he’s also zipping along relative to me, and why wouldn’t our time distortions cancel out, or that infinite mass would by definition have to include everything else out there, but that’s not it. It’s the concept of speed.
See, we happen to live on a planet that is way, way larger than we are, which gives us the illusion that it’s stationary, so when we think of speed, it’s relative to the great blob of stuff under our feet. If we go six mph, we mean six miles of earth has passed beneath us during an hour. But the earth itself is not standing still. It’s rotating at about 1,036 mph, and orbiting the sun at about 67,000 mph. As if that’s not enough, the sun is moving through the galaxy at about 447,400 mph, and the galaxy is moving … well, you get the point. You are really moving many, many thousands of miles per hour. Plus six.
All of this speed, of course is relative to something else, us to the earth, the earth to the sun, and so on. This means that it could be said that when we are moving six mph, the earth is moving that same speed relative to us. Put another way, two cars, each going 30 mph relative to the earth, might be going anywhere from 0-60 relative to each other.
So what is the speed of light relative to? According to Mr. E, nothing! Or rather, itself.
Okay, let’s see. If I wanted to measure the speed of light, I could count the number of some units of it that pass by during some time interval, like counting power poles from a train to figure out how fast it’s going. That might be waves, but that’s dependent on frequency, and you get tautological pretty quick doing that. Or it could be particles, but counting photons is worse than trying to figure the number of water molecules passing in a stream. You’re left with bursts of light. So you do that and get a good number. Then Cousin Bert (still alive for the nonce) does the same thing, with the same bursts, while zooming past you at cosmic speeds. And gets the same number.
What? I don’t even know what speed means in that context.
Don’t even ask what would happen if I got the velocity upgrade for the pea shooter.