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I’ve done a lot of impossible things in my life. I made first contact with an alien life-form, I survived a twelve-light-year interstellar journey while in an incredibly medically risky coma, and then I made first contact with an alien life-form. Again. But none of those things prepared me for the challenge at hand: explaining special relativity.
“Okay,” I tell Rocky, “I want you to picture a photon.”
Right away, we hit our first bump in the road. “What word mean, question?”
What, photon? We talked about that one already. It was actually surprisingly easy to get Rocky to buy into the concept of quantized light. I guess if you’re only familiar with light as an abstract scientific concept, it’s not that big of a leap. (I have a feeling he won’t be so forgiving about particle-wave duality, but baby steps.) What else could he mean?
Oh… right. I just asked an alien without any eyes to picture something. Good teaching requires knowing your audience and meeting them where they’re at—something I just forgot all about. “A picture is like… never mind. Just think of a single photon.”
“Yes. I think. Is very bright.” He doesn’t use the word “bright,” technically speaking. Eridians don’t have a term to describe the subjective intensity of light, because, well, they don’t need one. Instead, he calls it “light-loud,” a substitute that is as practical as it is charming.
I nod in approval. “Now think about that photon bouncing between two mirrors.”
“Not know last word.”
Again? I’m really nailing this so far. “Not important. Think about it bouncing between two… xenonite panels.”
That seems to do the trick. “Yes,” he says. “Bounce bounce bounce.”
“Couldn’t have put it better myself. So, how long would it take for the light to bounce between the panels?”
“Easy. Divide distance by speed, get time. You said this would be confuse.”
“Just wait, buddy. But yes—the time between bounces is equal to the distance between the panels divided by the speed of light. What if the photon and the panels were both moving along at a constant speed and you were watching them pass by? How long would each bounce take from your perspective?”
“Divide distance by speed,” Rocky repeats a little impatiently. He must think that the question is dumb, or that I am. I can’t say I blame him either way.
“Right again,” I say. “If the whole setup is moving relative to you, it looks like the photon has to travel farther each time in order to keep up with the panels, right? But from the photon’s perspective, it’s only traveling that original distance. That gives us two equations for time. You see the problem here?”
“If you not move, light seem to move faster. Time is same. No problem.”
Here’s where things get hairy. “Actually, no. The speed of light is constant regardless of your frame of reference.”
But Rocky doesn’t like that answer. “No. Not possible.” He’s entered the first stage of learning about special relativity: denial.
I get it. I really do. Heck, even Einstein was deeply unsettled by certain aspects of quantum mechanics. No one likes being told that the world, at the most fundamental level, doesn’t make a lick of sense. “I know it sounds hard to believe, but it’s true.”
“Not true. Would notice.” Hey, a small dose of skepticism is healthy. When I’m in the classroom, I want my kids to actually think through what I’m trying to teach them, not just blindly accept my word as gospel. Not that Rocky is anything like one of my kids. Well, maybe just a little.
“The time difference only becomes noticeable for objects moving at speeds close to the speed of light. Like the speeds our ships had to move to get here.”
“How you know, question?” Rocky demands. “You can see time move different, question?”
“Well… no,” I say. “But scientists on Earth have run experiments that prove that time dilation is real.”
“Tests are wrong. Humans not use good equipment. Not even have xenonite.”
I resist the urge to get defensive about humanity’s many (many!) scientific achievements. “We have good enough equipment to know we’re right about this.”
“If time is different, how you know which time is real time, question?”
“That’s the thing: There isn’t one objective time. It’s all relative.”
Rocky stamps a hand on the floor. “Time is time! Same everywhere!”
“I’m telling you, this is the accepted theory. When you were moving towards Tau Ceti but Tau Ceti was getting further away? Special relativity explains that.”
“That not time. Is distance.”
I scratch my head. “Yeah, about that…” He is really not going to like the idea of spacetime.
Before I can frustrate him further, he cuts me off. “Not want hear,” he says, and starts scurrying away.
“Wait, where are you going?” I call after him.
“Work on projects. Projects are real. Like time.”
As he storms off, I get this awful feeling of déjà vu. A guy has a bright idea about how the world should work, and gets mad when the world doesn’t agree. Stop me if you’ve heard this one.
But again, I really can’t blame him. Relativity is some real horseradish. If I’m going to get Rocky on board with such a strange idea, I’ll have to… take my time.
Yeah, okay, I’ll see myself out.