The Physics of Lightsabers | StarTalk

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Star Talk, we're back featuring my interview with the British physicist Brian Cox. So I had to bring up the fact that he and I had, like, a Twitter argument over the physics of lightsabers. Aha, yeah! And I just had to bring it up and just open up old wounds.

Let's find out how it went down. I don't remember how this happened. I think I tweeted something about lightsabers, then you jumped in, and then people just wanted a fight. What was it? Geek fight? I think I said if lightsabers are made of light, then they could surely do damage by cutting things, but they would not stop one another the way two swords would in a swashbuckling encounter. That's all I said.

There's a process that I've studied, actually. Photon-photon or gamma-gamma scattering, we call it. Okay, so it's a measured process at particle accelerators. So, very high energies, very energy collisions, there's a probability that photons will kick off each other, bounce off each other, rather than just pass through. So it's remarkable—a remarkable property of particle physics that they don't interact.

So I can look at you and all these other ones that are flying across there, and they don't mess up this view of you. But actually radio waves and microwaves too, same Wi-Fi all over the place, nothing colliding. But actually, when you go up high to high energies, then the probability that photons will collide with each other increases.

One of the interesting things in cosmic ray physics that you might know about is that there's a cut-off. Yes, where—where—where the cosmic rays can be such high energy that the probability they'll bounce off the photons in the cosmic microwave background becomes high.

So my point was just a technical one, that photons do have a probability they'll collide together. If you had this high-energy, ultra-high-energy lightsaber, it would have to be a really, really high-energy lightsaber. And so now, now this would come into the regime that you're describing, and they would come in contact, and you would feel this. Yeah, they interact with each other just like these things do.

Okay, okay! What I loved about that, though, as you said, was I love the fact that there's an audience for that, that kind of interaction that we had, and it's really geeky. It's just talking about lightsabers and the physics of the lightsaber. I appreciated how much people would geek out over that.