Here are 3 things you may have heard are faster than the speed of light, but you’d be surprised which ones actually are. I’m Greg, and what the physics is faster than light? What if, when you looked up at the night sky, instead of seeing this, you saw this. You actually would if all you were seeing were distant galaxies. Distant galaxies appear redder than you expect. The doppler effect says that things moving away from us are red-shifted. And the huge redshift that we see with galaxies seems to imply they’re moving away faster than the speed of light. But don’t be fooled, this red-shift isn’t from doppler, it’s from the expanding universe.
When light travels though space from galaxies to us, the space expands, literally stretching the light, making it redder. So nothing is moving faster than light, but the universe is getting redder. Was that faster than light? No, but I can do it faster. I took the blade off this paper trimmer. And if I touch one side of the blade to the paper, and hold the other side on spider silk width above the paper, then cutting at this angle will cause the cut to move the cut to move across the paper a million times faster than I move the blade down. So if I have the blade moving down as fast as, say, a speeding bullet, then the cut will move across the paper a few times faster than the speed of light. Ok, this is probably the weirdest one.
Quantum mechanically entangled particles. Or entangled coins. If I take these two quarters, flip them, and look at one of them, it’s tails, what’s the other one? It could be heads, it could be tails. But if the two quarters are shot out of this quantum entanglement machine, then the state of one coin depends on the other. If one flies to the other side of the universe, and one flies to me, and I look at it. It’s tails. That means the other one is head. It’s always the opposite. If it’s heads, then the other one must be tails.
But it gets even weirder. As the entangled quarters fly away from each other, their faces aren’t heads or tails, they’re actually quantum mixtures of both heads and tails, like Schrodinger’s cat who’s both dead and alive. When I find that mine’s tails, that means that if, right then, someone looked at the other one, it must come up heads. How could the two coordinate across the universe? One possible explanation is that there’s a faster than light influence between them. And there are a bunch of really cool experiments, including one by my colleague Marissa Giustina, showing that entanglement is real. Instead of a pretend box and coins, her experiment uses a crystal that emits entangled photons.
Wait, Einstein said that no matter or information could move faster than the speed of light. Did we just disprove him? Well, with galaxies nothing’s moving faster than the speed of light, so we’re good there. And with the paper cut, the only matter that’s moving are the atoms in the blade, and they’re moving down slower than the speed of light. No matter is actually moving along that fast cut, so we’re good there. But with entanglement, something may be faster than light, but it’s random. We didn’t choose what happened to the coin on the other side of the universe, so we didn’t send any information. So Einstein is right again. Ok, since you made it to the end, here’s a bonus one. Take a laser pen, shine it at the moon, and if you go like this fast enough, the laser dot will move across the face of the moon faster than the speed of light.
How’s that possible? Let me know in the comments. And if you have questions, throw them down there too..