WARNING TO ALL SCI-FI/FANTASY NERDS: Physics is totally about to totally ruin some of your favorite stories. If you don’t want to end up throwing out your forty disc Back to the Future Blu-Ray boxed set in a fit of rage, you might want to skip this particular blog post.

Time travel is one of the most popular tropes in science fiction books and movies. There is no official stance by the scientific community on whether time travel is at all possible, because the concepts are controversial and highly theoretical. Plus, there’s a ton of math involved, so we’re definitely not getting into that.

Check out this clip from Harry Potter and the Prisoner of Azkaban:

Hermione uses her Time Turner to send her and Harry back about three hours into the past. We get to see that time pass in reverse, as the dark sky outside the windows brightens and people’s forms shuffle about in fast-motion rewind. What’s important to notice is that Harry and Hermione stay put as everything else moves around them. They end up in the same spot they were standing in when they started the Time Turner.

Imagine you visited Orlando six months ago and had some of the best pizza you’ve ever tasted at Lazy Moon on Alafaya Trail. You go back there today and find, to your horror, that the restaurant has closed. Never one to fret, you pull out your trusty pocket time machine and set the dial for six months ago. Then, you freeze to death and die in the vacuum of space.

You didn’t see that coming, did you? You should’ve. Here’s why:

What time of year was it six months ago? It’s winter now, so it must have been summer when you were enjoying your pizza. Well, why do we even have seasons? If you remember from grade school, the weather changes because Earth revolves around the sun. One complete revolution takes a year — by definition! — so six months ago, Earth was on the opposite side of the sun as it is right now. What was right here six months ago? Lifeless void, and (probably) very little delicious pizza.

“But wait!” I hear you shrieking. “Harry and Hermione only went back about three hours. Certainly, Earth couldn’t have moved that far.”

Actually, as it turns out, Earth moves about thirty kilometers every second… in relation to the sun, that is (we’ll come back to that in a minute). So, in the 10,800 seconds (3 hours times 60 minutes per hour times 60 seconds per minute), Earth would’ve backed up about 324,000 kilometers along its path through space. That’s over 200,000 miles. And what’s 200,000 miles away in any straight line from the surface of Earth? Vacuum.

Boom. Dead.

“I’ll show you!” you now scream. “I’m not as dumb as a couple of schoolkids from a magical place where they don’t even teach math! I’ll just wait six more months, then go back in time a year! Then, Earth will be right back where it was the last time I ate my tasty slice of goat cheese and pineapple pizza pie. Hah!”

Ew. Dude. Goat cheese and pineapple? Really?

Anyway, that’s not a bad idea. Shows you’re thinking. After all, we’re not cavemen; we have a really good idea where Earth is at any one time… in relation to the sun. That’s the second time I’ve mentioned that. Why does it matter? Prepare to have your mind blown.

The sun? Yeah, it totally moves, too. It revolves around the center of our galaxy, at a speed of about 217 kilometers per second, or about seven times faster than Earth revolves around it. And before you get too froggy, yes, the galaxy is moving through space, too.

The problem here is that there is no absolute “center” of space. To assume that you can stand in place while you rewind or fast-forward through time violates the Copernican principle, which says that the universe doesn’t revolve around Earth — let alone the former home of your favorite pizzeria. So, while it might or might not be physically possible to reverse time’s heady flow, all your munchie runs through time are going to end the same way:

Frozen space death.