Time travel stories are some of the coolest tales in the universe. But sometimes, when you're lost in the time-space continuum, things can get pretty crazy. Time-lag, paradox overload, etc. So you gotta have rules to make sense of the vortex. Here are the 10 silliest rules for time travel that people have come up with.

Top image: Looper.

Before anybody else jumps in and says it, some physicists believe that it's impossible to change the past, and paradoxes are impossible. Maybe this is true — but at the moment, time travel is as fictional as teleportation and warp drives. Especially the kind of time travel where you can hop in a DeLorean or a phone booth, and come out in ancient Greece.

Anyway, I've always liked the version of time travel where you can change the past, but you'll create a new timeline.


1) If you change the past, you'll end up with flying baboons.

That's more or less the premise of the movie version of A Sound of Thunder, which takes massive liberties with Ray Bradbury's story. It's because stepping on a butterfly in the Jurassic era changes the past so much that humans "devolve" and turn into flying monkey people in the present. Shut up, it could happen. (Thanks, Faintdreams!)

2) If you touch your past self, you'll both melt into goop

Lots and lots of time-travel stories have a prohibition on touching your past or future self — in Doctor Who, it causes the Brigadier to have a mental breakdown. In Back to the Future, it makes Jennifer pass out. And so on. But the absolute best is Timecop, where you can't touch your past self, because the "same matter can't occupy the same space." Uh, whut? Or else you'll melt into goo, as Ron Silver learns to his everlasting rue. (Thanks, Eric!)

3) You can only travel in groups of three at a time

Why three? Because that's the size of the group they want you to use in the game Chrono Trigger. If you have more than three people traveling through time, it spits you out at the point of least resistance — which happens to be the end of time. This happens when you first meet the futuristic robot named Robo. (Thanks, Jordan!)

4) You can only use any particular time-travel method once.

This was the rule in DC Comics at one point, as expounded by Rip Hunter in the Time Masters comic. As this (now defunct) page explains, "time travel is so rough on the human system that people cannot survive the same method of time travel twice." But you can use a different method of time travel, and you'll be just fine. Needless to say, this rule was retconned out of existence long ago. (Thanks, Brian!)

5) You can be hypnotized into time travel — but snapped out with a penny

In the movie Somewhere in Time, Christopher Reeve uses self-hypnosis to send himself back in time to 1912, where he falls for the lovely Jane Seymour. It's all lovely until he finds a 1979 penny in one of his suit pockets — and this snaps him back to the future. So the lesson is, if you're going to use a trance to send yourself back 67 years, make sure you empty your pockets first. (Thanks, Tony!)

6) You can only jump back within your own lifetime

This was the somewhat arbitrary rule in Quantum Leap — where Scott Bakula is tossed into body after body, but only within the preceding few decades. (Probably for budgetary reasons, after all.) There was a fancy explanation involving quantum mechanics, as to why you couldn't travel to a point where you hadn't been born yet. But the whole setup was sort of magic in any case, so whatever. (Thanks, Joe!)

7) There are "fixed points" where you can't go, or change things

Why can't the Doctor save Adric, his companion, from crashing into prehistoric Earth? Why can't he go fetch Amy and Rory from the Great Depression? Why can he use time travel to get out of some scrapes, and not others? It's because there are "fixed points" in time. This logic reached its wackiest point when we were told that Lake Silencio in Utah was a "still point" in time, which could easily become a "fixed point" — because of the large body of water, maybe? You can see why it might be off-limits to prevent the Kennedy assassination, an event that causes lots of fall-out... but after a while the "fixed point" thing starts to seem just arbitrary.

8) If you travel back in time, your mind will revert to its past state

There are many strange rules of time travel in Star Trek, and it's hard to pick just one — but let's go with this notion that if you travel back in time your mind will regress somehow. (But only sometimes.) In one episode, the Enterprise goes back in time a few days and returns Christopher to his cockpit a moment after he left — and Christopher somehow doesn't remember anything that happened to him aboard the Enterprise. In another episode, Spock goes back to the past and suddenly starts reverting to the savagery of the primitive Vulcans.

9) If someone cuts off your past self's fingers, you'll suddenly be an amputee

Actually, Back to the Future does a pretty good job of sticking to the idea that when Marty changes his parents' past, he starts to fade out — so changes to the timeline affect you in real time. (Except that when Old Biff changes his own past, he remains unaffected in BTTF2.) But in Looper, this doesn't quite work as well — they can cut off Paul Dano's feet, and his future self is still in the trainyard, where he's walked to. If he hasn't had feet for the past few decades, how did he get that far? We asked Rian Johnson about this, and he said, "No time travel movie makes sense, if you look at it hard." (But we still love Looper.)

10) You can only time travel naked

Any excuse to see naked Arnold Schwarzenegger being a tough guy and taking clothes from punks and bikers, basically. But as we pointed out recently, why can your hair make the trip if your clothes can't? Seriously. Also, it's a little unclear how the T-1000's "liquid metal" counts as organic for the purposes of time travel. Basically, Skynet is a perv.

Thanks to Brian Huberd, Chris Granade, Madeline Ashby, Gili Bar-Hillel, Susana Polo, Jordan Lawson, Mark Strauss, Andrew Liptak, Eric France, Joe Duffy, Tony D. Clark, Cesium Comics, Lun Esex, Seanan McGuire, Faintdreams, John St. Lawrence, Chris Braak, Eric Zuckerman, Phoebe Kitandis, and everybody else who helped me with this one.