Stephen Hawking once held a dinner party for time travelers. He announced the date and time of the party after he held it and invited anyone capable of time travel now or in the future to attend. No one did. This suggests that time travel, at least into the past, isn’t possible. (I think it could just be that Hawking is a total bore and all the time travelers were washing their hair that night.) But that still doesn’t stop Hollywood from playing with the idea.

Some light spoilers ahead.

So if you could travel through time, what would the rules be? The two styles of temporal displacement typicaly fall into two schools of thought: either you can alter the past to change the future or events have always transpired the way they have including your time travel. The first style I’ll refer to as BTTF style in honor of Back to the Future, a movie built on the troubles that arise when you change past events such as Marty preventing his parents from falling in love. The second style I’ll refer to as B&T style because Bill & Ted’s Excellent Adventure exemplifies this when they run into their future selves and when they get out of a jam by being sure to come back and help themselves after they get out of it.

Of the movies I watched this week most of them featured the BTTF style of time travel. Project Almanac deals heavily with the unintended effects of changing the past. A bunch of attractive young people go back in time to attend Lollapalooza a few months earlier and manage to set off a chain of events that cause an airplane to crash and kill dozens of people. These kids party hard. Things only get worse as they try to fix their problems showing that the butterfly effect is strong. That same chaotic effect is taken to a logical fascinating extreme in About Time. Domhnall Gleeson possesses the ability to travel backwards to any point in his own lifetime and always occupies his own body at that time. No worries about meeting his younger self for him. He discovers though that the birth of his child is a sticking point. If he goes back and does anything even slightly differently it can result in a different sperm being the lucky winner and consequently a different child. As you can see BTTF style time travel movies are built around the unforeseen circumstances of making even small changes to the past.

In an effort to have a sequel the Hot Tub Time Machine movies actually add a new wrinkle to BTTF style time travel. In Hot Tub Time Machine 2 a character is nearly murdered when someone from the future shoots him in the junk. As he’s bleeding out the characters desperately jump in the hot tub in an attempt to go back and save him but accidentally go into the future instead. Oddly, the once bleeding man is alive and well in this future. This implies that, if we assume there is a way that events played out naturally, the future you travel to will vary depending on if your origin point is before or after a divergent change. Take the potential death of this character, Lou. In timeline A, the way things play out naturally, he lives. When the murderer from the future comes back and kills Lou he creates a new future, timeline B. When our protagonists travel to the future whether they travel forward on timeline A or timeline B depends on if they leave before or after the altering event of the murder. This intriguing stipulation begs the question, what if they travel forward beyond the point that the killer traveled back? Would their destination timeline still be dependent on when they left? Or would they automatically end up in timeline B since they have gone past their opportunity to stop the killer? That would imply that the time from the murder to the killer’s departure from the future form a sort of bubble, a limited window during which two timelines are still possible. Before the bubble there is a single timeline and after the bubble there is a single timeline even if you change what that single timeline is. Only from within the hiccup caused by the traveling can you access the two different possibilities at will.

Anyone’s head hurting yet?

Dealing with B&T style time travel can be more restrictive. Since this form of time travel is built on the notion that everything has always happened the way it happened there is none of the chaos and second chances one finds in BTTF style movies. These movies instead try to misdirect and confuse you until the ending when it’s revealed how all the pieces actually come together. Some movies don’t tell you immediately that time is immutable and the tension comes from the characters struggling to change things despite always barreling toward inevitability. Time Lapse does this quite well even if it doesn’t involve time travel per say. A trio of roommates discover a giant stationary camera that dispenses Polaroids of what will be in front of it 24 hours in the future. Armed with a tiny glimpse of what will be the characters send messages back to themselves while wondering if they can choose to deviate from what the picture predicts. What would happen if they did? Would they cease to exist since they chose not to take part in the one true future? Would the photo magically change to reflect the new reality?

This also brings up a corollary to the B&T laws of time travel that applies to any situation that involves knowledge of future events; I call it the Prophecy Problem. Simply put, would things have still played out according to the prophecy if you hadn’t been told the prophecy? The characters in Time Lapse quickly fall into the routine of thinking they HAVE to do the things the pictures show. Their knowledge of the future is affecting their decisions and influencing the future itself. Very likely they would not do these things if they were not shown they were going to do them. The camera, or whatever the prophecy teller is in any movie, is effectively deciding the future. Does this concept of self fulfilling prophecies and unchangeable fates mean we as people have no free will? Or do we have the ability to choose and time exists as a flat circle that already has taken all the choices that have been and ever will be made into account?

So as far as movies go those are you two main time travel narratives. With BTTF style you focus on the effects created by the events you change. With B&T style you focus on what could have caused the strange events that always have been. Which one is better? Well I’m a sucker for both, but a really clever B&T style story with a solid payoff when it comes together is probably my favorite. Whether it ends tragically as the victims rail against inevitability or triumphantly as a hero realizes the true meaning of earlier events I love it when it all falls into place.

The more important question, which form of time travel is the way it really works? Well that’s simple.

Neither. Time travel isn’t real.

Nerds.

Other movies I watched this week (potential minor spoilers):

Project Almanac – A group of improbably attractive teens discover a time machine in this movie that is pointlessly filmed as a “found footage” movie. Despite being totally by the numbers there is some fun to be had watching the kids use time travel the way kids would, including one particularly funny moment with the lottery. I also enjoyed seeing a person use time travel for purely selfish reasons portrayed less as a villain and more as simply a misguided young man who tries to fix his mistakes. Decent popcorn flick for fans of the genre.

Hot Tub Time Machine – Four friends travel back in time, via a hot tub, to one fateful night in 1986. With 80’s nostalgia abound they try to decide if they should do everything exactly as they did or make a few tweaks to better their sad sack lives. Very funny actors Craig Robinson and Rob Corrdry bring comedy that is a little blue and at times laugh out loud funny. This was one of those movies that surprises me by being better than the fairly average expectations I had going in.

Hot Tub Time Machine 2 – Instead of the past our heroes (minus John Cusack) must travel to…THE FUTURE! The laughs are fewer in this sequel that feels a little forced but there’s still enough here to make it worth watching if you enjoyed the first one’s humor.

About Time – Domhnall Gleeson is like a cute ginger puppy navigating life and love as he grows up. Oh, he also has the ability to travel back to any point in his life by standing in cupboards. With very little lasting conflict, this twee drama drags a bit as it moves from one vignette to another. Despite that Bill Nighy being delightfully British and a powerfully emotional message about making the most of the time you have makes this worth checking out if you want your heartstrings pulled.

Timecrimes (or Los Cronocrimenes) – This Spanish film follows a middle aged man as he witnesses a woman get attacked by a masked killer and gets chased…into a time machine. Going back in time an hour he tries set things right. A picture perfect example of B&T style time travel, there is fun to be had watching the truth behind events reveal itself. A solid film, especially if you don’t mind your time travel with just a dash of suspense.

Time Lapse – Armed with a camera that tells them what will happen in their living room at exactly 8pm every night, three roommates try to profit from their knowledge until the pictures start to show disturbing images. This low budget flick focuses on asking questions about free will and desperate people resorting to desperate measures. The quandaries this movie poses are more interesting than the movie itself, but it’s still better than average for a random Netflix movie I never heard of. Shout out to Danielle Panabaker, The Flash‘s Caitlin Snow, who should already be used to time travel.

Time Bandits – A young boy is whisked away by a band of very short thieves in this 1981 Terry Gilliam film. Using a map of time holes stolen from God himself, the bandits hop from the Napoleonic wars to ancient Rome and everywhere in between stealing treasure and valuables until they run afoul of Evil himself. The comedy is simple as the group bumbles from one situation to the next arbitrarily. What the movie lacks in structure it makes up for in wildly imaginative visuals, especially for Evil and his minions. I could easily see a child of the time being swept away by it all. For me now though it all felt frustratingly aimless.

Beyond the Time Barrier – This black and white 1960 film states that in the future everyone will wear unflattering jumpsuits. And cosmic rays will mutate everyone into deaf mutes. Except for the people who need to talk, they’ll be fine. And some mutants will have telepathy for reasons. And…yeah. There is little rhyme or reason to be found here. The 60 second trailer with the old timey voice over that was at the end of my copy was more entertaining than watching the movie itself.

Safety Not Guaranteed – How quirky and indie do you like your romcoms? If you said “totes” then you’ll enjoy this quirky indie romcom inspired by a true story. A journalist and two interns seek out a man who puts out a want ad for someone to travel with him back in time. Featuring no actual time travel this story explores the kind of person who would want to travel to the past. Regrets? Missed opportunities? Lost loved ones? A fun movie with more than a little heart and a very adult B plot, I enjoyed this one’s mix of silliness and emotion.

Back in Time – This documentary focuses on the creation of and fandom surrounding the perfect movie Back to the Future. There are a couple of interesting tidbits about the original film but the real joy here is seeing the fans and what they have done in the name of Marty McFly and Doc Brown. The best documentaries can carry you along no matter what the subject matter. This one will only speak to fans of Back to the Future. Luckily that includes me, so I thought it was all right.

Click here for a full list of all the movies I’ve seen so far.