Here’s your primer on the rules of time travel in NBC’s ‘Timeless’

If you”re a time travel geek or a history buff, chances are you”ve been looking forward to NBC”s new contribution to turn-back-the-clock television, Timeless, premiering tonight.

Time travel is ultimately just a device for co-creators Eric Kripke (Supernatural) and Shawn Ryan (The Shield) to put iconic moments in history on screen and take their characters on a journey where they”re soon faced with questions of fate and identity. But it”s still a device that required some carefully crafted rules.

“It definitely makes me want to put a gun in my mouth, the rules of time travel,” Kripke told me at San Diego Comic-Con. “As we were beginning this show, all my friends who were writers on time travel shows were like, ‘How's it going?” and it seemed like they knew something I didn”t. I was like ‘What do you mean? It”s going to be fine.” By week 2 in the writers room, I was like, ‘Oh dear God.” The rules of where things change – it”s very, very hard to keep straight. But so far I think we”re keeping it reasonably under control.”

Kripke added that they “want Timeless to be a throwback to the Quantum Leap style of time travel.” Simple is the word both he and Ryan used for what they”re aiming for. “Mindf–ky” – as Kripke points out is the way many time travel shows and movies have gotten lately – is not the kind of entertainment they”re creating.

“We don't want the show – this is not meant to denigrate something – we don”t want to go deep into a rabbit hole like 12 Monkeys in terms of the time travel stuff,” Ryan said at a press event on the Sony lot last week.

Rufus (Malcolm Barrett), Wyatt (Matt Lanter), and Lucy (Abigail Spencer) step out of the time machine and into 1937 in the premiere of Timeless. Photo credit: Joe Lederer/NBC

As simple as they try to make it though, this is still a time travel show, so there are still rules to figure out that”ll give the writers headaches and will probably soon have the viewers debating for days on end.

So, whether you want a primer on the rules of Timeless so you”re not hitting the rewind button to make sure you”ve got them figured out while you”re watching the premiere tonight or if you”re checking out this post later and want a review, here is (a relatively spoiler-free) breakdown of what we learn about how time travel works from the first two episodes of Timeless.

The past can be changed: Of course. This is central to the premise of the show, which has our three heroes chasing after a criminal who”s trying to change key events in history, apparently intent on destroying America by destroying its past. So this is not a Prisoner of Azkaban– or Terminator-esque causal loop.

You can”t return to a time and place where (when) you”ve already been: As Rufus says in the premiere, “You can”t go back to any time where you already exist, where you might meet a double of yourself. It is bad for the fabric of reality.” He ominously and vaguely explains to Wyatt and Lucy that they “tried it once. The pilot came back – but not all of him.” This allows the writers to keep the stakes high – there are no do-overs for our heroes – and it saves the show from ever having the technical headache of putting two Abigail Spencers or three Malcolm Barretts onscreen at once. 

“What I don”t want is there”s 19 clones of the lead, and they have eight doubles because they keep returning back to do it again,” Kripke told me at Comic-Con. “We want to show that we did the Hindenburg and now it”s time to move on. What we really want is a fun, forward momentum.”

When the past is changed, only those who traveled through time remember the previous reality: After visiting 1937 and 1865, Lucy, Rufus, and Wyatt return to the present to find that the history of the Hindenburg disaster and of Lincoln”s assassination that they knew is not the history known to the team back at Mason Industries. The only reality Connor Mason and Agent Christopher have ever known is the one that”s a new reality for our trio of time travelers.

Take something in the time machine with you, and that stays unchanged: Just as the memories of people inside the time machine remain unchanged, so do physical objects that take the leap through time with them. This is not like Back to the Future, where photos and newspaper headlines can fade and morph. Episode 2 reveals one memento of Lucy”s that”s now a relic of another timeline.

And that”s about all we learn about the rules of time travel in this world from the first two episodes. Know, though, that somewhere in the Timeless production offices is a bible with more rules and a timeline on the walls of the writers room that the show”s assistants are keeping updated.

“It's way more important to know the rules than it is to say the rules,” Kripke noted at last week”s event. “We spent an incredible amount of time – a stupid amount of time in the writers room talking about all sorts of complicated rules, but we would be canceled if we tried to convey all these rules to the audience because they're mind-numbingly dull.”

(Some time travel enthusiasts may beg to differ with you there, though.)

Encouragingly, Kripke and Ryan promised to be consistent with these rules. Thank you for not pulling a Cursed Child here, guys.

Timeless premieres tonight on NBC at 10 p.m. ET/PT.