So, you want to go back in time. Luckily, science fiction is here to help. Everything is on offer from “logical but impractical” to “it just works”. Let’s take a look at a few options:

Unspecified Magic

Poof! You’re in the past! Ever reliable, especially if when in the past you traveled to is more important than how. Very effective at leaving you stuck in the past, where you can try to use your modern knowledge and tools to rebuild an industrial society or reshape history. Generally overlaps with the concept of a “Time Slip”.

An early example (of the industrial revolution speed run sub-genre) is A Connecticut Yankee in King Arthur’s Court by Mark Twain from 1889. Modern novels with the same theme include Island in the Sea of Time and 1632, both of which involve a larger community being caught in the time slip. If industrializing isn’t your thing, you can go for military history a la the 1980 film The Final Countdown, or even romance like The Time Traveler’s Wife.

Realism: It totally works, just trust me bro.

Convenience: Entirely uncontrollable. Good luck!

Time Machine

Some mechanism that brings you through time the way a plane brings you through the air. Usually far more controlled than a time slip, and usually can bring you back to your own time as well – assuming you don’t ruin the timeline before that can happen.

First popularized in The Time Machine by H.G. Wells from 1895, which was primarily a trip to the future but technically counts since the main character returns back to the present. Extremely common in science fiction since then, with big names like Doctor Who and Back to the Future.

Realism: Varies. Could be a fully unexplained machine or could have some vaguely realistic backing.

Convenience: High, though they seem to be very fragile and easily misplaced.

Flying really fast

Listen, that guy Einstein was smart, right? And he told us that time slows down as you get faster. So obviously once you go super crazy fast it’s gotta go backwards, ‘cause that’s what’s slower than slow. No, I didn’t check the math, why do you ask?

Best fictional example might be the “light-speed breakaway factor” from Star Trek. Often the cutoff speed is the speed of light. Faster than light travel mathematically does allow you to send information back in time (though it doesn’t precisely send you back in time directly), but unfortunately requires infinite energy.

Realism: Kinda? See the infinite energy thing.

Convenience: Easy enough, if you can go fast enough.

Reversing the flow of time

Just like how you usually go forward at 1 second per second, now you go backward 1 second per second – probably through some kind of less convenient time machine or magic thing. Usually shows up in serious think-y works like Tenet or Primer. Makes time travel enough of a production that it keeps the plot interesting.

Oddly enough, you can mathematically treat antimatter as regular matter flowing through time backwards. Implications for the safety of time-reversed people is left as an exercise to the reader.

Realism: Moderate, at least physics-wise.

Convenience: Fine for short journeys, annoying for long ones.

Time Portal

You go in one end and come out the other end and it’s the past now. Unlike a time machine, this could be naturally occurring, or have fixed entrance and exit points. If you want to be maximally sci-fi, have it be a “wormhole” connecting two points in spacetime – which gets you effective faster than light travel to boot.

Some examples include the Star Trek episode “The City on the Edge of Forever”, or the Chrono video game series.

Realism: Wormholes are kind of plausible, at least.

Convenience: Really nice if there’s an exit point where you want it.

Closed timelike curves

For hardcore science fans. Mathematical ways that gravity can let you get back to where you started, before you left. Works inside a rotating black hole (which you unfortunately then can’t leave), or next to an infinitely long cylinder, or in various universes made of spinning dust. Way easier with negative energy, which is unfortunately not known to exist.

A bit too detailed for most fiction, though they do show up in Stephen Baxter’s Xeelee series.

Realism: As real as we can make ‘em, boss.

Convenience: Bring a starship and possibly cosmic-scale engineering.

Safe travels!

Coming Soon: Not Going Back