The tools and rules of time travel

Traveling through time can be a risky business — if you don’t follow the rules you could end up stuck in the future, rooted in the past or trapped between times. However, with a little bit of guidance and pretty much any kind of contraption, you could be well on your way. Here is a time traveling manual to help you through the stickiest situations.

Question #1: Can I change the past?

There are two answers to this question. One comes from the natural laws of physics and the other from the classic laws of time travel films.

The answer that science gives is that history is a fixed and unchangeable timeline. Based on the Novikov self-consistency principle, if you were to go back or forward in time, you can’t change anything because history is self-consistent.

The answer given more frequently in film, however, is that history is subject to change. This plot device is comically present in “Back to the Future,” where Marty McFly is accidentally thrown into 1955 and he must ensure his parents meet or he’ll never be born.

Another common idea is that history is subject to minor changes but major events are permanent, as presented in the 2002 remake of “The Time Machine.” Hartdegen cannot bring his lover Emma back to life because if she had not died, the time machine would not have been invented.

Question #2: What should I use?

The means of time traveling vary. In “The Time Machine,” Hartdegen builds a fantastic-looking machine with shiny metal and swirling lights. In “Meet the Robinsons,” Lewis and Wilbur travel in a spaceship.

Besides the classic machine idea, other interpretations include the police box from “Doctor Who” and the phone booth in “Bill & Ted’s Excellent Adventure.” In “Back to the Future,” Doc builds a time machine out of a DeLorean sports car, and Hermione Granger in “Harry Potter and the Prisoner of Azkaban” uses a simple watch to turn back the clock.

Question #3: Who else can I bring?

Every iconic time traveler needs someone else. Whether it’s Doc in “Back to the Future,” Rufus in “Bill & Ted’s Excellent Adventure” or Frank in “Donnie Darko,” there is always someone to guide the hero in his or her time travels. This person is usually knowledgeable about time travel, or in Frank the rabbit’s case, knows the hero inside and out.