Ars Live: Time Travel In Movies—The Science Behind The Fiction

Future travel is trivial, past travel is likely impossible

Carroll explains that traveling to the future is scientifically straightforward (we do it constantly, and relativity allows acceleration via high speeds or black holes), while traveling to the past, though theoretically conceivable via general relativity, lacks any practical mechanism and may be fundamentally impossible.

The Novikov self-consistency principle

If travel to the past were possible, physics suggests you cannot change history (e.g., preventing JFK's assassination is impossible because we know it happened), and you cannot travel to a time before the time machine was originally constructed.

Parallel universes change the rules

The only loophole allowing past alteration involves branching into alternate timelines or parallel universes, which physics permits in principle but renders the original timeline unchanged, effectively making the traveler a visitor to a different reality.

Internal consistency trumps scientific accuracy

Ed Solomon emphasizes that films operate under their own 'internal physics,' where adherence to self-established rules matters more than real-world accuracy; Jim Kakalios adds that egregious errors break immersion, but perfect physics isn't required for good cinema.

Comedy provides a leap of faith

Solomon argues that comedic tone creates an 'envelope' of acceptance allowing audiences to suspend disbelief for impossible premises, recounting a clash with Tommy Lee Jones over whether Men in Black could successfully blend sci-fi and comedy genres.

Budget constraints drive creative solutions

Short temporal jumps reduce production costs and minimize complex 'butterfly effect' narrative complications, as seen in the Japanese film The Infinite Two Minutes, where a two-minute window creates a complete story without requiring massive historical changes.

Bill & Ted's jailbreak scene represents perfect logic

Created under extreme budgetary constraints (no special effects or stunts allowed), the 'how do we get the keys' sequence earns praise from Carroll for 100% internal consistency, as characters use future knowledge to affect the present without creating paradoxes.

Superman's Earth reversal and general relativity

Kakalios retroactively defends the 1978 Superman scene by calculating the character's speed at 277,000 miles per second (faster than light) and applying the Tipler cylinder concept, suggesting Superman unknowingly created a closed timelike curve to reverse time.

Time loop narratives operate on magic, not physics

Films like Groundhog Day and Run Lola Run violate physics regarding memory retention across loops, but remain satisfying if audiences accept the premise; Run Lola Run specifically depicts branching realities rather than true time loops with retained memory.