Hours of research by our editors, distilled into minutes of clarity.
Time travel has fascinated humans for centuries. It appears in myths, literature, and science fiction. One of the earliest examples comes from the 400 BCE Hindu epic Mahabharata, describing time dilation long before Einstein’s Theory of Relativity. By the 19th century, stories introduced machines enabling time travel—setting the stage for modern sci-fi.
Although time travel is allowed—because all moments of the past, present, and future exist simultaneously and are locked in place—you will be unable to alter events beyond those that you changed because you were there before your travel to the past, including doing something to change your existence.
The equations of special relativity require these objects to possess imaginary mass, and they would travel faster the more energy is taken away from them. The existence of tachyons would necessitate an unknown form of matter and lead to paradoxes involving information that can hypothetically travel backward in time.
According to quantum physics, traveling back in time to kill one's grandfather would not cause a paradox because time travel would bring one to a new timeline, where the person killed is not one's grandfather. Alternatively, causality would not be violated because the universe would prevent the murder from occurring.
Much of the film Interstellar is centered on the existence of a wormhole and black hole, which happen to be two of the most perplexing things in the universe. Astrophysicist and StarTalk Radio host Neil deGrasse Tyson explains how wormholes and black holes work in real life in this two-minute video.
These hypothetical distortions in the fabric of spacetime may connect vast distances across or even between universes. While science fiction often portrays them as traversable tunnels, the energy and matter required to keep a wormhole open defy current physical understanding.
In 2009, Hawking hosted a reception but only sent out invitations afterward, hoping that time travelers from the future would attend and prove time travel possible. He later joked it was "experimental evidence" that time travel doesn’t exist.
This 8-minute video explores how time travel influences the narrative arc of several movies, books and video games, from Harry Potter to A Christmas Carol. (Warning: it contains spoilers!) J.K. Rowling and Charles Dickens set myriad parameters as they’re worldbuilding to avoid paradoxes and create quasi-logical timelines. By drawing diagrams as he’s speaking, the video breaks down how time works in some of popular culture’s most beloved fictional universes.
Humans have been captivated by the prospect of leaping forward and backward in time for thousands of years. Georgia Institute of Technology Science Fiction Studies Professor Lisa Yaszek recounts how the concept has been utilized by storytellers from 400 BCE to modern-day to explore our relationship with the supernatural, technology, and the past. In a way, this historical recounting is a journey through time.
Are you thinking of writing a story that involves time travel? You might want to read this guide first. It offers questions to consider, mistakes to avoid and strategies to employ to ensure you avoid paradoxes, plot holes and implausibilities.
This grandfather paradox – the notion that changing the past may alter the present conditions that motivated the time traveler in the first place – instills doubt in time travel. But, as this video explains, subatomic particles regularly do different things in parallel. So, what if the universe exists in two states: one where your grandfather is alive and another where he’s dead? Intrigued? Confused? Let the animations in this 2-minute video help you wrap your mind around the possibility.