Have you ever found yourself in the shower the morning of a big event—say, a job interview, a presentation, or a difficult conversation with a loved one—practicing what you’re going to say? You can create a scene in your mind, imagine the scene in countless ways, rehearse the situation – no different from Nathan Fielder’s newest HBO show.
You may not realize it, but what you are doing is actually mental time travel: drawing from your past to imagine a possible future and place yourself there in your mind.
“We have something like a virtual time machine in our heads,” says Thomas Sudendorf, professor of psychology at the University of Queensland and co-author of The invention of tomorrowa book about mental time travel published in 2022. “We can, in our minds, relive past events and project ourselves forward and imagine potential future situations.” Suddendorf and his late collaborator Michael Corballis coined the term in document from 1997.
The hindsight component of mental time travel is a form of episodic memory that psychologist Endel Tulving first pioneered described in 1972. This type of memory allows us not only to remember information, but also to relive specific experiences from our past.
For example, although you may know where and when you were born, you don’t actually “remember” it as a distinct experience; you can’t relive it in your head. However, the memory of receiving a Nintendo GameCube at your seventh birthday party would be episodic. Hence, the future-oriented counterpart is episodic anticipation: mental placement in an imagined future.
However, the representation of multiple possible futures is not present at birth. In a 2019 study, Suddendorf and colleagues used a deceptively simple experiment to test the development of foresight in children: a bifurcated tube with two outlets but only one inlet. Children may see a desired object, such as a ball, enter the tube in only one way, but must prepare for the possibility that it may exit the tube in two different ways. If the child successfully catches the ball as it exits the tube, they receive a reward, such as a cool sticker.
“When you do that with a two-year-old, […] what they’re doing is covering one of two exits,” Sudendorf says. “Whereas a four-year-old right from the first round will cover both outlets.”
This ability to make contingency plans, to accept that you cannot know the future for sure, is a product of childhood development. “It starts around three or four,” says Suddendorf.
Although it was obvious that people have cognitive abilities not seen in other animals, finding which mental skills are unique is hard to tease out. When it comes to mental time travel, it’s easy to start with our closest relative, the chimpanzee. A study used the same tube instrument for human children on chimpanzees and they did are not doing well.
“Like a two-year-old, the chimpanzee seems to be able to predict that if you drop [a ball] the top will come out from the bottom,” says Sudendorf. “What they don’t seem to do is prepare for more than one possibility.”
The terminology used in the scientific literature can sometimes complicate the study of mental time travel in animals. 2019 paper used the term “forecasting” while referring to future-oriented behavior for insect cognition and behavior.
Dragonflies that capture prey by intercepting it in the air, tune in beforehand. They don’t directly confront their prey in the moment, but instead predict where it will be in fractions of seconds in the future. But this foresight, although it involves future-oriented behavior and planning, is not the same as the episodic foresight used in mental time travel.
“Because these words are also used in ordinary language, we have different associations with them,” says Sudendorf. “There are a lot of different capacities that are forward-looking […] if you want to call them foresight, that’s perfectly fine, but they don’t need to include the ability to imagine future situations.
While there is a survey showing evidence that New Caledonian crows can mentally travel through time, or at least are prime candidates for it more stringent testsSudendorf remains skeptical that other species can time travel mentally.
“Perhaps the ravens have developed some capacity in this area, [but] even here there are some other alternatives that could potentially be raised,” he says. However, this does not mean that the ability definitely does not exist in ravens or any other animal. “We have to be open to the fact that future studies will show more competence than we can currently conclude.”