You may have noticed it the last time you went on a long journey — by foot, by car or by plane: the outbound portion of your trip seemed to take a lifetime, while the (more or less identical) leg that brought you home felt like it flew by.
Scientists have noticed this “return trip effect” too, and are beginning to hone their understanding of why we experience it. In past years, researchers have suggested that it has to do with the way our bodies experience and measure time as it passes, or the way we remember the trips we take after the fact, or perhaps a bit of both. On Wednesday, a team in Japan released a new report in the journal PLOS ONE detailing the latest effort to solve the mystery. This group’s take? That the return trip effect is created by travelers’ memories of their journeys — and those memories alone. “The return trip effect is not a matter of measuring time itself. Rather, it depends on time judgment based on memory,” said Ryosuke Ozawa of the Dynamic Brain Network Laboratory at the Graduate School of Frontier Biosciences at Osaka University.
To test out what is going on when the trip home seems shorter, Ozawa and colleagues, then at Kyoto University, created an experiment in which 20 healthy men, between 20 and 30 years of age, watched varying combinations of movies filmed by an experimenter who held a camera in front of the chest while walking two different routes. Half of the group viewed an outbound and return roundtrip on a single route; the other half, walking videos of two different routes in separate locations.