快猫短视频

Do try this at home. It鈥檚 an 鈥渋mpossible鈥� physical experience a bit like an optical illusion.

Take three empty matchboxes and fill one with something heavy. Now lift the weighted box on its own. Then put it down and next lift all three together. You won鈥檛 believe your brain. In tests by Isabel Won and colleagues at Johns Hopkins University in the US, 90 per cent of students who tried it said that the individual weighted box felt heavier than the trio held together.

That鈥檚 not possible 鈥� and the students knew it. They told the psychologists what they were feeling was wrong, and begged to try the experiment again to work out what was going on.

The team say their brains were being fooled in the same way as we are baffled by optical illusions, such as the impossible endless staircases drawn by Maurits Escher: 鈥淚mpossibility can not only be seen but felt,鈥� they write.

This weird physical illusion makes you think objects are impossibly light

鈥� 快猫短视频 (@newscientist)

The set-up is borrowed from magicians who have known about the illusion for years.

In the team鈥檚 version, 30 students lifted, in turn, a box weighing 250 grams on its own and then together with two that each weighed 30 grams.

The order of the lifting made no difference and the illusion persisted when the volunteers held the boxes suspended with string. Most weird of all, when they held all three on their palm and then snatched away the lighter pair, they felt the change as adding weight, not taking it away.

Daniel Huber, at the University of Geneva says its not clear what鈥檚 going on in the brain. But he says it鈥檚 probably related to a separate illusion where we perceive the smaller of two identically weighted objects as heavier. 鈥淭he most common theories are based on sensory prediction errors,鈥� he says. In that case, expecting the smaller object to be lighter, the brain might overcompensate and so misleadingly register it as heavier than it really is.