Optical illusions are interesting, but they're quite commonplace. Physical illusions provide an impossible experience that can actually be felt rather than just seen.
An Impossible Experiment
Say there are three matchboxes on a table. One box is filled with something relatively heavy — coins, pebbles, or even matches — while the other two are empty. Lift the filled box by itself. Then set it down and lift all three matchboxes together. Which one is heavier?
Simple logic dictates that the three matchboxes must be heavier, since there are more objects and therefore more weight involved. A single object could not weigh more than it does with other objects — or could it?
In fact, researchers noted that human perception goes against logic in this case. As demonstrated by New Scientist on Twitter, the single box filled with heavy objects actually feel heavier than all three boxes together.
This weird physical illusion makes you think objects are impossibly light https://t.co/SX1GHXQpDq pic.twitter.com/XvklyyxgFK — New Scientist (@newscientist) May 20, 2019
In a new study published online, the team share what they call "the first impossible perceptual experience that can be physically felt."
Similar to the experiment with the matchboxes previously mentioned, scientists from the Johns Hopkins University provided three boxes with box A weighing 250 grams and boxes B and C weighing 30 grams each. Thirty subjects from the university were instructed to lift the first box alone and the three all together.
Surprisingly, an overwhelming 90 percent of the participants reported that box A felt heavier on its own than it did with boxes B and C.
It was such a strange experience that a number of participants asked to try lifting the objects again after the experiments were concluded. Still, the illusion of box A being heavier persisted, even when the participants knew it was impossible.
The illusion remained consistent regardless of the order of lifting. It also persisted even when the researchers instructed the subjects to lift the boxes via string rather than by hand.
When all three boxes were placed on the hands of the subjects, then the two lighter boxes were taken away, most of the subjects said that they felt more weight being added even when the weight was actually being taken away.
It is, as the authors describe, the first reported impossible somatosensory experience, which means it's an impossibility that a person can actually feel.