Illusions Are Not Just Optical, This One Is Physical And You Can Try It At Home


Katy Evans

Katy is Managing Editor at IFLScience where she oversees editorial content from News articles to Features, and even occasionally writes some.

Managing Editor


This illusion will make you feel weight in a way that we know is physically impossible. Go on, try it at home. Robtek/Shutterstock

There’s a new illusion on the block, and no it’s not The Dress 2.0. It’s not even an optical illusion. This is a physical illusion, and you can try it at home.

The illusion involves making a single object feel heavier than a group of objects that the single object is part of, which is, of course, impossible. In a new study, purportedly the first to document a somatosensory illusion, researchers declare: “Impossibility can not only be seen, but also felt.”


The researchers, from Johns Hopkins University, admit they borrowed a conjuror’s trick to demonstrate this “impossible” perceptual experience. In the classic magicians’ version, two objects whose sizes differ but weigh the same are lifted up by a subject who is thus surprised to find the smaller object feels heavier than the larger.

In truth, they are both the same, but experience teaches us to expect smaller items to be lighter. When that is not the case, the brain overcompensates and instead registers it as heavier.

In this impossible illusion, the researchers had 30 volunteers lift a box that weighed 250 grams (9 ounces) on its own, and then lift it with two other boxes, each weighing 30 grams (1 ounce). You can try this yourself with matchboxes. Fill one with heavier items, and two with nothing. Hold the heavy box on its own, and then all three together. Which is heavier, the single or the group?


Thanks, New Scientist for the handy demonstration!


Ninety percent of the participants said the single box felt heavier than the group, which of course is a genuinely impossible experience of weight. There’s no way that a group of objects could weigh less than a single item in that group.

The order of lifting had no effect on the illusion, the researchers reported, nor did lifting the boxes by string rather than holding them in their hands. In fact, when holding all three boxes, and having the two lighter ones taken away, most people reported the feeling of adding weight when in reality weight was being taken away.

According to the study, published on the pre-print server PsyArXiv, the participants knew perfectly well this was impossible and thus appealed to the tester to try the experiment again, yet wielded the same results repeatedly, even knowing it was impossible.

So what is going on?


The team suggests the brain is being fooled here in the same way it is by optical illusions, and that it’s most likely sensory prediction errors creating the illusion, with the brain filling in gaps of our expected reality and possibly overcompensating to explain what it doesn’t understand.

“Impossible figures represent the world in ways it cannot be,” the researchers write in their paper. ”Such experiences show how some principles of mental processing can be so entrenched and inflexible as to produce absurd and even incoherent outcomes that the perceiver knows cannot occur in reality.”

And yet, this usually occurs solely in visual perception via optical illusions. This experiment, they say, is the first to show that impossibility can not only be seen and heard (or seen and heard), but also felt

[H/T: New Scientist]