By Christian Jarrett

In a world with magic, how much effort do you think it would take to cast a spell to make a frog appear out of nowhere? What about to turn a frog invisible? Or make it levitate? And would it be easier to levitate a frog than a cow?

The researchers John McCoy and Tomer Ullman recently put such questions to hundreds of participants across three studies and found they were in remarkable agreement. The findings, published in PLOS One, suggest that we invoke our intuitive understanding of the physical world – our “folk physics” – to make sense of imaginary worlds. And they help explain why fantasy TV shows and books can lose their magic as soon as it feels like anything goes. “Superman leaps tall buildings in a single bound, but a building takes more sweat than an ant-hill,” the researchers said. “And even for Superman, leaping to Alpha Centauri is simply silly.”

In the first of three studies, McCoy and Ullman asked over 200 online participants (aged 18 to 83) to imagine a world in which wizards cast spells and to rank 10 spells in order of how much effort they would require. There was striking agreement across the participants that the easiest spell would be one that changed a frog’s colour and the hardest would be to conjure a frog into existence. In between, from easiest to hardest, the participants ranked the other spells as follows: levitate; teleport; make bigger; turn invisible; turn to stone; split into two frogs; transform to a mouse; and make cease to exist.

A second study with nearly 400 participants was similar but this time some of the participants considered the same spells but applied to a cow, or involving a greater distance than before (for instance, levitating a frog 100 feet off the ground rather than one foot). Also, this time the participants specified how many magic points would be required for each spell (providing a continuous measure of perceived effort), and the researchers converted their estimates to rank the different spells in order of difficulty.

Once again, there was striking agreement among participants in the relative effort required for the different spell types. For instance, the conjure spell was seen as about four times more taxing than the levitate spell. And there was agreement that the same spell type would require more effort when applied to a cow than a frog, and when greater distances were involved.

Across these two studies and a third (a direct replication of the second involving 600 participants), the researchers also assessed the participants’ familiarity with fantasy and magic in books, TV, movies and games. There was no evidence that exposure to fantasy and magic made any difference to participants’ estimates of the difficulty of the spells, ruling out “cultural learning” as an influence on the judgments. “We suggest that the media does not primarily affect what spells are seen as more difficult, but rather than people bring their intuitive physics to bear when they engage with fiction,” McCoy and Ullman said.

Indeed, the pair note that the spells that were consistently judged most effortful – conjure, and cause to cease to exist – “… violate object permanence and cohesion, which are the earliest developing principles at the core of object understanding.” That is, even babies would have the intuition to recognise that something magical was going on if a frog suddenly appeared or disappeared out of nowhere. At the other extreme, the spells judged easiest, such as changing a frog’s colour or levitating it, “…change only accidental object properties such as location and colour.”

This research was conducted with US participants – it will be interesting to see if and how these findings differ in other cultures. For now, though, the results help explain why fantasy is most enjoyable when it is rooted in reality. The researchers conclude by citing the novelist George Macdonald: “The natural world has its laws, and no man must interfere with them … but they themselves may suggest laws of other kinds, and man may, if he pleases, invent a little world of his own” – to which McCoy and Ullman add “It seems people’s little worlds do not stray far from home.”

—Judgments of effort for magical violations of intuitive physics

Christian Jarrett (@Psych_Writer) is Editor of BPS Research Digest