Naïve physics or folk physics is the untrained human perception of basic physical phenomena. In the field of artificial intelligence the study of naïve physics is a part of the effort to formalize the common knowledge of human beings.
Many ideas of folk physics are simplifications, misunderstandings, or misperceptions of well understood phenomena, incapable of giving useful predictions of detailed experiments, or simply are contradicted by more thorough observations. They may sometimes be true, be true in certain limited cases, be true as a good first approximation to a more complex effect, or predict the same effect but misunderstand the underlying mechanism.
Usha Goswami, a professor at the University of Cambridge, defines naïve physics as an intuitive understanding all humans have about objects in the physical world.[1] Cognitive psychologists are delving deeper into these phenomena with promising results. Psychological studies indicate that certain notions of the physical world are innate in all of us.
Smith and Cassati (1994) have reviewed the early history of naive physics, and especially the role of the Italian psychologist Paolo Bozzi.[2]
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Some examples include:
The idea that the sun orbits the Earth (the geocentric model), was also, until about 2000 to 500 years ago, part of mankind's commonsense understanding of the world.
These and similar ideas, in some cases too obvious for anyone to think of questioning them, formed the basis for the first work in formulating and systematizing physics by (for example) Aristotle and the medieval scholastics. In the modern science of physics, they were gradually contradicted by the work of Galileo, Newton and others. The idea of absolute simultaneity survived until 1905, when the special theory of relativity and its supporting experiments discredited it.
As technology becomes more sophisticated, more research on knowledge acquisition is possible. Researchers measure physiological responses like heart rate and eye movement to quantify reaction to a particular stimulus. Concrete physiological data is helpful when observing infant behavior, because infants cannot verbally express their reactions.
Research in naïve physics relies on technology to measure eye gaze and reaction time in particular. Through observation, researchers know that infants get bored looking at the same stimulus after a certain amount of time.[1] That boredom is called habituation. When an infant is sufficiently habituated to a stimulus, he or she will typically look away, alerting the experimenter to his or her boredom. At this point, the experimenter will introduce another stimulus. The infant will then dishabituate by attending to the new stimulus. For both cases, the experimenter measures the time it takes for the infant to habituate to each stimulus.
Researchers infer that the longer the infant takes to habituate to a new stimulus, the more it violates his or her expectations of physical phenomena.[1] When an adult observes an optical illusion that seems physically impossible, he or she will attend to it until it makes sense. Until recently, psychologists believed that our understanding of physical laws emerges strictly from experience. But research shows that infants, who do not yet have such expansive knowledge of the world, have the same extended reaction to events that defy what is physically possible. Such studies conclude that all people are born with an innate ability to understand the physical world.
The basic experimental procedure of a study on naïve physics involves three steps: prediction of the infant’s expectation, violation of that expectation, and measurement of the results. As mentioned above, the physically impossible event holds the infant’s attention longer, indicating surprise when expectations are violated.[1]
An experiment that tests an infant’s knowledge of solidity involves the impossible event of one solid object passing through another. First, the infant is shown a flat, solid square moving from 0˚ to 180˚ in an arch formation. Next, a solid block is placed in the path of the screen, preventing it from completing its full range of motion. The infant habituates to this event, as it is what anyone would expect. Then, the experimenter creates the impossible event, and the solid screen passes through the solid block. The infant is confused by the event and attends longer than in probable event trial.[3]
An occlusion event tests the knowledge that an object exists even if it is not immediately visible. Jean Piaget originally called this concept object permanence. When Piaget formed his developmental theory in the 1950s, he claimed that object permanence is learned, not innate. Peek-a-boo is a classic example of this phenomenon, and one which obscures true grasp infants have on permanence. To disprove this notion, an experimenter designs an impossible occlusion event, such as the one pictured. The infant is shown a block and a transparent screen. The infant habituates, then a solid panel is placed in front of the objects to block them from view. When the panel is removed, the block is gone, but the screen remains. The infant is confused because the block has disappeared indicating that he/she understands that objects maintain location in space and do not simply disappear.[4]
A containment event tests the infant’s recognition that an object that is bigger than a container cannot fit completely into that container. Elizabeth Spelke, one of the psychologists who founded the naïve physics movement, identified the continuity principle, which conveys an understanding that objects exist continuously in time and space.[1] Both occlusion and containment experiments hinge on the continuity principle. In the experiment pictured, the infant is shown a tall cylinder and a tall cylindrical container. The experimenter demonstrates that the tall cylinder fits into the tall container, and the infant is bored by the expected physical outcome. The experimenter then places the tall cylinder completely into a much shorter cylindrical container, and the impossible event confuses the infant. Extended attention demonstrates the infant’s understanding that containers cannot hold objects that exceed them in height.[5]
The pivotal findings Renee Baillargeon published brought innate knowledge to the forefront in psychological research. Her research method centered on the visual preference technique. Baillargeon and her followers studied how infants show preference to one stimulus over another. Experimenters judge preference by the length of time an infant will stare at a stimulus before habituating. Researchers believe that preference indicates the infant’s ability to discriminate between the two events.[1]