Something is counter-intuitive if it does not seem likely to be true using the tool of human intuition or "gut-feeling" to perceive reality.

The phrase is most often used to describe bits of scientifically-discovered, objective truth that, for one reason or another, our so-called "right brain", intuition, emotions, and the sum of our cognitive processes outside of deductive rationality interpret as 'false' or 'wrong.'

Of course, the subjective nature of intuition make it impossible to say with any objective accuracy what is counter-intuitive -- what is counter-inuitive for one may very well not be for another, since the sources of intuitive 'knowledge' are very much open to debate and epistemological inquiry.

Examples of counter-intuitive theories

The twentieth century has seen a number of counter-intuitive theories developed, most notably:

• Quantum mechanics, which suggests that instead of being made out of particles, the universe is best described by complex-valued wave functions which behave very differently from particles in many situations.
• Relativity theory is also counter-intuitive, because it reformulates the conventional ideas of separate "space" and "time", "mass" and "energy" into a four-dimensional universe with non-Euclidean properties which is hard to visualise.

It is interesting to observe that, at scales and energies in the range normally associated with human experience, these counter-intuitive theories closely approximate the world of "common sense" folk physics and human intuition. However, in situations far removed from normal human experience, the predictions they make are quite different, and yet can be very precisely verified by experiments in the real world, suggesting that they are more "true" than the theories which preceded them.

Attempts to unify these theories, such as string theory and M-theory, are even more counter-intuitive, even from the viewpoint of many physicists whose intuitive abilities have expanded to take into account the earlier theories.

Michelson-Morley experiment

The Michelson-Morley experiment set out to measure the velocity of the Earth as it revolved around the Sun. The equipment was calculated to have sufficient sensitivity to measure the velocity against the backgound ether.

The result was a null result, there was no ether velocity at all. This null result might be considered a special case of counter-intuition - clearly something has been overlooked, but who knows what. Several years later Einstein showed what was missing; namely, that there is no ether and that the speed of light is constant.

See also

• common sense
• folk physics
• folk psychology
• Operations research
• Jesuit Ivy
• wave-particle duality / photoelectric effect - is light a wave or a particle?