# Real numbers don’t cut it in the real world, this physicist argues

## They may fall short in describing nature, potentially opening the door in physics to free will

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You would be forgiven for thinking that real numbers are, in fact, real — the word is right there in the name. But physicist Nicolas Gisin doesn’t think so.

He’s not questioning the mathematical concept of a real number. The term refers to a number that isn’t imaginary: It has no factor of i, the square root of negative one. Instead, Gisin, of the University of Geneva, debates the physical reality of real numbers: Do they appropriately represent nature? Physicists regularly use real numbers to describe the world: velocities, positions, temperatures, energies. But is that description really correct?

Gisin — known for his work on the foundations and applications of quantum mechanics — takes issue with real numbers that consist of a never-ending string of digits with no discernable pattern and that can’t be calculated by a computer. Such numbers (for example, 1.9801545341073… and so on) contain an infinite amount of