Why the tooth fairy is important for theoretical physics

Deterministic laws that match everyday experience break down for quantum systems such as radioactive decay and electron passage through slits. Conventional rules like adding velocities fail near the speed of light, requiring more complex relativistic laws. No object moves faster than light, yet the expanding Universe allows observation out to 46.1 billion light-years despite only 13.8 billion years since the hot Big Bang. Revolutionary ideas came not only from measurement but also from creative theorists proposing unintuitive concepts. Examples include Maxwell’s demon, a one-electron universe, and an instantaneously collapsing wavefunction. Theoretical physics also emphasizes responsible limits on speculative inventions, summarized by “You can only invoke the tooth fairy once.”

"However, as cosmologist Mike Turner made famous in the 1990s, we have a saying in theoretical physics about how we should responsibly limit our creative inventions, "You can only invoke the tooth fairy once." It's a brilliant piece of advice and an excellent guide for theoreticians everywhere. Here's the reasoning, and the science, behind it. In theoretical physics, we often compare different scenarios that are proposed to describe the Universe against one another."

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