- Quantum mechanics is usually thought of as inherently discrete, yet its equations are formulated in terms of continuous quantities. Discrete values emerge depending on how a system is set up.
- Digital partisans insist that the continuous quantities are, on closer inspection, discrete: they lie on a tightly spaced grid that gives the illusion of a continuum, like the pixels on a computer screen.
- This idea of pixilated, discrete space contradicts at least one feature of nature, however: the asymmetry between left- and right-handed versions of elementary particles of matter.
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Editors' note: Last year the Foundational Questions Institute's third essay contest posed the following question to physicists and philosophers: “Is Reality Digital or Analog?” The organizers expected entrants to come down on the side of digital. After all, the word “quantum” in quantum physics connotes “discrete” —hence, “digital”. Many of the best essays held, however, that the world is analog. Among them was the entry by David Tong, who shared the second-place prize. The article here is a version of his essay.
In the late 1800s the famous german mathematician Leopold Kronecker proclaimed, “God made the integers, all else is the work of man.” He believed that whole numbers play a fundamental role in mathematics. For today's physicists, the quote has a different resonance. It ties in with a belief that has become increasingly common over the past several decades: that nature is, at heart, discrete—that the building blocks of matter and of spacetime can be counted out, one by one. This idea goes back to the ancient Greek atomists but has extra potency in the digital age. Many physicists have come to think of the natural world as a vast computer described by discrete bits of information, with the laws of physics an algorithm, like the green digital rain seen by Neo at the end of the 1999 film The Matrix.
This article was originally published with the title The Unquantum Quantum.