New Theory of Everything Unites Quantum Mechanics with Relativity ... and Much More

Stephen Wolfram, a controversial physicist and computer scientist, has united relativity, quantum mechanics and computational complexity in a single theory of everything. But will other physicists be convinced?

One of the goals of modern physics is to determine the underlying rules that govern our reality. Indeed, one of the wonders of the universe is that just a few rules seem to describe many aspects of our world. What’s more, scientists have found ways to combine these rules into simpler, more powerful ones.

That has tempted many thinkers to suggest there might be a single rule, or set of rules, from which all else emerges. This pursuit of a theory of everything has driven much of the thinking behind modern physics. We have built multibillion-dollar machines and observatories to test these ideas, generally with huge success.

Despite this success, one outstanding challenge is to unite two entirely different but fundamental pillars of modern science: the theory of relativity, which describes the universe on a large scale; and the theory of quantum mechanics, which describes it on the smallest scale.

Both theories almost perfectly explain the results of almost every experiment ever performed. And yet they are entirely at odds with each other. Numerous theorists have attempted a unification, but progress has been slow.

That sets the scene for the work of Stephen Wolfram, a physicist and computer scientist who has spent much of his career categorizing simple algorithms, called cellular automatons, and studying their properties. His main finding is that the simplest algorithms can produce huge complexity; some even generate randomness. And his main hypothesis is that the universe is governed by some subset of these algorithms.

A New Kind of Science

In 2002, he published his results in a weighty tome called A New Kind of Science, which garnered mixed reviews and generally failed to make the impact Wolfram seemingly hoped for. Now he’s back with another, similar idea and an even more ambitious claim.

Once again, Wolfram has studied the properties of simple algorithms; this time ones that are a little different to cellular automatons, but which he says are as minimal and structureless as possible. And, once again, he says that applying these simple algorithms repeatedly leads to models — toy universes, if you like — of huge complexity. But his new sensational claim is that the laws of physics emerge from this complexity, that they are an emergent property of these toy universes.

Wolfram, who works with a couple of collaborators, describes how relativity and space-time curvature are an emergent property in these universes. He then describes how quantum mechanics is an emergent property of these same universes, when they are studied in a different way. By this way of thinking, relativity and quantum mechanics are different sides of the same coin. He goes on to show how they are intimately connected with another, increasingly influential and important idea in modern physics: computational complexity.

So his new theory of everything is that three pillars of modern physics — relativity, quantum mechanics and computational complexity — are essentially the same thing viewed in different ways. “At this point I am certain that the basic framework we have is telling us fundamentally how physics works,” says Wolfram. It’s a jaw-dropping claim.

The first thing to acknowledge is that it is hard to develop any coherent theory that unites relativity with quantum mechanics. If it passes muster under peer review, it will be a tremendous achievement.

But there are also reasons to be cautious. First, it is not clear that Wolfram is submitting the work for formal peer review. If not, why not?