The idea that two quanta could be instantaneously entangled with one another, even across large distances, is often talked about as the spookiest part of quantum physics. If reality were fundamentally deterministic and were governed by hidden variables, this spookiness could be removed. Unfortunately, attempts to do away with this type of quantum weirdness have all failed. (Credit: Alan Stonebraker/American Physical Society)

How the best alternative to “quantum spookiness” failed

Many still cling to the idea that we live in a deterministic Universe, despite the nature of quantum physics. Now the “least spooky” interpretation no longer works.

For all of history, there’s been an underlying but unspoken assumption about the laws that govern the Universe: that if you know enough information about whatever system you’re dealing with, you can predict precisely how that system will behave in the future. That’s what deterministic means: if you know enough information, you can determine what its properties will be not just now, but as far down the road as you care to calculate. The classical equations of motion — Newton’s laws — are completely deterministic. The laws of gravity, both Newton’s and Einstein’s, are completely deterministic. Even Maxwell’s equations, governing electricity and magnetism, are 100% deterministic as well.

But that picture of the Universe got turned on its head with a series of discoveries that began in the late 1800s. Starting with radioactivity and radioactive decay, humanity slowly uncovered the quantum nature of reality, casting doubt on the idea that we live in a deterministic Universe. Predictively, many aspects of reality could only be discussed in a statistical…