Probing the weird quantum world (Image: Hiroshi Watanabe/Getty)

Quantum theory is our most successful theory of physics. There is not one shred of experimental evidence that doesn’t fit with its predictions. So why, if it ain’t broke, is a growing number of researchers expressing a desire to fix it?

“Everything depends on whether you believe quantum mechanics is going to go on describing the physical world perfectly to whatever level you push it,” says Nobel laureate Anthony Leggett, who studies the quantum world at the University of Illinois at Urbana-Champaign.

Leggett thinks it won’t, that there are too many issues with quantum theory to think it anything more than an approximation of reality. “I’m inclined to put my money on the idea that if we push quantum mechanics hard enough it will break down and something else will take over – something we can’t envisage at the moment,” he says.

The question is, how hard can we push it? Experiments have never had the sensitivity to pinpoint a weak spot in quantum mechanics. But thanks to a breakthrough earlier this year, that might be about to change. A new swathe of experiments is coming onto the scene that should be up to the job. Welcome to the dawn of the quantum machines.

Such machines are promising to patch a gaping hole in every experiment that has ever been used to back up our view of the quantum world. Take the simple process of measuring a photon’s spin. Thanks to the strange nature of the quantum world, it can actually be spinning in two directions at once, a phenomenon known as superposition. …