Many physicists assume that gravitons exist, but few think that we will ever see them. These hypothetical elementary particles are a cornerstone of theories of quantum gravity, which seek to unify Albert Einstein’s general theory of relativity with quantum mechanics. But they are notoriously hard — perhaps impossible — to observe in nature.
The world of gravitons only becomes apparent when you zoom in to the fabric of space-time at the smallest possible scales, which requires a device that can harness truly extreme amounts of energy. Unfortunately, any measuring device capable of directly probing down to this “Planck length” would necessarily be so massive that it would collapse into a black hole. “It appears that Nature conspires to forbid any measurement of distance with error smaller than the Planck length,” said Freeman Dyson, the celebrated theoretical physicist, in a 2013 talk presenting a back-of-the-envelope calculation of this limit.
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