How Scientists Are Using Fuzziness To Solve the Mystery of Quantum Gravity

Gravitons could bridge the divide between general relativity and quantum mechanics. But efforts to find these hypothetical particles have proved tricky — until now.

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The renowned physicist Freeman Dyson suggested that a hypothetical detector sensitive enough to observe a single graviton would be so massive that the detector itself would collapse into a black hole. But what if we’re going about this the wrong way? What if instead of trying to find just one graviton, we search for a telltale sign that only a group of them can create? That’s what three researchers proposed in a paper from October of 2020.

The physicists were inspired by Brownian motion, which describes how particles in a fluid bounce around randomly. If gravity really is carried by bosons, then maybe they move around randomly too, creating a sort of “noise” or fuzziness that existing gravitational wave detectors like LIGO can suss out.

Of course, the noise has to be pronounced enough for LIGO to notice. It’s a bit beyond the scope of this episode but just know that waves like light can come in different quantum states— in fact, LIGO uses light in a “squeezed” state for enhanced sensitivity The researchers calculated that gravitational waves in different quantum states would produce different amounts of noise.

Sources Cited

How the Bits of Quantum Gravity Can Buzz…​ “New calculations show how hypothetical particles called gravitons would give rise to a special kind of noise.”

The Edge of Physics: Do Gravitons Really Exist?…​ “In an attempt to marry gravity with quantum theory, physicists came up with a hypothetical particle—the graviton. The graviton is said to be a massless, stable, spin-2 particle that travels at the speed of light.”

Is Gravity Quantum?…​ “To directly observe the minuscule effects a graviton would have on matter, physicist Freeman Dyson famously noted, a graviton detector would have to be so massive that it collapses on itself to form a black hole.”

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