Gravity experiments on the kitchen table: why a tiny, tiny measurement may be a big leap forward for physics

By Sam Baron, The University of Melbourne

Just over a week ago, European physicists announced they had measured the strength of gravity on the smallest scale ever.

In a clever tabletop experiment, researchers at Leiden University in the Netherlands, the University of Southampton in the UK, and the Institute for Photonics and Nanotechnologies in Italy measured a force of around 30 attonewtons on a particle with just under half a milligram of mass. An attonewton is a billionth of a billionth of a newton, the standard unit of force.

The researchers say the work could “unlock more secrets about the universe’s very fabric” and may be an important step toward the next big revolution in physics.

But why is that? It’s not just the result: it’s the method, and what it says about a path forward for a branch of science critics say may be trapped in a loop of rising costs and diminishing returns.

Gravity

From a physicist’s point of view, gravity is an extremely weak force. This might seem like an odd thing to say. It doesn’t feel weak when you’re trying to get out of bed in the morning!

Still, compared with the other forces that we know about – such as the electromagnetic force that is responsible for binding atoms together and for generating light, and the strong nuclear force that binds the cores of atoms – gravity exerts a relatively weak attraction between objects.

And on smaller scales, the effects of gravity get weaker and weaker.

It’s easy to see the effects of gravity for objects the size of a star or planet, but it is much harder to detect gravitational effects for small, light objects.

The need to test gravity

Despite the difficulty, physicists really want to test gravity at small scales. This is because it could help resolve a century-old mystery in current physics.

Physics is dominated by two extremely successful theories.

The first is general relativity, which describes gravity and spacetime at large scales.

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