Gravitational pull of half a sand grain measured in physics breakthrough

The weak gravitational pull on a particle just half the mass of a grain of sand has been measured for the first time. This most precise measurement of its kind is a breakthrough towards the quantum realm and a potential Theory of Everything.

Of the universe’s four fundamental forces – gravity, electromagnetism, and the strong and weak nuclear forces – gravity is the one we’re most familiar with in everyday life, but it’s actually the only one that we can’t currently explain using the Standard Model of particle physics, our best system for describing the universe. Finding a way to jam it in there would achieve a Holy Grail of science – a Theory of Everything.

If a quantum theory of gravity exists, clues will be hiding on the tiniest scales, in gravitational interactions between atoms and particles. The problem is, those tiny interactions are washed out by the immense gravitational influence of the Earth. It would be like trying to record the sound of a bug’s footsteps under an idling jet engine. If you were trying to measure electromagnetism between particles, you can set up a box that blocks all outside interference, but you can’t do that with gravity.

But now scientists have developed a new type of experiment that can cancel out the Earth’s pull to reveal gravitational interactions between small objects. The trick is to levitate a magnetic particle in a superconducting trap, isolate it all from external electromagnetism, heat and vibration, and swing a 2.4-kg (5.3-lb) weight on a wheel past to see if the particle moves.

And sure enough, the team measured a weak gravitational pull of just 30 attonewtons (aN) acting on this particle at points that corresponded to when the larger weight was closest to it. Weighing just 0.43 milligrams, that makes it easily the smallest mass for which gravity has been measured so far. The previous record was 90 milligrams – about the mass of a ladybug. Another recent study measured the difference in the passage of time, due to differences in gravity, across the small distance of just 1 mm.

This minuscule measurement, inches the world closer to the quantum realm. If gravity can be measured on objects that tiny, scientists might finally be able to start incorporating this strange force into our models of the universe and build a proper Theory of Everything.

“For a century, scientists have tried and failed to understand how gravity and quantum mechanics work together,” said Tim Fuchs, lead author of the study. “Now we have successfully measured gravitational signals at a smallest mass ever recorded, it means we are one step closer to finally realizing how it works in tandem. From here we will start scaling the source down using this technique until we reach the quantum world on both sides. By understanding quantum gravity, we could solve some of the mysteries of our universe – like how it began, what happens inside black holes, or uniting all forces into one big theory.”

The research was published in the journal Science Advances.

Source: University of Southampton