Scientists in the UK have made a giant leap towards proving Albert Einstein wrong, showing that it is possible to measure the effect of gravity on a minuscule particle.
The discovery could pave the way to unlocking the secrets of “quantum gravity”, which would in turn shed light on many of the greatest mysteries of the universe.
Researchers at the University of Southampton have managed to measure the gravitational pull on a metal particle weighing 0.43 milligrams, the “smallest mass ever recorded” in such a gravitational experiment. It smashed the previous record, a particle weighing 200 times more at 90 milligrams.
Einstein did not think it would ever be possible to test the effects of gravity at a subatomic scale, but the scientists behind the study are confident they will be able to scale their method down to about 1,000 times smaller within ten years.
Einstein’s theory of general relativity describes how vast objects such as stars, galaxies and black holes behave on the grand scale of gravity, space and time. Quantum mechanics describes how tiny particles such as electrons, protons, neutrons and photons behave on the subatomic scale.
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One of the greatest quests in science is finding a way to marry these two fields of physics. Three of the four fundamental forces in nature can be explained on a subatomic or quantum scale. It has so far proved impossible to do so for the fourth: gravity.
Understanding “quantum gravity” could unlock the secret of what goes on inside black holes or what creates dark energy.
The researchers set up a magnetic particle made of neodymium weighing 0.43mg, or less than half of one thousandth of a gram, and got it to levitate within a magnetic field at a temperature of about 273C below freezing, about a hundredth of a degree above the coldest temperature possible in physics, known as absolute zero. This minimised the effect of all other forces to focus only on the effect of gravity.
They then placed a 2.4kg weight about one metre away. The aim was to measure the tiny gravitational force exerted on the particle. To do this, they set the particle oscillating and co-ordinated the larger weight to oscillate at the same frequency.
With a child’s swing in a playground, if you want to make them swing higher you need to time your pushes at the very top of each swing cycle.
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Using a similar principle, the scientists used the 2.4kg weight to amplify the oscillations of the 0.43mg particle and recorded a force of 30 attonewtons. One newton is defined as the force needed to accelerate a mass of 1kg by one metre per second every second. An attonewton is one quintillionth — or one billionth of one billionth — of this force.
Professor Tim Fuchs, lead author of the study published in the journal Science Advances, said: “For a century, scientists have tried and failed to understand how gravity and quantum mechanics work together. Now that we have successfully measured gravitational signals at a smallest mass ever recorded, it means we are one step closer to finally realising 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.”
Asked when it would be possible to detect gravity at a quantum level, Professor Hendrik Ulbricht, the co-author, said: “I would hope in five years and I’m sure in ten years.”
