According to quantum mechanics, our universe is like a Lego set. All matter particles, as well as particles such as light that act as messengers between them, come in discrete blocks of energy. By rearranging these blocks, it is possible to build everything we observe around us.
Well, almost everything. Gravity, a crucial piece of the universe, is missing from the quantum Lego set. But while there is still no quantum theory of gravity, the challenge of detecting its signatures now looks a little more manageable thanks to a proposed experiment that takes inspiration from the photoelectric effect, which Albert Einstein used to prove the quantum nature of light more than a century ago.
Quantum mechanics and general relativity each, independently, provide accurate descriptions of our universe – but only at short and long distances, respectively. Bridging the two is one of the deepest problems facing physics, with tentative theories approaching it from different perspectives.
However, all efforts of describing a quantum theory of gravity agree on one thing: if gravity is quantum, then it, too, must have a particle that carries its force in discrete packages, just as other forces do.
In the latest study, which is described in Nature Communications, Germain Tobar and Sreenath K Manikandan of Sweden’s Stockholm University, working with Thomas Beitel and Igor Pikovski of the Stevens Institute of Technology, US, propose a new experiment that could show that gravity does indeed come in these discrete packages, which are known as gravitons.
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