An experiment, which has just received funding from the European Research Council, could provide the first direct evidence that space itself has a structure – and that structure is quantum.
For over a century, physics has been built on a quiet contradiction. Einstein’s theory of general relativity describes the universe on cosmic scales with breathtaking accuracy – the motion of planets, the bending of light, the ripples in spacetime from colliding black holes. Quantum mechanics does the same on the smallest scales – the behavior of particles, the structure of atoms, the nature of light. Both theories work. Neither gets things wrong. And yet, they are fundamentally incompatible. Unifying them is considered one of the greatest unsolved problems in science. That may be about to change.
A couple of weeks ago, Cardiff University announced that Professor Hartmut Grote of the university’s Gravity Discovery Institute had received a major European Research Council grant to conduct a groundbreaking experiment with a single goal: to find the first direct experimental evidence of quantum gravity. The idea behind the project is as elegant as it is radical. Spacetime – the fabric of the universe – might not be smooth and continuous as Einstein envisioned. It might be granular, pixelated. Built from discrete quantum units at a scale so small it has never been directly measured: the Planck length – a distance roughly twenty orders of magnitude smaller than a proton. These aren’t pixels you can see. But under the right conditions, theory predicts they create a kind of quantum fuzziness – a barely perceptible jitter in the positions of the objects around us.
Professor Grote’s team plans to detect exactly that jitter. Using a tabletop laser interferometer – an instrument so sensitive it can measure length changes smaller than a billionth of an atom – they will combine two cutting-edge quantum technologies never before used together: squeezed light, which reduces quantum noise in laser measurements beyond classical limits, and single-photon detection, which provides unprecedented precision with nearly zero noise. The experiment, named Single Photon Detection Interferometry for Quantum Gravity, directly leverages technologies developed for LIGO and Virgo – the gravitational-wave detectors already proven capable of sensing the faintest ripples in spacetime from colliding black holes billions of light-years away.
“Confirming the quantum signatures of spacetime would be an epoch-making achievement. It would change our understanding of reality at the most fundamental level and open up entirely new avenues for scientific investigation. More than a century after Einstein changed our understanding of space and time, this project could bring us one step closer to completing the picture he began. I think he would have been thrilled,” says Professor Hartmut Grote of Cardiff University.
Should the experiment succeed, the implications would reach far beyond a single discovery. Quantized spacetime would confirm that the universe is made not of smooth fields and continuous geometry – but of something akin to information: discrete, countable, fundamentally quantum. It would validate theoretical concepts that have been quietly forming for decades – from the holographic principle to the idea that spacetime geometry emerges from quantum entanglement. It would mean that what we call physical reality – space, time, matter – is not the bedrock of the universe. It’s how the universe’s quantum information appears from our perspective. As a bonus, the same experiment could detect traces of dark matter and primordial gravitational waves, echoes from the very earliest moments of the universe. Science, as Professor Grote puts it, doesn’t always announce itself loudly. Sometimes it arrives as a barely perceptible jitter in a laser beam on a lab bench.
