An ambitious new project designed to probe one of the deepest mysteries in modern physics has been backed by the European Research Council (ERC).
Combining cutting-edge laser interferometry with emerging quantum technologies, Cardiff University scientists will try and bridge a long-standing divide between Albert Einstein's theories of general relativity and quantum mechanics.
If successful, the experiment could deliver the first direct experimental evidence for quantum gravity – a long-sought theory that unifies Einstein's insights with quantum physics.
A discovery of this magnitude would mark a turning point in understandings of the universe, paving the way for a new era of fundamental physics, according to project lead Professor Hartmut Grote, based at the Gravity Exploration Institute at Cardiff University's School of Physics and Astronomy.
"Confirming quantum signatures of space-time would be an epochal achievement," he explains.
"It would transform how we think about reality at the most fundamental level and open up entirely new directions for scientific exploration."
More than a century after Einstein reshaped our understanding of space and time, this project may bring us one step closer to completing the picture he began. I think he'd be excited.
Professor Grote is one of 319 leading researchers across Europe to win the ERC Advanced Grants competition.
The funding, worth €838 million in total and part of the EU's Horizon Europe programme, gives senior researchers the opportunity to pursue ambitious, curiosity-driven projects that could lead to major scientific breakthroughs.
"One of the most important challenges in science"
For over a century, general relativity and quantum mechanics have independently described the universe with extraordinary accuracy – from the motion of galaxies to the behaviour of subatomic particles.
Yet, despite their successes, they remain fundamentally incompatible with one another.
"Resolving this conflict is widely considered one of the most important challenges in science," Professor Grote says.
"While this scale – known as the Planck length – is far too small to measure directly, certain theoretical frameworks suggest that its effects could become detectable under the right conditions."
The "holographic principle" is one of these theoretical frameworks. Rooted in black hole physics, it is accepted by many theoretical physicists today.
"These theories predict a kind of quantum 'fuzziness' in space-time," says Professor Grote.
"Although the underlying structure is incredibly small, the effect could manifest as minute but measurable fluctuations in the positions of objects around us."
The Cardiff team believes these fluctuations may be just within reach of today's most precise measurement techniques.
They plan to set up a table-top laser interferometer, an instrument capable of detecting changes in length smaller than a billionth of an atom.
The experiment builds on technologies originally developed for gravitational-wave observatories such as LIGO and Virgo, which have already demonstrated the ability to measure extraordinarily subtle distortions in space-time.
Their experiment extends these capabilities by integrating two advanced quantum technologies:
- Squeezed light – a technique that reduces quantum noise in laser measurements, improving sensitivity beyond classical limits
- Single-photon detection – offering unprecedented precision with extremely low noise
By combining these approaches in a single setup, the researchers aim to achieve record-breaking sensitivity in a compact, laboratory-scale experiment.
"This is the first time high-photon-number interferometry and single-photon detection are being brought together in this way," says Professor Grote.
"It opens up an entirely new regime of precision measurement."
While the team's primary goal is to test whether space-time is quantized, the implications of the project extend far beyond this single question.
The new experiment, dubbed "Single Photon Detection Interferometry for Quantum Gravity", could also enable more sensitive searches for other elusive phenomena, including dark matter and primordial gravitational waves from sources in the early universe.
