Researchers led by the University of Warwick have introduced the first unified approach to identifying ‘space-time fluctuations’ – tiny random distortions in the fabric of space-time that appear in many efforts to link quantum physics and gravity.
These tiny fluctuations were first proposed by physicist John Wheeler and are expected to occur in several major theories of quantum gravity. However, different theories predict different types of fluctuations, making it difficult for experimental scientists to know exactly which signals to look for.
Turn theory into measurable signals
The new research nature communicationsaddress this issue by grouping spatiotemporal fluctuations into three main categories based on how they behave across space and time. The researchers identified distinct and measurable patterns in each category that can be detected using laser interferometers, from large-scale systems like the 4km-long LIGO to smaller experimental instruments like QUEST and GQuEST, which are being developed in the UK (Cardiff University) and the US (California Institute of Technology), respectively.
Dr Sharmila Balamurugan, assistant professor at the University of Warwick and lead author, said: “Different models of gravity predict vastly different underlying trends in random space-time fluctuations, which has left experimenters with no clear target. Our work provides the first unified guide to converting these abstract, theoretical predictions into concrete, measurable signals.”
“This means we can test a whole class of quantum gravity predictions using existing interferometers, rather than waiting for entirely new technology. This is an important step in bringing some of physics’ most fundamental questions firmly into the realm of experimentation.”
What the research revealed
The findings highlight several important insights into how different instruments can detect these variations.
- Tabletop interferometers outperform LIGO in bandwidth.
Systems like QUEST and GQuEST have the potential to provide more detailed information about space-time variations, despite their much smaller size. Wider frequency range allows you to capture all major signal patterns. - LIGO is an excellent yes/no detector.
Because LIGO has a long arm cavity, it is very sensitive to the presence or absence of spatiotemporal fluctuations. However, the relevant frequencies are outside the range currently available in public data. - A long-standing dispute has been resolved.
This study addresses the ongoing question of whether arm cavities improve detection. The results show that sensitivity increases depending on the type of variation studied.
“Interferometers can measure space-time with extraordinary precision,” said study co-author Dr Sander Vermeulen of the California Institute of Technology. “We need to know what that looks like. With our framework, we can now predict this with a wide range of theories. Our results show that interferometry is a powerful and versatile tool in the exploration of quantum gravity.”
Flexible tools for fundamental physics
An important strength of this framework is that it does not rely on a single explanation of how these variations arise. Instead, only a mathematical description of the proposed variation and details of the measurement settings are required. This flexibility makes it useful not only for studying quantum gravity, but also for studying stochastic gravitational waves, dark matter signals, and certain types of experimental noise.
Professor Animesh Dutta, Professor of Theoretical Physics at the University of Warwick, concluded: “Using this methodology, we can now treat proposed models of space-time variation in a consistent and comparable way. In the coming years, we will be able to use it to design smarter tabletop interferometers to confirm or refute possible theories of quantum or semiclassical gravity, and even to test new ideas about dark matter and stochastic gravitational waves.”
This research was funded by the UK STFC’s “Quantum Technologies for Fundamental Physics” program (grant numbers ST/T006404/1, ST/W006308/1 and ST/Y004493/1) and the Leverhulme Trust under research grants ECF-2024-124 and RPG-2019-022.
