Researchers publish new guide to measuring spacetime fluctuations

A team of researchers led by the University of Warwick has developed the first unified framework for detecting “spacetime fluctuations” - tiny, random distortions in the fabric of spacetime that appear in many attempts to unite quantum physics and gravity.

These subtle fluctuations, first envisaged by physicist John Wheeler, are thought to arise naturally in several leading theories of quantum gravity. But because different models of gravity predict different forms of these fluctuations, experimental teams have until now lacked clear guidance on what to look for.

The new study, published in Nature Communications addresses this challenge by sorting spacetime fluctuations into three broad categories, each defined by how organised the fluctuations are in space and time. For each category, the researchers mapped out the distinct, measurable signatures that would appear in laser interferometers - from the 4km long LIGO, to compact laboratory systems such as QUEST and GQuEST being developed in the UK (Cardiff University) and USA (Caltech) respectively.

Dr. Sharmila Balamurugan, Assistant Professor, University of Warwick and first author said: “Different models of gravity predict very different underlying trends in the random spacetime fluctuations, and that has left experimentalists without a clear target. Our work provides the first unified guide that translates these abstract, theoretical predictions into concrete, measurable signals.

“It means we can now test a whole class of quantum-gravity predictions using existing interferometers, rather than waiting for entirely new technologies. This is an important step towards bringing some of the most fundamental questions in physics firmly into the realm of experiment.”

The study found that:

• Tabletop interferometers beat LIGO in bandwidth. Despite being far smaller than LIGO, QUEST and GQuEST could provide more detailed information about the nature of spacetime fluctuations. Their wide frequency coverage allows them to detect all the characteristic signatures.
• LIGO is an excellent “yes/no” detector. Thanks to its long arm cavities, LIGO is highly sensitive to the mere presence of spacetime fluctuations — although the relevant frequencies lie above the range currently available in public data.
• A long-running debate is resolved. A debate about whether arm cavities help or hinder detection has been answered as here arm cavities do enhance an interferometer’s sensitivity to spacetime fluctuations, depending on the type of fluctuation being tested.

Dr. Sander Vermeulen, Caltech, co-author of the study said: “Interferometers can measure spacetime with extraordinary precision. However, to measure spacetime fluctuations with an interferometer, we need to know where - i.e. at what frequency - to look, and what the signal will look like. With our framework we can now predict this for a wide range of theories. Our results show that interferometers are powerful and versatile tools in the quest for quantum gravity.”

Crucially, the new framework developed here is agnostic of the underlying mechanism for the fluctuations: it requires only the mathematical description of the hypothesised fluctuations and the geometry of the instrument. This makes it a powerful tool not only for quantum-gravity tests but also for searches for stochastic gravitational waves, dark-matter signatures, and certain forms of instrumental noise.

Prof Animesh Datta, Professor of Theoretical Physics at Warwick concluded: “With this methodology, we can now treat any proposed model of spacetime fluctuations in a consistent, comparable way. In the coming years, we can use this to design smarter tabletop interferometers to confirm or refute possible theories of quantum or semiclassical gravity and even test new ideas about dark matter and stochastic gravitational waves.”

ENDS

Notes to Editors

Spacetime Image Credits: ESA–C.Carreau

QUantum-Enhanced interferometry for Space-Time research (QUEST) tabletop experiment Credits: H Grote, Cardiff University.

For more information please contact:

Matt Higgs, PhD | Media & Communications Officer (Warwick Press Office)

Email: Matt.Higgs@warwick.ac.uk | Phone: +44(0)7880 175403

About the paper and funding:

The paper ‘Signatures of Correlation of Spacetime Fluctuations in Laser Interferometers’ has been published in Nature Communications. DOI: https://doi.org/10.1038/s41467-025-67313-3

This work was funded by the UK STFC “Quantum Technologies for Fundamental Physics” program (Grant Numbers ST/T006404/1, ST/W006308/1 and ST/Y004493/1) and the Leverhulme Trust under research grant ECF-2024-124 and RPG-2019-022.

About the University of Warwick

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