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A quarter of a century of stellar history
by Spektrum der Wissenschaft
Gravitational waves leave traces in quantum systems
18.4.2026
Translation: machine translated
Vibrations in space-time are not only noticeable in huge gravitational wave detectors. They apparently also influence quantum fields.
When two black holes merge several light years away, the collision of the massive objects shakes space-time. These waves make themselves felt on Earth in the kilometre-long arms of the high-precision LIGO and VIRGO gravitational wave detectors. But possibly not only there: As experts led by physicist Jerzy Paczos from Stockholm University in a paper published at «Physical Review Letters», the cosmic signals could even leave traces in the smallest dimensions, namely in quantum fields.
The interplay between quanta and gravity is difficult to investigate. In areas where the rules of quantum physics apply, gravity is barely noticeable. Conversely, quantum physics usually only plays a subordinate role in large, massive objects.
For more than 100 years, experts have been searching unsuccessfully for a unified theory that encompasses both pillars of physics. In order to approach such a quantum gravity theory, they consider quantum fields in curved space-time. In this way, it is at least possible to investigate how a gravitational field influences quantum systems - the reverse effect is ignored.
Paczos and his team calculated how passing gravitational waves influence a quantum system. To do this, they modelled a single atom that transitions from an excited to a ground state. In this so-called spontaneous emission, the atom emits the excess energy in the form of a photon.
According to the calculations, the spacetime wave is noticeable in the spectrum of the emitted light. The periodic change in spacetime acts like an external drive on the emission process. As a result, the photon energy no longer depends solely on the atomic transition energy, but also on the emission angle relative to the direction of propagation of the gravitational wave. In addition, its characteristic quadrupole-shaped pattern is reflected in the emission: perpendicular to the propagation of the gravitational wave, there are directions in which the frequency shift is stronger or weaker. The pattern could help to distinguish this effect from other external disturbances.
The total number of emitted photons should not change. This means that the gravitational wave does not influence the state of the atom, but rather the quantum field of the overall system. This in turn encodes the information in the emission spectrum. This means that it is not the individual atom that detects the gravitational wave, but the quantum field as a whole.
Paczos and his team explain in their employees' paper that the effect could already be demonstrated today in experiments with ultracold atoms. This would require millions of them to be cooled down and measured. This has already been achieved in the past. This would allow the interplay of quantum fields and curved space-time to be investigated directly in the laboratory.
Spectrum of Science
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Header image: © NASA's Goddard Space Flight Center / Scott Noble; simulation data, d'Ascoli et al. 2018 / Simulation of the light emitted by a supermassive black hole binary system where the surrounding gas is optically thick (detail)
Patrick Bardelli
Senior Editor
Patrick.Bardelli@digitecgalaxus.chFrom radio journalist to product tester and storyteller, jogger to gravel bike novice and fitness enthusiast with barbells and dumbbells. I'm excited to see where the journey'll take me next.
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