Gravitational waves were once purely theoretical, ripples in space-time predicted by Albert Einstein more than a century ago. That changed in 2015, when scientists first detected them directly, confirming that violent cosmic events like black hole mergers can send faint vibrations across the universe. Now, physicists are proposing a far more ambitious next step: not just detecting gravitational waves, but actively influencing them, as reported by ScitechDaily.
The idea comes from Professor Ralf Schützhold, a theoretical physicist at the Helmholtz-Zentrum Dresden-Rossendorf in Germany. In a new paper published in Physical Review Letters, Schützhold outlines a concept for an experiment that would allow light to exchange energy with gravitational waves. If realized, it could offer a rare window into one of the biggest open questions in physics: whether gravity follows the rules of quantum mechanics.
At the heart of the proposal is the interaction between light and gravity. Gravity affects everything, including light, and that interaction also applies when light waves encounter gravitational waves. Schützhold suggests that under the right conditions, tiny packets of energy could be transferred from a light wave to a gravitational wave, or vice versa. When this happens, the light would lose or gain an extremely small amount of energy, while the gravitational wave would do the opposite.
These energy packets correspond to gravitons, the hypothetical quantum particles thought to carry the gravitational force. Gravitons have never been directly observed, and their existence remains one of the most debated ideas in modern physics. In Schützhold’s proposal, the transfer of energy would slightly intensify a gravitational wave while producing a minuscule shift in the frequency of the light. Measuring that shift would be the key signal.
The scale of the experiment would be extreme. Schützhold calculates that laser pulses would need to bounce back and forth between mirrors up to a million times. In a setup roughly a kilometer long, this would create an effective optical path of about one million kilometers. Only at that scale would the tiny frequency changes caused by the exchange of energy become measurable.
To detect such subtle effects, the experiment would rely on an interferometer, a device that compares light waves after they travel different paths. Two light waves would experience slightly different frequency shifts depending on whether they absorbed or emitted energy from a gravitational wave. When recombined, they would produce an interference pattern that reveals what happened along the way.
The proposal draws clear parallels to existing gravitational wave observatories like LIGO, which already measure distortions in space-time smaller than an atom. Schützhold believes that with future refinements, including the use of quantum-entangled light, sensitivity could be pushed even further.
While the experiment would not directly prove the existence of gravitons, it could strongly support or challenge current theories. If the predicted interference effects failed to appear, it would cast serious doubt on graviton-based models of gravity. Either way, the idea has generated significant interest, because it suggests that humanity may one day do more than listen to gravitational waves. We might be able to touch them, ever so slightly.
Reference: “Stimulated Emission or Absorption of Gravitons by Light” by Ralf Schützhold, 22 October 2025, Physical Review Letters.
DOI: 10.1103/xd97-c6d7
