Bremsstrahlung of light through spontaneous emission of gravitational waves

Charles Wang* (Corresponding Author), Melania Mieczkowska

*Corresponding author for this work

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Zero-point fluctuations are a universal consequence of quantum theory. Vacuum fluctuations of electromagnetic field have provided crucial evidence and guidance for QED as a successful quantum field theory with a defining gauge symmetry through the Lamb shift, Casimir effect, and spontaneous emission. In an accelerated frame, the thermalisation of the zero-point electromagnetic field gives rise to the Unruh effect linked to the Hawking effect of a black hole via the equivalence principle. This principle is the basis of general covariance, the symmetry of general relativity as the classical theory of gravity. If quantum gravity exists, the quantum vacuum fluctuations of the gravitational field should also lead to the quantum decoherence and dissertation of general forms of energy and matter. Here we present a novel theoretical effect involving the spontaneous emission of soft gravitons by photons as they bend around a heavy mass and discuss its observational prospects. Our analytic and numerical investigations suggest that the gravitational bending of starlight predicted by classical general relativity should also be accompanied by the emission of gravitational waves. This in turn redshifts the light causing a loss of its energy somewhat analogous to the bremsstrahlung of electrons by a heavier charged particle. It is suggested that this new effect may be important for a combined astronomical source of intense gravity and high-frequency radiation such as X-ray binaries and that the proposed LISA mission may be potentially sensitive to the resulting sub-Hz stochastic gravitational waves.
Original languageEnglish
Article number852
Number of pages16
Issue number5
Publication statusPublished - 11 May 2021

Bibliographical note

C.W. is indebted to John S. Reid for stimulating discussions and grateful to the Cruickshank Trust for financial support. M.M. would like to thank the Student Awards Agency Scotland (SAAS) for funding.


  • quantum gravity
  • quantum gravity phenomenology
  • gauge symmetry
  • quantum vacuum
  • spacetime fluctuations
  • gravitational decoherence
  • gravitational bremsstrahlung
  • gravitational waves
  • gravitational astronomy
  • X-ray binary


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