Gravitational Waves Will Unveil Quantum Gravity express
Primordial black holes behave like boiling kettles: as they evaporate, they whistle gravitational waves. The character of the whistle, its spectrum, depends on how the hole's temperature relates to its mass. Ordinary particles quickly scatter, but gravitons, the carriers of gravity, carry this whistle without distortion. Physicists translated six competing theories of quantum gravity into mathematical rules of 'boiling' and calculated the corresponding spectra. Different models shift the pitch by tens of orders of magnitude, and for some, it falls right into the detection range of future detectors. Importantly, the shape of the spectrum does not depend on how the black hole formed: it is a reliable marker of the quantum structure of spacetime.
The most surprising conclusion: the smaller the black hole, the shriller its whistle and the faster it evaporates. A hole with the mass of a mountain, in its last seconds of life, would produce a gravitational signal rivaling the brightness of a galaxy.
Primordial black holes are hypothetical objects that formed shortly after the Big Bang. The tiniest of them have survived to this day and are now violently evaporating, ending their lives with a huge burst of energy.