Black hole radiation could provide insight into quantum gravity

Now, all we need is to observe it

Supermassive black hole

The evaporation of black holes could provide a way to what’s known as the “loop quantum gravity” theory.

Loop gravity is one of the many theories proposed as a way to unite general relativity with quantum mechanics, but it’s not easy to test; as Aurélien Barrau of the French National Institute of Nuclear and Particle Physics says, “Planck-scale physics has been thought to be untestable”.

It still is: what Barrau’s team has published in Physical Review Letters is a method for distinguishing the Hawking radiation (by which black holes are predicted to evaporate) from the noise signature of loop quantum gravity.

In fact, the group’s models suggest that primordial black holes – those created by the Big Bang – would, from a quantum gravity point of view, look different to later and larger black holes. The first, they believe, would produce “two distinct loop quantum gravity signatures”, while “larger black holes are expected to reveal one distinct signature”.

Hawking radiation brings our old friend Heisenberg into the story, demonstrating a mechanism by which black holes can lose energy and mass: vacuum fluctuations (discussed in this article) near the black hole’s event horizon create particles and antiparticles, the antiparticle falling into the black hole and causing it to lose mass.

The catch in using Barrau’s math to distinguish between Hawking radiation and loop quantum gravity is that nobody’s observed Hawking radiation yet: it’s beyond current cosmology. However, having a prediction before an observation is always a good thing.

Barrau says he is now “working on the cosmological side of loop quantum gravity”, and adds that there may even be signatures observable in the universe’s microwave background radiation. ®

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