Aliens, Black Holes and Quantum Computers

This post was triggered by a recent paper on the arxiv, which suggested that aliens could be located by detecting the Hawking radiation resulting from the back holes they use for quantum information processing. Intrigued? Read on.

Aim

The aim of the paper is to bolster SETI (Search for Extraterrestrial Intelligence).

Assumptions

The authors assume that

i) Other societies would also need a star, like we do the sun. And since most sunlike stars in the Milky Way are older than our sun, the corresponding societies would be more advanced than us. More advanced societies would use more powerful information technologies.

ii) The laws of quantum physics apply everywhere in the universe. And we already know that information processing based on quantum physics is more powerful than that based on classical physics. Therefore the authors assume the advanced aliens would be using the best kind of quantum information technology physically possible.

Why black holes are relevant

i) Black holes allow for the formation of the most compact objects in the universe: they can cram a lot of mass into a tiny bit of space.

ii) Quantum information can be stored inside black holes. The size of the storage space (this need not correspond to real space) can be found from the entropy of the black hole (and is large).

The connection between black holes and information storage was established by observations of people like Michael Duff who noticed that the entropy of a certain kind of black hole was given by the same mathematical quantity (a Cayley hyperdeterminant) as the entanglement of qubits.

iii) Information can be read out from black holes, since they put out Hawking radiation. The smaller the black hole, the faster it radiates.

Conclusions

Putting together all the above information, the authors conclude that advanced extraterrestrial societies would use quantum information technologies based on black holes as storage media. For fast readout, smaller black holes would be preferred. The authors propose looking for the same Hawking radiation (no Hawking radiation has ever been detected for real black holes) that the aliens would be using for readout.

Specifically, they argue that out of the various kinds of particles emitted by the black holes, neutrinos would travel most easily to earth (because they do not interact easily with matter). The paper estimates the rates of such arrivals and suggests that sufficiently advanced civilizations might already be visible to the IceCube neutrino detectors at the South Pole.