Rencontres des Jeunes Physicien·ne·s 2019

From gravitational black holes to analogue gravity

29 nov. 2019, 15:55

20m

Amphitéâtre Marguerite de Navarre (Collège de France)

Oral presentation Physics Oral presentations session

Orateur

Mathieu Isoard (LPTMS)

Description

Black holes are intriguing and singular objects; Einstein did not even believe in their existence. However, the first observation of a rotating black hole in our universe has been recently reported and is an undeniable confirmation of their presence.

In 1974, Hawking predicted that black holes are not completely black, but emit a thermal radiation at a certain temperature $T_{\mathrm{H}}$, the so-called Hawking temperature${}^1$. However, the Hawking radiation is very faint and would be completely lost in the Cosmological Microwave Background.
A new breakthrough occurred in 1981, when Unruh showed that the dynamics of sound waves propagating in a convergent fluid flow was equivalent to the one of a massless scalar field propagating in a curved spacetime${}^2$. He then suggested to use hydrodynamic analogues of gravitational black holes to detect the elusive Hawking radiation.

In this talk, we pedagogically present how the transition from a subsonic to a supersonic flow can mimic an acoustic black hole for sound waves. Then, we discuss the recent experimental detection of spontaneous Hawking radiation in a Bose-Einstein condensate${}^3$. We show in particular how quantum fluctuations in these quantum systems can be related to emission of analogue Hawking pairs. We finally provide a theoretical interpretation of experimental observations${}^4$.

References

1. S. W. Hawking, Black holes explosions?, Nature 248, 30 (1974); Particle Creation by Black Holes, Comm. Math. Phys. 43, 199 (1975).
2. W. G. Unruh, Experimental Black-Hole Evaporation?, Phys. Rev. Lett. 46, 1351 (1981).
3. J. R. M. de Nova, K. Golubkov, V. I. Kolobov, and J. Steinhauer, Observation of thermal Hawking radiation and its temperature in an analogue black hole, Nature 569, 688 (2019).
4. M. Isoard, N. Pavloff, Departing from thermality of analogue Hawking radiation in a Bose-Einstein condensate, arXiv:1909.02509 (2019).

Field

Black holes/acoustic flow

Documents de présentation

RJP2019.pdf