Observation of thermal Hawking radiation at the Hawking temperature in an analogue black hole (1809.00913v2)

Abstract: We measure the correlation spectrum of the Hawking radiation emitted by an analogue black hole and find it to be thermal at the Hawking temperature implied by the analogue surface gravity. The Hawking radiation is in the regime of linear dispersion, in analogy with a real black hole. Furthermore, the radiation inside of the black hole is seen to be composed of negative-energy partners only. This work confirms the prediction of Hawking's theory regarding the value of the Hawking temperature, as well as the thermality of the spectrum. The thermality of Hawking radiation is the root of the information paradox. The correlations between the Hawking and partner particles imply that the analogue black hole has no analogue firewall.

• The paper demonstrates the first precise observation of thermal Hawking radiation using a Bose-Einstein condensate to simulate an analogue black hole.
• It employs density-density correlation measurements and 7,400 experimental runs to verify the thermal spectrum at the predicted Hawking temperature.
• The findings validate Hawking's theoretical framework and offer critical insights into the black hole information paradox.

Analogue Black Hole and Thermal Hawking Radiation Measurement

In the paper "Observation of thermal Hawking radiation at the Hawking temperature in an analogue black hole," the authors focus on a precise experimental observation related to Hawking radiation, using a Bose-Einstein condensate system to simulate an analogue black hole. This research targets fundamental questions about the nature of Hawking radiation, such as its thermality and temperature, which are essential to understanding the information paradox surrounding black holes.

The experimental setup involves a Bose-Einstein condensate flowing in a laser-constrained one-dimensional system. This setup allows for the creation of supersonic and subsonic flow regions, separated by a sonic horizon—a key aspect of a black hole analogue. Negative-energy partners and Hawking radiation are examined on either side of this horizon. The paper reports a thermal spectrum of Hawking radiation with a temperature consistent with theoretical predictions based on the analogue surface gravity, offering direct evidence to support Hawking's theoretical framework.

The Hawking temperature in the experiment is derived through the expression $\frac{\hbar g}{2\pi c}$, where $g$ is the analogue surface gravity and $c$ is the speed of sound. By measuring the correlations between Hawking particles and their negative-energy partners through density-density correlation functions, the research validates the thermal character and magnitude of the Hawking radiation temperature. This corresponds well to theoretical Planckian predictions, demonstrating both the accuracy and reproducibility of the analog experiment.

The implications of these findings are significant for quantum field theory in curved spacetime and black hole thermodynamics. The paper not only validates Hawking's prediction about black hole radiation being thermal but also provides evidence vital to understanding the information paradox—whether information about matter within a black hole can be deduced from its emitted radiation. The absence of an analogue firewall, another layer to the information paradox, is also supported by the measured correlations.

The advancements in the experimental apparatus, including lower noise magnetic field environments and reduced optical aberrations, have been essential in refining the system to observe and accurately measure these phenomena. Their extensive repetition of the experiment, with 7,400 runs, enhances the reliability of their results.

Future developments in this field could involve exploring more complex analogue models or modifying parameters to paper different aspects of Hawking radiation and quantum gravity. Given that analogue systems allow precise control over variables difficult to manipulate in astrophysical settings, they hold potential for both theoretical and practical insights into the elusive properties of black holes and spacetime. Such work could influence the direction of research on quantum gravity and its intersection with information theory in the context of theoretical physics.