Physicists from Paderborn University, the Weizmann Institute of Science, and Cinestav observed the backreaction of stimulated Hawking radiation in a fiber-optical black hole analog. Published in Nature, the research identifies a direct mechanism for energy transfer from the analog black hole to its radiation, simplifying previous theoretical models of black hole evaporation.
How the fiber-optic analog simulates a black hole
Directly observing Hawking radiation in space is currently impossible because the signal is too faint to separate from cosmic background radiation, according to ScienceAlert. To bypass this, researchers build laboratory systems that mimic the physics of an event horizon. While some use water tanks or ultra-cold Bose-Einstein condensates, this specific study utilized an optical analog developed over a decade ago.
The setup involves ultrafast laser pulses traveling through a specially patterned optical fiber. One pulse modifies the fiber’s optical properties, creating a boundary that acts as an event horizon for a second pulse. This allows scientists to study the dynamics of light in a way that mirrors how gravity behaves at the edge of a black hole. Specifically, the “event horizon” in this fiber is the point where the velocity of the light pulse matches the speed of the modification of the fiber’s refractive index, preventing certain photons from escaping.
The shift from cascaded to direct radiation mechanisms
The core of the discovery lies in how the radiation is actually generated. Previous theories suggested a complex, multi-step “cascade” of quantum-mechanical processes. However, the international team provided evidence that the process is far more streamlined.
According to Bioengineer.org, the researchers found that the radiation arises from a direct process, provided the interaction between the radiation and the equivalent gravitational field is biquadratic. This shift in understanding removes layers of theoretical complexity.
“This simplifies the theoretical understanding and opens up new ways of calculating effects in such systems. It might even shed light on how Hawking radiation arises in the context of gravity.”
Lorenzo Procopio, Paderborn University, via ScienceAlert
What the observed backreaction reveals about mass loss
While previous experiments recreated Hawking radiation itself, this study captured the backreaction. In a cosmic black hole, Hawking radiation—first proposed by Stephen Hawking in 1974—suggests that black holes aren’t one-way streets but slowly lose energy and mass. This leads to the eventual evaporation of the black hole.
The backreaction is the feedback loop where the emitted radiation influences and alters the field that produced it. As The Debrief reports, this evidence shows that radiation interacts with the black hole system rather than just passively emitting into space. This interaction is the mechanism that allows a black hole to shrink over time.
In the fiber-optic analog, the backreaction manifests as a change in the properties of the laser pulse that creates the horizon. As the stimulated Hawking radiation is emitted, it extracts energy from the pulse, causing a measurable shift in the “black hole’s” characteristics. This mirrors the process in general relativity where the emission of a particle reduces the mass of the black hole, thereby altering the curvature of spacetime.
The rate of this evaporation is inversely proportional to the mass of the black hole. This means:
- Large black holes: Emit radiation slowly and evaporate over vast timescales.
- Micro black holes: Emit radiation at a much faster rate and can vanish quickly.
Implications for quantum gravity and other analog systems
The ability to measure these effects on a laboratory scale provides a testbed for one of physics’ biggest mysteries: the intersection of quantum mechanics and general relativity. General relativity describes gravity on a macroscopic scale, while quantum mechanics describes the behavior of particles. Hawking radiation is significant because it is a quantum effect that occurs in a region of extreme gravity, potentially providing a bridge toward a theory of quantum gravity.
Because the fiber-optic model identifies a non-cascaded generation mechanism, the findings may be applicable to other analog platforms. Researchers can now apply these insights to various other simulations of gravitational effects, including:
- Acoustic black holes (using sound waves in fluids)
- Superconducting circuits
- Quantum fluids of light
- Polariton condensates
By demonstrating that the backreaction is a direct process, the team has provided a new framework for calculating how energy is transferred from a gravitational field into observable quanta. This moves the study of black hole evaporation from purely theoretical predictions toward experimentally verified mechanisms, allowing physicists to test how the “evaporation” process behaves without needing to observe a stellar-mass black hole in deep space.
Find more reporting in our Tech section.
