Physicists Observe Backreaction in Analogue Black Hole Experiment

by johnsmith

Physicists from the University of Nottingham and the University of Cambridge have for the first time demonstrated that the evolution of black holes resulting from the fields surrounding them can be simulated in a lab experiment. Their results are published in the journal Physical Review Letters.

Lab experiment using water tank simulation to demonstrate backreaction in an analogue black hole. Image credit: University of Nottingham.

Lab experiment using water tank simulation to demonstrate backreaction in an analogue black hole. Image credit: University of Nottingham.

Dr. Sam Patrick from the School of Mathematical Sciences at the University of Nottingham and his colleagues used a water tank simulator consisting of a draining vortex, like the one that forms when we pull the plug in the bath. This mimics a black hole since a wave which comes too close to the drain gets dragged down the plug hole, unable to escape.

Systems like these have grown increasingly popular over the past decade as a means to test gravitational phenomena in a controlled laboratory environment. In particular, Hawking radiation has been observed in an analogue black hole experiment involving quantum optics.

Using this technique, the researchers showed for the first time that when waves are sent into an analogue black hole, the properties of the black hole itself can change significantly.

The mechanism underlying this effect in their particular experiment has a remarkably simple explanation.

When waves come close to the drain, they effectively push more water down the plug hole causing the total amount of water contained in the tank to decrease.

This results in a change in the water height, which in the simulation corresponds to a change in the properties of the black hole.

“For a long time, it was unclear whether the backreaction would lead to any measurable changes in analogue systems where the fluid flow is driven, for example, using a water pump,” Dr. Patrick said.

“We have demonstrated that analogue black holes, like their gravitational counterparts, are intrinsically backreacting systems.”

“We showed that waves moving in a draining bathtub push water down the plug hole, modifying significantly the drain speed and consequently changing the effective gravitational pull of the analogue black hole.”

“What was really striking for us is that the backreaction is large enough that it causes the water height across the entire system to drop so much that you can see it by eye! This was really unexpected,” he noted.

“Our study paves the way to experimentally probing interactions between waves and the spacetimes they move through. For example, this type of interaction will be crucial for investigating black hole evaporation in the laboratory.”

The team now plans to use quantum simulators to mimic the extreme conditions of the early Universe and black holes.


Sam Patrick et al. 2021. Backreaction in an Analogue Black Hole Experiment. Phys. Rev. Lett 126 (4): 041105; doi: 10.1103/PhysRevLett.126.041105

This article is based on text provided by the University of Nottingham.

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