Looking for Black Holes in Water?

Looking for Hawking Radiation in space is likely impossible with our current technology. But scientists here on Earth recently used flowing water to simulate a black hole and create event horizons, testing Stephen Hawking’s famous prediction that the event horizon creates particles and anti-particles.

Black holes resemble cosmic drains where space disappears like water draining out of a sink. Space seems to flow, and the closer one gets to the black hole, the faster it flows. At the event horizon, space appears to reach the speed of light, so nothing, not even light, can escape beyond this point of no return.

Researchers from the University of St. Andrews and the University of Nice used a water channel to create analogues of black holes, simulating event horizons.

The scientists sent waves against the current, varied the water speed and the wavelength, and filmed the waves with video cameras, looking for the place in the channel where the water begins to flow faster than the waves, which would be the event horizon. Over several months the team painstakingly searched the videos for clues.

They used a 30-meter-long water channel with a powerful pump on one end and a wave machine on the other, which is normally used to test the environmental impact of currents and waves on coasts or the hulls of submarines.

While the water didn’t create anti-particles, the researchers may have seen “anti-waves.” Normal waves heave up and down in the direction they move, whereas anti-waves do the opposite.

One of the researchers, Professor Ulf Leonhardt said, “It is probably impossible to observe the Hawking radiation of black holes in space, but something like the radiation of black holes can be seen on Earth, even in something as simple as flowing water.”

“We definitely have observed these negative-frequency waves. These waves were tiny, but they were still significantly stronger than expected. However, our experiment does not completely agree with theory and so much work remains to be done to understand exactly what happens at the event horizon for water waves.”

Their research will be published in the New Journal of Physics.

Original News Source: University of St. Andrews Press Release