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Faster than light

Joined: 20 Mar 2012
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Faster than light
PostThu Oct 31, 2019 1:45 pm 
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A black hole is a place where even light can't escape; a dumb hole is a place sounds can't escape from.  Scientists use them to study black holes by analogy.  Here's an article if this sort of thing interests you.

Scientists since the 1980s have designed, and more recently constructed, a slew of black hole analogs that attempt to recreate the weirdness of spacetime predicted by scientists like Albert Einstein and Stephen Hawking. Just this year, a team led by physicist Jeff Steinhauer at the Technion-Israel Institute of Technology discovered the strongest evidence yet of the radiation that Hawking predicted would emanate from black holes’ outer rims using one such analog, for example. But the comparison between the analog and the real universe can only go so far.


These first black hole analogs looked a lot more like waterfalls than interstellar points-of-no-return. As a postdoctoral researcher under Unruh at the University of British Columbia, Silkie Weinfurtner oversaw pumps moving water down a flume and across a barrier representing the black hole. The scientists initially hoped to send vibrations, also known as sound, through the water, but the speed of sound in water is 1,500 meters per second—a difficult speed to study in a small lab experiment, Weinfurtner told Gizmodo. Instead, they sent physical waves, like waves you’d see in the ocean, across the barrier.

The team published their first results in 2010. When the waves they produced interacted with the barrier, they created pairs of waves on either side of the barrier, similar to the pairs of particles that Hawking predicted would appear on either side of the event horizon, inside and outside of the black hole. Hawking and Unruh’s other theoretical work together implies that black holes emit a “thermal” or “blackbody” spectrum of wavelengths based solely on their temperatures, which for black holes is directly related to their mass. The waves from Weinfurtner’s flume generated a strikingly similar spectrum, and the team claimed to have measured “stimulated” Hawking emission in their analog system.

How to Make a Black Hole in a Science Lab
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