Scientists create a black hole in the laboratory, discovering evidence that support the existence of one of Stephen Hawking's most famous theories: Hawking radiation.
Albert Einstein's general theory of relativity predicted the existence of black holes for the first time. This theory described it as an object with such a powerful gravitational force that even light can't escape once it enters the black hole's point of no return known as the event horizon.
Hawking disagreed, saying that black holes aren't entirely black after all. He predicted that when quantum mechanics are considered, black holes actually emit a tiny stream of thermal radiation at a temperature that depends on their mass.
According to quantum physics, space is filled with pairs of particles that appear together and destroy each other immediately. If this process occurs near an event horizon, the black hole's overwhelmingly powerful gravitational force could pull apart the pair of particles and prevent them from destroying each other. One particle would be absorbed by the black hole, reducing its mass until it eventually vanishes, while the other particle would be able to escape as thermal radiation.
Fittingly known as Hawking radiation, it is far too weak to spot in the real world with current technology.
If scientists want to observe or prove the existence of Hawking radiation, they're going to have to recreate black holes — and that's exactly what a group of physicists did in a study published in the journal Nature.
The Making Of A Black Hole To Prove Hawking Right
The study authors built an analog of a black hole in the laboratory using an elongated Bose-Einstein condensate of ultra-cold rubidium atoms. By adjusting the energy from focused laser beams, one side of the condensate is made denser than the other side.
It mimics the forces of an actual black hole — using sound, instead of light — with a transition point on the condensate acting as the event horizon.
On the denser side, the speed of sound is faster, so sound waves are able to move in all directions either toward or away from the transition point. However, once the sound waves cross over into the less dense side of the condensate where the speed of sound is slower, they can only move in one direction: further into the "black hole."
When the researchers measured the sound waves or phonons that escaped and the ones that fell into the black hole, they found it had an estimated temperature of 0.35 billionths of a Kelvin, which is consistent with Hawking's theories, according to Science News.
The results also match another of Hawking's predictions that suggested the radiation would be thermal.
Black Hole Information Paradox
Gizmodo pointed out that the new study proves that Hawking radiation is a real effect that occurs in these types of systems. However, it remains to be seen if they actually occur in real black holes found in space.
Of course, if Hawking radiation is eventually proven to occur in the real world, it leads to another issue known as the black hole information paradox.
In quantum physics, no information is ever destroyed. However, in Hawking's theory, the black hole's mass is slowly reduced until it disappears into nothing. If a black hole disappears, all the information that it consumed in the past also disappears, which violates the laws of quantum mechanics.
"The solution to the information paradox is in the physics of a real black hole, not in the physics of an analog black hole," said study author and physicist Jeff Steinhauer of the Technion-Israel Institute of Technology.