We all know about Black Holes.
A black hole is a place in space where gravity pulls so much that even light can not get out. The gravity is so strong because matter has been squeezed into a tiny space. This can happen when a star is dying. Because no light can get out, people can’t see black holes. They are invisible. Blah… Blah…. Blah…..
A Black Hole | Image Source: vox.com
Can we artificially create a black hole?
In theory, to make a black hole all we would need to do would be to compress a huge amount of matter and energy into a tiny amount of space. In practical terms, however, this is incredibly difficult. There is much disagreement about the minimum size a black hole can be, and standard physics offers different answers to more exotic ‘multi-dimensional’ physics. Einstein said that mass and energy are equivalent – you can turn mass into energy and energy into mass – so very high energy particles smashing together could potentially lead to the creation of a black hole. However, the energy required for this would be the equivalent to taking the mass of a mountain range and converting it into energy. For reference, a nuclear weapon only releases the energy of a few grams worth of matter. So even the Large Hadron Collider at CERN, with its particles traveling at close to the speed of light will not, under standard physics, be able to create a black hole.
Large Hadron Collider at CERN | Image Source: spaceanswers.com
But we could create a similar one like black hole. We can not reach speed of light but we can reach few speeds lower than speed of light, like speed of sound, the sonic speed. So, a hole can be made similar to black hole which pulls sound like black hole pulls light.
Of course there is no problem in having something go faster than sound, but sound waves themselves are stuck with that speed limit. That fairly elementary fact inspired Bill Unruh(W.G. Unruh) years back to propose a clever idea: a black hole that you could make in the laboratory, but using sound rather than light. He called them
HOLES OF SILENCE
SONIC BLACK HOLE
although I’m not sure people get the right idea when they hear that name.
W.G. Unruh | Image Source: science.ca
W.G. Unruh explained this theory with a wonderful example:
Imagine you are a blind fish, and are also a physicist, living in a river. At one place in the river, there is a particularly virulent waterfall, such that at some point in the waterfall, the velocity of the water over the waterfall exceeds the velocity of sound in the water. It is clear that if another fish, which has fallen over the falls, shouts after passing that point, that sound will never get out to someone on the other side of the river. The sound will still travel through the water with its same speed as always, but the flowing water will sweep that sound over the falls faster than that sound could hope to travel out.
Furthermore, if a fish screams as it falls through that surface, the parts of the sound in that scream emitted at points closer and closer to that surface will take longer and longer to get out to a point far from the falls, because the net velocity of the sound will be smaller and smaller if the sound emitted is closer to that special surface. That last bit of sound emitted just before the fish goes through that surface will take an infinite time to get out, since the net outward velocity of the sound goes to zero as that surface is approached.
It is also clear that the fish itself, as it goes through that surface, will not note anything unusual—the velocity of the water will not cause anything unusual to happen in the local physics around that sonic horizon.
These phenomena are analogous to what happens in a black hole. If something falls through the horizon of a black hole, it can never again send out a signal to the outside world. As it falls into the black hole, the light takes longer and longer to get out, with the light emitted just as one falls through the horizon taking an infinite time. One can never see anything fall into the black hole, just as one can never hear anything fall into the sonic analogue.
Image Source: odec.ca
However, the first black hole analogue was not created in a laboratory until 2009. It was created in a rubidium Bose–Einstein condensate using a technique called density inversion. This technique creates a flow by repelling the condensate with a potential minimum. The surface gravity and temperature of the sonic black hole were measured, but no attempt was made to detect Hawking radiation. However, the scientists who created it predicted that the experiment was suitable for detection and suggested a method by which it might be done by lasing (using LASER tech) the phonons(sound perturbations). In 2014, self-amplifying Hawking radiation was observed in an analogue black-hole laser by the same researchers.
Stay tuned to mpag.in for further updates on “Dumb Hole”.
Thanks for reading….
- Sonic Black Hole – Wikipedia.
- Holes of Silence June 12, 2009
- Dumb holes: analogues for black holes – .
- What Is a Black Hole? – article which is part of the NASA Knows! (Grades K-4) series published on Sept. 30, 2008 in ‘nasa.gov’.
- Can we artificially create a black hole? question by Jonathan O’Callaghan, 14 December 2012 in spaceanswers.com which was answered by Sophie Allan from the National Space Centre.
- Featured Image: Black hole on Earth by pluty99 | Digital Art / 3-Dimensional Art / Scenes / Spacescapes.