Gravity simulation: A giant quantum vortex that mimics a black hole
Black holes are very strange. But there is at least one strange phenomenon that works in much the same way. The vortex in the helium tank recreates curved spacetime at the event horizon.
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The macroscopic vortex in superfluid helium exhibits multiples of the smallest possible spin. But the carriers of these vortex quanta repel each other. Therefore it is difficult to create a vortex as large as possible.
Recreating a black hole in a laboratory is easier than you think – all you need is a quantum vortex made of superfluid helium. A working group led by Patrik Savantara and Silke Weinfurtner has recreated curved spacetime near the event horizon of the black hole. The team also reported in the specialized journal Nature.A quantum vortex is made up of thousands of individual vortex quanta – the smallest spin a vortex can have in superfluid helium. These vortex quanta interact with the helium surrounding them in the same way that large masses interact with the spacetime surrounding them. So a group of thousands of them act on their surroundings like a rotating black hole – but unlike this, they do not destroy the Earth.
The working group developed a solution for their trial Gravity simulation, in this case a tank containing several liters of super liquid helium. Small stimuli such as sound or surface waves behave like fields in curved space-time. Such simulations – in addition to superfluids, ultracold atomic clouds can be used for this purpose – have already helped investigate predictions of quantum mechanics in curved spacetime. Superfluid helium, which forms at temperatures less than two degrees above absolute zero, has no internal friction and very low viscosity, a critical requirement for simulating gravity.
It also contains countless small paragraphs. However, these so-called topological defects should not be viewed as eddies in water, but rather like graphical errors in a computer game. Each of these vortices is quantized, meaning that its spin can only assume a very specific value, the quantum vortex. This means that a conventional vortex, such as one created above a drain, must have a multiple of that. However, these vortex quanta are so small that classical vortices appear to us as continuous. The trick here is again the gravity analogy. Since small vortices affect their surroundings in a similar way to rotating masses, A giant quantum vortex with thousands or more swirling quanta at its core is behaving more and more like a rotating black hole..
But the problem is that quantum vortices that have the same spin direction tend to move away from each other. For this reason, giant vortices with many eddy quanta at their core usually remain small, and the more eddy quanta accumulate, the more unstable they become. “This means that you can create a vortex in the superfluid in the same way as you would in a bathtub – which is what the team led by Švančara and Weinfurtner did – but if you keep feeding it alternately, it won't rotate. More micro-vortices break up and are distributed throughout the rest of the fluid.”
In addition to instability, this is the second central problem in black hole simulations: for the superfluid to resemble spacetime around a black hole, the rotation must be confined to the core of the vortex. The working group solved this problem with a special experimental setup in which a propeller creates the vortex—but at the same time allows as little rotation as possible to escape from it. The team also developed a “minimally invasive” technique to monitor the experimental setup without disturbing it: as a result, what was happening inside was precisely imaged as waves and structures on the surface, which could be easily observed from the outside.
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