Superfluid helium behaves like black holes

A team of researchers suggests that the forces controlling the strange behavior of black holes in space, is also applicable on cold helium atoms that can be studied in laboratories.

Talking about the discovery Adrian Del Maestro, a physicist at the University of Vermont who co-led the research said

“It’s called an entanglement area law. He further added that this law appears at both the vast scale of outer space and at the tiny scale of atoms, “is weird,” and it points to a deeper understanding of reality.”

Both Black holes and superfluid are very strange: One is known for being so dense that light can’t escape and other is a weird liquid that flows without friction.

The new findings was published in Journal Nature Physics on 13 March. To show the law in a superfluid, Christopher Herdman of the University of Waterloo in Canada and colleagues created a computer simulation of helium. The isotope they studied, helium-4, is the same one that we uses in balloons to keep them aloft, and it becomes a superfluid at temperatures below about 2 kelvins (–271° Celsius).

Undoubtedly, black holes are strange enough, but their relationship to entropy is something that celebrated physicist Stephen Hawking found himself particularly absorbed by. In 1970, Hawking along with Jacob Bekenstein calculated that when matter falls into one of these bottomless holes in space, the amount of information it gobbles up — what scientists call its entropy — increases only as fast as its surface area increases, not its volume. This would be like measuring how many files there are in a filing cabinet based on the surface area of the drawer rather than how deep the drawer is. As with many aspects of modern physics, check your common sense at the door.

“If you double the size of a box, you expect to be able to double the amount of information in that box,” says Christopher Herdman. That’s because the bigger a box, the more documents and other information can be stuffed inside. Progress toward a theory that unifies quantum mechanics and general relativity, a still thorny problem, has convinced many physicists that black holes follow this “area law.”

In the simulation, the researchers kept track of the helium atoms’ entanglement — quantum linkages that intertwine particles. Within the superfluid, scientists selected an imaginary sphere of the material, and studied the entanglement between atoms inside the sphere and those outside of it. That entanglement gives rise to a type of entropy in the superfluid. As the researchers increased the size of that sphere, the entropy of entanglement increased as well. The rate of increase matched that of the sphere’s increase in surface area, which grows more slowly than its volume.

The superfluid sphere is analogous to a black hole’s event horizon, the region of no return surrounding the black hole, beyond which light can’t escape. In black holes, particles on one side of the event horizon can be entangled with those on the other side, creating entanglement entropy in a similar way.

Sharing his satisfaction over the outcome physicist Joe Serene of Georgetown University in Washington, D.C said

“I think it’s a fascinating result.But, to advance from simulations to a measurement of entanglement entropy in real-life helium would likely be difficult. “It remains to be clear how much they can actually get out of real experimental systems,”

This area law has outsize importance in physics. The realization that a black hole’s entropy is proportional to its surface area led to the holographic principle, the idea that the information within a region of space might be completely reproduced on its surface (SN Online: 9/8/14). Scientists hope this concept could lead to a full theory of quantum gravity, uniting the physics of the very small with large-scale gravity.

What’s more, some scientists now believe that the very structure of spacetime might be the result of quantum entanglement (SN: 5/31/14, p. 16), an idea that also grew out of the area law.

“Entanglement entropy is a concept that is successful across many different areas of physics,” says physicist Markus Greiner of Harvard University. “The big problem is no one knows how to measure that in … real-world systems.”


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