The following article is a summary of the original scientific article published in Nature Physics.
Superfluids and black holes may not be two subjects you would expect to be intertwined. However, scientists have proven otherwise by showing that superfluid helium does actually show properties similar to black holes!
Helium-4 is the most abundant isotope of helium, making up over 99.99% of helium’s abundancy. Helium-4 contains two protons, two neutrons and has the same chemical structure as an alpha radiation particle.
It’s Helium-4 that has the odd similarities when it comes to black holes, however. One of the strange properties of Helium-4 is that its capable of existing in a superfluid form.
WHAT IS A SUPERFLUID?
There are a lot of theories, equations and studies surrounding superfluids and how they behave. In a very simplified approach, a superfluid is, essentially, a type of liquid that doesn’t exhibit any form of viscosity or friction. This lends itself to some extremely interesting and confusing properties.
So far, superfluidity is only present in the helium-3 and the helium-4 isotopes. No other element or isotope exhibits superfluidity.
Video source: Youtube/BBC
This video uploaded by the BBC 6 years ago explains how superfluid helium works. The video shows helium being supercooled to less than 3K. Due to the lack of viscosity in the helium, it manages to flow out of a solid container.
When helium becomes a superfluid, the atoms stop acting independently and start acting as if they are a singular entity in a quantum entanglement.
WHAT’S THE RELATION TO BLACK HOLES?
Christopher Herdman from the Univerity of Waterloo in Canada led a study that showed how superfluid helium obeys a rule that is known very well due to its application in black holes – the area law.
“If you double the size of a box, you expect to be able to double the amount of information in that box,” says Herdman.
Whilst this sounds like a reasonable assumption, the area law of black holes goes entirely against this principle.
The area law states that a black hole’s entropy – its measure of disorder – is dependent on the black hole’s surface area rather than its volume. Theoretically, black holes with similar surface areas but completely different volumes would still have the same entropy.
This is based on the theory that all the information of matter that ends up getting pulled into a black hole is stored on its event horizon, or what’s commonly known as “the point of no return” in which matter cannot escape the gravitational pull of the black hole.
The simulation was carried out on two supercomputers. 64 virtual helium atoms were used and measured as they transitioned into a superfluid state.
An imaginary sphere was selected and the entanglement between atoms were studied, both inside and outside of the sphere.
As the size of the sphere was increased, the entropy of the sphere also increased. The rate of the increase matched the rate of the surface area increase rather than the rate of the volume increase.
This theory is also what the holographic principle is based off – the idea that all of the universe’s information is stored on a 2D surface.
IS THIS MEANINGFUL IN THE REAL WORLD?
The understanding of the area law has huge implications in quantum gravity theories. By understanding how a black hole’s entropy is dependent on its surface area rather than its volume, scientists are hopeful that a full theory of quantum gravity can eventually be formed.
Quantum mechanics and Einstein’s theory of relatively have never seemed to work very well with each other. The fact that this area law has been observed in a laboratory rather than theoretical black holes means that the reconciliation of these theories may be closer.