A hidden quantum feature of protons is showing strange behavior. Like a black hole?

This could open an entirely new field of study.
Brad Bergan
An abstract depiction of gravity in a semi-ordered system.koto_feja / iStock

Protons, quantum entanglement, and a black hole walk into a bar.

This joke might actually go somewhere thanks to the recent discovery that fragments of a proton's interior exhibit maximum quantum entanglement — a find that, bizarrely, could point to another, much larger thermodynamic object: black holes, according to a recent study published in the European Physical Journal C.

While, no — no one is talking about a literal black hole hidden inside of a proton (that doesn't make sense), discovering similar physics on such a tiny scale signifies a rare overlap in the way we describe the physical universe — where theories about extremely big things also describe hidden features of unspeakably small things.

Quantum entanglement, protons, and black holes walk into a bar

Inside protons, there are several fragments that need to be maximally entangled with one another — if this isn't the case, then theoretical predictions wouldn't match data from experiments, according to the study. The model described by the theory allows the scientists to propose that, contrary to consensus, the physics going on inside protons might have a lot in common with entropy or temperature.

And these processes are most pronounced when dealing with exotic objects, like black holes.

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Two theorists are behind this study: Krzysztof Kutak from the Institute of Nuclear Physics of the Polish Academy of Sciences (IFJ PAN), in Poland's Cracow, and Martin Hentschinski, of the Universidad de las Americas Puebla, in Mexico.

Together, the two evaluated a scenario where electrons are shot at protons. An incoming electron with a negative electric charge, upon nearing a positively charged proton, will interact — resulting in the latter deflecting the former into a new pathway.

Electromagnetic interaction is when a photon is exchanged between the proton and electron — the stronger the two particles interact, the larger the change in momentum of the photon, which, in turn, cuts the time of the electromagnetic wave.

Bringing entropy into proton physics signifies black holes

"If a photon is 'short' enough to [fit] inside a proton, it begins to 'resolve' details of its internal structure," said Kutak, in a report from SciTech Daily. "The result of interacting with this sort of photon can be the decay of the proton into particles. We have shown that there is entanglement between the two situations. If the observation by the photon of the interior part of the proton leads to its decay into a number of particles, let's say three, then the number of particles originating from the unobserved part of the proton is determined by the number of particles seen in the observed part of the proton."

There is much more to the procedure of the research, but the recent tendency among quantum physicists of linking entropy with the internal state of a proton — via a well-known concept of classical thermodynamics — has enabled scientists to measure the degree of disordered motion among particles in an analyzed system. This disordered state gives systems high entropy, with order corresponding to low entropy.

As above, so below - And recent findings show that this is how things are inside the proton, which means physicists can describe entanglement entropy in that context. But, there remain many physicists who are resolute in their conviction that the protons are themselves a pure quantum state, which would mean we can't describe them with entropy. And the new study takes a massive step in bringing the entanglement thesis into prominence, for the proton. This relates to a wide spectrum of concepts — most notably the surface area of a black hole. And this means the beginning of a new and exciting field, in dire need of further investigation.

Study Abstract 

We investigate the proposal by Kharzeev and Levin of a maximally entangled proton wave function in Deep Inelastic Scattering at low x and the proposed relation between parton number and final state hadron multiplicity. Contrary to the original formulation we determine partonic entropy from the sum of gluon and quark distribution functions at low x, which we obtain from an unintegrated gluon distribution subject to next-to-leading order Balitsky–Fadin–Kuraev–Lipatov evolution. We find for this framework very good agreement with H1 data. We furthermore provide a comparison based on NNPDF parton distribution functions at both next-to-next-to-leading order and next-to-next-to-leading with small x resummation, where the latter provides an acceptable description of data.
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