Even the heaviest particles experience the usual quantum oddities, a new experiment shows.

One of the most surprising predictions in physics is entanglement, a phenomenon in which objects can be far apart and still be linked together. The best-known examples of entanglement involve tiny particles of light (photons) and low energies.

At the Large Hadron Collider in Geneva, the world’s largest particle accelerator, an experiment called ATLAS has just discovered entanglement in pairs of top quarks: the heaviest particles known to science.

The results are described in a new paper by my colleagues and me in the ATLAS collaboration, published today in Nature.

What is entanglement?

In everyday life, we think of objects as either “separate” or “connected.” Two balls a mile apart are separated. Two balls connected by a piece of string are connected.

When two objects are “entangled,” there is no physical connection between them, but they are not really separate either. You can measure the first object, and that is enough to know what the second one is doing, even before you look at it.

The two objects form a single system, even though there is nothing connecting them. This phenomenon has been demonstrated with photons located on either side of a city.

The idea will be familiar to fans of the recent streaming series 3 Body Problem, based on the science fiction novels by Liu Cixin. In the series, aliens have sent a tiny supercomputer to Earth, to disrupt our technology and allow them to communicate with us. Because this tiny object is entangled with a twin on the aliens’ home planet, they can communicate with it and control it, even though it is four light-years away.

This part of the story is science fiction: entanglement doesn’t actually allow signals to be sent faster than light. (It seems like entanglement should allow this, but according to quantum physics it can’t. All our experiments so far are consistent with this prediction.)

But entanglement itself is real. It was first demonstrated for photons in the 1980s, in what was then a cutting-edge experiment.

Today, it is possible to buy from a commercial supplier a box capable of producing pairs of entangled photons. Entanglement is one of the properties described by quantum physics and one of the properties that scientists and engineers are trying to exploit to create new technologies, such as quantum computing.

Since the 1980s, entanglement has also been observed with atoms, with some subatomic particles, and even with tiny objects undergoing very, very slight vibrations. These examples are all at low energies.

The new development from Geneva is that entanglement has been observed in pairs of particles called top quarks, where vast amounts of energy are found in a very small space.

So what are quarks?

Matter is made of molecules; molecules are made of atoms; and an atom is made of light particles called electrons, orbiting a heavy nucleus at the center, like the sun at the center of the solar system. We already knew this from experiments done around 1911.

We then learned that the nucleus is made of protons and neutrons, and in the 1970s we discovered that protons and neutrons are made of even smaller particles called quarks.

There are six types of quarks in total: the “up” and “down” quarks that make up protons and neutrons, and then four heavier ones. The fifth quark, the “beauty” or “bottom” quark, is about four and a half times heavier than a proton, and when we discovered it, we thought it was very heavy. But the sixth and final quark, the “top” quark, is a monster: slightly heavier than a tungsten atom and 184 times the mass of a proton.

No one knows why the top quark is so massive. That’s precisely why it’s being studied so intensively at the Large Hadron Collider. (In Sydney, where I’m based, most of our work on the ATLAS experiment focuses on the top quark.)

We think the very large mass of the top quark could be a clue. Perhaps the top quark is so massive because it experiences new forces, beyond the four we already know. Or perhaps it has some other connection to the “new physics.”

We know that the laws of physics, as we currently understand them, are incomplete. Studying the behavior of the top quark could point us toward something new.

So does entanglement mean that top quarks are special?

Probably not. Quantum physics says that entanglement is common and that all sorts of things can be entangled.

But entanglement is also fragile. Many quantum physics experiments are performed at extremely low temperatures, to avoid bumping into the system and disrupting it. So far, entanglement has been demonstrated in systems where scientists can create the right conditions to make the measurements.

For technical reasons, the top quark’s very large mass makes it a good laboratory for studying entanglement. (The new ATLAS measurement would not have been possible for the other five types of quarks.)

But top quark pairs won’t be the basis of any practical new technology: you can’t take the Large Hadron Collider and carry it around. Still, top quarks provide a new kind of tool for doing experiments, and entanglement is interesting in its own right, so we’ll keep looking to see what else we can find.

This article is republished from The Conversation under a Creative Commons license. Read the original article.