Universe

Quark-Gluon Plasma Is What Scientists Call A "Nearly Perfect" Fluid

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Long, long ago, before matter existed, the universe was a super hot, impossibly dense mass that violently expanded in an event known as the Big Bang. A millionth of a second later, that mass had turned into a dense plasma that was so hot that protons and neutrons couldn't even form yet. The more we know about how that plasma behaved, the more we'll know about the early universe, which is why scientists have been hard at work creating it in giant particle accelerators. What they've learned about it is beyond bizarre.

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Who's Down With QGP?

The elementary particles that made up the early stuff of the universe are quarks (the building blocks of protons, which in turn are the building blocks of atoms) and gluons (the particles responsible for the strong force, which holds those quarks together). Together, they make up quark-gluon plasma, a substance hundreds of thousands of times hotter than the sun that physicists have described as a "nearly perfect" fluid. It's exotic and fleeting and you know those physicists want to play with it.

In 2005, they got their first chance: by sending gold nuclei careening through a 2.4 mile (3.9 km) ring at nearly the speed of light until they smashed into one another. In those collisions, the nuclei heat up and break apart into their elementary particles, forming the quark-gluon plasma. That plasma only lasts for 10-23 seconds before it cools, leaving behind particles that bear the evidence of what once was — but that's enough for scientists to make some pretty cool observations.

You Spin Me Right Round

Plasma is usually described as an ionized gas, which is why the first thing scientists learned about quark-gluon plasma was so surprising: it behaves like a liquid. But not just any liquid: it's nearly frictionless. For comparison, take a fluid like honey. Honey has high viscosity, which means it's resistant to flow, and that different parts of it move in their own directions — as anybody who's struggled to free the remnants from a bear-shaped bottle can attest. Water, by contrast, has low viscosity. Turn a bottle over, and water flows out easily, with most of it going in the same direction. Quark-gluon plasma has near-zero viscosity. Its particles take coordinated paths, moving together with an ease that's never been seen in any other material.

In 2017, physicists discovered something else amazing about this exotic substance. Not only is it the least viscous fluid ever; it also has the highest vorticity — swirl speed, basically. That makes sense, according to the researchers. "Viscosity destroys whirls," said Ohio State University physicist Michael Lisa. "With QGP, if you set it spinning, it tends to keep on spinning." That spin is faster than the cores of super-cell tornadoes, the churn of Jupiter's Great Red Spot, and the swirl of superfluid helium, which has the fastest spin on record. Physicists aren't done studying this strange substance, and they're confident it has more secrets up its sleeve.

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