heavy ion collision

The pendulum in these clocks doesn't swing from a spring or a weight, but from a tiny kick inside the atomic nucleus. Ordinary atomic clocks keep time by the oscillations of electrons, but here the pendulum is the nucleus itself — a dense ball of protons and neutrons.

An old factory where instead of machines there are atomic nuclei, and neutrino radiation seethes all around. When a massive star exhausts its fuel, its core compresses a hundredfold, and the temperature skyrockets to billions of degrees.

In accelerators like the Large Hadron Collider, heavy nuclei collide at enormous speeds. For an instant, quark-gluon plasma (QGP) is born — a state of matter where quarks and gluons float freely, just like in the first microseconds after the birth of the universe. This plasma is not just hot.

At accelerators, by smashing heavy nuclei, physicists briefly create a quark-gluon plasma — a state of matter where quarks and gluons are not confined inside particles but are free. For a long time, it was imagined as a gas, but experiments showed it's an almost perfect liquid.

The story began almost a century ago, when Edwin Hubble showed that galaxies are receding, and Fritz Zwicky and Vera Rubin later realized: to explain their motions, invisible mass is needed — dark matter.

Atomic nuclei are not always like billiard balls. Some are elongated, like cigars, others are flattened. But xenon-129 resembles a potato — a bumpy triaxial ellipsoid.

Inside a neutron star, matter is squeezed so hard that atomic nuclei stop being separate clumps. Neutrons and protons get closer together, and their innards, quarks, begin to feel their neighbors through the walls of their 'bags'. A neutron star is a sphere about the size of a small city but with a mass of one and a half Suns.

Ice, water, steam — phase transitions we all know. But what happens if you squeeze and heat an atomic nucleus itself? Theorists think protons and neutrons inside it 'melt,' releasing smaller building blocks — quarks and gluons.

Deep inside the detector at the Large Hadron Collider, protons collide, and for a fleeting moment something heavy is born. It instantly shatters into two Higgs bosons — particles that, like nesting dolls, each hide two pairs of b-quarks.

Inside the proton, life is boiling. Quarks don't just sit there: they're glued together by carrier particles called gluons (from the word glue). Usually, this glue is spread evenly, like butter on a skillet. But when energies become enormous, gluons start clumping together. This is the gluon condensate — an ultra-dense state of the gluon field.

If you stick two identical thermometers into a pot of hot water, they'll both read the same, and we relax, thinking the temperature is measured correctly. But in a rarefied gas heated to millions of degrees, this trick stops working.

The Higgs boson is like a conductor that gives mass to all other particles. Without it, electrons would be massless and atoms would fall apart. But how does the conductor interact with itself? That is the key question a future muon collider aims to answer.

In a giant particle accelerator, particles smash into each other, and sometimes after the collision only two photons, particles of light, remain. Physicists can predict how often this happens, but their calculations have long disagreed with what detectors see. Each refinement of the theory changed the answer, and there was no consensus.

In collisions of heavy nuclei at colliders, quark-gluon plasma is born — a state of matter where quarks and gluons are as free as water in steam. Heavy quarks, such as b-quarks, entering this plasma lose energy, and their bound states, bottomonia, are destroyed.

In a dark room, an invisible lamp flashes. Its light is unlike anything familiar: it has no steady brightness, only rare but powerful bursts. This is bright squeezed vacuum — a state of light with no ordinary wave but strong quantum fluctuations. It is with such light that physicists bombarded xenon atoms.

When heavy nuclei collide in accelerators, a multitude of particles is produced, and physicists want to understand how electric charge moves through this chaos. Two trains crash into each other: the passengers (quarks) scatter, but their luggage (charge) may end up far from the crash site.

In plasma where some atoms remain neutral, magnetic field lines can rearrange at different speeds. This is like two rubber bands that are initially stuck together, then suddenly snap apart and contract, releasing energy.

In collisions of heavy nuclei, a fireball of thousands of particles is born. Among them are pions and kaons, two kinds of light particles that look very much alike. To understand what happens in this fireball, physicists need to know exactly how many of each particle flew out.

In the 2010s, physicists working at the Large Hadron Collider learned to create in the lab a substance that doesn't exist in the ordinary world.

The atomic nucleus is not a solid ball but a drop of liquid that can be squeezed. To understand how elastic it is, physicists accelerate gold nuclei and smash them into each other. On impact, the matter compresses to densities like those in a neutron star, then flies apart. The shape of this debris tells us about the properties of the matter inside.

A laser strikes a target, and a cloud of plasma, accelerated to hundreds of kilometers per second, shoots into the chamber. The chamber isn't empty: it's filled with a tenuous gas that plays the role of the cosmic medium. The plasma slams into this gas like a speedboat hitting still water, shoving it aside.

Ten microseconds after the Big Bang, the Universe resembled a pot of boiling broth. Floating in it were quarks and gluons — the particles that would later assemble into protons and neutrons. As the broth cooled, at some point the quarks clumped together into lumps — the very protons and neutrons that make up all visible matter.

Two spinning tops are set off simultaneously in opposite directions. If one spins left, the other always spins right — no matter how far apart they fly. That's roughly how quantum entanglement works, except instead of tops, we have top quarks, the heaviest known particles.

Water in a kettle heats to 100 degrees, and stops being water, turning into steam. Something similar happens to atomic nuclei when they are smashed together at enormous speeds in the Large Hadron Collider.