The greatest machine ever built is taking a well-earned breather.

Adam Spencer
2 days ago
5 min read

On 29 June, the Large Hadron Collider smashes its last protons for four long years. NerdNews raises a glass to the 27-kilometre marvel that caught the Higgs, and peers down the tunnel at what its supercharged successor might find.

(First published on my Substack where you can get #NerdNews, marvellous maths and general geekery.)

The bling ring thing.

One hundred metres underground, beneath farmland on the French-Swiss border, sits a ring of pipe 27 kilometres around that holds the most extraordinary machine our species has ever built. The Large Hadron Collider takes protons, the tiny hearts of hydrogen atoms, accelerates them to 99.9999991 per cent of the speed of light, and steers two beams into a head-on smash 40 million times every second.

Those protons start somewhere gloriously ordinary. A bottle of hydrogen gas, with the single electron stripped from each atom to leave a bare proton ready for the ring. And while we are dealing with mind-blowing numbers, get this: a single cubic centimetre of hydrogen could run the LHC for over a century.

**(straight down the Atlas barrel: Image: Maximilien Brice/CERN)**

All this takes serious plumbing. The collider is chilled to minus 271.3 degrees, colder than deep space, so that more than 9,000 superconducting magnets can bend the beams without a whisper of resistance. Four cathedral-sized detectors, ATLAS, CMS, ALICE and LHCb, have observed the wreckage of quadrillions of these collisions, each of which for an instant recreates the conditions that defined the cosmos a sliver of a second after the Big Bang.

LHC you later?

Before the switch was first flipped in 2008, a combination of a lack of physics literacy, and humans’ love for a headline, saw some bizarre rumours surface. A noisy handful of doomsayers insisted the collider would spawn a planet-swallowing black hole and rip a hole in the universe itself. Sounds almost feasible? Except that cosmic rays far more energetic than anything the LHC can muster have been pelting the Earth for billions of years, and the planet is still very much here.

As a buddy of mine put it so succinctly;

"Anyone who thinks the LHC will destroy the world is a twat." — Brian Cox, particle physicist and ATLAS collaborator.

**‘Did I mention I’ve met Brian Cox (flex!)?’**

A big Higgs deal.

The collider's crowning moment arrived on 4 July 2012, when the ATLAS and CMS teams unveiled a new particle, roughly 130 times the mass of a proton, weighing in at around 125 billion electronvolts (its mass written as energy, thanks to our good friend E=mc²).

This was the Higgs boson, the final missing piece of the Standard Model. The Higgs is the fingerprint of an invisible field that soaks all of space and hands fundamental particles their mass. The find earned Peter Higgs and François Englert the 2013 Nobel Prize, nearly fifty years after they dreamed it up.

There is a majesty in that moment for me. Super-geeks first postulated the boson in 1964. At the time many thought ‘great theory guys, but we will never be able to test it’. Fifty years later, with Peter Higgs sitting there wiping a tear from his eye, we could tell him, ‘Mate you were right. The LHC found the little bugger!’

But for everything the Higgs gave us, it also came up short of what some experts wanted to know. While the Standard Model is now complete, it still says nothing about dark matter, struggles to explain why the cosmos is built from matter and not antimatter, and leaves gravity out in the cold.

Plenty of physicists had hoped the LHC would also cough up brand-new particles to crack those mysteries open. It has not, leaving unanswered some of the greatest mysteries in modern science.

Another charm offensive.

But it’s not all about the Higgs. The LHC has racked up more than 80 new composite particles, exotic relatives of the proton built from even more fundamental particles called quarks.

Just weeks ago, in the dying days of its current run, the LHCb experiment announced the discovery of the Omega-cc, the last missing member of the doubly charmed baryon family, oddballs that carry two heavy charm quarks apiece.

INSERT IMAGE LHCb

(artist’s impression of an Omega-cc baryon; courtesy Daniel Dominguez/CERN)

Huh? Non-physics speak please, Adam. Fair enough. Picture a proton as a tiny bag holding three quarks, the smallest building blocks we know of. Quarks come in six types, but everyday matter only ever uses the two lightest. The rest are heavier and rarer, and they vanish almost the instant they appear. What LHCb caught is one of those same three-quark bags, with two of its quarks swapped for the weighty "charm" kind.

Cramming two heavyweights into a single particle is fiendishly hard, which is why capturing the final one took a mountain of collisions. This will provide invaluable insights into the strong force, the glue that holds every atomic nucleus together.

For a microscopic mic-drop, it doesn’t get much better than that.

"This is a moment of beautiful historical significance." — Paula Collins, incoming LHCb deputy spokesperson.

Time for a gravitational glow-up.

So why power down a machine that is still bagging discoveries? Because there is far more to find, and the present collider has started to hit the law of diminishing returns. From early July, engineers begin Long Shutdown 3, an overhaul of roughly four years that will transform the LHC into the High-Luminosity LHC.

The job involves swapping out roughly 1.2 kilometres of the ring for new superconducting magnets and ingenious gadgets called crab cavities. This new rig will spit out ten times more data, providing a real shot at catching the vanishingly rare events that slip past unnoticed today.The made-over machine is due to fire up again in mid-2030.

"The High-Luminosity LHC represents a major opportunity for a new discovery." — Mark Thomson, director-general of CERN.

Light at the end of the tunnel.

What might all that extra brightness reveal? Well right near the top of the list is understanding how Higgs bosons interact with one another. Understanding the shape of the Higgs field might even give a hint as to whether our universe might, in some colossally distant future, collapse to a lower energy state, with catastrophic consequences (don’t worry – not for us!).

We can also expect renewed hunts for dark matter and for anything else that dares to break the Standard Model.

Looking further still, CERN is weighing up an even bolder successor. The Future Circular Collider; a ring about 90 kilometres around with an estimated price tag of 10 to 15 billion pounds. Whether the world chooses to build it is anyone's guess.

(Elon, we’re talking chump change my man).

But for now, let’s lift a glass to the greatest machine humanity has ever built.

On 29 June the tunnels under Geneva fall quiet for the first time in years, though the physics won't pause with them: a generation of researchers still has a mountain of collision data to peruse.

The all new, looksmaxxed collider should return around 2030 with ten times the brightness and a fresh crack at the questions the Higgs left hanging.

Lights out for now. Back soon, with an even bigger bang.