The Large Hadron Collider

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Podcast Transcript

Straddling the border of Switzerland and France is the largest scientific instrument ever created. 

It sits in a tunnel 27 kilometers or 17 miles long, at points, it rests 174 meters or 574 feet below the surface, and it cost a whopping €7.5 billion.

It consists of thousands of powerful magnets, one of the world’s largest vacuum chambers and uses a great deal of energy. With it, we can probe the secrets of the basic particles that make up the universe.

Learn more about the Large Hadron Collider, how it works, and why it was built on this episode of Everything Everywhere Daily.

Before we get into the history of the Large Hadron Collider, it is necessary to first talk about what particle accelerators do and why.

As the name would suggest, particle accelerators accelerate particles. Technically speaking, a particle accelerator doesn’t have to be very expensive or sophisticated. 

Certain particles have an electrical charge: electrons, protons and their anti-matter equivalents, positrons, and anti-protons.

If you take a particle with an electrical charge, let’s say an electron with a negative charge, it will be repelled by anything with a negative charge and attracted to something with a positive charge.

Using this property of charged particles, you can pretty easily create a device that could accelerate them. You create two metal plates with holes in them. One has a negative charge, and one has a positive charge.

Put an electron into the hole in the plate with a negative charge, and it will be repelled away and also attracted to the plate with the positive charge. You can then set up another one of these for when the electron passes through the hole in the positively charged plate. 

Put enough of these in series, and you can accelerate an electron to very high speeds.

If you can remember old television sets that had cathode ray tubes, those were particle accelerators. Electrons were shot at a screen which is how an image was made. 

There is a good chance there is an even more powerful particle accelerator not far from where you are right now. Particle accelerators have industrial uses in sterilizing medical equipment, cancer treatments, and viewing inside objects. 

These, however, are a far cry from what physicists use particle accelerators for. 

In the late 19th and early 20th centuries, physicists discovered most of what we know about the basic structure of the atom. They learned, first, that atoms existed and that there were negatively charged things dubbed electrons. Then they also figured out that atoms had a nucleus that consisted of positively charged protons and neutrally charged neutrons. 

That is what most of you probably learned about the atom in physics class in high school. 

However, they soon found out that there was more to it. 

In 1936, while studying high-energy cosmic rays, researchers at Caltech found that were other subatomic particles. They discovered a particle they dubbed a muon. Muons behaved differently than either electrons or protons when they passed through a magnetic field.

Muons were short-lived and created when high-energy cosmic rays from space collided with other particles in the atmosphere. 

The problem with observing particles created by cosmic rays is that you couldn’t really control what was happening. The ability to study these particles was highly random.

The obvious solution was to study these particles in a more controlled environment. To recreate the conditions of high-energy cosmic rays in the laboratory. 

If you remember back to my episode on cosmic rays, they are tiny subatomic particles that travel near the speed of light at extremely high energies. Some come from our sun, but others may have traveled from other parts of the galaxy or even outside the galaxy. 

The tool that was used to do this was a particle accelerator. 

The first particle accelerator for scientific use was built in 1930 before the discovery of the muon. Ernest O. Lawrence at the University of California Berkley created a device known as a cyclotron. 

A cyclotron is a spiral that accelerates particles from the center and holds them in place along the spiral using magnetic fields. 

Lawrence was given the 1939 Nobel Prize in Physics for the invention of the cyclotron. 

The cyclotron was basically a first-generation particle accelerator. The amount of energy that could be put into a particle, in other words, how much it could be accelerated, was limited to the length of the spiral and by the maximum electrical potential that could be achieved in the accelerating region. 

This was solved in the 1950s with the development of the synchrotron.

A synchrotron is a particle accelerator that is a circle. There are two parts to a synchrotron. One part is the acceleration section. This section, as I described above, uses electrical potential to accelerate a particle. 

The rest of the synchrotron consists of magnets that guide the particle along a curved path right back to the acceleration section. This allows the particle to loop around and around, picking up energy the entire way. 

So how much energy are we talking about?

In particular physics, energy is usually given in electronvolts. An electronvolt is a very small unit of energy which is defined as the energy gained or lost by an electron when it moves through an electric potential difference of one volt.

To put this in everyday terms, one electronvolt is about one ten quintillionths of a joule of energy. One joule is approximately the amount of energy required to lift and apple up one meter in the Earth’s gravity. 

So, a single electron volt is really small. The amount of energy in a cosmic ray can be anywhere from 1 billion electronvolts to 8 trillion electronvolts. Naturally, lower-energy cosmic rays are more common, and very high-energy cosmic rays are very rare.

The more energy a particle has, the greater the collision when it hits something and the greater the ability to smash apart the particle, releasing subatomic particles that wouldn’t be released at lower energies. 

In order to get these very high energies, you need a larger area for acceleration, which means you need a very large synchrotron.

Roughly speaking, the larger the particle accelerator, the higher energy particle you can create, the more you will be to see in the resulting collision. 

This has resulted in increasingly large particle accelerators over time. 

By the 1990s, the largest particle accelerator in the world was the Tevatron, located at Fermilab, outside of Chicago, Illinois. It had a circumference of 6.3 kilometers and could accelerate particles to 900 billion electron volts. 

There was a need for even larger particle accelerators, but at this scale, you entered the realm of extremely big science projects that could only be funded by governments. The costs would run into the billions of dollars and would be on par with the cost of running a space program.

In the 1980s, the United States approved funding for the Superconducting Super Collider or SSC. It would, by a wide margin, have been the biggest particle accelerator in the world, with a circumference of 87.1 kilometers or 54.1 miles. Over 22.5 kilometers or 14 miles of tunnel had been bored in Texas at a cost of $2 billion dollars when the program was canceled in 1993.

The cancellation of the SSC left a massive hole in the world of high-energy physics. 

The Europeans picked up the gauntlet. 

The European Organization for Nuclear Research, known as CERN, was launched in 1954. They operated the Large Electron-Positron Collider, which operated from 1989 to 2000. It was one of the largest particle accelerators in the world, but it eventually reached its limits for what it could do at 209 billion electron volts.

In 1994, just a year after the SSC was canceled in the United States, CERN began working on feasibility plans for a new particle accelerator which they dubbed the Large Hadron Collider (LHC).

Here I should take a moment to note what a hadron is. A hadron is a subatomic particle that is made up of other smaller subatomic particles called quarks. Because they are made up of smaller particles, they are uniquely suited to be studied in particle collisions. 

A more in-depth discussion of what is called The Standard Model of particle physics I will do in a future episode. 

Approval for the LHC was given in 1995 with a budget of 2.6 billion Swiss francs. The LHC was to be 27 kilometers or 17 miles in circumference, almost five times the size of the previous largest supercollider. It lies in both Switzerland and France and actually makes four border crossings along its loop.

Construction took years, and there were various setbacks, including problems with the superconducting magnets and leaks in the vacuum-sealed tube.

However, on September 10, 2008, the first beam was sent around the collider. These were actually at very low speeds and took almost an hour to travel the complete circuit. 

On November 9, 2009, they managed to accelerate particles to 1.18 TeV, beating the record previously set by the Tevatron.

2010 and 2011 saw increased energies in their particle beams, and as they continued to run collisions, teams of researchers began to see the thing that they hoped to find. Proving or disproving the existence of the Higgs Boson particle was one of the primary reasons why the LHC was built. 

In 2012, it was accounted that they had conclusive proof of the existence of the Higgs Boson particle. Two different teams running different experiments and kept apart from each other so they couldn’t share information came to the same conclusion.

The confidence of the discovery was that it could only be one in three million odds that it was chance. 

The 2013 Nobel Prize was awarded for the discovery of the Higgs Boson. One of the big debates in awarding the prize was who to award it to as there were literally thousands of people who took part in the discovery. 

From 2013 to 2015, the LHC was shut down for upgrades. When it was fired back up in 2015, it was able to fire protons of 6.5 trillion electron volts and have them collide with each other with a total energy of 13 trillion electron volts. 

It was shut down again from 2018 to 2022, and as of the time of this recording, it is operational again. It is scheduled to shut down for upgrades in 2026. One of its primary objectives now is searching for a potential 5th fundamental force in nature. 

Despite being the most powerful particle accelerator on Earth with plenty of years of operation ahead of it, there is now talk about building a successor to the LHC. 

The new proposed CERN particle accelerator would be 100 kilometers in circumference, almost four times the size of the LHC. They would be able to accelerate particles over six times the energy LHC, and much of it would be in a tunnel underneath Lake Geneva.

The Chinese government has also proposed its own 100-kilometer particle accelerator known as the Circular Electron Positron Collider.

There has even been talk of restarting the American Superconducting Super Collider, but the odds of that happening are pretty slim.

There are still many unanswered questions in physics that might require an even more powerful particle accelerator to answer. These include the mystery of dark matter and dark energy, the prevalence of matter over antimatter in the universe, and the nature of the neutrino. 

The bigger these particle accelerators get, the more money they require and the more difficult it will be to get these projects approved. 

Wherever and whenever these future super particle accelerators are built, they may help unlock the remaining secrets of the universe.