“We are made of star-stuff,” as the great Carl Sagan once succinctly stated. Everything you know, even yourself, is all made of the same fundamental particles.
But at the start of the universe, none of these particles had mass; they all moved at the speed of light. It is only because particles got their mass from a fundamental field linked to the Higgs boson could stars, planets, and life form.
Or so the theory goes. But, this idea got some serious actual support when the Higgs boson particle was found at CERN in 2012, finally proving that this field gives matter, well mass.
Needless to say, this was a big deal in the world of physics! Why this was such a big deal is that the Standard Model (more on that later) accounts for all 17 of the elementary particles and three of the four fundamental forces that make up our universe.
These are, in effect, the LEGO bricks of the universe! But, they wouldn’t exist without the so-called Higgs boson.
So what is it? Let’s find out.
What is the Higgs boson?
Back in 1964, English physicist Peter Higgs submitted a paper to a scientific journal that contended that all of space is filled with a field, which came to be called the Higgs field, that imparts mass to objects. Scientifically, mass is defined as the resistance offered by a body of matter to a change in speed or position on the application of force.
For some eminent scientists at the time, including the late, great, Stephen Hawking, the concept of a field imparting mass seemed ludicrous.
He actually made a $100 wager with physicist Gordon Kane that physicists wouldn’t find the Higgs boson. When physicists found the particle in 2012, Hawking lost his bet and said that the discovery made physics less interesting.
Not only had he lost his bet, but the discovery made him come to a very dire conclusion about the particle. He explained in a book of essays and talks called “Starmus,” that the particle could one day cause the end of the universe as we know it.
Scientists besides Hawking agree with this. The theory of a Higgs boson doomsday has been around for a while. It says that a quantum fluctuation could cause a vacuum “bubble” that will expand through space and destroy the universe. However, scientists don’t think this will happen any time soon.
But why? And how?
You can think of the Higgs field this way: Push a ping-pong ball through the air and it moves almost without resistance, but push that same ping-pong ball through water, and it will be much harder to push. The Higgs field is a bit like water.
When the scientific journal initially rejected Higgs’ paper, he revised it with the significant addition that his theory predicted the existence of a heavy boson.
In the 1970s, physicists realized that there are very close ties between the weak force and the electromagnetic force. They developed the basic equations of a unified theory which proposed that electricity, magnetism, light, and some types of radioactivity are all manifestations of a single force known as the electroweak force. This force is carried by the photon, and the W and Z bosons.
But there was a problem. The equations predict that these particles have no mass, and physicists already knew that the W and Z bosons have mass. Fortunately, theorists Robert Brout, François Englert, and Peter Higgs made a proposal to solve this problem. They proposed that the W and Z bosons interact with a force called the “Higgs field”. The field gives mass to the particles exchanged in weak interactions but not to the photons exchanged in electromagnetic interactions. The stronger a particle interacts with the Higgs field, the heavier the particle ends up being.
Gradually, other physicists came to realize that Higgs’ idea fit perfectly with the equations of the Standard Model. The only problem was that there was no experimental evidence to back up the theory. If the Higgs field existed, it should involve a gauge boson (a “force-carrier” particle that mediates or transmits the electromagnetic force), which was called the Higgs boson, and physicists’ calculations showed that the Higgs boson should be very massive and that it should decay almost immediately.
How do you induce such a massive and ephemeral particle to appear? It would take another 30 years before particle colliders, detectors, and computers capable of looking for Higgs bosons were created.
Enter the Large Hadron Collider.
What is the Standard Model in physics?
The Standard Model first began taking shape in 1897, when the English physicist J.J. Thomson discovered the electron, and it wasn’t considered “complete” until 2012, with the discovery of the Higgs boson.
As the chart above shows, our universe is comprised of six quarks and six leptons. These are the particles that make up atoms — quarks within protons and neutrons, and electrons surrounding the nuclei.
Four fundamental forces are at work in our universe: electromagnetism, the strong force, the weak force, and gravity. Unfortunately, the Standard Model cannot account for gravity (if indeed it is a real force), so for now, we’re going to have to ignore it.
The remaining three forces result from the exchange of “force-carrier” particles, or gauge bosons. Particles transfer discrete amounts of energy by exchanging bosons with each other. Each fundamental force has its own corresponding boson.
The Electromagnetic Force is transmitted between electrically charged particles by the photon, which is massless. The Weak Force is transmitted between quarks and leptons by the W+, W−, and Z gauge bosons, which are massive particles, with the Z boson being more massive than the W±.
The Strong Force is transmitted between quarks by eight gluons, which are massless. Quarks and gluons are “color-charged”. Color-charged particles exchange gluons in strong interactions. Two quarks can exchange gluons and create a very strong color field that binds the quarks together. Quarks constantly change their color charges as they exchange gluons with other quarks. Because gluons themselves have a color charge, they can interact with one another.
Standing by itself on the far right side of the Standard Model chart, like a king or queen, is the Higgs boson. It may not be farfetched to call it royal. In fact, the physicist Leon Lederman once famously dubbed it “The God Particle”. Lederman coined that phrase for the title of his 1993 book, The God Particle: If the Universe Is the Answer, What Is the Question?
What does the Large Hadron Collider have to do with the Higgs Boson?
The Large Hadron Collider (LHC), which opened in September 2008, is located at CERN, or the European Council for Nuclear Research. It is a 17-mile-long (27.35 km) ring that runs primarily beneath Geneva, Switzerland, and it uses around 9,000 superconducting magnets to corral millions of protons that are circling the ring in both directions, at close to the speed of light.
At specific points along the ring, the two proton beams collide and produce sprays of particles which are observed by enormous detectors. On July 4, 2012 physicists around the world gathered in meeting rooms to hear and see a press conference being given at CERN.
The purpose of the press conference was to announce the discovery of the Higgs boson and in the audience was 83-year-old Peter Higgs. The video of Higgs taking out his handkerchief and wiping his eyes went viral.
In 2013, a year after the discovery of the Higgs boson, Peter Higgs, along with François Englert, was at last honored with a Nobel Prize in Physics. On the day of the Nobel announcement, Higgs, who doesn’t own a cell phone or have an email, went to the store and it was only when he bumped into one of his neighbors that he found out that he had won the prize.
What is the Higgs field?
The Higgs field differs from other fields, such as electromagnetic or gravitational fields, in that it is unchanging. The strength of an electromagnetic field waxes and wanes depending on the distance. The strength of a gravitational field is also determined by distance — stand next to a black hole and you’ll experience a much stronger gravitational field than you would be standing on Earth.
By contrast, the Higgs field appears to be the same no matter where you are in the universe, and it appears to be a fundamental component of the fabric of space-time. The property of “mass” is a manifestation of potential energy transferred to elementary particles when they interact with the Higgs field, which contains that mass in the form of energy.
Spin is the intrinsic angular momentum of an elementary particle. In quantum field theory, the spin of a particle is related to its behavior. For example, bosons have an integer spin (0, 1, 2, etc), and so can occupy the same quantum state at the same time. In contrast, particles with half-integer spin (1/2, 3/2, etc) cannot. In the Standard Model, the components of matter (electron, quarks, etc.) are half-integer spin particles, while the particles which transmit force (photon, W/Z, gluon) are integer spin particles.
The Higgs field is the only scalar, or spin 0, field. The Higgs field imparts large masses to the W and Z gauge bosons. Their masses affect how far the W and Z bosons can travel, thus confirming the weak force’s extremely short range.
The Higgs boson is a massive scalar boson, having zero spin, no electric charge, and no color charge. As predicted, it has a hefty mass of 125 GeV, and a predicted mean lifetime of 1.56×10−22 seconds. The Higgs boson has been observed decaying into a pair of bottom-antibottom quarks, two W bosons, a tau-antitau pair, two Z bosons, and two photons. It is also predicted to decay into two gluons, a muon-antimuon pair, and possibly others particles.
While the Higgs field generates the masses of the leptons — the electron, muon, and tau — and the masses of the quarks, it does not generate mass for the photon and the gluon. And, because the Higgs boson is itself massive, that means that it must itself interact with the Higgs field.
The future of the Higgs field
Currently, scientists are trying to determine if the Higgs field gives mass to the three “flavors” of neutrinos — electron neutrinos, muon neutrinos, and tau neutrinos. It was long believed that neutrinos were massless, however, it is now known that each neutrino has its own distinct mass.
In addition, physicists now believe that 95 percent of our universe is not made of ordinary matter, but consists of dark energy and dark matter. Scientists at CERN are trying to determine if dark energy and dark matter interact with the Higgs field.
According to CERN, dark matter has mass, and physicists have suggested that dark-matter particles could interact with the Higgs boson, with a Higgs boson decaying into dark-matter particles.
Even though finding the Higgs boson appeared to complete the standard model (in effect), scientists have not stopped looking into this elusive particle. Since 2012, one of the most important things learned is that the Higgs particle breaks down.
And more will be learned about this elusive particle during run 3 of the LHC and especially when the high luminosity upgrade to the particle accelerator is finished in 2029.
This will allow the LHC to have more collisions, giving scientists more chances to explore strange physics, like things that don’t fit into the standard model.
After the upgrade, CERN thinks that the accelerator will make 15 million of these particles every year. This is a big difference from 2017 when the LHC made 3 million Higgs bosons. This could be the key to finding other types of Higgs bosons.
Theories that go beyond the standard model of particle physics also predict that there could be up to five different types of Higgs boson, which may each be less common than the main Higgs boson. Even before the upgrades, scientists had already given us hints of a “magnetic Higgs boson.”
Exciting times ahead, if you are a particle physicist that is.