What does your weight on a bathroom scale, the expansion of our universe today, and the Big Bang have in common? If modern ideas in physics are correct, they are all caused by a new family of particles called "spin-zero bosons." Like coats of paint on a wall, these particles represent new fields embedded in space. Let's have a look!
(Credit: USAF)
The Higgs Field
Discovered in 2012 at the Large Hadron Collider in CERN, Higgs bosons represent "quanta" of the Higgs field. They interact with quarks, electrons, and the other known fundamental particles to give them the quality we call mass. Higgs bosons are fundamental particles. The current standard model of physics says that they have no internal structure, just like the more familiar quarks, electrons, gluons, neutrinos, and photons. Some theories, such as "technicolor" theories, disagree, but they have yet to be experimentally verified.
The Higgs field represents the primer coat of paint on your walls. It is present everywhere in the universe at exactly the same strength, so an electron or a quark in our solar system has exactly the same mass as its cousin in a distant galaxy across the visible universe. This has been the case for the Higgs field since about one thousand-trillionth of a second after the Big Bang, when the masses of electrons and quarks and the other particles became important in defining what our universe would look like.
When the universe was very hot and young, the Higgs field particles only weakly interacted with each other. As the universe cooled, these interactions became stronger and stronger. The result was that the Higgs bosons gained mass as the universe cooled. As they continued to interact with electrons and quarks, these particles also gained mass, having originally been completely massless. Today the Higgs field, which permeates all of space, acts like an invisible molasses that elementary particles interact with and travel through.
So today, when you weigh yourself on the bathroom scale, 96 percent of your mass is the energy of the (gluon) fields holding the quarks in your protons and neutrons together, while the remaining 4 percent is a gift from the Higgs field! If it were not for the Higgs field, you would be made entirely of invisible field energy, not matter as we have come to know it! Your constituent massless quarks and electrons would be buzzing about at exactly the speed of light. It's that 4 percent that anchors you to the here and now.
The Dark Energy Field
Our universe has been in a state of expansion for over 13.8 billion years. In the 1990s astronomers discovered that the expansion rate is actually getting faster and faster as the universe grows older. This switch from constant to accelerated expansion began about 7 billion years ago. The only way the mathematics of the Big Bang makes sense in terms of Einstein's theory of general relativity is if this accelerated expansion were caused by a new field in nature that exists everywhere in space. The only fields that can have this property and satisfy relativity (looking the same for all places and times) are fields with spin-zero, like the Higgs field. So the discovery of the accelerated expansion of our universe is also the discovery of the handiwork of a new sibling to the Higgs field.
Currently there are no direct observations of the particle related to this "dark energy" field. Given that this effect is only detected at scales of hundreds of millions of light years, it will be very hard if not impossible to isolate or manufacture the particle and study its field. It is frustrating to know that this acceleration is occurring and is probably the result of a hidden field in nature without being able to directly study it in our research labs!
The Inflaton Field
In 2014 astronomers announced the detection of gravity B-modes in the cosmic background radiation. This technically difficult measurement confirmed that the universe indeed went through a period of rapid expansion when it was about a trillion-trillion-trillionth of a second old. It was widely hailed as confirmation of the inflationary Big Bang theory.
Before inflation the universe expanded at a much slower rate. Space (actually spacetime) consisted of the gravitational field of the intense matter and energy of this era, but painted on top of this was a new field, hypothetically called the inflaton field. Like the Higgs and "dark energy" fields, it was a spin-zero field. Because of quantum variability, the field was not perfectly smooth but more intense in some regions of spacetime than in others. As the universe expanded and cooled, the inflaton field tried to quickly cool down as well, but instead it lagged behind the cooling universe. This caused one of the many microscopic quantum patches of this field to start expanding at an exponential pace. Eventually, when the cooling had completed itself and the inflaton field was finally at its lowest energy, like water cooling to ice, the expansion rate slowed down and inflation stopped. We live within one of these inflated patches today.
The way the inflaton field cooled as it expanded was by raining out particles from this field. These particles quickly decayed into matter, antimatter and other particles. Because there were about 10 billion and one matter particles for every 10 billion antimatter particles, after all the annihilation was finished, we ended up with 10 billion photons of light for every quark we see around us today, with no surviving antimatter at all! Dark matter was also produced in this mix and has survived to the present time. In the other patches different conditions may have resulted in a carpet of multiverses! After inflation this field completely vanished from the universe.
So spin-zero fields are more than a mathematical curiosity. They are essential to our universe and account for some of its most important and peculiar properties today!