What are we and the entire universe made of?

How is it possible that water, steam and ice are the same? What is light? Why do stars shine? What is the origin and destiny of the Universe? The answer to any question about nature lies in knowing the indivisible “bricks” from which everything is made. We continue to explore the “building blocks” of the world and the laws that govern them; that is, the forces between them so that they can come together to form matter: us, the stars, the entire universe.

The 17 known elementary particles

Knowing them is the goal of particle physics. These “bricks” are the elementary particles. The one known as Standard Model it is the theory that so far represents the best understanding of the subatomic world. It is a legacy of the 20th century and the foundation of modern technology. Despite its extraordinary success, the theory holds great mysteries to which it cannot answer. However, this is the best way that theoretical and experimental physicists have today of explaining what matter is made of.

According to this model, the “periodic table” of elementary particles is much simpler than that of chemical elements. Instead of more than 100 elements, it is made up of only 17: 12 matter particles, 4 force-carrying particles and a very special one, the Higgs boson. Particles of matter are organized into three families. The first family is composed of stable particles: the electron, the “up” and “down” quarks that make up the protons and neutrons of atomic nuclei, and the electron neutrino.

The stable matter that surrounds us is composed of stable particles of the first family. The particles of the second and third families are “identical” copies of those of the first, but heavier and more unstable. They quickly “convert” to particles of the first family and are therefore difficult to find in nature. Experimental data indicates that with exactly 3 families of particles we describe all matter, but why 3? Is 3 really a magic number?

There could be an entire universe made of antimatter

Each of these particles also has its antiparticle equivalent, identical but of opposite charge. For example, the antiparticle of the negatively charged electron is called the positively charged positron. has been achieved create the simplest anti-Hydrogen atom with antiparticles.

There could thus exist an entire universe made of antimatter very similar to ours. We also know that if we put matter and antimatter together, both disappear and become an immense amount of energy. The reverse process is also possible, energy can be converted into equal amounts of matter and antimatter. If this is what happened in the Big Bang, how has only matter survived in the universe?

The forces that bind them

In order for matter to exist, there must be forces that hold matter particles together. In the subatomic world, the forces between particles are described by the exchange between them of other particles: the photon for the electromagnetic force that keeps electrons attached to the nucleus of atoms; the W and Z bosons for the weak force responsible for radioactivity or powering the sun; and the gluon, the carrier of the strong force that binds the quarks within the protons and neutrons, also allowing them to be held together in the atomic nucleus.

But what about the force of gravity? Just the force with which we are most familiar we do not know how to describe it at these quantum scales of the subatomic world. The hypothetical graviton, corresponding to the force of gravity, has not been found so far. Gravity is the most “rogue” of the four existing classes of force.

The Higgs field gives particles mass.

The last piece of the Standard Model “periodic table” is the Higgs boson. This particle is the quantum excitation of its quantum field, the Higgs field. The Higgs boson would be the equivalent of the “waves” that we can create by exciting the “water” of a pond, which would be the energy field, by throwing a stone, for example.

The Higgs field permeates the entire Universe, creating a kind of sticky vacuum. As particles interact with this field, they become slower and heavier. If the particles do not interact, they do not have mass, it would be the case of the photons of light. The greater the force of interaction, the more massive the particle. This is how elementary particles acquire their mass.

This happened very soon, in much less than a second after the Big Bang. Before that instant, the Higgs field was null, the particles had no mass and traveled at the speed of light. Everything would have been very different without that appearance of the Higgs field: neither atoms, nor galaxies, nor life would have formed.

Exactly how such a crucial transition for the existence of the universe as we know it occurred remains a great mystery. Among the things we cannot explain is also how the neutrinos gained mass. According to the model they shouldn’t have it, but they do.

We only know 5% of the universe

Now, it is important to emphasize that our mass is much greater than that of the sum of all the elementary particles that we have in our body, electrons and quarks, which only contribute 1%. The rest comes from the energy that holds the quarks together in the protons and neutrons of our atoms.

We go even further: if we consider all known mass, ours, that of stars, galaxies, etc., this only represents 5% of the Universe, according to astronomical observations. The remaining 95% is totally unknown, and is what we call dark matter and dark energy.

The most sophisticated microscopes in the world

In order to be able to answer all the enigmas still to be solved, we need to push technology to the limit, designing and building very powerful experiments, which must process and analyze huge amounts of data.

Particle accelerators are our microscopes. The most powerful in the world, the one with the highest energy, is the accelerator Large Hadron Collider (LHC) at CERN, which accelerates protons to speeds close to the speed of light, to make them collide at certain points, surrounded by gigantic detectors the size of a great cathedral.

These “photographs” with very high resolution and speed the particles that are produced in each collision, providing 40 million “photos” per second. Analyzing these “photos” in exquisite detail, the trail of the Higgs boson was discovered in the ATLAS and CMS experiments, a major milestone recognized with the 2013 Nobel Prize in Physics.

The LHC and its experiments are now even more powerful, thanks to the technological work carried out in the last three years by physicists and engineers. They will start again this summer to explore new frontiers of knowledge, in search of answers to the great mysteries of the universe. This journey to knowledge will last decades and will require the dedication of thousands of scientists from around the world working together to decipher the laws of nature. The resolution of these enigmas will lead to a new conception of the world, with its consequent technological revolution, possibly marking the beginning of a new era for humanity.

Font: Maria Jose Costa Mezquita / THE CONVERSATION

Reference article: https://theconversation.com/what-we-and-the-entire-universe-are-made-of-181422