What are we and the whole universe made of?


How is it possible that water, steam and ice are the same? What is light? Why do the 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 so-called Standard Model is the theory that represents the best understanding of the subatomic world to date. It is a legacy of the 20th century and the foundation of modern technology. Despite its extraordinary success, the theory conceals great mysteries to which it cannot answer. Yet this is the best way available to theoretical and experimental physicists today to explain 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 composed of only 17: 12 matter particles, 4 force-carrying particles and a very special one, the Higgs boson. Matter particles are organized into three families. The first family is made up 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” into particles of the first family and are therefore difficult to find in nature. Experimental data indicate 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 negatively charged electron is called positively charged positron. The simplest anti-hydrogen atom was created with antiparticles.

There could therefore exist an entire universe made of antimatter very similar to ours. We also know that if we put matter and antimatter together, the two 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 during the Big Bang, how did only matter survive in the universe?

The forces that bind them

For matter to exist, there must be forces that hold particles of matter 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 which maintains the electrons attached to the nucleus of the atoms; the W and Z bosons for the weak force responsible for radioactivity or powering the sun; and the gluon, carrier of the strong force that binds quarks within protons and neutrons, also allowing them to be held together in the atomic nucleus.

But what about the force of gravity? The force with which we are most familiar, we don’t know how to describe on 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 force classes.

The Higgs field gives the mass of the particles.

The last element in 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 can be created by exciting the “water” of a pond, which would be the energy field, by throwing a stone, for example.

The Higgs field pervades the entire Universe, creating a kind of sticky vacuum. As the particles interact with this field, they become slower and heavier. If the particles do not interact, they have no mass, this would be the case for photons of light. The greater the force of interaction, the more massive the particle. This is how elementary particles acquire their mass.

It happened very quickly, well under a second after the Big Bang. Before this moment, the Higgs field was zero, the particles had no mass and moved at the speed of light. Everything would have been very different without this 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 can’t explain is also how neutrinos acquired mass. According to the model, they shouldn’t have it, but they do.

We only know 5% of the universe

However, 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 up to 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 represents only 5% of the Universe, according to astronomical observations. The remaining 95% is totally unknown and corresponds to what we call dark matter and dark energy.

The most sophisticated microscopes in the world

In order to be able to answer all the puzzles that remain to be solved, we must push technology to its limits, design and build very powerful experiments, which must process and analyze enormous amounts of data.

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

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

The LHC and its experiments are now even more powerful, thanks to the technological work carried out over the past three years by physicists and engineers. They will begin 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 around the world working together to decipher the laws of nature. Solving these puzzles will lead to a new conception of the world, with its consequent technological revolution, perhaps marking the beginning of a new era for humanity.

Character font: Maria José Costa Mezquita / THE CONVERSATION

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

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