The Microscopic Universe

FAS Astronomers Blog, Volume 31, Number 5.

This is part 4 of a 5-part series on the Universe (The Visible Universe, The Dark Universe, The Expanding Universe, The Microscopic Universe, and The Multiverse).

The universe is huge and filled with light. We can see out 46 billion light-years in any direction. It is full of stuff, including stars, planets, galaxies, and galactic structures. It is also dark; full of black holes, built with dark matter, and driven by dark energy. However, everything we see, and maybe some things we can’t see, are built from microscopic fundamental particles, and influenced by four fundamental forces.

Things are made of quarks and electrons. Quarks combined in triplets to form protons and neutrons. Protons and neutrons are bound together in atomic nuclei. Atomic nuclei combine with electrons to form atoms. Different combinations of protons yield up to 118 different types of atoms (elements). Atoms bond together to form molecules. Molecules, in turn, bond together to form bigger molecules. Bigger molecules then bond together to form even bigger molecules. Minerals, DNA, amino acids, bases, and many other building blocks of our macro universe are built from these molecules.

The Standard Model

So, let’s go back to the beginning.

The fundamental structure of everything is described by the Standard Model of Particle Physics.

There are Fermions, which are the building blocks, and Bosons, which are the forces.

• Fermions are quarks and leptons. There are six of each. Interesting though, only two quarks and one lepton are important in making things.
  • Quarks come in six flavors: Up, Charm, Top, Down, Strange, and Bottom. The first three have a +2/3 charge, the last three a -1/3 charge.
  • Leptons come in six flavors: Electron, Muon, Tau, Electron Neutrino, Muon Neutrino, and Tau Neutrino. The first three have a negative 1 charge. The last three a neutral charge.
• Bosons are unique for each force: photon (electromagnetic), gluons (strong nuclear force), W^+/- and Z⁰ (weak nuclear force), the Higgs, and there is also the hypothetical graviton (gravity).

Things made up of three quarks (e.g., protons and neutrons) are called baryons. Things made up of two quarks are called mesons.

The nucleus of an atom is composed of nucleons. There are two types: protons and neutrons.

• Protons have a positive charge and are made of two up quarks and a down quark.
• Neutrons have a neutral charge and are made of two down quarks and an up quark.

There are four fundamental forces in nature. Each is carried by a fundamental particle (a boson – see above). In order of strength, the forces are:

• Strong Nuclear force. This force binds the nucleons together. It becomes increasingly stronger at a greater distance, so we can never see individual quarks – only those bound together as nucleons.
• Electromagnetic force. This is electricity and magnetism. It is also light in its many forms.
• Weak Nuclear force. This force doesn’t hold anything together. It does, however, control the decay of atoms.
• Gravity. This is the force we feel every day. It is also the force that holds the moons and planets in their orbits. It is by far the weakest of the four forces. We notice it the most because it is everywhere. It is also the least understood force at the microscopic level. It is thought to be carried by gravitons, but these particles have yet to be found.

The Higgs is an interesting particle. It is a boson that doesn’t mitigate a force but gives mass to some of the other particles. You can learn more about the Higgs in a previous article.

Atoms

Nucleons (protons and neutrons) combine with electrons to create neutral atoms. The number of protons in the nucleus of an atom defines which element it is.

• An element can have several isotopes, which are atoms with the same number of protons, but a different number of neutrons.
• Normal atoms have the same number of electrons as protons giving them a neutral charge. However, atoms can gain or lose electrons creating either negative or positive ions.

There are 118 unique elements that can form atoms. They are most often described using the periodic table.

• Hydrogen is the simplest consisting of a single proton and electron. Although it does have a least two isotopes: deuterium (proton, neutron, and electron) and tritium (proton, two neutrons, and an electron).
• Helium is next with two protons, two neutrons, and two electrons.
• Carbon (6 protons), Nitrogen (7 protons), Oxygen (8 protons), and Phosphorus (15 protons) are four common elements found in nature.
• Heavier elements, such as Uranium (92 protons) are unstable and will decay over time to lighter stable elements such as lead (82 protons).

Molecules

Atoms will bond together to create molecules. Molecular bonds are created because atoms share electrons. Electrons populate different shells around the atomic nucleus. Without going into too much detail, atoms like to have full electron shells. Some elements, for example the noble gases such as Helium (2 protons) and Neon (10 protons), have completely full shells. As such, they don’t combine with other elements to create molecules. Most other atoms have empty spaces, so they tend to bond with other atoms by trading or sharing electrons. Carbon has four electrons in its outer shell – it really wants to have eight. So, it readily bonds with many other elements and creates complex organic molecules.

You are probably very familiar with some of the simple molecules such as Oxygen (O₂), Water (H₂O), Carbon Dioxide (CO₂), Methane (CH₄). Yes, two atoms of oxygen can combine together to create a molecule of oxygen.

DNA, the code of life, is built from molecules.

• There are four (Nitrogen) Base molecules; cytosine (C₄H₅N₃O), guanine (C₅H₅N₅O), adenine (C₅H₅N₅), and thymine (C₅H₆N₂O₂).
• The backbone is a sugar molecule deoxyribose (C₅H₁₀O₄).
• A phosphorus group (PO₄) is found attached to the sugar molecule in the backbone.

RNA is similar, but uracil (C₄H₄N₂O₂) replaces thymine and the backbone is the sugar ribose (C₅H₁₀O₃).

Proteins in the human body are complex molecules built from twenty simpler amino acids. Each amino acid is constructed from four molecules; a central carbon/hydrogen, a carboxyl group (CO₂H), an amino group (NH₂), and a variable group, which defines the specific amino acid.

To learn more about DNA and amino acids, see the article DNA, RNA, Genes, Chromosomes, and the Code of Life.

Rocks are formed from minerals. Minerals have a specific molecular structure and are formed from molecules. Two examples are quartz, made of silica (SiO₂) and calcite, made of calcium carbonate (CaCO₃). To learn more about rocks and minerals, see an earlier article.

A Few Twists

There are, however, a few twists to all this.

The above describes what matter is made of. There is also anti-matter, which does exist, although we don’t see it around us or when we look out into the universe – except in cosmic rays. Each fundamental particle above has a corresponding antimatter equivalent with the opposite electric charge. For example, the electron has the positron, which is just like an electron, but with a charge of +1. One of the outstanding questions in physics is why is there so much matter, but very little anti-matter? Just after the Big Bang, equal parts matter and anti-matter should have been created. So, where is all the anti-matter?

There is also supersymmetry (SUSY), which says that everything has a supersymmetric partner (sparticle). Every fermion has a corresponding boson, and every boson has a corresponding fermion. For example, quarks have squarks, electrons have selectrons, photons have photinos, and gluons have gluinos. There is also a higgsino for the higgs. This is more conjecture at this point and supersymmetric particles have yet to be discovered.

Quantum Mechanics describes the interaction among all these fundamental particles and forces. Quantum Mechanics is strange … very strange. It says that things at this level are not deterministic but are governed by probability. Particles are not fixed objects; they act like waves. The exact position and momentum of a particle is always uncertain. Electrons don’t have a specific position but are more like fuzzy balls of probability. Particles can become entangled where a change to one will instantaneously change the other, even if they are a great distance from each other. This is what Einstein called spooky action at a distance.

This can all become very complicated, so I’ll stop here. Just remember, everything is built from simpler things with quarks and electrons way down at the bottom of it all. Maybe … until we get to dark matter and dark energy … but that’s another story (see The Dark Universe).