The universe has been evolving for roughly the last 13.7 billion years. This cosmic evolution, as it is called, started with a period of pure energy right after the Big Bang, until subatomic particles started to appear. According to String or M Theory, these particles where created from vibrations of multi-dimensional space-time. We do not know where these vibrations came from but it seems that the fabric of the universe vibrates in at least three dimensions of space and one dimension of time, and that these vibrations formed the first subatomic particles from which the first atoms were built, but most importantly, they gave subatomic particles certain charges which made them attract or repulse each other. Once we got attraction and repulsion, the rest is prehistory.
These simple atoms formed the first stars from which heavier elements were formed due to the pressure inside the stars. Bigger stars exploded as supernovas and formed all the rest of the heavier elements known. These explosions created lots of gases and particles called nebulas where more stars and, most importantly, planets formed. Since all planets, moons, asteroids and comets are also made from the rests of these nebulas, they contain lots of light and heavy elements from which molecules are produced. These molecules started combining and evolving until very complex organic molecules were created, including amino acids, lipids, RNA, proteins and, eventually, proto-cells where constructed. When DNA evolved inside some of these basic cells, many forms of bacteria and archaea appeared, and later, more complex eukaryotic cells formed the first multi-cellular organisms. The cells in these organisms specialized into organs and neurons from which, eventually, brains where formed. Some of these organisms with brains developed technology and here we are.
But why did this happen? Is all that came after the formation of charged subatomic particles a direct consequence of these charges or is there anything else required for life and for us to be here? Actually, nothing else is required. Living systems exist because charged subatomic particles are moving and those movements are not random but are guided by the attraction and repulsion produced by the values of those charges. Charges have a sign and particles with different sign charges attract each other while those with the same sign charges repel each other.
Subatomic particles are quarks, leptons and bosons. The most important leptons required for life are electrons, and the most important bosons (force particles) are photons and gluons. Force particles have no mass, so when they are exchanged between certain other particles with the same type of charges, only a force is produced. The Higgs boson, for example, gives mass to quarks and leptons.
Quarks and gluons possess a type of charge called “color charge” (nothing to do with their visual color but with the “signs” of their charges, which cannot be called “plus” or “minus” because they are three, so, just for convention, they are called “red”, “green” and “blue”). These color charges produce a force called the “strong nuclear force” which attracts certain types of quarks called “up” and “down” quarks with each other by exchanging gluons (the color force particle). This nuclear force is so strong that quarks cannot exist alone but have to always be joined to other quarks. When one “down” and two “up” quarks of the three different color charges are combined, they form a proton, but when one “up” and two “down” quarks of the three different color charges are joined, a neutron is formed. Nucleons (protons and neutrons) are also attracted to each other by a weaker residual nuclear force which is a secondary consequence of the color charges of quarks. When protons and neutrons are joined, the nucleus of an atom is formed by combining equal numbers of protons and neutrons, since the residual force is equal for both types of nucleons.
Subatomic particles also have another property called electric charge, which can be positive (+) or negative (-). Particles with different signs attract each other while those with the same signs repel each other with a force called the electromagnetic force. “Up” quarks have an electric charge of 2/3, “down” quarks have a -1/3 charge and electrons have a -1 electric charge. This means that a proton will have a sum of +1 (2/3 + 2/3 – 1/3 = 1) and neutrons will sum up to 0 (2/3 – 1/3 – 1/3 = 0). When the atomic nucleus is formed from the combination of protons and neutrons, it will add up to a positive electric charge which equals the sum of all the protons in it (considering that neutrons do not contribute any electric charge). Depending on the number of protons in the nucleus, the same number of negatively charged electrons will be electrically attracted to it, and thus atoms are formed. The electromagnetic force is produced when photons (particles of light) are exchanged between positively charged protons and negatively charged electrons. Since this force is not as strong as the strong nuclear force, the electron will orbit the nucleus at a certain distance which depends on the number of protons and electrons present in the atom. While the nuclear forces can act only at very short distances inside the nucleus, the electromagnetic force has an infinite range, but becomes weaker as distances between particles increase.
There is a third force which also acts on subatomic nuclear particles. It is even weaker than the electromagnetic force and is related to the decay of neutrons into protons by emitting an electron. The force is mediated by the exchange of other force particles called W and Z bosons. With the addition of energy, a proton can turn back into a neutron by absorbing an electron. This is not directly related to the creation of life, since it does not normally happen under natural conditions but is important in understanding the origin of new subatomic particles from existing ones and the existence of radiation.
Finally, there is a fourth force which acts on all particles. It is called gravity and, even though it is by far the weakest of all forces, it also has an infinite range like the electromagnetic force, but it always adds up, meaning that it is positive. The more particles that come together, the greater their gravitational force becomes. Gravity depends on the mass property of the particles involved so its force is negligible at the subatomic level but becomes important for combinations of billions of particles into more massive objects. Gravity is important in the creation of life since it acts as an environmental variable affecting the adaptation of organisms. It is believed that another force particle, the graviton, is exchanged when objects with mass are attracted by their gravity but this has not yet been confirmed. There is also a negative gravity (called dark energy) that fills the intergalactic space in the universe where there are no mass particles, but its origin is unknown. In any case, it is not a property of known particles even though it does repel particles with mass causing the accelerated expansion of the universe.
Once atoms join together to create molecules, the only two forces still acting are gravity and electromagnetism. Nuclear forces are no longer an issue. Molecules are formed by chemical bonds and other weaker attractions related to residual electromagnetic charges. A chemical bond is created when two or more atoms share or transfer electrons holding the atoms together. Atoms of the same type form elements while atoms of different types join to form compounds. Large molecules are made of many different organic compounds, including amino acids, proteins, lipids, RNA and DNA, from which cells are made. Eukaryotic cells form multi-cellular organisms and specialize into organ tissue, including neurons from which brains are formed. Finally, some of these organisms with brains are capable of developing technology, but still, the same four forces are all that’s needed, combining the same basic elements. In other words, there is no difference between cells and molecules, they are all made of the same stuff, and the only difference is how they are organized.