Timeline of the Big Bang
Particle Accelerator
What happened in the first fractions of a second after the Big Bang? How did the microstructures (for example: atoms and even smaller particles) and the much larger structures originate?
The answers to these kinds of questions are very physical in content, insofar as scientists have answers to them at all. The first phases of the Big Bang are the subject of many speculations. Some aspects of the Big Bang are being attempted to be simulated by physical cosmologists in an underground particle accelerator.
A particle accelerator is an underground device (in kilometer-long tunnels) in which charged particles (subatomic, elementary particles, and the like) are brought to high energy levels by accelerating them to speeds near the speed of light. This acceleration is done using strong electric fields. For steering the direction in which the particle beam goes, especially powerful magnetic fields are used.
In these tunnels, scientists have been able to demonstrate all kinds of—until now unknown—subatomic particles, which corresponded to suspicions arising from mathematical models and calculations.
A subatomic particle is a particle that is smaller than the atom. Some subatomic particles can be part of atoms, others are formed only in stars, in the laboratory, or in other extraordinary circumstances. The particles are smaller than 1 fm (= 10−15 m). They are studied by the university science called 'particle physics'.
Cosmic Inflation
In the most common models, the universe was filled with an enormously high energy density and enormous temperatures and pressures. It was isotropically (= equal in all directions) filled with homogeneous reactions. It expanded very rapidly and cooled quickly.
About 10−37 seconds into the expansion, a phase transition caused a cosmic inflation, where the universe grew exponentially in size.
Figure A: Development stages of the universe. Time is on the horizontal axis.
Antiparticles
After inflation stopped, the universe consisted of both quark-gluon plasma and other elementary particles (these are particles even smaller than an atom, also called subatomic particles). A quark-gluon plasma (QGP) is a (presumed) phase of matter that arises at extremely high temperatures and densities. It is suspected that it occurred in the first 20 to 30 microseconds after the Big Bang.
The temperatures became so high that the random motions of particles reached a relativistic speed. Particle-antiparticle pairs of all kinds of particles were continuously created and destroyed in collisions with each other.
An antiparticle is a particle whose physical properties are the same as a 'normal' particle, but other properties (including charge) are exactly opposite.
At some point, an unknown reaction called baryogenesis occurred, which caused an asymmetry in the baryon number, leading to a small excess of quarks and leptons versus antiquarks and antileptons - ordered as 1 excess particle per 30 million. This led to the dominance of matter over antimatter in the current universe.
Annihilation
Subsequently, the decreasing temperature and decreasing density caused a breaking of symmetry. Hereby, the fundamental forces of nature and the parameters of elementary particles took their current form, through phase transitions.
After 10−11 seconds, the events are less speculative, because the conditions can be simulated in underground experiments with subatomic particle accelerators (for example at CERN in Switzerland).
After about 10−6 seconds, quarks and gluons combined to form baryons such as protons and neutrons (from which atoms are built).
A small excess of quarks versus antiquarks led to a small excess of baryons versus antibaryons.
When the temperature was no longer high enough for the creation of new proton-antiproton pairs (the same applies to neutron-antineutron pairs), a mass annihilation immediately followed, leaving only 1 in 1010 of the original protons and neutrons, and none of their antiparticles.
Big Bang Nucleosynthesis
A similar process occurred after about 1 second for electrons and positrons. After these annihilations, the remaining protons, neutrons, and electrons no longer moved at a relativistic speed. Thereby, the energy density of the universe was dominated by photons (with a small group of neutrinos).
A few minutes into the expansion, the temperature was about a billion degrees Kelvin and the density was about as large as the Earth's atmosphere at sea level. Under these curcumstances neutrons fused with protons to form deuterium and helium nuclei. This process is called Big Bang nucleosynthesis. Most protons remained unpaired as hydrogen nuclei.
Cosmic Microwave Background Radiation
As the universe cooled, the energy density of the rest mass of matter began to gravitationally dominate radiation. Thus, gravity became an important factor in the formation of objects.
After about 379,000 years (after the Big Bang), the electrons bonded to the atomic nuclei and formed the first atoms (mainly hydrogen atoms).
As a result, space became transparent and radiation decoupled from matter. This allowed radiation to continue largely unhindered through space. This radiation is known as the cosmic microwave background radiation.
Conclusion
The story described above shows that the physical objects in the universe (such as subatomic particles) did not already exist. They are believed to have originated through a complex physical process that lasted many millions of years, before taking on forms as we know them today.