The question of where matter comes from is a fundamental one in cosmology and particle physics. According to the current understanding based on the Big Bang theory, the universe began as a hot, dense, and rapidly expanding state about 13.8 billion years ago. At this early stage, the universe was filled with a hot and energetic soup of particles called a "quark-gluon plasma" (QGP).
The QGP is a state of matter in which quarks and gluons, the fundamental building blocks of protons and neutrons, are not confined within individual particles but move freely. In the extremely high temperatures and densities shortly after the Big Bang, the energy was sufficient to break apart the bonds between quarks and gluons, resulting in the existence of a QGP.
As the universe expanded and cooled down, the energy of the QGP decreased, allowing quarks and gluons to come together and form protons and neutrons. These protons and neutrons then combined through nuclear reactions to form the nuclei of the first atoms, primarily hydrogen and helium. This process is known as nucleosynthesis.
The exact mechanisms that caused the QGP to warm up and transform into the first atoms are still the subject of ongoing research and investigation. The early universe was governed by the laws of particle physics and thermodynamics, and understanding the detailed processes requires a deep understanding of these fundamental principles. Cosmologists and particle physicists study these processes using theoretical models, computer simulations, and experimental observations made at particle accelerators, such as the Large Hadron Collider (LHC).
Regarding the rapid expansion of the early universe, it is described by a phase called cosmic inflation. According to the inflationary theory, a brief period of exponential expansion occurred very early in the universe's history, driven by a hypothetical scalar field. This rapid expansion is thought to have smoothed out the initial irregularities and led to the homogeneity and isotropy observed in the large-scale structure of the universe today.
It's important to note that our understanding of these concepts is based on the best available scientific theories and evidence. Ongoing research and future discoveries may refine or expand our understanding of these fundamental processes further.