The changeover from radiation to matter domination happened around z=3400, time around 50,000 years. At that stage the matter was still in the form of plasma and the universe not transparent. At ~378,000 years it cooled enough to become transparent, but it happened over a period of time.wolram said:Radiation dominated the universe 4,700yrs to 378,000yrs, do the facts in the literature mean there was no baryonic matter between those yrs or was there still plasma or some sort of mass?
During the radiation-dominated era, the baryonic particles had kinetic energies much greater than their mass-energies, so that they acted like radiation.wolram said:Radiation dominated the universe 4,700yrs to 378,000yrs, do the facts in the literature mean there was no baryonic matter between those yrs or was there still plasma or some sort of mass?
Chalnoth said:During the radiation-dominated era, the baryonic particles had kinetic energies much greater than their mass-energies, so that they acted like radiation.
But was there not a significant amount of photon energy around as well?Chalnoth said:During the radiation-dominated era, the baryonic particles had kinetic energies much greater than their mass-energies, so that they acted like radiation.
Yes, and in fact most of the energy was carried by photons. After matter/antimatter annihilation, there were about a billion photons for every baryon: this fact is often expressed via the tiny baryon-photon ratio, [itex]\eta \approx 6 \times 10^{-10}[/itex].Jorrie said:But was there not a significant amount of photon energy around as well?
Yes. When the energies were very high, each species of particle would have occurred in approximately equal numbers, as when the typical photon energy is much higher than, say, the electron mass, then interactions are, for the most part, just as likely to produce a pair of photons as an electron/positron pair.Jorrie said:But was there not a significant amount of photon energy around as well?
I understand that relativistic particles had lots of kinetic energy and that this portion decayed just like photons (de Broglie wavelength increasing inversely with scale factor a).
Baryonic matter is the ordinary matter that makes up the universe, including protons, neutrons, and electrons. It is made up of particles called baryons, which are made up of quarks. Baryonic matter is the matter that we can physically see and interact with, such as planets, stars, and galaxies.
Radiation domination is a period in the early universe when radiation was the dominant energy source, before the formation of stars and galaxies. During this time, the universe was filled with high-energy particles, such as photons and neutrinos, and was expanding at an incredibly fast rate.
This is a cosmic mystery because according to the standard model of cosmology, known as the Big Bang theory, baryonic matter was not expected to exist during radiation domination. The extreme conditions and high energy levels during this time were thought to prevent the formation of stable baryonic matter. However, recent observations have shown evidence of the existence of baryonic matter during this period, challenging our understanding of the early universe.
Scientists use a variety of methods to study the presence of baryonic matter during radiation domination. One method is through the observation of the cosmic microwave background (CMB), the residual radiation from the Big Bang. Another method is through the study of the large-scale structure of the universe, which can provide information about the distribution of baryonic matter. Additionally, laboratory experiments can also be used to simulate the extreme conditions of the early universe and study the formation of baryonic matter.
If confirmed, the existence of baryonic matter during radiation domination would challenge our current understanding of the early universe and the processes that led to the formation of baryonic matter. It could also have implications for our understanding of dark matter, which is thought to make up a majority of the matter in the universe. Further research and observations are needed to fully understand the role of baryonic matter during this period and its implications for our understanding of the universe.