Technically, atoms couldn't form and remain stable until the recombination epoch, about 380,000 years after the Big Bang. Some of the best evidence for the Big Bang theory itself, comes from the analysis of the expected proportion of light elements during this initial phase of nucleosynthesis.zaman786 said:TL;DR Summary: how do we calculated the number of atoms at the start , after big bang?
hi, how do we calculated the number of atoms at the start of universe i.e, after big bang?
Wikipedia says 0.25 per cubic meter in the observable universe.Vanadium 50 said:Are you sure?
Their references areIn the observable universe, atoms have an average density of 0.25 atoms/m³. According to the Big Bang model (Lambda-CDM model), they make up around 4.9 percent of the total energy density. The remaining 95.1 percent, whose nature is still largely unclear, is composed of about 27 percent dark matter and 68 percent dark energy, as well as small contributions from neutrinos and electromagnetic radiation.
It is estimated that there are around 1080 atoms in the observable universe. This number is derived from calculations based on the estimated number of galaxies, stars, and the average mass of matter in the universe.
The observable universe is the portion of the entire universe that we can potentially observe from Earth, given the finite speed of light and the age of the universe. It spans about 93 billion light-years in diameter.
Scientists estimate the number of atoms in the universe by first estimating the number of stars in a typical galaxy, the number of galaxies in the observable universe, and the average mass of these stars. They then use the average atomic mass to convert this mass into the number of atoms.
The most common type of atom in the universe is hydrogen, making up about 74% of the universe's elemental mass. Helium is the second most common, constituting about 24%. Heavier elements make up the remaining 2%.
While the total number of atoms in the universe is relatively stable, the forms and types of atoms can change due to nuclear reactions, such as those occurring in stars. These processes can convert hydrogen into helium and other heavier elements, but they do not significantly alter the total count of atoms.