Number of atoms in the Universe

[zaman786]

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?

 

[Orodruin]

In what part of the universe? To the best of our knowledge it is highly possible that the universe is infinite in extent and therefore contains an infinite amount of atoms.

 

[PeroK]

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?

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.

https://en.m.wikipedia.org/wiki/Recombination_(cosmology)

 

[Andy Resnick]

I think the OP asks a good question, which I will gently re-phrase:

How can one estimate/calculate the Eddington number? Is this a reasonable effort?

 

[alantheastronomer]

From the observed intensity of the microwave background radiation, you can approximate the number density of hydrogen atoms that produced it...

 

[Vanadium 50]

Are you sure?

 

[fresh_42]

Are you sure?

Wikipedia says 0.25 per cubic meter in the observable universe.

In 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.

Their references are
https://physicsworld.com/a/planck-reveals-almost-perfect-universe/
https://arxiv.org/abs/astro-ph/0406095

 

[Vanadium 50]

I got it - number density, not number. The question was number, not density, and as mentioned, number is problematic as the universe may be infinite.