The Number of Atoms in the Universe
The number of atoms in the entire observable universe is estimated to be between
to
The actual universe is believed to be much larger.
The number of atoms in the Universe is roughly constant. Early in the history of the Universe, matter and radiation interchanged freely. Radiation and matter are decoupled now, and so we believe the number of atoms to be about constant, ignoring that the stars are gradually turning lighter elements into heavier elements.
It is calculated there are about 500 billion galaxies, each with up to 400 billion stars. The total number of stars is up
On average, each star weighs about
kilograms. Thus, the total mass would be up to about
kilograms. Each kilogram of matter is known to have about
protons/neutrons or about the same number of hydrogen atoms – since stars are mostly hydrogen, one hydrogen atom having only 1 proton, so the total number of hydrogen atoms should be roughly
The number of atoms is only a fraction of the number of particles. There are many more photons and neutrinos than atoms, as well as electrons, muons, gluons, gravitons... Every force has an associated particle that mediates the force, and every species of particle has an associated antimatter particle.
