The Number of Atoms in the Universe

The number of atoms in the entire observable universe is estimated to be betweento 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 aboutkilograms. Thus, the total mass would be up to aboutkilograms. Each kilogram of matter is known to have aboutprotons/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.

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