ATOMS IN THE UNIVERSE.

The entire Universe is made up of atoms. How many such atoms are there in the Universe?

As we know there are innumerable numbers of atoms everywhere. As an example the human body alone consists of 7 Octillion or 7 raised to the power of 27 atoms.

Now, there is a difference between the observable universe and the actual universe. As you well know the Universe is expanding and its origin the Big bang has taken place 1380 crore years ago. But the point is we are seeing today what started 1380 crore years back. During this period it would have expanded much more (as the expansion of the Universe is going at constant speed).

Matter comprises of only 5% of the Universe. The rest consists of Dark Energy and Dark matter, but they are not made up of atoms and therefore we need not take that into account for calculating the number of atoms in the Universe.

As per Einstein’s equation, mass and energy are interchangeable, but at any point in the Universe as a whole, the matter created and the matter destroyed cancel each other out, so the mass remains constant. That means the number of observable atoms in the Universe are constant all the time.

According to the observations of the known Universe, the physical laws that govern it are the same everywhere (at least to our knowledge). We know that the expansion of the Universe is constant which means that on a large scale matter is distributed uniformly throughout the Universe. This is known as the Cosmological Principle. This idea allows scientists to estimate the number of stars and galaxies in the observable universe.

Now we know that atoms are mostly in stars. But we have no means of knowing what is the extent of atoms that are present in planets, moons and space rocks. But for estimation purposes the matter in stars is much larger than in these smaller separate bodies and therefore the mass of the minor bodies can be neglected in our calculation. This does deviate from our estimation, but the deviation would be minuscule.

Hydrogen atoms consist of about 90% of all atoms in the Universe. However, for simplifying things, we have to assume that all the atoms in the Universe are Hydrogen atoms.

There are about 10¹² stars in each galaxy and there are about 10¹² galaxies in the Universe. Therefore the total number of stars in the universe is 10²⁴. An average star weighs around 10²⁹ tons. Thus the mass of the Universe is 10⁵³ tons.

On an average 1 gram of matter contains 10²⁴ protons, so a ton of matter contains 1000*1000*10²⁴ protons or 10³⁰ Hydrogen atoms since the mass of the Electron is negligible compared to the proton.

Then the Hydrogen atoms in the Universe would be 10³⁰*10^53, or 10^83..

Now, this number is only a rough estimate based on certain assumptions. However, looking at the current understanding and observations, this would not be far off the mark.

See that mind numbing number which simply passes beyond our imagination.

Let alone our mind fathoming this number it fails even to understand the number of atoms in the human body which by itself is mind boggling. How can 10²⁷ number of atoms come together to form the various organs of the body and integrate it into an organism? Assuming that a single cellular organism first appeared and flourished in the seas, how did it slowly acquire the organs due to evolution and then grow into a multitude of species? It simply defies anyones imagination.

Astrobiology studies the origins, early evolution, distribution and future of life in the Universe.  It also studies as to whether life exists outside earth, and if it does, then as to how to detect it. It uses the multiple sciences of molecular biology, biophysics, chemistry, biochemistry, astronomy, geology, cosmology etc. for the purpose of its investigation.