All matter in the universe – no matter how big, small, young or old – consists of atoms.
Each of these building blocks consists of a positively charged nucleus composed of protons and neutrons, and negatively charged electrons orbiting. The number of protons, neutrons and electrons that an atom has determines which element it belongs to the periodic system and affects how it reacts with other atoms around it. All you see around you is just a configuration of different atoms interacting with each other in unique ways.
So if everything is made of atoms, then do we know how many atoms there are in the universe?
Related: Why does outer space look black?
To start “small”
However, it is possible to calculate approximately how many atoms there are in observable the universe – the part of the universe that we can see and study – using some cosmological assumptions and a little math.
The observable universe
The universe was created during Big bang 13.8 billion years ago. As it exploded into existence, from a single point of infinite mass and temperature, the universe began to expand outward and has not stopped since.
Because the universe is 13.8 billion years old, and the observable universe extends as far away from us as light can move in the time since the universe was born, you might assume that the observable universe extends only 13.8 billion light years in all directions. But because the universe is constantly expanding, this is not the case. When we observe a distant galaxy or star, what we really see is where it was when it first emitted the light. But when light reaches us, the galaxy or star is farther away than it was when we saw it. Using cosmic microwave background radiation, we can find out how fast the universe is expanding, and because this speed is constant – which is currently the scientists’ best guess (although some scientists believe it can slow down) – it means that the observable universe actually stretches 46 billion light-years in all directions, according to WordsSideKick.com Space.com.
But knowing how large the observable universe is does not tell us everything we know about how many atoms there are in it. We also need to know how much substance or thing is in it.
However, matter is not the only thing in the universe. In fact, it amounts to only approx. 5% of the universe according to NASA. The rest consists of dark energy and dark fabric, but because they do not consist of atoms, we do not have to worry about them for this mystery.
Related: What is happening in the intergalactic space?
According to Einsteins famous E = mc ^ 2 equation, energy and mass or matter are interchangeable so that it is possible for matter to be created from or converted into energy. But on cosmic on the scale of the universe, we can assume that the amount of matter created and not created is mutually exclusive. This means that matter is finite, so there are the same number of atoms in the observable universe as there always have been, according to Scientific American. This is important because our image of the observable universe is not a single snapshot in time.
According to our observations of the known universe, the physical laws that govern it are the same everywhere. Combined with the assumption that the expansion of the universe is constant, it means that matter on a large scale is evenly distributed throughout the cosmos – a concept known as the cosmological principle. In other words, there are no regions in the universe that have more matter than others. This idea allows scientists to accurately estimate the number of stars and galaxies in the observable universe, which is useful because most atoms are found in stars.
Simplification of the equation
Knowing the size of the observable universe and that matter is evenly and finely distributed across it makes it much easier to calculate the number of atoms. However, there are a few more assumptions we need to make before we break out the calculator.
First, we must assume that all atoms are contained in stars, even if they are not. Unfortunately, we have a much less accurate idea of how many planets, moons, and space rocks there are in the observable universe compared to stars, which means it’s harder to add them to the equation. But because the vast majority of atoms in the universe are contained in stars, we can get a good approximation of the number of atoms in the universe by finding out how many atoms there are in stars and ignoring everything else.
Second, we must assume that all atoms in the universe are hydrogen atoms, even if they are not. Hydrogen atoms account for about 90% of the total atoms in the universe, according to Los Alamos National Laboratoryand an even higher percentage of the atoms in stars that we focus on. As you will soon see, it also makes the calculations much simpler.
Now it’s finally time to do math.
To find out the number of atoms in the observable universe, we need to know its mass, which means we need to find out how many stars there are. There are about 10 ^ 11 to 10 ^ 12 galaxies in the observable universe, and each galaxy contains between 10 ^ 11 and 10 ^ 12 stars according to European Space Agency. This gives us somewhere between 10 ^ 22 and 10 ^ 24 stars. For the purposes of this calculation, we can say that there are 10 ^ 23 stars in the observable universe. Of course, this is just a best guess; galaxies can vary in size and number of stars, but because we can not count them individually, this must be done for now.
On average, a star weighs about 2.2 x 10 ^ 32 pounds (10 ^ 32 kg) according to Science ABC, which means that the mass of the universe is about 2.2 x 10 ^ 55 pounds (10 ^ 55 kg). Now that we know the mass or amount of matter, we need to see how many atoms fit into it. On average, each gram of substance has about 10 ^ 24 protons according to Fermilab, a national particle physics laboratory in Illinois. This means that it is the same as the number of hydrogen atoms, because each hydrogen atom has only one proton (hence we made the previous assumption about hydrogen atoms).
This gives us 10 ^ 82 atoms in the observable universe. To put it in context, it is 100,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 atoms.
This figure is only a rough guess, based on a number of approximations and assumptions. But given our current understanding of the observable universe, it is unlikely to be too far away from the mark.
Originally published on WordsSideKick.com.