- 3219 - ATOMS - how many are in the Universe? Once we know the mass of the Universe, we can calculate how many atoms fit into it. On average, each gram of matter has around 10^24 protons. That means it is the same as the number of hydrogen atoms, because each hydrogen atom has only one proton. This gives us 10^82 atoms in the observable universe. Here is how the calculation was made:
------------------ 3219 - ATOMS - how many are in the Universe?
- I had nothing else to do this weekend so I started counting atoms. All matter in the universe is made up of atoms. At least that is what we define as “matter“. Matter is made of atoms. But, we don’t know what “Dark Matter” is yet. Dark matter is another story.
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- Each of these “ordinary matter” building blocks consists of a positively charged nucleus, made up of protons and neutrons, and negatively charged orbiting electrons. The number of protons, neutrons and electrons an atom has determines which element it belongs to on the periodic table and influences how it reacts with other atoms around it.
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- Everything we see is just a configuration of different atoms interacting with one another in different ways. There about 90 elements in the Periodic Table of Elements, not counting the fleeting radioactive ones.
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- Everything we know and understand is made of atoms. So do we know how many atoms are in the universe? It has to be a big number because atoms are so small and the Universe is so big.
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- For example to start out "small," there are around 7 octillion, or 7x10^27 (7 followed by 27 zeros), atoms in an average human body. You might think it would be impossible to determine how many atoms are in the entire universe. We have no idea how large the entire universe really is, so how can we calculate out how many atoms are in it.
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- The “observable universe” is the part of the universe that we can see and study. This universe was created during the Big Bang 13.8 billion years ago. As it exploded into existence, from a single point of infinite mass and temperature, the universe began expanding outward, cooling, and hasn't stopped. If fact, it is still speeding up in its expansion.
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- Because the universe is 13.8 billion years old and the observable universe stretches as far away from us as light can travel in the time since the universe was born, and the observable universe stretches only 13.8 billion light-years in every direction.
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- But because the universe is constantly expanding when we observe a distant galaxy or star, what we are really seeing is where it was when it first emitted the light. But by the time the light reaches us, the galaxy or star is much farther away than it was when we saw it.
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- Using “cosmic microwave background radiation“, we can work out how fast the universe is expanding, and because if that rate is constant the observable universe actually stretches 46 billion light-years in all directions.
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- “Matter” is not the only thing in the universe, however. In fact, it makes up only about 5% of the universe. The rest consists of dark energy and dark matter, but because they are not made up of ordinary atoms, we don't need to worry about them for this particular mystery.
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- According to Einstein's famous E=mc^2 , energy and mass, or matter, are interchangeable, so it is possible for matter to be created from or transformed into energy. But on the cosmic scale of the universe, we can assume that the amount of matter created and uncreated cancel each other out.
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- This means matter is finite, so there are the same number of atoms in the observable universe as there always have been. According to our observations of the known universe, the physical laws that govern it are the same everywhere.
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- Combined with the assumption that the expansion of the universe is constant, this means that, on a large scale, matter is uniformly distributed throughout the universe, a concept known as the “cosmological principle“.
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- In other words, there are no regions of 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.
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- Knowing the observable universe's size and that matter is equally and finitely distributed across it makes it easy to calculate the number of atoms.
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- We assume that all atoms are contained within stars, even though they aren't. Unfortunately, we have a much less accurate idea of how many planets, moons and space rocks there are in the observable universe compared with stars, which means it is harder to add them into the equation.
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- Because the vast majority of atoms in the universe are contained within stars, we can get a good approximation of the number of atoms in the universe by figuring out how many atoms there are in stars and ignoring everything else.
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- We assume that all atoms in the universe are hydrogen atoms, even though they aren't. Hydrogen atoms account for around 90% of the total atoms in the universe, and an even higher percentage of the atoms in stars, which we are focusing on.
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- To work out the number of atoms in the observable universe, we need to know its mass, which means we have to find out how many stars there are.
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- There are around 10^11 to 10^12 galaxies in the observable universe, and each galaxy contains between 10^11 and 10^12 stars.
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- This gives us somewhere between 10^22 and 10^24 stars. We can say that there are 10^23 stars in the observable universe. This is just a best guess; galaxies can range in size and number of stars.
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- On average, a star weighs around 2.2x10^32 pounds , which means that the mass of the universe is around 2.2x10^55 pounds.
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- 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 matter has around 10^24 protons. That means it is the same as the number of hydrogen atoms, because each hydrogen atom has only one proton.
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- This gives us 10^82 atoms in the observable universe.
- 10,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 atoms.
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- This number is only a rough guess, based on a number of approximations and assumptions. But, it does give us a number to chew on.
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- July 14, 2021 ATOMS - how many are in the Universe? 3219
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