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Mass of hydrogen atom6/24/2023 ![]() But on the cosmic scale of the universe, we can assume that the amount of matter created and uncreated cancel each other out. Related: What happens in intergalactic space?Īccording to Einstein's famous E=mc^2 equation, energy and mass, or matter, are interchangeable, so it is possible for matter to be created from or transformed into energy. The rest consists of dark energy and dark matter, but because they are not made up of atoms, we don't need to worry about them for this mystery. In fact, it makes up only about 5% of the universe, according to NASA. Matter is not the only thing in the universe, however. (Image credit: Shutterstock) Cosmic assumptions Notice how the universe has expanded since the Big Bang happened 13.8 billion years ago. We also need to know how much matter, or stuff, is in it. Using cosmic microwave background radiation, we can work out how fast the universe is expanding, and because that rate is constant - which is currently scientists' best guess (although some scientists think it may be slowing down) - that means that the observable universe actually stretches 46 billion light-years in all directions, according to Live Science's sister site .īut knowing how big the observable universe is doesn't tell us everything we know about how many atoms are in it. But by the time the light reaches us, the galaxy or star is much farther away than it was when we saw it. When we observe a distant galaxy or star, what we are really seeing is where it was when it first emitted the light. But because the universe is constantly expanding, this isn't the case. As it exploded into existence, from a single point of infinite mass and temperature, the universe began expanding outward and hasn't stopped since.īecause 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, you might assume that the observable universe stretches only 13.8 billion light-years in every direction. The universe was created during the Big Bang 13.8 billion years ago. The relative atomic mass is worked out using the following formula, illustrated for two isotopes, where the abundances are given in percentage values.However, it is possible to work out roughly how many atoms are in the observable universe - the part of the universe that we can see and study - using some cosmological assumptions and a bit of math. ![]() In any sample of chlorine, 75 per cent of the atoms are 35 Cl and the remaining 25 per cent are 37 Cl. But the relative atomic mass of chlorine is not 36. The relative atomic mass of an element is a weighted average of the masses of the atoms of the isotopes – because if there is much more of one isotope then that will influence the average mass much more than the less abundant isotope will.įor example, chlorine has two isotopes: 35 Cl and 37 Cl. Calculating relative atomic mass from isotopic abundance The A r values also allow you to work out that three oxygen atoms have the same mass as two magnesium atoms.Ĭhlorine’s A r of 35.5 is an average of the masses of the different isotopes of chlorine. They also tell you that hydrogen atoms have 12 times less mass than a carbon atom. These values tell you that a magnesium atom has twice the mass of a carbon atom, and 24 times more mass than a hydrogen atom. ![]()
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