The Earth is missing 3 trillion tons of mass

If you were to add up the mass of all the atoms in the Earth, you’d get a number 3 trillion tons more than the Earth’s actual mass. We didn’t have to count all the atoms down to the Earth’s core to figure this out. It’s a consequence of the laws of physics. Let’s start with a related puzzle. You might have heard that nuclear reactions work by converting mass to energy, according to Einstein’s famous equation E=mc2. Most nuclear reactors work by hitting atoms of Uranium-235 with neutrons, breaking the atoms apart and producing more neutrons in a chain reaction. But these nuclear reactions don’t destroy any protons or neutrons. So what mass are they converting into energy? Here’s an example nuclear fission reaction you might find in a nuclear power plant.1 At the start, we have one neutron hitting an atom of Uranium-235, which has 92 protons and 143 neutrons. So in total, we have 92 protons and 144 neutrons. After the fission, we have Caesium-137 with 55 protons and 82 neutrons,…