To my understanding, at the very beginning there was the big bang when nothing (or everything?) existed in singularity, and then at some early point hydrogen came to existence. I understand how stars churn with gravity and heat and whatnot those bigger atoms such as iron at later stages of the universe. But how and why did hydrogen happen as the first atom, and why didn’t we have, say, uranium straight from the beginning?
In: Physics
If you look at the periodic table of elements, basically atoms are set apart by how many protons they carry in their nucleus or center. The most basic element is hydrogen, which is just one proton. Uranium has 92 protons. Atoms formed earliest because they were the simplest — as soon as the universe had cooled enough to start forming protons, and then for those protons to hold electrons around them, you had hydrogen atoms.
To get progressively heavier elements than hydrogen, you have to somehow apply enough energy to get protons to fuse together into a larger nucleus. Protons are positively charged and resist this (think about trying to push the north ends of two magnets together — a different kind of natural force, but the same effect — they repel each other, so you have to push to force them together.
For that reason, to get any meaningful quantities of the heavier elements, you have to wait for there to be enough hydrogen to get pulled together into clouds and ignite stars. The stars provide the heat and pressure necessary to fuse together protons and make heavier elements — mostly helium (two protons), but trace amounts of heavier elements.
The more generations of stars you go through, the more amounts of heavy elements you have, thanks to all the fusion from the previous generation. This planet we’re living on is the debris from old star fusion, which in turn used the hydrogen that formed in the early universe.
Latest Answers