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
The idea is that there is a time very early, when the universe is so hot that if two protons collide with each other, they are more likely to create some exotic particles than they are to simply fuse. Think of the universe as being a bit like a particle collider. After some time passes, the universe has cooled. Then, protons and neutrons become the favorable particles, and the exotic particles decay away. Once that happens, there is a very brief time that the protons and neutrons can fuse to each other before the universe becomes too cool for that. The time during which the universe is cool enough for protons and neutrons to fuse instead of creating exotic particles, but also hot enough for them to fuse, is too brief for very heavy nuclei to be produced.
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