Why was hydrogen the first atom in the universe?

Question

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

Answer 1

> at the very beginning there was the big bang when nothing (or everything?) existed in singularity

This is not correct. There is no data which suggest singularity at the beginning, the singularity pops up when people imagine and we don’t have another idea to refute the infinity. We have better ideas now that smart people have had decades to think and work the math on the subject. 

A singularity is an infinite thing, but infinities don’t exist in nature. Any time we find one it’s a problem with our model, not actually how things are. Our best model right now has the universe coming from a super hot foam that we think was “everywhere”, but of course that model includes another infinity so it can’t be entirely right either.

The short answer to why uranium didn’t just form is that it needs lots of pressure to make protons and neutrons overcome the forces that keep them apart, and that pressure didn’t exist in the early universe. 

Hydrogen was the first atom because it’s the most simple combination of things that the quarks made when they cooled off and slowed down to combine into something. To put it in math terms, it’s 1+1, as straightforward a combination as possible.

Uranium comes after stars spend millions of years squishing stuff together to make heavier elements (up to iron and nickel.) Those stars explode and the pressure wave squeezes some of the heavier than nickel elements into existence and leave behind a core remnant that we call a neutron star. And then – millions or billions of years later – those neutron stars smash into each other and make a different type of explosion that makes the rest of the heavy elements.