For a few hundred thousand years after the Big Bang, atoms could not form. Electrons could not stay bound to protons or helium nuclei. However, eventually, atoms did combine when
A) there was enough angular momentum that protons and electrons acquired spins.
B) the universe had expanded and cooled sufficiently.
C) the curvature of spacetime increased by 50%.
D) the theory of everything became active.

Question

Quizplus · Accepted Answer

Atoms were able to form when the universe had expanded and cooled sufficiently. This allowed electrons to become stable and remain bound to protons and helium nuclei. The other options provided are not relevant to the formation of atoms.

For a Few Hundred Thousand Years After the Big Bang