Here is something I've never understood, and nobody I've asked has been able to explain to my satisfaction. There are four forces, right? Gravity, electromagnetism, weak nuclear, and strong nuclear. Three are attractive, only electromagnetism is repulsive. But electromagnetism didn't exist until electrons existed, which wasn't the case in the first few nano-seconds after the big bang. But then right after the big bang, all the forces were attractive. Why did the universe expand, instead of collapsing?