In the moments before the Big Bang, our universe was a hot, dense, and extremely high-energy place. That all changed when the universe exploded 13.8 billion years ago. Rapid inflation divided a single “super” force into the four fundamental forces we know today: gravity, electromagnetic force, weak nuclear interaction (responsible for radioactive decay), and strong nuclear interaction (which holds atomic nuclei together). Elementary particles were created. And, eventually, the cosmic flash dance left behind scars in the fabric of space-time. Physicists call them cosmic strings.