Too Long; Didn't Read
Fourteen billion years ago the universe was immensely hot, dense plasma. Then, as the universe expanded after the Big Bang, the gases within it cooled. When these gases reached a temperature of around 2,700°C (billions of years before galaxies existed) protons and electrons were able to combine into hydrogen atoms, releasing energy in all directions in the form of electromagnetic <a href="https://hackernoon.com/tagged/radiation" target="_blank">radiation</a>.