We Have No Idea: A Guide to the Unknown Universe

by Jorge Cham

So the fact that we have any structure at all—rather than perfect smoothness—is due to the quantum fluctuations that created the first wrinkles, which were then blown out of proportion by inflation, creating the seeds that led to our current universe. But how do those seeds turn into the planets, stars, and galaxies that we see? The answer is a balancing act between two powerful effects: gravity and pressure. Around 400,000 years after the Big Bang, the universe was a big blob of hot, neutral gas with a few little wrinkles in it. That’s when gravity started to do its thing. The fact that everything was neutral is very important. All of the other forces were approximately balanced at this point. The strong force grouped the quarks into protons and neutrons. Electromagnetism pulled protons and electrons together to make neutral atoms. But gravity can’t be balanced or neutralized. It’s also very patient: over millions and billions of years, it pulled those wrinkles together into denser and denser clumps.