Why Isn't Our Universe Perfectly Smooth?

When we examine our Universe, looking out at the planets, stars, galaxies, and vast cosmic voids separating them, "smooth" isn't exactly the first word that comes to mind. The enormous cosmic web is one of the clumpiest things imaginable in the Universe, with a planet like Earth some 10³⁰ times denser than average. Yet the Universe wasn't always this clumpy, or it wouldn't have evolved to appear the way we see it today. It had to have been born almost perfectly smooth, where the imperfections were just a few parts in 100,000, or it wouldn't have taken hundreds of millions of years to form the first galaxies. Yet those tiny imperfections were vital, or we wouldn't have formed the structure we see today at all! After centuries of not understanding how this happened, one of cosmology's most controversial theories, inflation, provided the answer. And now that our measurements have achieved unprecedented precision, its predictions check out spectacularly.