Ze-Yu Peng

In its first moments, the Universe expanded faster than light could cross it. This process, inflation, left behind ripples — tiny density fluctuations from which galaxies later grew. The spectrum of these ripples is usually described by a number: if it is exactly 1, then all fluctuations, large and small, were equally strong.

The cosmic microwave background is a frozen portrait of the universe at the age of 380,000 years, when it first became transparent.

The cosmic microwave background is the first light that pierced the dense fog of the early universe. Its spectrum, like a frozen score of a cosmic symphony, preserves the tiniest density fluctuations from which galaxies grew.