The formation of cosmic structure, on both large scales and small scales, is highly dependent on how dark matter and normal matter interact, as well as the initial density fluctuations that have their origin in quantum physics. The structures that arise, including galaxy clusters and larger-scale filaments, are indisputable consequences of dark matter. (ILLUSTRIS COLLABORATION / ILLUSTRIS SIMULATION)

This Is How Quantum Physics Creates The Largest Cosmic Structures Of All

How can physics on the smallest scales affect what the Universe does on its largest ones? Cosmic inflation holds the answer.

On a macroscopic level, the Universe appears to be entirely classical. Gravity can be described by the curvature of space according to the rules of General Relativity; electromagnetic effects are perfectly well-described by Maxwell’s equations. Only on ultra-tiny scales do quantum effects begin to come into play, showing themselves in features like atomic transitions, absorption and emission lines, the polarization of light, and vacuum birefringence.

And yet, if we extrapolate back to the earliest stages of the Universe, every relevant interaction that occurred was purely quantum in nature. Individual quantum particles and fields interacted on short scales and at enormous energies, leading to many observables today that have a quantum legacy imprinted on them. In particular, the largest galactic and supergalactic structures owe their origins to quantum physics, too. Here’s how.

Galaxies comparable to the present-day Milky Way are numerous, but younger galaxies that are Milky Way-like are inherently smaller, bluer, more chaotic, and richer in gas in general than the galaxies we see today. For the first galaxies of all, this ought to be taken to the extreme, and remains valid as far back as we’ve ever seen. The exceptions, when we encounter them, are both puzzling and rare. (NASA AND ESA)