The universe, according to scientists, started with a big bang. Let me, the sound engineer, just gloat a little bit here -– they don't call it The Big Flash, The Big Light, or The Big Visual Thing That Was Really, Really Quiet. It was a BANG!!! It all started with sound. And the cool thing is, we can even measure its echoes.
Although I've had a lifelong fascination with astronomy, I won't pretend to be an expert. I'll oversimplify things the best I can, because even this is way over my head. Just after the...you know...BANG!, the universe contained pockets of ionized gas that contained photons, or light. These eventually clumped together into stars and galaxies. But early on, these densely clumped pockets of gas contained trapped photons that counteracted their growth and caused oscillations, or sound waves, within the gas. It was like a bell ringing.
Then the universe started to cool and form hydrogen, which allowed the photons to escape. These photons are seen by astronomers today as an ancient "afterglow" of light. The sound waves were released as well, traveling outward about 500,00 light years. It was a ripple, like a handful of stones thrown into a pond. Galaxies were born at the leading edge of this ripple. Two independent studies (by people that are way smarter than all of us put together) found that early galaxies are slightly more likely to be 500,000 light years apart – a statistical mile marker in astronomical terms.
Much like sound in our world today, this huge rippling of energy can still be measured at different frequencies and resonances. They even lowered in pitch the further they traveled because they were stretched out like a slinky. Sound waves on earth behave this way as well.
Does all this counteract what we were taught, that there is no sound in space? It's true that no one would hear you scream "Marco!" if you pulled off your helmet while spacewalking. But the universe is full of matter that propagates sound waves on a much larger and slower scale: interstellar gas, dark matter, and energy. Cosmic sound waves are a result of stars exploding, stellar collisions, and the movement of matter and energy. Of course most of this is at glacial speed. If you step back and view the universe as a giant bathtub filling up with water, that sound you hear of water sloshing around is matter and energy, supernovae, black holes, solar wind, and galaxies bumping into each other.
All this makes me wonder. If the Big Bang happened in a total void and no one was there to hear it, did it really make a sound? God only knows.