Big Bang Acoustics

Sounds From The Newborn Universe

Mark Whittle

University of Virginia 

Cosmic Microwave Background

the first million years, compressed to about 8 seconds,

shifted up by 50 octaves, and played at constant volume

use controls above to replay sound

Far into space and far back in time, everything was different: there were no stars or galaxies, no planets or people, not even atoms were yet fully formed.  At that time, the newborn Universe was pristine and formless — a brilliant expanding fireball of light and matter.

And yet within that sea of brilliance, the seeds for all that we now know were already present, latent, waiting to unfold.  Most remarkable of all, perhaps, these seeds were sounds — pressure waves coursing through the fluid.  A symphony of sorts, though not one that we would recognize as music.  This symphony had three movements, each with its own form and character.  The final movement built to a unique crescendo, unlike any other before or since: its final cacophonous chord dissolved to become the first generation of stars, whose light brought to a close the Universe's first cold dark night with a new dawn.

Even more remarkable: this story isn't fiction, or even myth; it is history.

Not too musical, I know, but three movements nevertheless: a descending scream; a deep roar; and a final growing hiss, which ultimately spawns the first generation of stars.

How Can We Possibly Know This?

The extraordinary truth is that we can see the sound waves, exactly as they were, just 400,000 years after the Big Bang. We see them imprinted on a glowing foggy wall — caught, frozen in motion as they crossed the wall.

Because of cosmic expansion, we see the glowing wall not in its original brilliant orange light, but in faint microwaves. This is the famous Cosmic Microwave Background. It is our window on the infant Universe, and is one of nature's most generous and revealing gifts.

Our story, then, is set in ancient times — the era of sound sits firmly in creation's first million years. Let's start by getting a feel for the conditions of that remote time without, initially, any justification. Once the stage is set we can then introduce our main character, the cosmic microwave background, whose frozen sound waves reveal much that is now known about the ancient Universe.

It's quite a shock to find out that the sound spectrum of the early Universe is a bit like a vibrating object – it has a fundamental with harmonics!

Three Incredible Truths

First, all structures in the Universe, from stars to galaxies to the cosmic web, arise from sub-sub-microscopic quantum fluctuations. Colossally amplified by inflation, this imperceptibly fine froth of Nature yielded the very seeds which ultimately grew into galaxies. What poetic notions – the largest objects in the Universe come from the smallest; and all structure has roots in the quantum world, without which the Universe would be forever smooth and silent, dark and lifeless.

Second, this explanation for the origin of all structure also answers the philosophical riddle of infinite causal regression. Quantum fluctuations are a-causal, since they are deeply random. In a sense, they are a true first cause – the start of a chain of cause and effect which ultimately ends with the Sun and stars, me and you.

Third, inflation makes the Universe vastly bigger than previously imagined. If our entire visible Universe was once a sub-horizon patch in the otherwise chaotically lumpy Big Bang, then "out there" beyond our current 14 billion light year horizon lie countless regions of space, each as large or larger than everything we now see.