This is what the birth of the universe sounded like | Mark Whittle

**Elise Hu** (0:04)
You're listening to TED Talks Daily, where we bring you new ideas to spark your curiosity every day. I'm your host, Elise Hue.
What if you could hear the beginning of the universe? Not a recreation, not a metaphor, the actual sound of the cosmos in its first moments, still echoing more than 13 billion years later.
Astronomer and Professor Mark Whittle says you can, because space, it turns out, has never been silent. Pressure waves move through it all the time, moving between stars and across galaxies, and the most astonishing example comes from the very beginning of everything. Not long after the Big Bang, the universe was apparently ringing like an instrument. In this talk, Mark visualizes it.

**Mark Whittle** (0:45)
The bright and dark patches are the peaks and troughs of huge sound waves moving through the primordial atmosphere.

**Elise Hu** (0:53)
Mark's talk takes us all the way back to the universe's conception. Vast sound waves rippling through the cosmos for millions of years, slowly becoming the tapestry of galaxies we see today.
It's a cosmic chord roughly 50 octaves below anything a human could hear, where a single wave might take 50,000 years to pass.

**Mark Whittle** (1:12)
Those particles and atoms from that first acoustic era went on to make stars and galaxies and planets and of course, us.
And right now, some of those atoms are inside your brain, somehow witnessing and understanding their own ancestry. They were out in that hot glowing gas, participating in that first symphony.

**Elise Hu** (1:40)
And then Mark does something remarkable. He plays it out loud. For one brief, stunning moment, we get to hear the sound of creation itself. But maybe the most astonishing part is how close to home that ancient music turns out to be. That's all coming up right after a short break.
And now our TED Talk of the day.

**Mark Whittle** (2:14)
You may have heard the phrase, in space, no one can hear you scream.
But that's true only for human ears. The universe is filled with tenuous atmospheres of one kind or another. And through those atmospheres, pressure waves sound moves. Through stars, across galaxies, even between galaxies. One of the most wonderful and recently discovered examples of cosmic sound is in the very young universe, shortly after the Big Bang. Now, you may be wondering, how would we know that? Well, famously, as you look very far out into space, you also look back in time, simply because it takes time for the light to get to you.
Remarkably, if you look far enough, past all the galaxies, you can see to a time before any galaxies had yet formed, even to a time when the universe itself had only just been born.
So what do you see coming from this new-born universe? You see the light of the Big Bang's hot glowing youth.
At that time, the universe was filled with an almost uniform, hot glowing gas of atomic nuclei and electrons and intense light. That light, on its way to us, has crossed an expanding universe. That expansion not only carried those regions far away from us, but also, as the light waves crossed an expanding space, they were stretched from micron-sized waves to millimeter-sized waves. So although it is light that leaves the young universe, it's microwaves that arrive, and they are the famous cosmic microwave background. Now, because every direction in which you look ends back in the young universe, then the microwave radiation comes to us from all directions. And for many years, its brightness was thought to be extremely uniform around the full spherical dome of the sky. But as microwave telescopes became more sensitive, they began to see slight variations in brightness from place to place. So more recent images of the microwave sky appear completely covered in very slight patches. It spans 8 million light years and shows us the newborn universe when it was only 400,000 years old. Now, that's equivalent to a one-day-old human.
So what are these patches? Why is it slightly brighter and darker in different places? Well, these are places where the temperature and pressure in the glowing gas are slightly higher and slightly lower. Or stated differently, the bright and dark patches are the peaks and troughs of huge sound waves moving through the primordial atmosphere. The brightness contrast reveals 90 decibels. That's rock concert loudness. And their gigantic size reveals a frequency or pitch, a whopping 50 octaves below the human range. One wave might pass you by in 50,000 years.
So, well, what causes this sound? Now, don't be fooled. It's not the bang of the big bang. No, it's a slowly growing sound driven by gravity. The distribution of matter at that time was slightly uneven. And where there was a denser region, a stronger gravity pulled in the surrounding gas, which compressed and bounced back out again, only to fall back in again, creating an approximately spherical sound wave. Now, the landscape included small and medium and large regions. And so, what bit like a set of organ pipes of different sizes? Together, they create a wide range of pitch. So what did the primordial sound sound like? Well, to find out, you must first measure the sound's spectrum. Now, a computer can do that. And here is the remarkable result.