Was the Big Bang really a big bang?
“They say it all started out with a big bang, but what I wonder is was it a big bang or did it just seem big because there wasn’t anything else to drown it out at the time.”
Karl Pilkington gets quoted for his humorous interpretations of the world, but he’s onto something here. In terms of volume, how big was the big bang? The very first fact in the QI book 1,234 Quite Interesting Facts to Keep You Speechless states:
“The Big Bang was quieter than a Motorhead concert.”
According to Dr. Stephen Serjeant, the sound of the Big Bang was less than 120 decibels, the loudest a human voice can get. You don’t even start to experience pain in your ears until about 125dB. So, Pilkington’s intuition is right: It wasn’t that loud. In fact, Serjeant goes on to say that the notes (not the volume but the pitch) was too low to hear with human ears. So if you would have been there, you would have heard silence.
But wait! We know from our nerdy inclinations to criticize sci-fi movies that there is no sound in space. Movies like Sunshine, for example, have rockets that make engine rocket noises through space, and we all know it’s wrong. Even the science adviser to the film, Professor Brian Cox, points this out in The Infinite Monkey Cage:
“Obviously, if there’s a spacecraft going past you in space, you can’t hear it. But it just didn’t look right on the screen. It just looks like you didn’t have any money to spend on special effects.”
So isn’t that the reason it would have been silent?
Actually, the early universe was like a dense fog, particles close enough together to carry sound waves. We can even see this “fog” at the edge of our observable universe. So if you were to transpose the notes of the sound of the Big Bang up enough octaves to land in human hearing range, you could have heard the Big Bang. Though, it wasn’t a bang but, as T.S. Eliot might say, a whimper.
“Using cosmic background radiation leftover from the Big Bang as a guide, we’ve gone back in time to predict what the early universe would have sounded like… and guess what? It sounded like it was whining. Seriously, it sounded like a big long whine which starts off high-pitched and then gets lower and lower. As the universe expanded, it stretched these sound waves out, lowering their frequency and pitch.”
— Charlie McDonnell, Fun Science
It’s funny that Pilkington should reference a lack of background noise during the Big Bang because the stretched out whining of said Big Bang has become the background noise to our universe. That noise, part of the cosmic microwave background, is still around us today. In fact,
“One percent of the interference on an untuned television is actually the background radiation of the Big Bang.”
— Robin Ince, The Museum of Curiosity, season 4 episode 3
So, if we were to transpose the pitch, could we hear this whine? Janna Levin wrote in her book Black Hole Blues about labs called LIGO (Laser Interferometer Gravitational-Wave Observatory), which detect gravitational waves. Gravitational waves are the ripples in spacetime caused by some disturbance, such as colliding black holes or the Big Bang. Think of it like the ripples in a pond caused by some disturbance, like a pebble dropped in. Gravitational waves are the sound of the universe.
In September and December 2015, the LIGO labs detected gravitational waves of colliding black holes, only shortly after they turned on the machines. A massive event like black holes colliding creates waves that are strong enough for our instruments to pick up here on Earth, but what about the faint, stretched waves of the Big Whine? Janna Levin writes,
“There’s no expectation that LIGO would hear the earliest moments since the gravitational waves are too quiet by now. While they’re below the LIGO range, ifos in space could directly detect the remnant sounds of the big bang in several decades if those missions succeed.”
An ifo is an interferometer — a very long, double-limbed detector running parallel to the ground. As these arms are in the earth, you can imagine all of the interference they pick up, from lumberjacks felling trees to the crashing of nearby traffic. The ifo in Louisiana has been susceptible to all kinds of earthly problems: from rodents and chlorine-urinating black widow spiders, to getting shot by deer hunters. Imagine now you could reduce these hurdles by placing the ifo in space.
While it certainly comes with its own set of problems, the European Space Agency plans to install the first space-based gravitational wave detector (called eLISA) in the year 2034.
On December 3, 2015, the Agency launched the LISA Pathfinder to test some of the new technologies needed for eLISA.
ELisa will “study a variety of cosmic events and systems with high sensitivity,” including “possibly most interesting of all, the uncertain and unpredicted sources, for example relics of inflation and the symmetry-breaking epoch directly after the Big Bang” (arXiv:1201.3621[astro-ph.CO]).
So stick around. The LIGO made its goal to detect gravitational waves by 2016, the 100th anniversary of Einstein’s paper on gravitational waves, so we know it can be done. Maybe in twenty years, you’ll be able to listen to the transposed hiss of the birth of the universe, recorded from our detector in space.
Sources:
- 3 Minute Wonder, hosted by Karl Pilkington [TV program]
- 1,234 Quite Interesting Facts to Keep You Speechless by John Lloyd, John Mitchinson, and James Harkin [book]
- “Dark Matter, Dark Energy and the Sound of the Big Bang” by Dr. Stephen Serjeant [essay]
- The Infinite Monkey Cage, “USA Tour: Los Angeles” [radio program]
- Fun Science by Charlie McDonnell [book]
- The Museum of Curiosity, season 4, episode 3 [radio program]
- Black Hole Blues and Other Songs from Outer Space by Janna Levin [book]
- arXiv:1201.3621[astro-ph.CO] [essay]
