If you are one of the millions of people out there riding the buzz of the first direct detection of a gravitational wave, we feel you. It’s not every day that an entirely new window into the universe is opened.
But before you zone out to contemplate the kaleidoscopic marvels of spacetime and the geniuses who endeavor to capture them, be sure to treat yourself to the “sound” this cosmic ripple made as it passed through the Laser Interferometer Gravitational Wave Observatory (LIGO). The audio kicks off this Caltech explainer on today’s discovery.
Explainer on gravitational wave discovery. Video: Caltech/YouTube
That right there is the heartbeat of the universe, and LIGO is the stethoscope. But while today’s landmark announcement is widely being reported as the first instance of “hearing” the universe, it’s worth delving into what that means.
First off, that subtle droplet-like sound featured in the video is a manipulated version of the oscillation signature left by a gravitational wave in the early morning hours of September 14, 2015. LIGO did not record that exact sound when the ripple passed by its interferometers.
What the observatory picked up was a minute gravitational distortion as the wave tripped the ribbon of laser light within LIGO’s vast tunnels. It only lasted for 20 milliseconds, and the frequencies were measured with a precision equal to the width of a human hair over four light years.
The result was a pulse that was so short and weak it needed to be exaggerated in order to be properly heard. “What we have done is taken the real signal and shifted it a bit in frequency, but it is still the real signal,” explained LIGO research scientist Gabriela González during this morning’s announcement.
Basically, that means that the audible version has been beefed up to a higher sound frequency. If you want to hear the difference between the exact signature of the wave compared to the manipulated on that has been making the media rounds, check out the below comparison.
Exact wave frequencies compared to manipulated frequencies. Video: Caltech/YouTube
But audio-hacking aside, the frequencies of gravitational waves are typically within human hearing range. Unlike light waves, which propagate wavelengths that are smaller than the object that emits them, gravitational ripples produce wavelengths larger than the objects that produce them. In that way, they are more analogous to acoustic energy than electromagnetic energy, so recording them is usually considered akin to recording rather than light.
“We can hear gravitational waves,” González said. “We can hear the universe. That’s one of the beautiful things about this. We are not only going to be seeing the universe. We are going to be listening to it.”