You've probably heard the news that's rocking the science world: yesterday, researchers from the Laser Interferometer Gravitational-Wave Observatory (LIGO) announced that they had detected gravitational waves in space. The discovery is the last puzzle piece of Einstein’s general theory of relativity, and one scientists have been trying to make for a century.
But with this groundbreaking discovery—one that was featured on TV and in print all over the world—came a major design challenge: how to explain a complicated theory, one that took decades to prove, to the general public? Why are gravitational waves significant? And how did LIGO finally detect them?
There's been no shortage of explainers on the topic since the news broke, ranging from punchy animations to elegant illustrations to Neil deGrasse Tyson's own description. But the best visual explainer we’ve seen comes in the form of a video and accompanying comic strip from PHD Comics. Like the best data visualizations, it breaks down gravitational waves, and the method by which LIGO detected them, in a clear, visually compelling and digestible way. Take a look:
What Are Gravitational Waves?
As the video explains, a gravitational wave is a ripple in spacetime. According to Einstein’s general theory of relativity, spacetime isn’t a void, but rather a four-dimensional "fabric" that can be pushed or pulled as objects move through it. In the video, this is visualized by placing a bowling ball on a taut sheet of rubber and seeing the sheet sag around it. If you put the bowling ball into motion, it causes waves of distortion in the rubber like ripples in a pond. That's how gravitational waves behave in space.
Why Did It Take So Long To Detect Them?
Any movement can cause ripples in the fabric of space and time, but it takes something massive—like, black hole-level massive—moving at the speed of light to create ripples that you can actually detect. Gravitational waves have been so difficult to find because they are usually too small to detect.
So How Did LIGO Make This Discovery?
LIGO built two detectors—one in Livingston, Louisiana, and one in Hanford, Washington—each consisting of two 2.4-mile-long tunnels placed perpendicular to each other. The detectors use lasers to measure the changes in the distance between the two tunnels. When a gravitational wave comes through, it stretches space in one direction and squeezes it in another, causing the lasers to change ever so slightly. The detectors are located far enough apart that they don't pick up on one another's local disturbances (like earthquakes or other vibrations on Earth); it's only when both pick up on the change that researchers know those cosmic ripples are occurring.
On September 14, the detectors picked up on the gravitational waves caused by two massive black holes colliding. Each black hole was about 150 km (90 miles) in diameter, which is about 30 times the mass of the sun. They were also traveling at half the speed of light. In other words, they were big enough and fast enough for their collision—which occurred 1.3 billion years ago—to send a signal through the detectors here on Earth.
Why Is This Significant? And What's Next?
PHD Comics likens the ability to detect gravitational waves to suddenly being able to hear after being deaf your whole life—it opens up an entire new way to explore the universe. It could, for example, provide clues to what happened just after the Big Bang, an explosion so huge its waves are likely still rippling through spacetime. Confirming Einstein's prediction from 100 years ago also opens up an entire new set of questions about the universe that the science community will keep exploring. As PHD Comics puts it, "anytime there's a new way to discover the universe, we discover things we never expected." And that's extremely exciting.