Massive Bodies Warp Space-Time; Image Credit: T. Pyle/Caltech/MIT/LIGO Lab

All we used were these: a large sheet, a watermelon, a smooth round pebble about 2cm in diameter, and a tiny red bead. As the finale of a recent mathematics session I conducted, four people held the corners of the sheet tight and someone else carefully dropped the watermelon on it.

As you can imagine, it sank into the sheet, causing a depression. When we placed the pebble at one edge of the sheet, it rolled straight down to the watermelon. And when we pushed the bead firmly across the sheet, it too rolled down to the fruit, but in a long spiral path.

As a demonstration of Albert Einstein’s vision of spacetime, this model worked beautifully. We got a vivid picture of the way objects curve spacetime, and how gravity is best understood as a manifestation of the way other objects follow these curves. Even the way the bead moved was revealing, in the suggestion of how a planet might settle into an orbit around a star.

Once everyone got a sense of Einstein’s simple yet profound idea, it was easy to simulate what we were actually trying to comprehend: gravitational waves. Shake one edge of the sheet and even those holding the opposite edge feel the resultant “wave”. Though unlike with the first detection of the real thing, in the news last week, they didn’t have to wait 1.3 billion years.

If you consider that the real waves we caught were almost unimaginably small, that detection was one fantastic feat. It’s a tribute to the design of the two LIGO (Laser Interferometer Gravitational-Wave Observatory) detectors in the USA; to their remarkable sensitivity. Just as remarkable is everything scientists have been able to divine from the tiny waveforms that flashed across LIGO’s detectors last September. They know it was caused by two massive black holes. They know their masses. They know they were revolving around each other. They know how fast they were moving. They know they spiralled into each other in one cataclysmic collision. They know how much energy that collision generated, and the mass of the resultant larger black hole. They know when all this happened — 1.3 billion years ago.

All of which is just for starters. They know plenty more too. Besides, what this achievement has opened up is a whole new way to look out at the universe. To light, X-rays, radio and other waves in the electro-magnetic spectrum, we can now add gravitational waves. Einstein told us they existed. A century later, we finally know how to detect them.

As with every great scientic advance, there are questions to ask about what the resultant benefits to humankind are. Sure, the extreme sensitivity of the LIGO detectors holds promise for other scientific pursuits, and not just with gravitational waves. Building such detectors will galvanize other technologies and industries. Techniques of data analysis will find uses in other areas too.

But the reality is probably that we don’t know the full extent of what lies ahead. Yet this is not an unfamiliar feeling. Remember that in 1943, Thomas Watson, president of IBM, said this: “I think there is a world market for maybe five computers.” Even if that was a remarkably naive statement, who in 1943 could have predicted that in 70 years, there’d be a powerful computer or two in the pockets of most humans on Earth?

That’s the spirit in which to think about gravitational waves. Seventy years hence, perhaps they’ll be an intimate part of our lives in ways we cannot even comprehend today. And perhaps nobody will need to explain them using a sheet and a watermelon.