The physicist searching for quantum gravity in gravitational rainbows

THE fans roar into life, pumping air upwards at 260 kilometres per hour. Decked out in a baggy blue jumpsuit, red helmet and plastic goggles, Claudia de Rham steps forward into a glass chamber and… whoosh! Suddenly she is suspended in mid-air, a wide grin on her face, thrilling to the simulated experience of free fall.

I had persuaded de Rham, a theoretical physicist at Imperial College London, to come indoor skydiving with me at iFLY London. It seemed fitting, given that much of her life has been dedicated to exploring the limits and true nature of gravity – and launching ourselves out of a plane wasn’t an option, at least on this occasion.

As she describes in her new book, The Beauty of Falling, de Rham trained to be a pilot and then an astronaut, only for a medical problem to scupper her chances of the ultimate escape from gravity. But she has gone on to explore this most familiar and mysterious force in a more profound way, as a theorist, and made an impression by asking a radical question: what does gravity weigh?

By that she means the graviton, the hypothetical particle thought to carry this force. If it has mass, as de Rham suspects, that would open a new window onto gravity. Among other things, we might finally spot a “gravitational rainbow” that would betray the existence of gravitons – and with them, a long-sought quantum description of gravity.

As de Rham floats on air, she makes it look easy. She is soon ascending to…