Pick something up. Hold it in your hand.

Right now you are exerting more force on that object than the gravitational force of planet Earth.

For all the talk about the power of gravity - supermassive black holes, neutron stars, and the fact that it keeps us in orbit around the Sun - it’s actually pretty weak.

But, it is also everywhere; entwined in the very fabric of our existence. So how is it that we still don’t actually know what it is?

Richard Panek is the author of “The Trouble with Gravity: Solving the Mystery Beneath Our Feet” which is out in July. He joins Jonathan