This is the third installment in Adam Frank's series "How To See The Universe In A Grain Of Sand", looking for the extraordinary in the ordinary.
From the day we are born to the day we die, it's always there. Never changing, never wavering, it holds us down and binds us to the Earth. We live under the tyranny of gravity and its constancy bears down on our spirits, allowing us to fly only in our dreams. But what if gravity was less the tyrant than we suppose? What if we could, if even for a minute, feel it become unhinged and, in that moment, come to see a deeper truth about the cosmos itself. Well we can have that moment and it can come to us, as it did for Einstein, in the most unlikely of places: an ordinary, everyday elevator.
Isaac Newton and his apple is a familiar story to most folks. The apple was, supposedly, the seed of Newton's insight into gravity as a force, a force that reaches out and pulls one object toward another. And intuitively, that's how we all understand gravity. It is a force relentlessly pulling us down, keeping our butts in our chairs and our feet on the ground.
Einstein, however, saw deeper into the Universe around us and you can too. All you have to do is take an elevator ride and pay very, very close attention.
When you first step into an elevator your legs bear the same weight as when you waited for the doors to open. But press the button for an upper floor and, for an instant, something wonderful, something magical happens. Your legs buckle. For a brief instant it feels as if your weight increases. In other words, it feels as if gravity gets a little bit stronger. Then the moment passes and you begin cruising upwards. But just as your reach your floor it happens again, only this time you feel yourself rise up just a bit. Your weight changes once more, as gravity momentarily seems to weaken.
There! You have just experienced variable gravity.
When Einstein looked at those little gravity jolts, he saw into the very heart of the cosmos. They were the key to his "ah-ha" moment. He realized that gravity isn't about forces, it's about falling.
Gravity, Einstein saw, is what happens when you take away forces and let things go with the flow — the flow of space. Cut the cables on your elevator and what happens (other than a lot of yelling and panic)? Inside, everything appears to go weightless. During the fall you'd float like an astronaut in a space capsule.
That was how Einstein realized that apples don't fall because of forces; they fall because that is what space wants them to do. Gravity is space bending and stretching like taffy. Even though you can never touch space you can see it has a shape just by watching how things fall.
So the variable gravity you feel in the elevator ... that's just one way of getting past old Newton and his force idea. Sometimes I need to remind myself of this. So I always carry a little red ball with me. When I'm in an elevator and the doors slide shut I start tossing it into the air hoping to witness the elusive moment of the elevator's brief acceleration. Get it right and, just as my legs buckle, the ball begins its rise upward and then hangs for a moment in the air before it starts rising up again. It's always a heart-stopping moment as, for an instant, I see gravity vary and see a hint of the bending space around me.
When I catch that brief moment of wonder, the elevator becomes a portal, allowing me to see past the small details of the everyday to the grand universe that is always and forever right there before us.