Feeling the Weight of the World? There’s Good Reason

The next time you struggle to push that unbudgeable sofa across the room, or accidentally bash your car into a concrete post, it may be comforting to remember that the force of resistance you feel is the cumulative push of all the matter in the cosmos.

In other words, that’s not just some lousy concrete pillar in a parking garage that thumped your bumper. It’s the weight of all the stars in the universe. Indeed, we push off the stars every time we take a step, accelerate in a car or blast a rocket into space.

This charming notion is known in physics circles as Mach’s principle, after physicist Ernst Mach, who came up with it. It supposes that the resistance to change in the universe--in other words, inertia--is due to the gravitational interaction of every bit of matter with every other bit of matter in the universe.

Each particle, each star, each begonia and sofa, is attracted to every other bit of matter by the force of gravity in a sticky interlocking web. When you try to push the sofa, you disturb the entire gravitationally entangled cosmos. No wonder it’s so hard to move.

Until recently, no one was sure whether Mach’s principle was consistent with Albert Einstein’s remarkably successful theory of gravity. According to Einstein, space and time are linked in a unified fabric that gets warped and otherwise distorted by the gravity of very massive objects. Imagine Arnold Schwarzenegger sitting on a water bed and you get an idea of what happens to space-time in the presence of something really big, like a star or a black hole.

If Mach’s ideas are right, then massive rotating objects should drag Einstein’s space-time along with them as they move. In other words, if Arnold rolls around, the rubber surface of the bed gets dragged with him.

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Now, it seems, this dragging of space-time has actually been seen around objects larger than Arnold--black holes and collapsed stars. If so, it’s good news for Mach.

The discovery “shows us that [Einstein’s theory of gravity] is in agreement with Mach’s principle,” said Italian physicist Luigi Stella, who recently claimed to see evidence for dragging of space-time around collapsed stars.

It’s also good news for those of us seeking a sense of connection with the rest of the cosmos. Like a fly caught in a spider web, everything we do has an effect on the whole of our universe. Every time we twitch, the whole thing twitches with us.

“What a remarkable idea,” wrote physicist B. K. Ridley, “that when you accelerate into a run, your muscles are fighting the influence of galaxies scarcely visible even with the most powerful telescopes!”

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It’s all so nicely connected: Matter reaches out to other matter with its sticky gravitational glue, creating a web of influences that molds space-time and moves everything in the universe. Conversely, it’s the structure of space-time that determines how planets move and keeps that sofa firmly planted to the floor.

Or as the physicist John Wheeler is often quoted as saying: Curved space-time tells matter how to move and matter tells space-time how to curve.

The appeal of science is its power to make just such unlikely connections. An apple falls on Earth propelled by the same forces that keep the moon in orbit and keep stars spiraling in galaxies. Radio waves as big as mountains and X-rays (also waves) as small as atoms are different-sized versions of the same electromagnetic vibrations. The genetic code behind apes, people, begonias and bacteria is remarkably similar, built of the same basic ingredients and even spiraling the same direction.

Ultimately, we’re even related to granite and gold--all “star stuff,” in the words of Carl Sagan. Trace back your ancestry far enough, and your great-great-great-great-great- (and so on) grandmother is an exploding star.

Even matter and energy, Einstein taught us, are different versions of the same fundamental stuff.

Einstein also made the connection between gravitational glue that attracts objects to each other and the stubborn force of inertia. He did it in a quantitative way that could be tested through experiment.

Mach never did the heavy-duty mathematics needed to turn his idea into a real theory, but he did come up with a philosophical scheme grand and graspable enough to connect the sofa to the cosmos.

So think of Mach the next time your car rounds a corner too fast and your coffee goes flying onto the lap of your passengers. It’s not your fault, you can tell them. It’s the pull of the stars.