The Philosopher's Stone (Page 1)

[Wheeler] studied with Niels Bohr, taught Richard Feynman, and boned up on relativity with his friend and colleague Albert Einstein. John Archibald Wheeler's fascinating life brings us face to face with the central characters and discoveries of modern physics. He was the first American to learn of the discovery of nuclear fission, later coined the term "black hole," led a renaissance in gravitation physics, and helped to build Princeton University into a mecca for physicists. From nuclear physics, to quantum theory, to relativity and gravitation, Wheeler's work has set the trajectory of research for half a century.

I think of my lifetime in physics as divided into three periods. In the first period, extending from the beginning of my career until the early 1950’s, I was in the grip of the idea that Everything Is Particles. I was looking for ways to build all basic entities – neutrons, protons, mesons, and so on – out of the lightest, most fundamental particles, electrons, and photons.

I call my second period Everything Is Fields. From the time I fell in love with general relativity and gravitation in 1952 until late in my career, I pursued the vision of a world made of fields, one in which the apparent particles are really manifestations of electric and magnetic fields, gravitational fields, and space-time itself.

Now I am in the grip of a new vision, that Everything Is Information. The more I have pondered the mystery of the quantum and our strange ability to comprehend this world in which we live, the more I see possible fundamental roles for logic and information as the bedrock of physical theory.

Instead of shying away from questions about the meaning of it all, Wheeler relishes the profound and the paradoxical. He was an early advocate of the anthropic principle, the idea that the universe and the laws of physics are fine-tuned to permit the existence of life. For the past two decades, though, he has pursued a far more provocative idea for an idea, something he calls genesis by observership. Our observations, he suggests, might actually contribute to the creation of physical reality. To Wheeler we are not simply bystanders on a cosmic stage; we are shapers and creators living in a participatory universe.

Wheeler's hunch is that the universe is built like an enormous feedback loop, a loop in which we contribute to the ongoing creation of not just the present and the future but the past as well. To illustrate his idea, he devised what he calls his "delayed-choice experiment," which adds a startling, cosmic variation to a cornerstone of quantum physics: the classic two-slit experiment.

Austrian physicist, Erwin Schrödinger, is one of the founders of quantum mechanics. But he's most famous for something he never actually did: a thought experiment involving a cat.

He imagined taking a cat and placing it in a sealed box with a device that had a 50% chance of killing the cat in the next hour. At the end of that hour he asked, "What is the state of the cat?"

Common sense suggests that the cat is either alive or dead. But Schrödinger pointed out that, according to quantum physics, the cat is equal parts alive and dead at the same time. It's only when the box is opened that we see a single definite state. Until then, the cat is a blur of probability: half one thing and half the other.

However, the double-hole experiment's mind-boggling conclusions don't end there. In recent years, technology has allowed scientists to perform a fascinating variation of the test. Its results call into question the perception of time itself.

This is like a high-tech version of the double-hole experiment. Electrons are being fired towards a barrier with two holes in it. But the scientists can delay their decision about whether to observe the electrons until after they've passed through the holes but before they've hit the screen.

It's as though I'm on a baseball field and there's a baseball being pitched towards the barrier with the holes in it. But my eyes are closed, so it goes through and it behaves like a wave. But then, at the last second before it hits the screen I open my eyes and decide to observe it.

At that moment, the electrons, in essence, become particles — and seemingly always were particles from the time they left the electron gun. So it's as though they went back in time to before they went through the holes, and decided to go through one or the other — not through both, as they would have if they'd been behaving like waves. That's really crazy!

That's the enigma — that our choice of what experiment to do determines the prior state of the electron. Somehow or other we've had an influence on it that appears to travel backward in time.

I'm going to think of a number between 1 and 100. You have to guess it. You can only ask binary true/false questions. Let's play!

You: Is it more than 50?

Me: No

You: Is it more than 25?

Me: Yes

You: Is it more than 38?

Me: Yes

You: Is it more than 44?

Me: No

You: Is it more than 41?

Me: Yes

You: Is it 42?

Me: Congratulations! You guessed the number.