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No. 2630:
Determinism and the Many Worlds Interpretation

Tomorrow, and tomorrow, and tomorrow. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

When I strike the cue ball on a billiards table, it moves about the table bumping into the walls and the other balls. And I can describe exactly where all the balls will be as time moves forward. That's because billiard balls — like planets, cars, and old socks — live in a world subject to natural laws like the conservation of energy.

The balls on a billiard table are subject to classical physics, such as the conservation of energy

These classical laws are deterministic: if I know where everything is located and how it's moving at a particular instant then, at least in theory, I can calculate exactly where everything will be at any time in the future.

Causal determinism espouses the position that the universe operates much like a billiards table. The idea had been around in various forms for a long time. But it was Newton who in the late seventeenth century breathed new life into it with his laws of motion, and for centuries many well known engineers and scientists embraced the concept. 

It was not until the early twentieth century that quantum mechanics upset the apple cart. In the quantum mechanical world, things apparently happened at random. For example, uranium atoms spontaneously emit radiation without any provocation. There's no action to cause this reaction. To some this was utter sacrilege. Einstein was a vocal critic of such non-deterministic beliefs, leading him to utter his now famous phrase, "God does not play dice with the universe."

But then in 1957, a graduate student named Hugh Everett offered a way out of the quantum mechanical predicament. It wasn't necessary to give up determinism; we simply had to accept an infinite number of universes branching off from one another as random events both do and do not occur.

A visual representation of Schrodinger's famous thought experiment
A visual representation of Schrödinger's famous thought experiment

It sounds preposterous. For years after Everett published his paper, the idea was ridiculed and ignored by the scientific community. But ultimately, there was no ignoring his mathematics. What came to be known as the many worlds interpretation of quantum mechanics now has a large following. By some polls it's the most accepted worldview of quantum mechanics today. In the eyes of many physicists, it's simply the least strange of all the interpretations out there. Among other things, it doesn't require that we abandon determinism.

For many engineers and scientists it's reassuring to believe in a mechanical universe. Science couldn't exist if the world was haphazard. But is the price we pay something straight from the realm of science fiction — an infinite number of parallel universes? Or is that really such a crazy idea after all?

I'm Andy Boyd at the University of Houston, where we're interested in the way inventive minds work.

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Notes and references:

For a related episode, see OTHER SELVES, OTHER CHRISTMASES.

P. Byrne. The Many Worlds of Hugh Everett. Scientific American. October 21, 2008. See also Accessed July 20, 2010.

Causal Determinism. From the Web site of the Stanford Encyclopedia of Philosophy: Accessed July 20, 2010.

Many Worlds Interpretation of Quantum Mechanics. From the Web site of the Stanford Encyclopedia of Philosophy: Accessed July 20, 2010.

Both pictures are from Wikimedia Commons. The picture of Schrödinger's cat is used under the Creative Commons Attribution-ShareAlike 3.0 License. For author information, and for the terms of using this picture, see the Wikipedia article about the cat. Accessed July 20, 2010.