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OPINION | ART HOBSON: Experimenting with quantum spookiness leads to the Nobel Prize in physics

The path to the Nobel Prize in physics by Art Hobson | November 22, 2022 at 1:00 a.m.

This year's physics Nobel Prize was awarded for quantum physics experiments investigating "entangled quantum states." These are situations in which a pair of microscopic particles behave like a single unified object even when widely separated.

Such "wholism" was first suggested when quantum physics was invented in 1900. To resolve a certain conundrum involving electromagnetic radiation such as x-rays, ultraviolet, and light, Max Planck hypothesized that electromagnetic energy is not continuous but is instead "quantized." This means that it comes in small bundles of energy rather than as a continuous stream of energy. These radiation bundles are now called "photons."

Although each photon occupies a certain volume of space, nature will not allow a fraction of a photon to exist. A light beam, for example, cannot contain just half a photon. It must contain a whole number of photons: zero or one or two, etc.

Individual photons are wholistic: They are created whole whenever you switch on a light and destroyed whole when your skin absorbs light. It's all or nothing: Each photon must be created or destroyed whole and instantaneously.

We have learned that quantization extends to all material substances. For example, a rock is ultimately made of electrons, protons, and neutrons. These objects are wholistic "bundles" of quantized energy, just as photons are. There are many other kinds of quantum bundles, but all obey the rules of quantum physics and are highly unified.

"Entanglement" occurs when two quantum objects, such as two photons, meet and interact with each other. After the interaction, they remain entangled until one of them interacts with some third object. For example, the photons created in the Big Bang became highly entangled with each other during the universe's hot early seconds. Eventually, they separated and traveled through empty space for billions of years, some of them arriving at Earth where we can detect them. According to quantum physics, these photons retain their entanglements that formed during the Big Bang.

All entangled objects are highly unified in the same way that individual photons are highly unified: They behave as a single unit, reacting instantaneously and simultaneously regardless of how far apart they may be.

Einstein had the genius to understand, earlier than any other scientist, that this wholism is predicted by quantum physics. But he didn't much like it, dismissing it as "spooky action at a distance" and suggesting that we replace quantum physics with something more in line with the older physics of Isaac Newton.

Entanglement was not understood until the brilliant work of John Bell. He published a paper in 1964 showing that, according to quantum physics, entangled particles must behave wholistically or "non-locally" in a manner that can be checked experimentally. Bell would have been first on the Nobel Committee's list this year had he not died in 1990. The prize went instead to John Clauser (USA), Alain Aspect (France) and Anton Zeilinger (Austria).

Clauser in 1972 was the first to perform an experiment demonstrating the wholistic behavior of entangled photon pairs. Because such work on quantum foundations was regarded as impractical, Clauser had been advised to "shut up and calculate" instead of experimenting with exotic theories. But Clauser persisted.

His experiment showed that, if you suddenly alter the behavior of photon 1, the entangled photon 2 changes its behavior in the manner that Bell predicted. But a crucial condition remained to be demonstrated: Do the changes in the two photons' behavior occur simultaneously? If the two events were not simultaneous, the two photons were not behaving wholistically and one could argue that photon 1 simply sends a conventional message, at light speed, to photon 2.

Aspect in 1982 showed that the two photons alter their states "faster than light speed." Any time lapse between the two alterations was so small that even a light beam could not fly from photon 1 to photon 2 during that time. According to Einstein's relativity, this means that the two alterations were "non-causal" and essentially instantaneous.

Since 1982, physicists have argued about the significance of these experiments. Several "loopholes" in the experiments were suggested. Zeilinger contributed his phenomenal talents to experiments that closed these loopholes.

Finally, in 2015, three large independent groups performed the same kind of experiments with absolutely no plausible loopholes. Since then, the debate has stopped, and physicists are trying to figure out what to make of the verified fact that wholistic action across a distance is real.

The universe now seems a little spookier than Einstein had thought.

Print Headline: Quantum spookiness

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