The Riddle of the Quantum Triplets

An interactive analogy to an actual experiment—
which contradicts common-sense assumptions about reality.

References: Quantum Roulette and the Nature of Reality and Quantum mysteries revisited.

In the Quantum Queendom, the quantum queen regularly gives birth to quantum triplets. Each of the triplets is taken into a separate examining room and observed by one of the three royal physicians. According to quantum custom, the physicians agree in advance that a single physician will observe a triplet's left eye and the other two physicians will observe the right eyes of the other two triplets, or, instead, all three physicians will observe left eyes. Every observed eye is either brown or blue.

After observing many sets of quantum triplets, the physicians establish the following facts:

Fact 1. Whenever one physician observes a triplet's left eye and the other two physicians observe right eyes, an odd number of brown eyes is observed. More specifically:

Fact 1a. Whenever the left eye of the first triplet is observed, and the right eyes of the other two triplets are observed, an odd number of brown eyes is observed. For example:

(The triplet's left eye is on our right when we're looking at the triplet's face. Quantum triplets are strange, but left and right still work the usual way.)

According to common sense, the triplets are born with their eye colors, so their eye colors are completely independent of how they're observed. Even if the triplets' eyes change color as they mature, surely the observation of an eye doesn't change its color. However, we've already run afoul of the empirical facts. The number of brown-eyed triplets depends on how many left eyes the physicians decide to observe: the number of brown-eyed triplets is odd if only one physician observes a triplet's left eye (Fact 1), and the number of brown-eyed triplets is even if all three physicians observe left eyes (Fact 2).

But wait—maybe a quantum triplet can have one brown eye and one blue eye. So, we were mistaken to assume that a triplet is either entirely brown-eyed or entirely blue-eyed. However, we were surely correct to assume that the triplets' eyes are unaffected by observation. Each eye of each triplet surely has a predetermined color, regardless of whether a physician is observing it. But what combination of predetermined colors is needed?

A viable combination of eye colors must comply with all empirical facts (1a, 1b, 1c, and 2) because each set of triplets may be observed by the physicians in any one of the four ways (corresponding with Facts 1a, 1b, 1c, and 2). Can we find any combination of eye colors that complies with all the empirical facts? Answer: No! But please feel free to try!

If the eye colors already exist prior to observation, they must exist in one of the combinations we can choose above. But no combination of eye colors complies with all the empirical facts! So we've contradicted our assumption that the eye colors exist prior to observation. Prior to observation, the eye colors are unknowable and somehow undecided, not merely unknown. But then how do the triplets conspire to satisfy the facts that depend on how their siblings are observed? For example, if all three left eyes are observed, and the first two twins have brown eyes, what causes the third twin's eye to be blue (in accordance with Fact 2)?

Are the triplets in some kind of spooky collusion, through the walls of their separate examining rooms? Do they choose their eye colors at the last minute, according to the observations made on their siblings? Or do the triplets somehow know in advance which eyes the physicians will examine? Each combination of eye colors complies with a subset of the empirical facts (1a, 1b, 1c, and 2). Can the triplets somehow predict which eyes will be examined so that they can choose an appropriate combination of eye colors? Or are we wrong to even think of the quantum triplets as separate individuals? Are they somehow a single entity, though they appear in three locations?

The quantum triplets are analogous to entangled particles in the real world. Measurements of entangled particles contradict our common-sense assumptions. Our common sense is false, but what is true? What does quantum physics say about the ultimate nature of reality? These and other questions are explored in my book.

The quantum triplets continue to wink at us. They know the answers. But they're not telling. (Perhaps because they have no mouths in their crudely sketched rectangular heads.)

Now that you've read about the quantum triplets, you're entangled with them forever. So this is not goodbye.