Hello, friends, and welcome to a special Halloween edition of Sciency Words! Today, we’re talking about the spookiest of scientific terms. And that super spooky term is:
QUANTUM ENTANGLEMENT
Quantum mechanics is the study of the tiniest of tiny things in our universe: things like atoms and quarks and electrons. And these super tiny things do some pretty weird stuff, if our current mathematical models are to be believed. Stuff that seems to defy our human notions of common sense.
In the 1930’s, when quantum theory was still brand new, Albert Einstein did not approve of all that common-sense-defying stuff that quantum mechanical models were predicting. So in 1935, Einstein and two of his colleagues, Boris Podolsky and Nathan Rosen, published a paper that was supposed to prove quantum theory was incorrect, or at least that it was woefully incomplete.
The Einstein-Podolsky-Rosen paper (or E.P.R. paper, as it’s now commonly known) didn’t quite get the job done. Quantum theory survived the attack. In response to the E.P.R. paper, Erwin Schrödinger (of Schrödinger’s cat fame) wrote a letter to Einstein. It was in this letter, from Schrödinger to Einstein, that the word “entanglement” was first used in reference to quantum theory. Well, actually, Schrödinger used the word Verschränkung, a German word which translates into English as “entanglement.” (The relevant section of Schrödinger’s letter is quoted in this article from The Stanford Encyclopedia of Philosophy.)
Entanglement refers to the way a pair of quantum particles can interact with each other and then remain “entangled” with each other after their interaction is over. If you measure the quantum state of one entangled particle, the other will instantaneously change to match. This implies that entangled particles can somehow exchange information at faster-than-light speeds. As Schrödinger wrote in his letter, this is not just a weird quirk of quantum theory; it’s the “characteristic trait” that makes quantum mechanics so radically different from classical physics.
Einstein was still not happy. Neither was Schrödinger; however, as I’ve come to understand the story, Schrödinger was able to set his personal feelings about quantum theory aside and continue his research. Einstein, meanwhile, kept trying to prove quantum theory was wrong until the day he died.
You might even say the idea of quantum entanglement haunted Einstein for the rest of his life. In 1947, in a letter to another physicist named Max Born, Einstein referred to entanglement as spukhafte Fernwirkung, a phrase which is commonly translated into English as “spooky action at a distance.” (The relevant section of Einstein’s letter is quoted in this book.)
Thus, quantum entanglement is the spookiest scientific term.
Planet Pailly 
LOL I love this, thank you
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You’re welcome! It’s such a natural fit for a Halloween post. I’m surprised more people don’t post about quantum entanglement on Halloween.
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Most of what Einstein and Schrodinger were reacting to was the Copenhagen Interpretation, in which it’s worth noting the spookiness and paradoxes come from the wave function collapse postulate. I often wonder how they might have reacted to the larger landscape of interpretations available today. We know Einstein didn’t care for deBroglie / Bohm pilot-wave theory, but he supported that kind of theoretical work.
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I’ve read a lot of biographies about Einstein. He was really fixated on this need for physics to be deterministic. He had an almost religious obsession with determinism. I don’t think he would be happy with any interpretation of quantum theory unless he could get a purely deterministic universe back.
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You do get determinism with pilot-wave. The problem is you don’t get locality, which was as important to Einstein as determinism. I wonder how he would have reacted to the Many Worlds interpretation, where you get both determinism and locality, but at the cost of the universe being in a superposition of constantly increasing branches. Would the cost have been worth it to him?
I’m sure you’ve read about Einstein’s belief in Spinoza’s god, a pantheistic notion equating God with nature, one embodying a fully deterministic universe. Interestingly, at least one of the people behind Copenhagen, Max Born, admitted to having a preference for a universe where everything isn’t determined, over concerns about free will. Philosophical preferences influence when a scientist thinks they’re done, versus when they think the search needs to continue.
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Somehow I was under the impression that pilot-waves still didn’t save determinism. My mistake.
Yes, I remember reading about Spinoza’s god and Einstein’s ideas about “cosmic religion.” I also remember something about the Veil of Maya… something about how we live in a world of divisions and separations, but if we could look behind the Veil we’d find that everything is actually united as one. I’m not sure I’m remembering that clearly.
I could probably do with a refresher course on Einstein. He had a very interesting way of thinking about the world.
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