Thursday, February 15, 2007

The peculiar scarcity of books on quantum entanglement

I've been blogging periodically about the weirdness of a universe where quantum entanglement is real, but it was a somewhat supercilious essay in Wired magazine that convinced me I needed to read a real book ..
Wired 15.02: What We Don't Know

How do entangled particles communicate?

... In 1997, scientists separated a pair of entangled photons by shooting them through fiber-optic cables to two villages 6 miles apart. Tipping one into a particular quantum state forced the other into the opposite state less than five-trillionths of a second later, or nearly 7 million times faster than light could travel between the two [jf: probably instantaneously]. Of course, according to relativity, nothing travels faster than the speed of light - not even information between particles.

Even the best theories to explain how entanglement gets around this problem seem preposterous. One, for example, speculates that signals are shot back through time. Ultimately, the answer is bound to be unnerving: According to a famous doctrine called Bell’s Inequality, for entanglement to square with relativity, either we have no free will or reality is an illusion. Some choice.
- Lucas Graves, New York City-based writer
I was sure I'd find a lot of books on the topic, but the best I could do was 'Schrodinger's Kittens' -- written about 13 years ago! I did find some a more recent text, but it belonged to what a Wikipedia article calls Dirac's "shut up and calculate" school [1]. The other relatively recent texts I found were either fluffy or preferred to deal with familiar topics like modern cosmology.

So what gives? Is this such a scary topic that almost no-one dares to explore what it means?

I'm write some more as I work my way through the Kittens ...

[1] Easy for Dirac to say -- he died before we were doing quantum teleportation, quantum encryption, and irrefutable entanglements.

Update 2/15/07: After finishing the last chapter of Schrodinger's Kittens I understand why Graves setup the choice of 'reality is not what we think' versus 'no free will'. The 'transactional model' preserves our familiar "reality" of time and relativity, but the handshakes between past and future seem to constrain the future. In the enhanced (Wheeler) slit model, for example, the photon assumes its wave or particle behavior as it crosses the slit based on a handshake with the future absorbed photon. The nature of the future absorbed photon however, is based upon an observer choosing whether or not to "drop the screen". Since the photon adopts its configuration before the screen is dropped, however, the observer cannot really be choosing whether or not to drop the screen. The choice must be made in a way that's consistent with the form of the photon. Gribbin tries to dodge this trap with some handwaving about micro vs. macro causality, but it's obvious his heart isn't in it.

Hmmm. I'm beginning to see why Feynman warned us about 'going down the [quantum] drain', and why there are so many books on cosmology and so few on Bell's theorem. Next thing you know I'll be ready to start believing that our universe is both simultaneously vast and unbelievably small, that all things that will happen have happened, and that time's arrow really is an illusion ...

There is an escape clause. Gribbin's framed the transactional model as being dependent upon a closed universe. We appear to live in an open (perhaps excessively open) universe (but see below). In an open universe, might we get a true arrow of time and the possibility of choice? Maybe one day, if we ever "understand it all", we'll learn that you can determine whether a universe is open or closed by testing for action-at-a-distance.

Update 3/4/07: I'm reading through Gribbin from page one, and since I'd read the last chapter first I know to watch for references to a closed universe. I've found a few, it seems that more than a few of the foundations of QM, and even QED, do assume a closed universe. I'd thought that the universe is now thought to be "open", so I wrote Professor Gribbin asking if he'd written any updates. He graciously replied:
... It is entirely possible for the Universe to be closed but with accelerating expansion! All we know for sure is it is indistinguishably close to flat, and it is probably on the closed side of flat, pushed there by inflation.
Which reminds me of my old post about the respiratory rate of the universe ...

I'll just keep on reading, reading, reading ...

Update 5/13/07: My Amazon review of Gribbin's book. Five stars, despite being 12 years old.

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