By Science News Staff

Web edition: January 28, 2011
Print edition: February 12, 2011; Vol.179 #4 (p. 30)

Quantum quirkiness
Your special issue on quantum weirdness (SN: 11/20/10, p. 15) was certainly the best presentation I have ever seen. You folks are geniuses and what you did was little short of incredible. It will be difficult (probably impossible) to top it, but keep up the good work. As an aside, could you include more book reviews? They are my favorite part of the issue.
Ken Lawrence, Highland, Mich.

Your articles on quantum mechanics and entanglement were much appreciated, and I hope to see more articles on quantum mechanics in future issues. As Gerard 't Hooft (who is quoted in one article) stresses on his website, physics amateurs such as myself cannot hope to contribute anything of significance to quantum mechanics. Nevertheless, we amateurs can appreciate the philosophical issues quantum mechanics raises and engage meaningfully in the discussion, if only on the sidelines, thanks to the ongoing discourse in nontechnical popular venues like Science News.

It appears the field may be entering a renaissance. The evidence for entanglement is solid, and some sort of unseen, instantaneous, universal connectedness has now become thinkable and even likely. Yet the underlying mechanisms remain a total mystery. This state of affairs would seem to reopen the field for quantum interpretations that have been out of vogue for decades. One hopes theoretical physicists will take a fresh look at the possibilities of hidden variables and of a substantial "reality," composed of objects with physically real properties not created by observation.
John Day, Santa Barbara, Calif.

Tom Siegfried's article, "Clash of the Quantum Titans," is a beautifully written piece that makes sense of an uncommonly difficult issue: quantum weirdness. I am convinced the central problem with our lack of understanding quantum reality is that electrons, protons, photons, quarks, etc., are neither particles nor waves. The fact that they may "act" as particles or "act" as waves, or act both ways simultaneously, is due to the fact that humans have constructed analogies to things we can see, feel, know and understand.

But I suspect those tiny entities will turn out to be — if we ever can go beyond the "particle" or "wave" analogies — something utterly different. When/if we ever uncover the true nature of those tiny entities, our understanding will increase by magnitudes. In the meantime, we're stuck with analogies that make sense at our size scale, analogies which simply fall short when trying to describe things so small, even if the analogies have been good enough to yield mathematically and observationally correct results.
Bruce Barnbaum, Granite Falls, Wash.

"Schrödinger's cat was born 75 years ago. Its date of death remains uncertain." Great opening sentence! Thanks!
Patricia A. Williams, Birmingham, Ala.

The photograph of Einstein and Bohr (SN: 11/20/10, p. 19) clearly renders a verdict in favor of Bohr, Bell, Aspect, et al. Though the slight blurriness of Einstein's shoes might be dismissed as a lens defect, Bohr's shoes manifestly lack definite position and momentum.
Douglas Lackey, Wayne, N.J.

I thoroughly enjoyed the two long articles on quantum mechanics. A comment and two questions, however. Tom Siegfried writes, "When James Clerk Maxwell developed the idea of electromagnetic fields...." It is worth reminding people of the sorely underappreciated Michael Faraday, who really developed the idea of an electromagnetic field. Even Maxwell gave full credit to Faraday and claimed that all he did was mathematize Faraday's research.
My first question is this: Siegfried's article says in talking about the polarization of two entangled photons that when photon A is horizontal that photon B is horizontal also. The large graphic in Laura Sanders' article says that photon B will be vertical. There's either a subtle distinction lost on me or someone got it wrong.

Finally, Sanders also talks about how entanglement can be lost and reclaimed. If entanglement is lost by the act of measurement, then how does that reclamation recur? If it is lost in some other manner, then how would anyone know without measurement?

Thanks again for the fascinating articles. In my opinion one can never get enough of this topic.
Dennis Summers, Tajique, N.M.

The reader is completely correct about Faraday; the phrasing should have said that Maxwell "developed the mathematics" of the electromagnetic field. Regarding entanglement, in some cases entangled photons will show the same polarization; in other cases, the polarizations will differ. It depends on the details of how the experimental apparatus to entangle them is arranged. And measurement can indeed sometimes destroy entanglement irretrievably, but in some cases can also restore it, depending on the nature of the experiment. — Tom Siegfried and Laura Sanders

I was surprised to read that double-slit interference patterns have been observed with 70-atom fullerenes. Is there any theoretical or experimental maximum size for particles that show this effect?
Dean Brown, via e-mail

In principle, quantum effects apply to all matter of whatever size. As objects get bigger, however, interactions among their own internal parts or with other particles in the environment usually eliminate the quantum effects so rapidly that their detection is very difficult and at some point becomes technologically infeasible. — Tom Siegfried