Alice and Bob and Spooky Effects in Time

The little comic strip reproduced here is from the NASA website. “Alice” and “Bob” are not people, certainly. They might be particles, but they don’t have to be. They’re pretty much complete abstractions, and the relationship between them is all that really matters. Or, their relationship is real, but Alice and Bob as such are not.  The names — more or less a and b, but easier to remember — are used in speaking about game design, cryptography, and I guess a lot more.

In my very limited reading about particle physics, Alice and Bob do tend to stand for particles, bits of actual matter. In the comic strip, they have humans attached, presumably to make the idea of a relationship more prominent.

It’s worth remembering that Einstein was talking about reality when, in a letter to fellow physicist Max Born in 1947, he called the behaviour of entangled subatomic particles “spukhafte Fernwirkung”. The phrase is now established in English as “spooky actions at the distance” (I think it should be “effects” rather than “actions”, but whatever).  

The news now, in any case, is that entangled particles affect one another not only across space, but apparently back and forth in time as well.  Nikolai Sinitsyn, a theoretical physicist at Los Alamos National Laboratory, and Bin Yan, a post doc in the Center for Nonlinear Studies, also at Los Alamos, have published a paper describing how they returned entangled particles to an earlier state, damaged them (?), and then reversed the reversal, that is, brought them back to the present.  They found that the damage had somehow been repaired.  I don’t pretend to understand it, but repairing damage sounds like a good thing, right? There’s a report from Los Alamos at https://www.lanl.gov/discover/news-release-archive/2020/July/0728-quantum-time-travel.php.  I always think of families.