Tuesday, February 23, 2010

Neither Special nor Trivial

Note: this is a navel-gazing post with no external links.

I'm thinking again about my modal realism and the status of the actual vs. the rest of the possibilities.  I summarized in a prior post (Actual as Indexical, After All?) my conclusion that, while my metaphysical model is very different from that of David Lewis, his idea that what it is actual is just what is local to a point of view made sense.  This implies that our actual world is not the result of a special creative outcome, and that we should probably assume that all metaphysical possibilities are actualized "somewhere" in modal space.  I saw this as just an extension of the Copernican trend familiar from science:  our local situation is not special; it's just another local neighborhood in a huge expanse of reality.

But more recently I've been reconsidering this.

Monday, February 22, 2010

Dieks on RQM

This is a quick follow up on the prior post.  Van Fraassen was a pioneer in the 1970's of the modal interpretation of QM (which became over time a family of interpretations), and he’s now clearly an admirer of RQM.  I'm not a careful student of the modal interpretations (here's the SEP article by Michael Dickson and Dennis Dieks), but the starting point involved an attempt to do away with the measurement collapse postulate (which was why I originally had a hard time getting interested in the program).  The goal was instead was to append actual values to dynamically evolving states.  The SEP article details the various challenges and developments over the years;  what was new to me was the fact that a subset of the philosophers involved had proposed a perspectival or relational approach in an effort to solve some of the problems.  These efforts come close to the spirit of RQM despite the very different starting point.  This is discussed in a recent paper by Dieks called "Objectivity in Perspective: Relationalism in the Interpretation of Quantum Mechanics".

Below for bookkeeping are some past posts on interpreting QM.

Monday, February 15, 2010

Van Fraassen on "Rovelli's World"

I’ve long been interested in Carlo Rovelli’s Relational Quantum Mechanics (RQM), and had been aware that philosopher of science Bas C. van Fraassen had an unpublished paper discussing RQM.  Recently, I saw that a preprint draft of this paper, called “Rovelli’s World,” had appeared on his website.

In the opening paragraph, van Fraassen calls RQM an “inspiring” original vision, and says “its presentation involves taking sides on a fundamental divide within philosophy itself.”  Unfortunately, he doesn’t return explicitly to this last statement (and there is no conclusion section in the paper), but it is pretty clear that the key controversy of RQM revolves around the issue of realism.  RQM seeks a consistent and complete interpretation of a quantum mechanical world, but this comes at the expense of fully objective realism.  We give up the idea of absolute observer-independent quantum states, likewise observer-independent values of physical quantities; “the theory describes only the information systems have about each other.”

The main content of van Fraassen’s paper is a careful exercise in analyzing RQM to see what higher-order aspects of the world it describes are actually “absolute” (or objectively known) even as the states and measurement outcomes only exist relationally.  He wants to compare what Rovelli - qua the author of the paper on RQM - seems to know about the world, as opposed to what a particular system in the world (playfully denoted “ROV”) can know, assuming the theory is correct.  He looks at length at a specific example, where ROV is a third observer following on a “Wigner’s friend”-style example:  based on his analysis he concludes an additional postulate should be added to RQM to clarify the scheme.

Below the fold are my notes on the paper:  they are somewhat sketchy; please refer to the paper for the real deal.

Monday, February 08, 2010

Quantum Photosynthesis Update

There's an new paper in Nature (full text behind the paywall) which looks very interesting.  The authors found evidence that quantum coherent effects are utilized to drive more efficient photosynthesis in algae at room temperature.  This result, along with other research, suggests this is a ubiquitous aspect of photosynthesis in nature.  A SciAm article describing the research with quotes from team leader Greg Scholes is here.  Wired has an article here (hat tip: Cosmic Variance).  In other work on this topic, the research group behind the Engel, et.al. paper from 2007 (the subject of my post: "Quantum Biology Goes Mainstream") also has a new arxiv preprint with updated results.

I suspect that non-trivial quantum effects are widespread in biology, and I hope researchers continue to get the inspiration (and funding ) to continue these efforts.