Thursday, March 30, 2006

Top-Down or Bottom-Up Quantum World?

At Antonio’s suggestion in his comments on the last post, I reviewed more of Ulrich Mohrhoff’s work on interpreting quantum physics contained in this paper and on his website, thisquantumworld. I also plowed through some of the debate between Mohrhoff (posting as koantum) and Patrick Van Esch (vanesch) on this thread at physicsforums. This was extremely fascinating although often over my head.

From my reading so far, Mohrhoff is saying two things which I think have some merit:

1. He rejects the assumption that the wave function represents something real. Many physicists extrapolate from the elegance of the idea of the deterministically evolving wave function to an ontological interpretation of QM (many-worlds or many minds) which tries to elevate this side of the story and minimize the measurement process. There is no quantum theory without measurements!

I’m sympathetic here, since while I believe the both of the quantum processes are fundamental, I think the measurement events are the “more real”: they constitute our concrete world while wave functions are the abstract possibility space available to be actualized by measurements (they are “real”, too, but not in a concrete sense).

2. While rejecting the naïve assumption that the wave function represents something real, Mohrhoff does want to find an objective description of reality which doesn’t appeal to consciousness. QM gives the probability distribution for unperformed measurements. It is a mistake to see these as subjective probabilities. They are objective probabilities.

I agree with this to an extent: I don’t see full-blown human consciousness as the sole avenue to measurement, and think natural systems implement measurements ubiquitously. However, in my view, the phenomenon of first-person consciousness is rooted in an experiential quality which is part of all measurement events (in the spirit of panexperientialist proposals such as Whitehead's or Gregg Rosenberg's).

But what is Mohrhoff’s positive proposal? What is “this quantum world”?
Here are some notes I took from his writing with my editorial comments in italics.

1. The world is intrinsically non-local. (Don’t be confused by thinking about the existence of a space-time background of points and instants – we contribute that to the theory, its not intrinsic).

2. Identical particles cannot be distinguished from each other independent of their possession of properties which can be distinguished.

So, these two statements imply that the quantum world cannot be built from the bottom up.

So how is it built? From the top-down.

“What ultimately exists is one. Call it whatever you like. Matter and space both come into being when this enters into (more or less fuzzy) spatial relations with itself…””…the relations are self-relations,”

This sounds like the world possesses a power of self-measurement. This is certainly an interesting rearrangement of the mystery, but I don’t see how it increases our understanding of reality.

Nothing has a property until it is measured (including the property of existing in a space-time continuum). Measurements create their outcomes (it isn’t that these properties are ontologically carried by the wave function between measurements). No measurements/no world.

OK (although I would say the wave function carries properties in their form as possibilities, and they are not created but made concrete when measured).

The macroscopic world is real in a way the microscopic world is not, since the probability of finding macro-objects where classically they should not be is very low. “… we must be allowed to look upon the positions of macroscopic objects – macroscopic positions, for short—as instrinsic, as self-indicating, or as real per se.” “The ‘foundation’ is the macroworld… not the micro-world.” “As philosophers would say, the properties of the quantum domain supervene on the goings-on in the classical domain.”

But the existence of macroscopic objects is just a primitive in this interpretation. This top-down view is equivalent to saying we just can't explain macroscopic events or objects. I find this unsatisfactory. I want to see us build an improved bottom-up explanation of the world, where the raw material is a property dualism matching the properties embedded in the quantum probability space with an “ability to measure” property possessed by natural systems.

Friday, March 24, 2006

Futuristic Links

The Future of Philosophy
Brian Weatherson has an interesting post predicting that the trend toward specialization by academic philosophers will reverse in the future. As an onlooker who reads some philosophy, I’d say this would be a very good thing. My specific suggestion would be a plea for more metaphysics. Too often, it seems to me that metaphysical presuppositions go unexplained or unexamined in the specialized areas.

The Future of Fundamental Physics
As I’ve discussed in previous posts, fundamental physics seems stuck. Here’s Lee Smolin’s latest manifesto which stresses the need for more work on the philosophical foundations of theory. Also, here’s a slide show from John Baez which discusses “Where We Stand Today”. (Hat tip: Peter Woits’ blog).

Thursday, March 16, 2006

Quantum Physics and Reality (Again)

I want to address this essay in Tuesday’s New York Times by science writer Dennis Overbye entitled, “Far Out Man. But Is It Quantum Physics?” (available with free registration). The essay correctly criticizes the misuse of physics by fuzzy-minded New Age people. But Overbye also errs in buying into an all-too-common misconception about the implications of Quantum Mechanics (QM).

Overbye begins with a discussion of the recent film “What the Bleep Do We Know!?” (which I have not seen). According to his account, the movie's premise is that QM implies the human mind essentially creates reality, so we should be able to alter and improve it as we like. Overbye traces the inspiration of this idea to Eugene Wigner’s suggestion (which followed on John von Neumann’s formulation of QM) that consciousness is the factor responsible for implementing measurements which collapse the superpositions of quantum states into a particular outcome. This idea has been enthusiastically picked up by the filmmakers and other New Ager’s, who inappropriately extrapolate it into the notion that the mind is somehow in control of reality. This opens the door to idealism, paranormal phenomena, and Deepak Chopra.

So far so good. But then we start running into problems when Overbye contrasts this improper use of physics with what he sees as the sober reality of the situation.

He starts by quoting Columbia’s David Albert as saying “It has been decades since anybody took Wigner’s idea seriously.” First, this is incorrect. There are people who have tried to build on the proposal; first and foremost I would cite Henry Stapp (see post here). Second, I believe the reason the mainstream hasn’t worked on the idea is because they lacked good research programs which had traction on the proposed intersection between consciousness and quantum systems; it is not because the idea has been shown to be wrong, which is the impression Overbye’s quick account leaves the reader. I’m personally skeptical that full-blown consciousness is the trigger for wave function collapse, but this remains an open question.

Next, Overbye misinterprets decoherence theory in this passage: “Many physicists today say the waves that symbolize quantum possibilities are so fragile they collapse with the slightest encounter with their environment. Conscious observers are not needed.” I’m sympathetic here since I made the same mistake for years. While I think we can legitimately infer from modern quantum theory and experimental results that natural systems ubiquitously implement measurements all around us, that is not what decoherence theory has shown. Decoherence describes how the interaction of a quantum system with the environment leads to a suppression of interference effects; rather than provide for an objective collapse, it still leaves a ‘mixture’ of states which prevails until we conduct a measurement (see this post for further discussion). The measurement problem remains. (Physicists also continue to explore explicit collapse models, but I think it's fair to say these remain problematic.)

Here’s Overbye’s bottom line:
“In other words, reality is out of our control. It’s all atoms and the void, as Democritus said so long ago. Indeed, some physicists say the most essential and independent characteristic of reality, whatever that is, is randomness. It’s a casino universe.”

This is a very common perspective, among scientists, philosophers and laypeople alike. They take the lesson of QM as being that the strictly deterministic clockwork metaphysics implied by classical physics should be simply overlaid with randomness. But regardless of the details, they assume that a worldview of materialism/physicalism which safely ignores the quantum measurement problem remains the correct stance.

I believe this is wrong. One cannot ignore that the reality implied by QM consists of both deterministically evolving quantum waves and the measurement events which give rise to the concrete phenomena of the macroscopic world. Measurement events remain unexplained within present-day physics. But I conclude the metaphysics necessary for a solution must be richer than physicalism. A property dualism where the ability to measure is an additional aspect of reality is needed (perhaps this could be incorporated into a version of neutral monism, too). And the proposal that this (likely ubiquitous) property and the emergent phenomena of life and consciousness are essentially linked is alive and well. It’s a shame the New Age antics seem to have raised a credibility hurdle for serious consideration of this view.

Monday, March 13, 2006

Environmentalism Talks at Swarthmore

Here's a plug for an upcoming "Public Issues Forum" (2 lectures plus discussion) being sponsored by the Board of Governors of the Greater Philadelphia Philosophy Consortium:


1:00 to 5:00 pm
Saturday, March 25

Science Center 199
Swarthmore College
Free and Open to the Public, followed by a reception with light refreshments

Mark Sagoff
Institute for Philosophy and Public Policy, U. of Maryland
Talk: "The Artist or the Watchmaker: Two Approaches to Environmentalism"

David Macauley
Dept. of Philosophy, Penn State
Talk: "Re-placing Environmental Philosophy: Walking as a Critical Practice"

Directions to Swarthmore below the fold

Driving Directions To Swarthmore College:
Swarthmore College is located 11 miles southwest of the city of Philadelphia in the borough of Swarthmore, Pennsylvania.

The automated campus directions hotline: (610) 328-8001
The main campus number: (610) 328-8000
Swarthmore College
500 College Avenue
Swarthmore, PA 19081

>From the North (New Jersey Turnpike or I-95)
Take the New Jersey Turnpike to Exit 3 and follow the signs to the Walt Whitman Bridge. Take I-95 South, pass Philadelphia International Airport and continue to exit 7, I-476 North/Plymouth Meeting. Take I-476 North to Exit 3, Media/Swarthmore. At bottom of exit ramp, follow sign for Swarthmore by turning right onto Baltimore Pike. (See below for ". . . the rest of the way.")

From the South
Follow I-95 North to Exit 7 (in Pennsylvania), I-476 North/Plymouth Meeting. Take I-476 to Exit 3, Media/Swarthmore. At the bottom of the exit ramp, follow the sign for Swarthmore by turning right onto Baltimore Pike. (See below for ". . . the rest of the way.")

From the East (via the Pennsylvania Turnpike)
>From Exit 333, Norristown, follow signs for I-476 South. Stay on I-476 approximately 17 miles to Exit 3, Media/Swarthmore. At the bottom of the exit ramp, follow the signs to Swarthmore by turning left onto Baltimore Pike. (See below for ". . . the rest of the way.")

From the West (via the Pennsylvania Turnpike)
>From Exit 326, Valley Forge, Take I-76 East, Schuykill Expressway, about 4 miles to I-476 South. Take I-476 approximately 12 miles to Exit 3, Media/Swarthmore. At the bottom of the exit ramp, follow the signs to Swarthmore by turning left onto Baltimore Pike. (See below for ". . . the rest of the way.")

From the Airport
Take I-95 South. Continue to exit 7, I-476 North/Plymouth Meeting. Take I-476 North to Exit 3, Media/Swarthmore. At bottom of exit ramp, follow sign for Swarthmore by turning right onto Baltimore Pike. (See below for ". . . the rest of the way.")

". . . the rest of the way"
Stay in right lane and in less than 1/4 mile turn right onto Route 320 South (watch turns on Route 320). Proceed through second light at College Avenue to the first driveway on your right to visitor parking at the Benjamin West House. The Benjamin West House is the College's visitor center and has someone there to hand out maps and directions 24 hours a day.

". . .to the DuPont parking lot" (this is the lot adjacent to the Science Center)
Follow the directions under "the rest of the way" but instead of passing through the second light, turn right onto College Avenue. On College Avenue take your first right onto Cedar Lane. At the next stop sign turn left onto Elm Avenue. Before the next stop sign a driveway flanked by stone pillars will appear on your left. Turn there onto Whittier Place and follow it to DuPont parking lot on the right.

Wednesday, March 01, 2006

Sean Kelly Blog

{UPDATE 24 March 2008: please note this blog I linked to below never really got going. Updated the link to Kelly's homepage at his new Harvard digs.}

Now I see that philosopher and phenomenologist Sean Kelly has a blog. It's focus is on Merleau-Ponty and the Phenomenology of Perception, of which Kelly is undertaking a new translation. I mentioned Kelly's work in admiring fashion in old posts here ,here, and finally here.