Monday, April 11, 2011

Power Property Papers Perused

Here are some brief thoughts on papers I read recently on the metaphysics of powers/dispositions.

I thought “A Powerful Theory of Causation” by Rani Lill Anjum and Stephen Mumford was an important paper. The authors set out to show that powers have the right degree of “modal strength” to support a theory of causation. Powers have been long thought to necessitate their manifestations, and necessity (and the sense of constant conjunction) is too strong to describe causation. The notion of metaphysically necessary connections in nature has long supplied a basis for arguing against powers and associated theories of causation. Anjum and Mumford say that powers (dispositions) “dispose” toward their manifestations, but don’t necessitate them.

One way of seeing that powers fall short of necessity is to note that when placed in a context, a disposition can be enhanced or, importantly, hindered by other powers. The authors use a vector addition model as a heuristic to see how this works. Only when the sum of vectors (with various strengths and directions) exceeds some threshold do we get the manifestation.

In later sections of the paper the authors deal with various potential objections and place their theory in a historical context of the difficulties faced by causal models, showing again that the unwarranted assumption of necessitation was the key stumbling block.

While the vector model was interesting, my favorite section of the paper (section 5) deals with explaining probabilistic causation. Here Anjum and Mumford endorse a propensity (propensity=probabilistic power) interpretation for a single disposition. I myself think this is the key to understanding how powers can have the right modal strength “all the way down”; it also has the virtue of fitting with our best physical theory of how the actual world works (quantum mechanics).

I eagerly look forward to a forthcoming book from Mumford and Anjum called Getting Causes from Powers – this will elaborate upon the theory in greater detail. Also note that a podcast and slides from a recent talk by Stephen Mumford from the PhilSci forum at UMB (Norwegian University of Life Sciences) are available here (scroll down for previous talks). It is a very nice introduction to powers, and focuses on contrasting a powers approach with a laws-based theory of causation.

Some quick takes on other papers.

Michael Esfeld argues that a metaphysics of powers has an advantage in terms of compatibility with physics in his paper “Humean metaphysics versus a metaphysics of powers.” In the paper, Esfeld summarizes the difference between a Humean approach and the powers approach: in contrast to the above he does characterize powers as having necessary connections with their manifestations. However, he does then describe the option of treating powers as propensities to explain probabilistic causation. His main point in the paper is that while physics can be compatible with more than one metaphysical picture, the powers model is the best fit given the commitment of physics (and other sciences) to describing dispositional and functional properties.

William A. Bauer takes up the issue of the ontological grounding of powers in "Four theories of pure dispositions". Can they exist without depending on categorical properties for their being? What is the nature of powers when they aren’t manifesting if they lack such grounding? He reviews several approaches to this problem, and concludes that the best model is one where they are self-grounding via a continuous low-level manifestation (which is distinct from their more pronounced, distinguishing potential manifestation).

This was a thought provoking paper, which prompted me to go back and review others on this topic, including Mumford’s “The ungrounded argument”, Neil E. Williams’s response “The ungrounded argument is unfounded”, and Stathis Psillos’s 2006 paper “What do powers do when they are not manifested?”. My quick two cents on this issue is inspired by QM and the idea of powers as propensities: I think powers have a real-but-not-concrete status akin to possibilities in a framework of modal realism. Unlike a static notion of possibilia, however, propensities causally impact our world through their disposition toward actual manifestation events. This is again consistent with QM: between measurement events, quantum systems don’t have concrete existence, but they certainly exist in a causally relevant way, as their influence on events is apparent and measurable.

Finally, I note with interest that two philosophers have recent papers endorsing the Heil/Martin view of powers as inherently qualitative: Jonathan D. Jacobs in “Powerful qualities, not pure powers”, and Robert Schroer, in “How far can the physical sciences reach?”. Both make for interesting reading, as do other papers by these authors.

Here is a list of prior posts on powers/dispositions (chronological).

George Molnar and the Powers That Be


Powers and Property Dualism

Modal Problems with the Theory of Powers

John Heil Gets Very Close

Suarez on Quantum Propensities

Notes on C.B.Martin's The Mind in Nature

Power Holism

Powers vs. Humean Supervenience

Abilities vs. Dispositions


Thoughts said...

Prior to speculating on the nature of causation the philosopher needs to address whether four dimensional forms exist. If objects are inherently four dimensional (ie: if they exist) then the whole project of the analysis of causation is suspect because there is either a block universe or, if Everrett is right or the universe has more than 4 dimensions, an infinity of block universes.

A simple block universe is an entire form, it does not change and there can be no eye of a beholder scanning through time because the eye would be outside time. If any observer has time passing they cannot be locked into a particular, simple block universe.

A multiverse of block universes implies backward causation because if an observer finds themselves at a particular point in classical spacetime then decoherence guarantees that there is a history that is consistent with the state of that point.(Each classical spacetime point has an associated entangled environment).

So either we toy with presentism and make up poorly defined words like "power" and "disposition" to explain our bewilderment or we accept 4 dimensionalism and deal in terms of entire 4D forms. If we accept the latter then the mystery is how time can pass, does our observation move along a succession of spacetime points and if so what is the extra degree of freedom that allows us to escape being fixed?

Steve said...

Thanks: I agree that one needs to grapple with the static block universe alternative (which is what those who would reduce powers to categorical properties would typically endorse).

One thing which has influenced me in recent years is a trend in quantum gravity research that questions the fundamentality of 4 dimensions. Spacetime geometry is viewed by more researchers as an emergent regularity: and dimensionality may differ at different scales. What it emerges from is some pre-space causal network of quantum mechanical events. So the power/propensities of quantum systems have priority according to this view.

Thoughts said...

Emergent spacetime is a hot topic but I have been disappointed by the apparent failure of the theorists to incorporate time as an observable (See On the significance of a recent experiment demonstrating quantum interference in time). One of the most sober reviews of the subject is provided by John Ashmead Quantum Time. However, it still remains true that a groundbreaking qm experiment was performed by Lindner et al in 2005 and this has scarcely been mentioned in the qm theory literature.

The experiment has been repeated and refined (see for instance Attosecond double- and triple-slit experiment).

If time is an observable, to be treated in qm in the same or a similar way to space then observers are treated to a 4D classical world at each spacetime point. This blows presentist theories of causality clean out of the water because it is not 3D objects that emerge - if emergence is true - it is 4D objects, complete histories, that are attached to every point observer and to every other classical point in an environment. From the point of view of a multiverse there are an infinity of these entangled, classical environments.

F. Lindner, M. G. Schätzel, H. Walther, A. Baltuška, E. Goulielmakis, F. Krausz, D. B. Miloševi ́ ,
D. Bauer, W. Becker, and G. G. Paulus. Attosecond double-slit experiment. Physical Review Letters,
95:040401, 2005.

Steve said...

Thanks. I will look at this some more. My first thought when I first looked at this time interference effect was that there are several ways QM theory can be adjusted to handle it, not all of which have the implications you posit.

Thoughts said...

Steve, I suspect you are thinking of quantum "time of arrival". Galapon considers this in depth and concludes that:

"Quantum mechanics is inherently non-local in time and that means "the description of the past must bear actions of the present. .. Temporal non-locality then replaces the spatial non-locality inherent in the spontaneous localization of the wavefunction in the standard interpretation." Galapon, E.A. 2010. Time in Quantum Mechanics Vol 2. Springer-Verlag

My last comment set me perusing the literature. Certainly quantising arrival times leads to a non-self adjoint operator but Stueckelberg
theory does deal with time itself as an observable. My impression is that we are in the same position as scientists in 1895, we are fiddling with a presentist theory of physics and getting hugely complex answers when lurking somewhere there is a simple theory that incorporates time naturally.