The empirical backing for physical closure

Only a small handful of people tried to think through the empirical, inductive support for the causal closure principle, based on our best scientific knowledge. The most important text taking up the job of evaluating arguments for the causal closure principle is Papineau (2001). According to him, the real turning point in the story of physicalism happened in the middle of the 19th century with Helmholtz’s establishing the conservation of energy in 1847.

With this new synthesis all previously established conservation principles concerning physical forces were brought together to form a universal principle of the conservation of energy. But synthesis in this case meant more than just bringing together all known conservation equivalences. Helmholtz considered cases where apparently non-conservative forces like friction were given microscopic interpretations in terms of conservative fundamental physical forces. The third element that made his work exceptional was his interest in physiology. Helmholtz was a physician by training and had a close connection with eminent German physiologists who were committed to a reductionist program the goal of which was to show that the same laws operate in the organic realm as in the inorganic realm. These three pillars formed the bases for many reductionist/physicalist programs that followed later. Papineau’s reconstruction of the reasons why most philosophers have yielded to physicalism in the last fifty years also follows this tripartite approach.

2.3.2.1 The conservation of energy premise

First and foremost, physical closure is supported by (i) the conservation laws themselves. A suitable general formulation of the idea of a general conservation law can be found in Gibb (2010):

„Every physical system is conservative or is part of a larger system that is conservative (where a system is conservative if its total amount of energy and linear momentum can be redistributed, but not altered in amount, by changes that happen within it.)” (Gibb 2010:367)

This formulation says nothing about the forces involved and below, following Papineau and Gibb I will consider the conservation of energy and momentum only in abstract terms as for my purposes it doesn’t matter which forces are involved in a general conservation principle. This abstract principle tells us that there are no other ways of changing things in a physical system then (1) by changing the amount of energy or momentum which can only be done from a more extended conservative system or (2) by redistributing energy or momentum inside the system. Normally anything that happens inside a closed physical system can be described as some kind of redistribution. (1) and (2) provide us with a good general characterization of the physical realm. It has a fixed amount of energy and momentum rendered in a pattern we might also call a distribution. According to this picture, whenever a physical change or a physical event takes place in that realm it is a change in the pattern, the distribution of energy or momentum. Naturally, for the purposes of physicalist philosophers, a suitable general law of conservation excludes the possibility of interventions by forces from outside the physical realm itself. More on this later, first we should examine some further points.

2.3.2.2 The successful reductions to fundamental forces premise

The second source of support (ii) for physical closure is the success of reductive attempts at explaining apparently non-conservative or dissipative forces like friction in terms of basic conservative forces. Here, it would be natural to add further examples to see the wider consequences of the issue. Even though Papineau restricts his discussion to friction, there are a handful of other non-conservative forces there are reduced to more basic conservative forces: viscosity, tension, compression or drag in fluid mechanics are the most important.

The reduction of certain other physical macro-properties (not necessarily forces) like temperature or properties of solids like hardness36 _{are similarly interesting as today these are}

considered to be reduced to complex fundamental level electrical and mechanical forces. In the case of temperature its conservativeness was proven independently of its reduction. Micro-level kinetic energy formed the reduction base for temperature and this fact is even more interesting if we add that most non-conservative, dissipating forces dissipate energy via releasing heat.

The case of hardness requires some clarification. Hardness is not a force, it is the resistance of a solid to deformation, in other words a theory of hardness describes the behaviour of solids under forces like compression or sheering. So, it is not a force, but it is directly connected to activities of certain non-conservative forces. What the reduction of hardness properties, like deformation hardness, aim to explain is how compression or sheering forces are resisted by molecular or ionic bonds. This is where a problem of macro level mechanics is translated to the language of fundamental forces. The different aspects of

36 _{Since ancient times hardness is one of the most important macro properties for human purposes. From}

engineering to architecture, it is indispensable to understand hardness. It is a complicated property of solids that is usually divided into three categories: scratch hardness, elastic hardness and deformation hardness.

hardness, resistance capacities of solids, are reduced to complex, bonding and crystal structure type dependent37 _{conservative micro and meso-level electrical and mechanical}

forces.

Together such developments suggest that because more and more macro or higher- level forces and properties turned out to be amenable to reduction in terms of conservative fundamental forces other properties (if not forces) will probably also yield to scientific inquiry and will “reduce to a small stock of basic physical forces which converse energy” (Papineau 2001:27). I added hardness and temperature to the list to show that there are way more interesting cases relevant to the inductive base of this argument than friction. So, to sum it up: many apparently special forces and properties in nature were reduced to the workings of a small stock of basic conservative physical forces, therefore we have good inductive reasons to think that what we learned while investigating certain meso and macro-level properties can be extended to mental and other higher-level properties.

2.3.2.3 The support from physiological research

The third source of support (iii) for physical closure comes from physiology, from inductions based on advancements in the life sciences. It is a negative argument stating that there is no evidence for the workings of alternative forces inside living systems. Or in other words, as we get to know more and more about the inner nuts and bolts of organisms, we see the same basic physical laws at work as in the inorganic realm. This is contrary to what many scientists thought before the middle of the 20th _{century. From the middle of the 19th century onwards}

more and more evidence was found supporting the view that living systems fall under the

37 _{Advancements in the reduction of hardness properties and the disunited, multiply realized nature of hardness}

properties are relatively new results in science. Originally physicists expected a unified explanation. (see: Gilman 2009, introduction).

scope of the second laws of thermodynamics38_{, contrary to all appearances. The issue became}

more straightforward in the second half of the twentieth century with the advent of biochemistry, biophysics and later neuroscience. As Papineau says “detailed physiological investigation failed to uncover evidence of anything except familiar physical forces.“ (Papineau 2001:31) „...there is no direct evidence for vital or mental forces. Physiological research reveals no phenomena in living bodies that manifest such forces. All organic processes in living bodies seem to be fully accounted for by normal physical forces.” (Papineau 2001:27) This amounts to a strong inductive argument against traditional vitalism that postulated and expected the existence of special vital forces over and above basic physical forces in special contexts. If there had been such forces scientists should have found deviant processes in living systems, processes the unfolding of which deviate from the course set by basic conservative physical laws.

38 _{This is a historically very important case. It seems that life on Earth has a tendency to maintain a highly ordered}

state and what is even more to increase order and complexity. One simply has to consider the biosphere as a whole to see this second wonder. Both tendencies seem to go against the second law of thermodynamics. This seemed to require explanation and for some time it was taken to be a special or “vital” property only living systems exhibit. As these phenomena seemed to go against a basic physical principle people thought that their explanation requires the postulation of special vital forces. One important milestone in this story is Schrödinger’s 1944 book “What is Life?”. In it, he explains away a few apparent conflicts between physics and biology, among them the conflict with thermodynamics. This account later became the received view in biology. Schrödinger observes that living systems are open systems capable of increasing complexity locally but not globally. Relying on constant energy inflow provided by our Sun living systems can increase complexity even though this achievement is more than paid for by the increase of disorder outside, so the phenomenon is sustained by a net increase of disorder in the physical universe as a whole.