Reductionism Reconsidered

From: Edward Remler

I read this with a heavy heart. An eminent physicist confusing an already hopelessly confused subject. Consider the statement:

"Superfluidity, like the fractional Hall effect, is an emergent phenomenon - a low-energy collective effect of huge numbers of particles that cannot be deduced from the microscopic equations of motion in a rigorous way, and that disappears completely when the system is taken apart"

This presumably defines "emergent phenomenon" but does so in so loose a manner as to be positively harmful. The actual practice in theoretical physics is that rigorous deduction is the exception rather than the rule in the study of any system involving even a few particles, let alone a many-body problem (meaning huge numbers of particles). And, of course, if I take a system of particles apart, I am left with isolated particles, which obey only the law of inertial motion. So neither major part of the definition restricts 'emergent' to anything worthwhile and one can see why and how people can and do draw any and every conclusion from such descriptions.

This is a serious problem. My experience has been most people use emergent to suggest a breakdown of natural law, and/or of the explanatory abilities of laws of the microscopic laws of physic, and generally link the two. This requires an understanding of what explanation means in physics, and this is a complex subject, but as my remarks indicate, it does not generally entail rigorous deduction.

The quote goes on to say:

"those students who stay in physics long enough to seriously confront the experimental record eventually come to understand that the reductionist idea is wrong a great deal of the time, and perhaps always."

The word reductionism is used today in such a rhetorical sense as to also be meaningless. Again this quote makes an already very bad matter even worse. He surely does not mean to imply that he foregoes quantum mechanics and electrodynamics in his work. Quite the contrary, if he used anything else -- if he invoked some new force of nature to explain some aspect of superfluidity -- no one would pay much attention to him (again for reasons which we need not get into now). If he does, in this sense, base his work on the well established' microscopic equations of motion of physics alone, I would call that a fair definition of the practice of reductionism.

Of course, you may use an unreasonable definition, like requiring everything to be derived explicitly, and rigorously from these equations. That will never happen given simply the complexity of nature. But then what does such a definition prove. Its value is only rhetorical--used to support anti-science and supernatural explanation--sneakily.

All the foregoing will certainly not prove much to anyone not already converted--except that Prof. Ellis parting comment:

"but the message from those seriously concerned with solid state physics (theory and experiment) is unambiguously clear."

is demonstrably untrue.

From: George Ellis

I note with interest the rebuttal taking issue with a Physics Nobel prize winner, writing about a lifetime's experience in his own territory where he has achieved the distinction of creating profound new understanding of unexpected physical phenomena. In my view what he says needs to be taken seriously. The issue is more profound than the comment that reductionism is an `in principle' proposal that can hardly ever be put into effect in practice (although this does indeed need to be taken seriously - it shows that reductionism is a faith rather than an achievement). Perhaps it may help to comment as follows:

There is a point that is fundamental but it is surprising how little it is noted. It is that in a hierarchically structured system, there is *top-down action* (or `whole-part causation') as well as bottom-up action from the micro to the macro level. That is the reason that a simple reductionist view will not work. You can't reduce the behaviour of the macrosystem simply to a summation of the effects of microsystems, because the way the microsystem functions is dependent on the macrosystem! The Quantum Hall effect is one example, as noted in the quotation I sent [and those really interested in this issue should read the whole article from which the quote comes]. I cite two other examples from physics:

(a) The quantum measurement process - collapse of the wave function to an eigenstate of a chosen measurement system - is a fundamental example. The experimenter chooses the details of the measurement apparatus - e.g. aligning the axes of polarisation measurement equipment - and that decides what set of microstates can result from a measurement process, and so crucially influences the possible micro-state outcomes of the interactions that happen. If you believe the Copenhagen interpretation of quantum theory, the distinction between the measuring apparatus and the system observed is crucial and you cannot deduce the resulting set of microstates from the microsystem itself - the macrosystem is the key. If you do not accept this distinction, you are involved in the miasma of many-worlds interpretations of quantum mechanics or similar, where the essential problem remains but becomes highly obscured because of the unresolved issue of the nature of the quantum measurement process.

One of the key issues then is that we do not have a clear statement of when a `measurement process' takes place in a naturally evolving system with interactions but without a conscious observer present (you do not know when collapse of the wave function takes place, and if so along what eigenstates).

One response to all this is that the measurement process interferes with the system and bottom-up causation works for the system, as long as it is not being interfered with. But the point here is that it is precisely the fiction of an isolated system that is at fault: they do not exist in the real world. And if you try to construct a 'bottom up' proposal for explaining how the macroscopic measuring apparatus will work through summation of the effects of the microscopic particles that comprise the measuring instrument, this will not work - because the process involved in observations due to the measuring macro system (collapse of the wave function to an eigenstate) is non-unitary - but the Schroedinger or Dirac evolution of the microsystem is unitary. You can't derive the latter by summation of the former.

(b) The arrow of time: You cannot tell how a macrosystem will behave in the future on the basis of the laws of physics alone and the properties of the micro particles that make up the system because time-reversible micro-physics allows two solutions - one the time reverse of the other - but the macro-system rigorously allows only one of those solutions. The absolute prohibition of one of the allowed microsolutions is mathematically put in by hand to correspond to the real world situation where only entropy-increasing solutions are allowed at the macrolevel. It was the failure to solve this issue that apparently lead to Boltzmann's suicide - he brilliantly proved his H-theorem on the basis of microphysics - and then realised that this solution worked equally well with both directions of the arrow of time!

Physically, the only known solution to this arrow of time problem seems to be that there is top-down action by the universe as a whole [or perhaps boundary conditions at the edge of space-time] that allow the one solution and disallow the other. Whether this is the explanation or not, reductionism crucially fails in that the microphysics apparently allows two quite distinct macro solutions (each the time reverse of the other) but in fact one of them is disallowed at the macro level. You cannot tell which is the disallowed solution by looking at the microlevel alone. [This is actually related to the previous example: collapse of the wave function takes place with a preferred direction of time. It is not clear how that direction is determined if we look at the microlevel of the system alone.]

There are numerous other interesting examples of top-down action in the physical universe when looked at from the macro viewpoint. I will mention three more: two from biology and one from society.

(c) The central theme of evolutionary biology is the development of particular DNA codings through an evolutionary process, in order to adapt an organism to its ecological niche. This is a classical case of top down action from the environment to detailed biological microstructure - in essence the DNA coding incorporates an image of the ecosystem environment in which the organism functions. There is no way you could ever predict this coding on the basis of biochemistry or microphysics alone. The environment acts in a top-down way in the biological hierarchical structuring and so [along with other causal factors] fixes that coding.

(d) The reading of DNA by an organism in the developmental process is not a mechanistic process but is context dependent. For example recent research on genes and various hereditary diseases shows that existence of the gene for such diseases in the organism is not a sufficient cause for the disease to in fact occur.

(e) When a human being has a plan in mind (say a proposal for a bridge being built) and this is implemented, then enormous numbers of micro-particles (comprising the sand, concrete, bricks, etc that become the bridge) are moved around as a consequence of this plan and in conformity with it. Thus in the real world the detailed micro-configurations (which electron and proton goes where) of many objects is in fact to a major degree determined by the macro plans that humans have for what will happen and then the way they implement them [cf Popper and Eccle's discussions of Worlds 1, 2, and 3 and the interactions between them].

At this point the physicist shouts "Foul! that's not the kind of situation I had in mind". That's too bad - I'm talking about real world situations. The truth is that much of physics deals with idealisations that do not describe well the real world as it is -
only some restricted aspects of it. In the real world, top-down action is ubiquituous and has a crucial effect on what happens in physics terms at the micro and the macro levels. As a specific and important example I cite the case of the effect of human actions on the earth's atmosphere through the combined effect of human causation moving very large numbers of micro-particles (CFC's) around in the atmosphere [this is made explicit in the article by H J Schellnhuber on p. C19 in the millenium survey in Nature, 2 December 1999, issue 6761 (supplement to vol 402)].

Finally, perhaps the last remark I made in my previous comment was overstated, but the fact is that there is a considerable reaction in much of the physics community against exaggerated reductionist claims by some. As a specific example, see pages 12-13 of the Millenium survey edition of Physics World [Vol 12, No 12, December 1999]. One quote will have to suffice: "Reductionism has failed in a grandiose manner," said Itamar Procaccia from the Weizmann Institute of Science in Israel. "To understand macroscopic phenomena, which are all around us, we cannot start from strings. Every level of description has its own logic, mathematics, and phenomenology. A tremendous lot remains to be done even if a unified theory [of fundamental physics] is achieved'.

Maybe Edward Remler has some sophisticated version of reductionism in mind that gets round the issues raised above. What is clear is that many versions of that idea are far too simplistic to describe the real world.

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