The physicalist is the materialist who has learnt the lessons of twentieth-century physics. The most basic teaching of both relativity and quantum physics is that our intuitions are of no help in the scientific quest to understand the fundamental nature of matter. The world, as conceived by modern physics, both in its vastness, as described by astrophysics and cosmology, and in its minuteness, as revealed by the quantum mechanical Standard Model of particle physics, is so strange, so immensely complex and difficult to grasp, that speculations based on ordinary ideas can contribute nothing to the painstaking practice of science.
In the face of the extraordinary progress in the human understanding of reality, as expressed in the edifice of modern physical sciences and manifested in the technological fruits of that science, the physicalist also acknowledges that the ultimate nature of reality remains something of a closed book, to scientists as well as everyone else. Chapter 6 argues that not only do we not know what the fundamental ‘level’ of reality is like, we do not even have good grounds for believing there is a fundamental level at all. We know that reality in itself, separate from human science and observation, is not in levels, it just is what it is. The idea of levels arises when we realise that we can study reality at different scales, and this may or may not be a process that goes on indefinitely. As things stand at the moment, the most fundamental levels observed with the most powerful microscopes, both real and metaphorical, are described in a highly abstruse mathematics, employing concepts that have no simple description in the language of everyday life. In the physicalist perspective, reality loses none of its capacity to astonish and amaze.
The physicalist bows before science – what exists is what science tells us exists. This, however, needs qualification. All scientific theories are subject to potential revision and abandonment, so all ontological claims are taken with a greater or lesser degree of tentativeness. It is true that we cannot seriously deny the existence of the objects of our everyday world, and few scientists would give much credence to the idea that future science will have done away with the concepts of atom, proton, neutron and electron. However, as more fundamental physics becomes more speculative our confidence in the existence of hypothesised entities such as superstrings diminishes, in the sense that a new framework could supersede the existing one with a different range of entities. However, the physicalist inherits from materialist predecessors the negative ontological claim, and the advent of physicalism makes clearer just how central to materialism the negative claim was. Only now are we able to formulate it in a more sophisticated fashion.
Materialism claims there are no gods and demons, ghosts and ghouls, spirits and fairies. It does acknowledge the existence of psychological phenomena, most obviously the sensations, thoughts, feelings and volitions of our own human experience. However, it recognises all psychological phenomena as supervenient on – wholly dependent for their existence on – a non-psychological base. That is to say, physicalism predicts that physics will not hypothesise the existence of spiritual or psychological phenomena for the purpose of explaining psychological phenomena. In this way physicalism is a refutable theory. If physics were to hypothesise an entity with demonstrably psychological properties in order to account for psychological phenomena, that hypothesis would be incompatible with physicalism, and if it proved successful and became adopted as out best physics then physicalism would be refuted.
The epistemological perspectives are carried forward from materialism to physicalism. The materialist has always grounded knowledge in the empirical study of reality. However, hand in hand with developments in science, the scientific method has undergone profound refinement and elucidation. In particular, higher and higher critical standards have been set for the acceptance of theories, and many theories are only ever held with some degree of tentativeness. Too many shocks and surprises in the investigation of the world have left scientists wary of claims of certainty.
The connection between the scientific method and materialism and physicalism is complex. On the one hand, much about science as it is now done, especially in biology and chemistry, presupposes physicalism, and the origins of modern science lie in the repudiation of immaterial essences and forms. On the other hand, physicalism is a falsifiable theory, and in virtue of this falsifiability physicalism claims legitimacy as a theory about reality. In principle science could disprove physicalism. However, the physicalist outlook is so deeply embedded in the practice of theoretical physics, that if the point were reached where it was felt necessary to postulate the existence of a mental or spiritual entity to provide an explanation of some phenomenon, science would have reached a stage in its development so revolutionary, demanding such a profound change in perspective, that everything would be up for question, including the fundamental epistemological outlook established in the seventeenth century.
There is greater humility in physicalism than materialism. Indeed, Epicurus and Lucretius are all too sure of themselves for modern sensibilities. Nonetheless there is probably a fundamental division amongst people with regard to the question of whether or not reality has a spiritual dimension. Of course, there may be a large constituency of people who remain neutral, agnostic, on the question. But for the others, there seems to be something almost ungraspable about how anyone could hold the opposite view to their own. For much of history, the idea of there not being a god has been thought by the vast majority of people whose views have been expressed in written language as absurd. The majority of adults living now also ascribe to a belief in god. For the materialists, taking on board the strange news from twentieth-century physics did not involve a heart-searching with regard to the non-existence of the spirit for very long. It became clear that in the extraordinary description of the worlds of the very large and the very small given by modern physics, spiritual things were not being offered or suggested as part of the story.
However, the physicalist has discarded the social militancy that became attached to materialism in the nineteenth century. It is a philosophical theory; it has an attitude to science and ontological claims; it ascribes to a scientific methodology; it makes predictions about future theory. It is not a social theory, nor part of a political programme. It meets its opponents in philosophical debate, not in physical combat. Many physicalists will adhere to the principles of the radical enlightenment of d’Holbach and others, but this is true of vast swaths of the population now.
In more general terms, physicalism is aligned with a belief in rationality and its importance in human society. This transcends differences in philosophical theories and perspectives. As considered in the final chapter, rationality faces many challenges in the modern world, and its defence is not straightforward. There is no consensus about the foundations of rationality, and the enemies of rationality, as understood by the philosophical community, may choose physical combat over discussion. But that is not a new phenomenon. The pen is mightier than the sword – sometimes.