Thinking that reality bottoms out in a fundamental level is a commonly held belief in both philosophy and physics. But Tuomas Tahko argues that alternatives to this foundational picture are equally compatible with the evidence. For example, we can interpret what the Standard Model of particle physics says about quarks in a coherentist light rather than a foundationalist one: since quarks depend on each other for their existence, quarks do not exist independently – something we normally think is true of fundamental entities. We should therefore not prejudge what the structure of reality might look merely based on our intuition that it might be foundational.
Philosophers and scientists alike often talk about “fundamentality” or the “fundamental level”. We might say that, fundamentally, everything is made of waves or that quantum field theory is as close to a fundamental theory as we currently have. More colloquially, we might say that ultimately everything is made of the fundamental “building blocks” of reality, whatever they may be – fields, particles, or something else. The thought is that these building blocks compose everything else, and so everything else depends on them, while these building blocks themselves do not depend on anything else because they are simple or have no further parts. The supposed fundamentality of a particle such as an electron is different from the supposed fundamentality of a theory such as quantum field theory. A fundamental theory may describe the “fundamentalia” – the fundamental entities – but as a representational device, the theory itself is not part of reality in the same way as the entities that it describes.
The “building blocks” approach to the question of what reality is fundamentally like is common, but not the only approach. Philosophers have also speculated about turning the order of priority on its head and conceiving the universe as a whole as the only fundamental thing, where everything else depends on it. In this type of picture, the fundamental level, far from being simple, is maximally complex and has everything else depends on the whole. Interestingly, one motivation for the view comes from quantum theory, where entangled systems consisting of spatiotemporally separated entities could be seen as having features that can only be ascribed to the whole, not the individual parts. Accordingly, the entangled whole seems be more fundamental than its parts.
While it may come naturally to us to think that there must be something fundamental, whether at the “bottom” or “top” level of reality, knockdown arguments to this effect are notoriously difficult to come by. There is almost a poetic aspect to some of them: in the absence of something fundamental “Being would be infinitely deferred, never achieved”, as Jonathan Schaffer puts it . The underlying thought is that chains of dependence cannot be infinite, since something needs to explain the existence of dependent entities, and that explanatory base could only consist of independent entities. A child may wish to keep asking “why” forever, but at some point, we must reach the bedrock; there are no further answers. It is difficult to shake this basic reaction, but the lack of conclusive arguments or evidence in favour of a fundamental level should encourage us to explore what alternatives there might be.
Quarks lack one of the defining features that are typically ascribed to fundamentalia, namely, independence
There are two primary alternatives to foundationalism, the view that reality does have a fundamental level. The first is coherentism, which suggests that we should take a more holistic view, whereby the foundation of reality could be constituted by entities that are themselves dependent on each other, in a symmetric fashion. The second is infinitism, which endorses the possibility of infinite descent and hence infinite chains of dependence. Let us discuss each of these in turn.
Coherentism, or something very much like it, may be motivated both empirically and by way of some puzzles that foundationalism faces. For empirical motivation, we may look to The Standard Model of particle physics. On the face of it, The Standard Model looks rather like a list of fundamental particles, so one might think that it supports foundationalism. For instance, it includes quarks, which are treated like point-like particles – or “simples” – that have no internal structure and may appear like a paradigm case of fundamental entities. However, some of the particles on that list have certain peculiar features. For instance, quarks do not exist independently; they come in groups of two or three, such as in the case of mesons (group of two), and protons and neutrons (groups of three). So, you do not get freely existing quarks, simples though they may be. This immediately suggests that quarks lack one of the defining features that are typically ascribed to fundamentalia, namely, independence. In some sense, the quarks in these quark pair or triplets seem to be symmetrically dependent on each other.
In a little more detail, the strong bond between quarks is known as quark confinement and it is sometimes illustrated with the so called “bag model”. The idea is to think of a quark triplet as if it was inside a stretchy bag. If you then try to separate one of the quarks in the triplet, you’ll discover that the bag resists your efforts with an increasing force. What happens is that before the isolation could occur, the energy being directed to the process produces mesons – quark-antiquark pairs. Instead of pulling apart a quark from a quark triplet you end up with a quark-antiquark pair (and the original quark triplet remains intact).
It is not entirely clear how these empirical details are best interpreted in the context of fundamentality, but quarks certainly do not seem to behave in a way that would be independent in the sense that one might expect from fundamentalia. In fact, it’s not clear that anything is independent in the strongest possible sense – this is the puzzle that the classic foundationalist picture of fundamentality faces. If we combine all this with other data that we have regarding quantum entanglement and the nature of quantum fields, the picture is certainly open to a coherentist interpretation. Ultimately, this could lead to a completely circular picture, where everything, or at least all the candidate fundamentalia, end up being dependent on each in a circular fashion.
The lack of conclusive arguments or evidence in favour of a fundamental level should encourage us to explore what alternatives there might be
What about the other primary alternative to foundationalism: infinitism? As the name suggests, infinitism eliminated the fundamental level altogether, in favour of infinitely descending chains of dependence. For the infinitist picture to be palatable, we need to abandon the intuition that dependence needs to bottom out in something fundamental. As we saw earlier that intuition is generally tied to explanation. However, it may be driven simply by our psychological need to find the ultimate explanation. While infinite regresses are generally regarded as an alarming sign in philosophy, not all regresses or infinite sequences need to be vicious. For instance, in mathematical contexts we commonly refer to infinite sequences of numbers, and speculation about the possibility of an infinite universe is not hard to come by. Still, it’s difficult to see what kind of evidence could properly speak in favour of infinitism: even if science keeps taking us forward one level at a time, this would not seem to be enough to show that those levels could go on forever.
There is an intriguing, hypothetical version of infinitism that could in principle be corroborated by empirical evidence. This version, sometimes called boring infinite descent, suggests that while chains of dependence could go on infinitely, there could be a point where the entities or the structure involved in these chains starts repeating; it’s turtles all the way down. The thought here is that a full-blown version of infinitism seems very demanding: if each level has a new kinds of entities governed by some hitherto undiscovered laws, then not only would there be infinite chains of dependence, but also an infinite number of different kinds of entities and laws. On the “boring” version, only chains of dependence need to be infinite while the kind of entity involved and the way that these are structured could reappear in the chain. This would also have the advantage of enabling us to give a full description of reality in an algorithmic fashion, since we might be able to capture the principles that govern the repeating structure with a finite description. Finally, if we did in fact empirically discover that at some point there is a repetition in structure, then this could be counted in favour of boring infinite descent. Of course, it would hardly be conclusive evidence!
What should we make of all this? Given the very limited empirical evidence available, the sensible conclusion would be to keep all the options open, and to examine them further. While we often think that reality bottoms out in something fundamental, we should clearly not prejudge the issue.
 Schaffer, J. (2010) 'Monism: The Priority of the Whole', Philosophical Review 119 (1): 31-76, p. 62
Tuomas Tahko’s research on fundamentality and other related topics has been funded by the European Research Council under the European Union’s Horizon 2020 research and innovation programme, Grant Agreement No 771509, The Metaphysical Unity of Science (‘MetaScience’) Consolidator grant.