Fundamental Disagreements
There are many ways to define “fundamental”. In regular discourse, it often means nothing more than important. A more precise definition would stress that this importance is central, or basic.
In science and philosophy, it can be argued that the term conveys an additional connotation of independence: something is fundamental if it does not need to be explained by something else, or if it can explain things without the help of anything else.The Standard Model, especially in the improved “Super Model” version that we imagined in the previous section, possesses the attributes of fundamentality that we just described. Because its constituents exist at the smallest scale accessible to us, we obviously cannot understand it in terms of even smaller things. And because everything in the Universe is made up of its particles/fields, it should, in theory at least, be able to explain everything without the help of anything else.
However, if we define “fundamental” in a more restrictive way, by insisting that something that is truly fundamental should exhibit a high level of coherence and elegance, the Standard/Super Model will have a harder time meeting our criteria. Particle physicists are well aware that the collection of quantum fields that make up the model is a patchwork that lacks fundamental elegance. More than 20 years ago, in the CERN Courier, Christine Sutton wrote:
The Standard Model is a synthesis of our present understanding of the quarks and leptons and the forces that act upon them. The key word here is “synthesis”, for the model is not an elegantly hewn theory from which the quarks and leptons and their interactions emerge. Instead it is an amalgam of the best theories we have, which we can bolt together because they have enough in common to suggest an underlying unity, although due to our ignorance the joins still clearly show.
[7]Must we conclude that there is no such thing as true fundamentality in physics (at least in physics as we know it), and by extension, that no scientific theory can be considered fundamental?
Maybe we’ve been too restrictive by adopting a straightforward, reductionist viewpoint that led us to look for fundamentality only at the smallest scale accessible to physics. Indeed, a case can be made that fundamentality can be found in multiple places, at various levels across all scientific disciplines.
Consider the field of chemistry, which stands just above particle physics in terms of scale. Beyond historical convention, there is a good reason why it is not simply called “molecular physics”. In theory, chemistry should be nothing more than electromagnetism and quantum mechanics applied to protons, neutrons and electrons. But in practice, essentially none of the knowledge base of chemistry has been derived that way. The properties of an isolated hydrogen atom can be easily computed from Coulomb’s law and the basic equations of quantum mechanics. However, for molecules even as simple as H2O, it is essentially unrealistic to derive their basic properties from physics, starting from scratch so to speak [8]. Basic chemistry is fundamentally dependent on empirical measurements. Many principles of physics are used in chemistry, to model relationships between empirically obtained values, but, from a practical point of view, even the most basic chemistry cannot be said to be derived from particle physics. In that sense, chemistry can be thought of as an autonomous science, and its basic principles are, for all practical purposes, fundamental. In the same way, even within the traditional boundaries of physics, many general principles and laws that apply to the study of complex systems (thermodynamics, fluid dynamics, chaos theory) can be considered independently fundamental.
Biologically relevant molecules like DNA contain so many atoms that it is essentially impossible to model them starting from particle physics.
Even from a chemical point of view, the study of DNA’s structure and behavior needs empirical inputs and cannot be undertaken from basic principles alone. If we hadn’t discovered DNA in nature, we would almost certainly never have predicted its existence starting from the fundamental principles of chemistry.Because of the emergence of complex behavior that we witness at all levels, from biologically relevant molecules to cells, organisms and conscious beings, a case can be made that fundamentality exists in a meaningful way at many levels. In the scientific study of the phenomenon of emergence, it is still an open question whether there are phenomena whose behavior, although compatible with lower-level principles, is guided by higher-level principles and laws that cannot be derived, even in principle, starting from the principles at the lower levels [9]. Such an eventuality is called strong emergence: if there is such a thing, the case for fundamentality at many levels becomes even more compelling. If higher-level theories and principles possess an independent fundamentality, it becomes possible to fundamentally explain complex phenomena, like the behavior of a living organism, without having to apply quantum field theory to each of its constituent particles. which is a relief.
The independent existence of fundamentality at many levels can be viewed as a challenge to the widely held idea that science forms a united whole and that it would be possible, at least in principle, to explain everything from a unified and complete set of basic principles. Indeed, there are philosophers of science, like Nancy Cartwright, that explicitly deny that science can be thought of as a coherent whole with physics at its fundamental anchor [10].
But we must exert caution. It would be detrimental to conclude carelessly that apparently fundamental principles that operate at a given level are independently fundamental and cannot be derived from the known principles at lower levels.
For instance, we still do not know how the chemistry-to-biology transition at the beginning of life on Earth took place. If we refrain from trying to reduce basic biological phenomena to the principles of chemistry, because we believe that it is computationally (weak emergence) or fundamentally (strong emergence) impossible, we will never shed light on this event. It may be that the chemistry-to-biology transition is so incredibly improbable that the only way to make sense of it is to postulate a vast universe and invoke the helping hand of the anthropic principle. But it we do not ascertain independently the likelihood of the transition by modelling it through the lens of chemistry, we will never know.Steven Weinberg, ever the champion of reductionism, warns that even though a high-level principle may be so useful and so ubiquitous that it is tempting to think of it as independently fundamental, it could still be that it can be reduced all the way back to the fundamental principles of particle physics. He considers the laws of thermodynamics:
Thermodynamics is more like a mode of reasoning than a body of universal physical law; wherever it applies it always allows us to justify the use of the same principles, but the explanation of why thermodynamics does apply to any particular system takes the form of a deduction using the methods of statistical mechanics from the details of what the system contains, and this inevitably leads us down to the level of the elementary particles. In terms of the image of arrows of explanation that I invoked earlier, we can think of thermodynamics as a certain pattern of arrows that occurs again and again in very different physical contexts, but, wherever this pattern of explanation occurs, the arrows can be traced back by the methods of statistical mechanics to deeper laws and ultimately to the principles of elementary particle physics. As this example shows, the fact that a scientific theory finds applications to a wide variety of different phenomena does not imply anything about the autonomy of this theory from deeper physical laws. [2]
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