Introduction
Anthony Aguirre, Brendan Foster and Zeeya Merali
When a stranger, hearing that I am a physicist, asks me in what area of physics I work, I generally reply that I work on the theory of elementary particles.
Giving this answer always makes me nervous. Suppose that the stranger should ask, “What is an elementary particle?” I would have to admit that no one really knows.Steven Weinberg (1997) [1]
We do not know what the rules of the game are; all we are allowed to do is to watch the playing. Of course, if we watch long enough, we may eventually catch on to a few of the rules. The rules of the game are what we mean by fundamental physics.
Richard P. Feynman (1964) [2]
The fundamental laws of physics do not describe true facts about reality. Rendered as descriptions of facts, they are false; amended to be true, they lose their explanatory force.
Nancy Cartwright (1983) [3]
Physics is often believed to hold a privileged status among the sciences as the discipline that most closely seeks to understand fundamental reality. Historically, this search has revealed ever tinier building blocks from which the physical world is constructed. Atoms, once thought to be fundamental, have had to give way to a plethora of subatomic particles, including electrons, protons and neutrons, with the latter two entities being broken down further into constituent quarks. Debates rage over whether these too will eventually surrender to a description in terms of tiny vibrating strings.
Given this zoo of elementary particles, that themselves may not be the most basic constituents of physical reality, it seems fair to ask whether a reductionist approach
A. Aguirre
Physics Department, UC Santa Cruz, Santa Cruz, CA, USA
B. Foster • Z. Merali (B)
Foundational Questions Institute, Decatur, GA, USA
e-mail: merali@fqxi.org to physics can ever yield a final, fundamental description.
What, indeed, do we mean when we invoke the concept of the “fundamental”?There are many possible answers to this question—many different layers and scales to our description of ‘things’ in the physical universe. Elementary particles may intuitively be identified as “more fundamental” than higher-level emergent features, such as human consciousness; but it is not clear that this hierarchy provides the best or the correct way to think about nature. What does it really mean for something to be more or less fundamental? Is it enough to say that fundamental things are smaller, simpler, more elegant, and more economical? Are less-fundamental things always made from more-fundamental things? And how do less-fundamental descriptions relate to more-fundamental ones?
These are some of the questions that were addressed by participants in FQXi’s 2017-2018 essay contest, which asked, “What is Fundamental?” The contest drew 200 entries from 43 countries (from every continent bar Antarctica), and this volume brings together all 15 prize-winning entries.
Our first prize winner, Emily Adlam, argues that smaller does not always mean simpler—as splitting the atom has proven—and that history has taught us that what we consider to be fundamental will change in the face of scientific advances, probing ever deeper layers of reality. But rather than just focus on how to explain features and things in terms of other ‘more fundamental’ things, we should be asking ourselves what needs explaining. In Chap. 2, Adlam makes the case that science should be able to explain the existence of the sorts of regularities that allow us to make reliable predictions. But this does not necessarily mean that it must also explain why these regularities take some particular form, giving rise to one family of particles, with certain properties, rather than another. In addition, Adlam says, we may even need to revise our attitude about what counts as an adequate explanation.
It is easy to take for granted that physics is the discipline that most closely deals with the fundamental—whatever the fundamental may eventually turn out to be.
But in Chap. 3, Matthew Leifer challenges this assumption, noting that sociologists may be equally justified in claiming that sociology is the most fundamental field of study. Leifer has developed a framework to explain why no one discipline can claim to be more fundamental than all others. In his picture, knowledge takes the form of a scale-free network, with hubs of equal importance; specialists who focus on one hub, the sociology hub, say, will view sociology as the trunk from which all other forms of knowledge branch, but others located at the physics hub, for instance, might hold the equally valid view that physics has foundational status.Defending the opposing view that physics as a discipline can make a unique claim to being fundamental, is Alyssa Ney. In Chap. 4, she explains that accepting this requires one to give up the expectation that our current best theories of physics—and potentially our future theories—must be able to explain everything in order to be worthy of fundamental status. Rather, she argues, we should only expect “explanatory maximality”—which physics does provide. This is something that should be acknowledged by funding agencies, Ney claims, when assessing how to allocate money.
Dean Rickles also strives to unpack the commonly understood view of what a fundamental discipline should offer. This is the idea that physics should be able to offer a complete account of the world. However, he notes that there can be other notions of fundamentality within physics, for instance, as defined by the effectiveness of mathematics at describing the physical world. In Chap. 5, Rickles assesses alternative views of what it means to be fundamental. Marc Seguin, meanwhile, notes in Chap. 6 that many hold up the Standard Model of particle physics as the most fundamental theory we have, while others may ascribe fundamentality to higher levels of description, such as to consciousness. He reviews these and other options while distinguishing between epistemological fundamentality (the fundamentality of our scientific theories) and ontological fundamentality (the fundamentality of the world itself, irrespective of our description of it).
A number of prize-winners homed in on the issue of consciousness and mind. Markus Mueller argues that while most attempt to explain how mind can be constructed from fundamental physical building blocks, it is worth considering that some notion of the mind is actually the most fundamental aspect of reality. In Chap. 7, he outlines how this may help elucidate some conceptual problems in the foundations of physics. Tejinder Singh meanwhile ponders the process by which the human mind converts things in the observed universe into laws. He further proposes, in Chap. 8, that probing down to the deepest layers of reality reveals that laws and things become more and more like each other. And in Chap. 9, Sabine Hossenfelder investigates one potentially fundamental aspect of human experience, free will. While the prevailing view among physicists may be that truly free will is an illusion, she argues that free will may indeed exist, and be an emergent phenomenon.
Others stayed within the conventional realms of physics to identify candidates for the fundamental. In Chap. 10, Sean Carroll and Ashmeet Singh make the case that quantum mechanics provides the most fundamental description of the universe and, among its possible interpretations, the Everett or Many-Worlds interpretation has the simplest ontology. They then attempt to identify the most pared down mathematical elements from which this description of nature can be constructed. Ian Durham also scrutinises quantum theory but, in Chap. 11, he focuses on another aspect of the theory that has been debated: whether it is capable of describing what is (‘beables’) rather than merely what is observed. Durham suggests that in a framework in which the universe is considered to be a beable, the universe cannot be fundamental.
While we may not yet have found the fundamental theory of reality, it is still possible to ask what features such a theory should have. In Chap. 12, Gregory Derry argues that a fundamental explanatory structure should have four key attributes: irreducibility, generality, commensurability, and fertility.
Karen Crowther asks why our current best theories of physics are not considered to be fundamental and, in Chap. 13, uses the answers to propose her own checklist for fundamentality in physics. And in Chap. 14, Ken Wharton argues that the one feature that a fundamental description of reality cannot hold is randomness.Finally, two special prizes were given to entrants that grappled with the meaning of the essay question in unusual ways. Mozibur Ullah won the creative writing prize for seeking to understand the word ‘fundamental’ through a mock dialogue between Socrates, Theaetetus and Polydorus, in Chap. 15; while Aditya Dwarkesh was awarded a student prize for his linguistic approach to analysing the connotations of the word ‘fundamentally’, which appears in Chap. 16.
Perhaps unsurprisingly this compilation is dominated by contributions from researchers specialising in various branches of physics and philosophy, with an emphasis on quantum foundations. Nonetheless the contest yielded a diverse range of answers: some positing specific candidate aspects of reality that could be held up as fundamental—from the interpretation of quantum theory that sprouts parallel worlds, to claims that consciousness is itself fundamental—while others examined whether fundamentality should be applied to things or models and laws, and what is even meant by a fundamental explanation. Given the huge scope of the question, there is little wonder that no consensus can be found. What is clear, however, is that in attempting to answer one of the deepest questions—“What is fundamental?”—we have opened up a rich vein of insights into what should constitute scientific and philosophical understanding.
References
1. Weinberg, S.: What is an elementary particle? Beam Line 27(1) (1997). Stanford Linear Accelerator
2. Feynman, R.P.: The Feynman Lectures on Physics (Sect. 2-1, “Introduction”). Lecture 2, “Basic Physics”, vol. I, pp. 2-1. Addison-Wesley, Reading (1964)
3. Cartwright, N.: How the Laws of Physics Lie, p. 54. OUP, Oxford (1983)