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What is a theory of everything?

Curt Jaimungal dismantles the most seductive phrase in modern physics not by proving it impossible, but by revealing how loosely it is defined. While the public imagines a single mathematical equation waiting to be discovered, Jaimungal argues that we are actually arguing past each other, using the same label for five distinct and often incompatible ambitions. This piece is essential because it exposes the intellectual debt we owe to the term 'Theory of Everything' before we can ever hope to pay it off.

The Wikipedia Problem

Jaimungal begins by exposing a fundamental incoherence in how the concept is currently understood, noting that even standard references fail to agree on the definition. He writes, "If you read the Wikipedia article on 'Theory of Everything' closely, you'll notice it actually calls something a TOE differently almost each time." He dissects six common definitions, pointing out that unifying the four fundamental forces does not automatically explain the origin of the universe's initial conditions or the nature of consciousness. The author's critique here is sharp: a theory that successfully merges gravity with quantum mechanics might still fail to predict why there are three generations of fermions or why the cosmological constant has its specific value. This distinction is vital, as it separates a mere mathematical consistency from a true explanation of reality. Critics might argue that demanding a theory explain every physical parameter is setting an impossibly high bar, but Jaimungal's point is that the term 'everything' implies exactly that, and current candidates fall short of the promise.

A cocktail's not a marriage… though one may unhappily lead to the other.

The Hierarchy of Ambition

The core of Jaimungal's contribution is his classification of these theories into a descending ladder of rigor, moving from the strict to the speculative. He identifies "Type A" theories as the traditional physics goal: unifying gravity and the Standard Model. He notes that while candidates like String Theory or Loop Quantum Gravity are often touted as the answer, they often only hope to be consistent with the Standard Model rather than deriving it uniquely. He writes, "These include Woit's approach, Loop Quantum Gravity, String Theory, and even Wolfram's approach," but emphasizes that many of these fail to uniquely predict the particle content we observe. This is a crucial historical context; as Jaimungal points out, the term was popularized by John Schwarz and John Ellis in the mid-1980s specifically to mean a theory that explains the number and couplings of all elementary particles, a standard that many modern contenders struggle to meet. The author suggests that what we often call a Theory of Everything is actually just a theory of quantum gravity, which is a noble but incomplete step.

What is a theory of everything?

As the classification moves down to Type B and Type C, the scope expands to include dark matter, dark energy, and eventually metaphysical questions about why laws exist at all. Jaimungal observes that Type C theories, such as the Mathematical Universe Hypothesis, attempt to explain not just the entities but the fact of following laws. He writes, "That is, you explain in a single framework the 'laws' the universe follows, but then simultaneously why (and how) it 'follows' those laws to begin with." This shift from physics to ontology is where the term begins to lose its scientific precision, becoming more of a philosophical weltanschauung. The author acknowledges that while this is a "mild bastardization" of the term, it remains forgivable due to its ambition. However, this expansion creates a friction where physicists and philosophers talk past one another, each claiming the mantle of the 'Theory of Everything' for vastly different projects.

The Democratic Dilution

The most provocative section of Jaimungal's argument is his descent into Type D and Type E, where the definition of 'everything' expands to include sociology, psychology, and even the mundane quirks of daily life. He describes Type D theories as those that incorporate economic dynamics or emotions, often formalized not in LaTeX but in "Word documents all the way down." He writes, "They are also characterized by not formalizing with LaTeX," highlighting the shift from mathematical rigor to narrative coherence. By Type E, the concept dissolves entirely into personal anecdotes, where a theory must explain why a specific car makes a noise or why a dog circles three times before lying down. Jaimungal argues that everyone has a Type E theory, noting, "Your uncle has one. Guaranteed." This observation serves as a biting critique of the term's overuse: when 'everything' includes the absorption rate of paper towels, the term loses its power to describe the fundamental structure of the universe. The author suggests that this dilution is inevitable because "everyone thinks they have a shot at it," turning a scientific pursuit into a democratic exercise in personal modeling.

Unity in contempt. Interdisciplinary interestingly means hating more people.

The Finite Chips of Understanding

Jaimungal concludes by framing the pursuit of a Theory of Everything as a zero-sum game of intellectual resources. He introduces the metaphor of a casino, stating, "Everyone only has somewhere between six and nine chips that they can place among any of these Types of theories of everything." This means that a researcher who dedicates their life to the rigorous mathematics of Type A has no capacity to address the metaphysical questions of Type C or the sociological nuances of Type D. The author writes, "The people who are within a specific Type either believe that you can solve the problems of any other type from within their Type, or that insights from other Types are not required for them to make progress within their Type." This insight explains the deep tribalism in scientific discourse: it is not just a difference of opinion, but a fundamental mismatch of resources and goals. A counterargument worth considering is that true progress might require the very interdisciplinary synthesis Jaimungal describes as impossible, but his point stands that the current culture of specialization makes such a synthesis unlikely. He ultimately concludes that a Theory of Everything is a "regulative ideal," something we asymptotically approach while arguing about what 'approach' means.

Bottom Line

Jaimungal's most significant contribution is the realization that the 'Theory of Everything' is not a single destination but a spectrum of competing ambitions, ranging from rigorous particle physics to personal philosophy. The piece's greatest strength is its ability to clarify why the field feels so fractured: we are not failing to find the one true theory, but failing to agree on what the theory is supposed to do. The biggest vulnerability in the argument is that by categorizing these ambitions so strictly, it risks discouraging the very cross-pollination that might eventually bridge the gap between the mathematical and the metaphysical. Readers should watch for how the scientific community responds to this taxonomy, as it may force a necessary reckoning with the limits of what physics can actually explain.

Deep Dives

Explore these related deep dives:

  • Theory of everything

    Linked in the article (21 min read)

  • Electroweak interaction

    The article directly discusses how electromagnetism and the weak force were 'unified' into the electroweak interaction, and uses this as a key example of the complexity of defining unification. Understanding the actual physics of electroweak unification would help readers grasp the nuances the author is raising about what counts as a true unification.

  • String theory landscape

    The article explicitly mentions the 'string theory landscape' as an example of why unifying interactions doesn't necessarily predict specific particles. This concept of 10^500 possible vacuum states is central to understanding why string theory, despite being a leading TOE candidate, faces criticism about predictive power.

Sources

What is a theory of everything?

by Curt Jaimungal · · Read full article

What is a theory of everything?

In other words, when someone hands you a theory, how do you know it’s a TOE?

I’m in the awkward position of having a channel called Theories of Everything where I explicate different theories, yet I have never defined this term.

This isn’t as straightforward a question as you may think… To answer it rigorously, we’d need to explore what a “theory” is, what a “thing” is, and what “every” of that “thing” means. Indeed, it means exploring what “unification” even means.

Each of these bolded terms (what’s a theory / thing / every / unification) will be explored in more detail in upcoming Substack posts here, so feel free to subscribe.

Defining unification, for instance, isn’t as undemanding as one thinks, as although it’s commonly said that electromagnetism and the weak force have been “unified” into the electroweak interaction, you can rightfully claim this is not a unification because there’s mixing. John Donoghue said this to me here. There’s still no single interaction with a single coupling in the electroweak case.

So what? Can’t you just extend “unification of X and Y” to just mean “X and Y are brought into a coherent framework”? Sure, but then you have to define what “coherent framework” means, which is equally demanding! Indeed, EM+GR are already coherent with one another (you can write Maxwell coupled to dynamical spacetime), but few would say that standard EM has been “unified” standard GR. A cocktail’s not a marriage… though one may unhappily lead to the other.

There are various lists of contenders to a TOE (I even have a cheeky Top 10 list) but today I’m writing an exposition on what I have not seen before. Namely, a classification of the different kinds of TOEs.

In this article, I won’t be specifying exactly what quantum field theory is, nor the standard model, nor general relativity, nor interpretations of quantum mechanics, nor what a law is, nor what “existence” is, nor what “reality” is. I’ll assume you have a rough understanding, but if you don’t you can click the hyperlinks. If you don’t understand, just nod like everyone else.

Wikipedia Has Six Inconsistent Definitions.

If you read the Wikipedia article on “Theory of Everything” closely, you’ll notice it actually calls something a TOE differently almost each time; at least as of Jan 19, 2026. To the untrained eye, these look ...