How Accurate Is the Term 'Theory of Everything' in Physics?

01/10/2018 12:10 pm ET
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Photodisc/Getty Images

Why can't you take a lot of physics terms literally? Shouldn't “the Theory of Everything” be called “the theory of some things but not everything”? originally appeared on Quora: the place to gain and share knowledge, empowering people to learn from others and better understand the world.

Answer by Viktor T. Toth, IT pro, part-time physicist, on Quora:

Why can't you take a lot of physics terms literally? Shouldn't “the Theory of Everything” be called “the theory of some things but not everything”?

What is commonly (though colloquially) called a Theory of Everything (ToE) in physics really is meant to be a theory of everything: a unified theory of all physical fields, including fields that we usually associate with various forms of matter as well as fields that we usually think of as forces, the latter including gravity. In principle, if one had the equations of a ToE at hand, it would be possible to derive every other natural law from them, including all the laws of physics, chemistry, even molecular biology. So yes, everything very much means everything in this case.

A ToE would be a step up from a GUT, or Grand Unified Theory, which unifies all forms of matter and the three “gauge” fields of interactions: electromagnetism, the weak and the strong nuclear force, but not gravity. Such a theory would replace the rather imperfect unification in the Standard Model of particle physics with something more fundamental, while also accounting for a few things that the Standard Model cannot explain, such as the observed masses of fermions or the fact that the electron and the proton have opposite but otherwise identical electric charge.

That said, the assertion implied by the first half of this question is quite true. There are indeed many terms in physics that cannot, should not, be taken literally. I mentioned gauge theories, for instance. The name comes from the term gauge invariance, Eichinvarianz in German, which literally meant invariance under a change of scale; but later, the meaning changed, nowadays referring to invariance under a variety of abstract continuous symmetries, e.g., changes in the complex phase of the quantum wavefunction.

Speaking of which… how about the word “quantum”? Sure, it originally came to be because the fledgling theory was part of an attempt to explain why atoms emit or absorb energy in set units (quanta). This leads many to a false understanding of the quantum theory: the belief that the theory is about chopping up macroscopic things into microscopic building blocks. But that’s not the case (even though often, it is in fact a consequence). The theory is fundamentally about representing physical degrees of freedom using mathematical entities that behave differently from numbers.

So yes, it often happens that, as things change, old names acquire new meaning. I do not believe that physics is unique in this regard.

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