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Unifying the Universe
Thinking up a single theory that explains everything within the physical world is what seems to drive several theoretical physicists. From the dynamics of the largest cosmological structures down to the twists and turns of quantum systems at the smallest of scales.
The leading position in the search for a unifying mathematical scheme is arguably occupied by string theory — an overarching theoretical framework that conjectures one-dimensional vibrating strings as the most fundamental components of the Universe.
This article throws some light on another, more controversial contender, namely Garrett Lisi’s Exceptionally Simple Theory of Everything.
Unifying What?
The toughest hurdle along the way towards unification is supposedly epitomized by the quest of consistently marrying quantum mechanics and Albert Einstein’s theory of general relativity across the entire energy spectrum.
The natural laws that predominately describe the behaviour of systems at short distance scales (atomic and subatomic levels) are called quantum mechanics, and they underpin the workings of the Standard Model of Particle Physics, which brings together all currently known particles and their interactions — except for gravity — under one theoretical roof.
In fact, quantum mechanics is only part of the full conceptual framework that underlies the Standard Model, i.e., quantum field theory, which envisages particles as energy fields stretched across space rather than point-like objects. According to this theory, a particle is manifested as a local excitation of its accompanying quantum field. The various fields that are incorporated within the Standard Model are fermions (the matter particles), gauge bosons (the carriers of the forces), and the Higgs field.
Fermions can be subdivided into leptons (the electron, the muon, the tau, and the corresponding neutrinos) and quarks (there are six: up, down, charm, strange, top, and bottom). Moreover, the leptons and quarks are set up in three generations (see Fig. 1) — the masses generally increase as one moves up a generation in ascending order. Given the high stability of first-generation fermions, ordinary matter is made exclusively of electrons, up quarks, and down quarks.
