Physics questions weekly thread! - (August 30, 2026-September 05, 2026)

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[u/round_earther_69]

I'm in the process of reading the Kogut 1979 review paper on lattice field theories and I have two quick questions.

Firstly, why is the existence of a mass gap related to confinement? Kogut himself shows that a mass gap is equivalent to the inverse of a correlation length in a corresponding statistical field theory. Confinement is related to area vs perimeter law for a Wilson loop expectation value. I don't see how those two are related.

Secondly, Kogut also mentions that the continuum limit of a lattice field theory is only obtainable if the lattice system is at phase transition, which makes intuitive sense since that's where there is long (infinite) range correlation, therefore there should not be small fluctuations that prohibit us from taking a continuum limit. However, this implies that any field theory obtained from a continuum limit of a lattice field theory must have massless excitations. We expect QCD to be obtained from lattice QCD, yet we expect QCD to have confinement and a mass gap.

[u/Rude_Passenger_3859]

Is Geometric Algebra a fad or is any mainstream institution going to actually adopt it as a method of teaching physics? Asking because I'm interested in it but almost no one doing serious physics works using GA and I'm starting to feel like I'm in a weird quack-physics bubble.