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Title: Do four expanding spacetime dimensions emerge in the IKKT model
Plain: A model built from ten large matrices is proposed as a complete definition of one string theory. Whether it produces a universe with three large expanding space directions is unknown.
Precise: The type IIB (IKKT) matrix model of ten $N$ x N Hermitian bosonic matrices and fermions is proposed as a nonperturbative definition of type IIB string theory. Determine whether its Lorentzian version at large N dynamically generates a smooth expanding $(3+1)$-dimensional spacetime with $\mathrm{SO}(9) \to \mathrm{SO}(3)$ breaking, rather than singular configurations.
Settled by: Large-N simulations of the Lorentzian model with controlled sign-problem treatment showing (or excluding) smooth emergent 3+1 expansion.
Kind: well-posed
Answer type: yes-no
References: (empty)
Literature status: contested
Status note: Early Lorentzian simulations (2012) reported three expanding directions; later work found singular Pauli-matrix-like structures tied to approximations, and complex Langevin studies continued through 2025.
Posed since: 1996