Full-dimensional projection conjecture for non-degenerate families in three dimensions

Let JRJ\subset\mathbb{R} be an open interval, and let γ:JS2\gamma:J\to S^{2} be a C3\mathcal{C}^{3} curve satisfying

span{γ(θ),γ˙(θ),γ¨(θ)}=R3,θ(0,1).\operatorname{span}\{\gamma(\theta),\dot{\gamma}(\theta),\ddot{\gamma}(\theta)\}=\mathbb{R}^{3},\qquad \theta\in(0,1).

Set θ:=span(γ(θ))\ell_{\theta}:=\operatorname{span}(\gamma(\theta)) and Vθ:=θV_{\theta}:=\ell_{\theta}^{\perp}, and write ρθ:=πθ\rho_{\theta}:=\pi_{\ell_{\theta}} and πθ:=πVθ\pi_{\theta}:=\pi_{V_{\theta}} for the corresponding orthogonal projections. Let BR3B\subset\mathbb{R}^{3} be an analytic set.

Full-dimensional projection conjecture. For almost every θJ\theta\in J,

dimρθ(B)=min{dimB,1}anddimπθ(B)=min{dimB,2}.\dim\rho_{\theta}(B)=\min\{\dim B,1\}\quad\text{and}\quad \dim\pi_{\theta}(B)=\min\{\dim B,2\}.

The conjecture strengthens the known lower bounds for non-degenerate one-dimensional families of line and plane projections. It predicts the maximal dimension allowed by the target spaces, but the source provides no evidence of a resolution.

Sources & referencesView supporting material

Primary source

Tuomas Orponen, “Hausdorff dimension estimates for restricted families of projections in R^3”, arXiv:1304.4955 (2015).

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