Discussion Overview
The discussion revolves around the necessity of invoking the axiom of choice in the context of defining the length of curves on differentiable manifolds, particularly when the manifold has a standard topology that is not induced by a metric structure. Participants explore the implications of this scenario in differential geometry and mathematical physics.
Discussion Character
- Exploratory
- Technical explanation
- Debate/contested
Main Points Raised
- Some participants question whether defining the length of a curve on a differentiable manifold without a natural metric requires the axiom of choice, particularly when no canonical isomorphism exists between vectors and their duals.
- One participant clarifies that the question can be reframed to whether the proof that every differentiable manifold admits a Riemannian metric requires the axiom of choice, suggesting that it may not be necessary due to the properties inherent in the definition of differentiable manifolds.
- Another participant complicates the scenario by introducing the idea of a pseudoriemannian metric that does not agree with the manifold's topology, raising concerns about whether choice is needed to determine the signature convention for timelike vectors at each point.
- Some participants express that the axiom of choice may not be applicable in the context of finite-dimensional manifolds, as the properties involved are topological and algebraic rather than reliant on individual point selection.
- There is a discussion about the potential need for weaker forms of choice, such as the axiom of countable dependent choice, in the definitions of differentiable and pseudoriemannian manifolds.
Areas of Agreement / Disagreement
Participants do not reach a consensus on whether the axiom of choice is necessary in the discussed context. Multiple competing views remain regarding the implications of the axiom of choice in differential geometry and the specific scenarios presented.
Contextual Notes
Some participants note that the axiom of choice may be hidden within certain results used in the proofs related to differentiable manifolds, and there is uncertainty about the assumptions required in the definitions of these manifolds.