Important part of the criteria up front:

Although anything decided will not be made official by redefining the SI second until at least the 2030 conference, this market is about what consensus, if any, is reached at the 2026 conference.

The General Conference on Weights and Measures (CGPM) takes place every four years, and is next scheduled for 2026.

There is currently a push to redefine the SI second, which at the moment is defined in terms of the hyperfine transition of Cesium.

Here is a paper detailing the current state of play for redefining the SI second:

Roadmap towards the redefinition of the second

In this paper, there are three possible timelines outlined for the redefinition of the second:

Scenario 1 is already ruled out, as the 2022 CGPM did not propose a redefinition option.

Scenario 2 is still in play. This question asks: what will CGPM 2026 decide? If they propose a redefinition option, what will it be? Or will they not propose a redefinition option? Or will they propose to not change the defintion of the SI second?

This question resolves to the outcome of the CGPM 2026 conference, with regard to the definition of the SI second. Although anything decided will not be made official by redefining the SI second until at least the 2030 conference, this market is about what consensus, if any, is reached at the 2026 conference.

It will be judged based on what is proposed, if anything, in the 2026 conference, that in the sense described in the timelines in the linked paper.

I've listed all options in play that I know about. Please feel free to suggest more, and I may add them.

The three classes of options on the table are:

• Define the second in terms of a single atomic transition

• Define the second in terms of a weighted sum of atomic transitions

  • Either with fixed weights, or

  • With dynamic weights that can change according to some prescribed rule or process

• Define the second by fixing a dimensionful constant

  • Such as the Rydberg constant

I've added all of these options, with the list of current secondary representations of the second as the candidates for the next primary definition, if it is to be defined in terms of an atomic transition.

Clarification Oct 18 2023: the "weighted sum" options are actually likely to be implemented as a weighted geometric mean, and thus not technically a sum. Nonetheless if these weighted geometric mean options are decided, this market will resolve to one of the "weighted sum" options. Or I'll rename these options if Manifold introduces the ability to edit them.