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Title: Does the dark energy equation of state cross $w = -1$?
Plain: The current best fits say dark energy was once stronger than empty-space energy and is now weaker. A simple rolling field cannot do that, so either the fits mislead or the physics is more exotic.
Precise: DESI $w0-wa$ best fits imply $w < -1$ at redshift $z > \sim 0.4$ and $w > -1$ today, which a single minimally coupled canonical scalar field cannot produce. Determine whether the data require crossing $w = -1$ when fitted with physically consistent models (thawing quintessence, coupled dark energy and dark matter, scalar-tensor gravity) or whether the crossing is an artifact of the linear parametrization and priors.
Settled by: Model comparison using reconstructions of w(z) in redshift bins and physical models, showing whether non-crossing models fit as well as crossing ones.
Kind: well-posed
Answer type: yes-no
References: (empty)
Literature status: open
Status note: (empty)
Posed since: 2005