The Cosmological Equation of State
Lumo has an interesting comment on a new measurement of the cosmological equation of state. That equation, we might recall, relates pressure to energy density in the universe considered as a perfect fluid: w = pressure/energy density. The new measurement suggests that w may be less than -1, which apparently argues against the most natural interpretation of dark energy as Einstein's cosmological constant.
Lumo is appropriately skeptical, both because of the statistics and because |w| > 1 implies a speed of sound greater than that of light.