Tantalizing new physics from the cosmic purview.

The emergence of a highly improbable coincidence in cosmological observations speaks of a remarkably simple cosmic expansion. Compelling evidence now suggests that the Universe's gravitational horizon, coincident with the better known Hubble sphere, has a radius improbably equal to the distance light could have traveled since the Big Bang. The confirmation of this unexpected result would undoubtedly herald the influence of new physics, yet appears to be unavoidable after a recent demonstration that the Friedmann–Lemaître–Robertson–Walker metric is valid only for the so-called zero active mass equation of state. As it turns out, a cosmic fluid with this property automatically produces the aforementioned equality, leaving little room for a cosmological constant. The alternative — a dynamical dark energy — would suggest an extension to the Standard Model of particle physics and a serious re-evaluation of the Universe's early history. [ABSTRACT FROM AUTHOR]