Measurements of the distances to SNe Ia have produced strong evidence that the expansion of the Universe is accelerating , implying the existence of a nearly uniform component of dark energy with negative pressure .
We show that constraints to this mysterious component based upon large-scale structure nicely complement the SN Ia data , and that together they require \Omega _ { X } \in ( 0.6 , 0.7 ) and w _ { X } < -0.6 ( 95 % cl ) , for the favored flat Universe .
Other cosmological data support this conclusion .
The simplest explanation , a cosmological constant , is consistent with this , while some of the other possibilities are not .