Some music just feels timeless — like it was always there, etched into the planet or in communal consciousness, just waiting to be unearthed by those in the right place at the right time. Sigur Ros’ art is of this sort. The word “ethereal” was made for acts like it. Delicate and abstract as a tendril of smoke yet colossal like an elemental force, Sigur Ros makes pop music that seems to seep in from another world. In its hands, beauty becomes something other, something not merely gorgeous but profound, transcendent. It’s been nearly four years since Sigur Ros’ last proper release, but it hardly matters. Its trademark aesthetic — sweeping soundscapes, pastoral moods and wraithlike vocals — is of the kind that’s immune to cultural trends and genre. Sigur Ros’ live concerts, as womblike and grandiose as its recorded music, are moments of total escape in which the world seems to recede and reality’s edges blur.