Complex sentence: In particular, gravitational waves are expected to be unaffected by the opacity of the very early universe before space became "transparent"; observations based upon light, radio waves, and other electromagnetic radiation further back into time is limited or unavailable.
Split into simpler sentences: In particular, gravitational waves are expected to be unaffected by the opacity of the very early universe. In these early phases, space had not yet become "transparent," so observations based upon light, radio waves, and other electromagnetic radiation that far back into time are limited or unavailable.