Complex sentence: The exact distribution of dark matter is challenging to map in fine detail; since gravity is a long-range force, observations such as galaxy rotation curves and weak lensing only probe the integrated distribution over substantial volumes of space.
Split into simpler sentences: The exact distribution of dark matter is challenging to map in fine detail. Since gravity is a long-range force, observations such as galaxy rotation curves and weak lensing only probe the integrated distribution of dark matter over substantial volumes of space.