Our knowledge of the Universe is expanding in three dimensions of three majorbisic parameters: Time, Energy, Scale. These three parameters are conected by Evolution, Reaction and Relativity. Three bisic parameters form another seven minor parameters with different composition:
Time + Scale -> Chemistry abundance (Z)
Scale + Time -> Population (P)
Time + Energy -> Stage (Phase) (S)
Energy + Time -> Frequency (F)
Energy + Scale -> Temperature (T)
Scale + Energy -> Mass (M)
Time + Energy + Scale -> Velocity (V)
So in total there are 13 parameters and connections formed a 13 dimension parameter space. The knowledge of the Universe is the knowledge of these parameters and their relationships. Astrophysicists use both observational and theoretical tools to push our knowledge of the universe to both higher and lower extremes of these parameters and find both more generally and more detailed relationships between them.
Hotest topics of astronomical research would be at one or more extremes of these parameters or dimensions, like: cosmology, AGN, the Galaxy, black holes, supernove, gamma-ray bursts, first stars, white dwarfs, brown dwarfs, exoplanets.
ZengHua Zhang, Hatfield, Summer 2011