Final answer:
Edwin Hubble's observation that galaxies were moving away from each other is a concept in the field of Physics, dealing with cosmology and astrophysics. It led to the creation of Hubble's Law and provides evidence for the expanding universe and the Big Bang theory.
Step-by-step explanation:
Edwin Hubble's observation that galaxies are moving away from each other in space falls under the category of Physics, specifically within the field of cosmology, which is a part of astrophysics. This observation led to the formulation of Hubble's Law, stating that the farther away a galaxy is, the faster it is receding from us. This discovery is fundamental to our understanding of the expanding universe and provides evidence for the Big Bang theory. In this context, the data indicating redshifts in the galaxies' spectra implies that as the light travels through expanding space, its wavelength is stretched, leading to the redshifts observed and supporting the conclusion of a universal expansion.