Astrophysics is the study of the nature and makeup of galaxies, stars, planets, and other objects in outer space. Physics and chemistry play major roles in astrophysics. The author’s doctorate is in astrophysics.

Cosmic microwave background is made of photons that were created early in the universe when it had expanded enough for atoms to form and to release photons. These photons have traveled nearly 14 billion years across an expanding universe; that expansion has cooled them off to a mere 1,000th of the energy they had when they were formed. When they strike our detectors, their frequency is in the low-energy microwave band. Slight variations in CMB temperatures from different regions of space enable scientists to diagram the shapes in the mass of the early universe, shapes that comport with the superclusters of galaxies we detect.

CMB gave cosmologists their first real tool to decipher the universe’s history, “bringing cosmology from a nursery of clever but untested ideas into the realm of a precision, experimental science” (56). 

Einstein’s 1916 theory of general relativity describes gravity as a warpage in the space around objects. Large masses curve space more, somewhat in the way that a bowling ball suspended on a rubber sheet warps the sheet.