Our Cosmic Archaeological Dig

(Image credit: Greg Wyatt)The Universe started with nearly the same initial conditions in all directions and distances. As a result, cosmic time was nearly synchronized everywhere we look. This means that the Big-Bang instant in our past, when the density of matter and radiation diverged, occurred at the same time everywhere we look. As a result, light traversed the same distance towards us since that singular beginning from all directions. As we look out, our cosmic horizon is a spherical boundary, defined by the distance that light traversed over the past 13.8 billion years. That the initial conditions were similar out to much greater distances is a moot point because we cannot access these regions.The Universe was transparent to gravitational waves since the earliest Planck time of its expansion history. But the thermal background of gravitons is extremely difficult to detect, as explained in my paper with Sunny Vagnozzi here.(Image credit: Greg Wyatt)The hot cosmic gas cooled and rarefied enough to become transparent to light about 400,000 years after the Big-Bang. The transition to electromagnetic transparency occurred as soon as free electrons were cold enough to combine with protons and make hydrogen atoms. We observe the resulting cosmic microwave background photosphere from the inside in the form of a spherical last-scattering surface surrounding us. This inside-out orientation is geometrically opposite to the outside-in orientation of the spherical photosphere of the Sun.(Image credit: Greg Wyatt)The light emitted by sources farther away from our location must have propagated for a longer travel time in order to reach us today. This means that we see earlier images of the Universe, the farther we look. Observational cosmology is like an archeological dig in which we uncover layers that are progressively more ancient as we dig deeper. The benefit of the finite speed of light is that we can unravel cosmic history by surveying the observable spherical volume