Our Light Sphere and Horizon

The outgoing light cone departing from Earth into the future is sometimes called our “light sphere,” which represents the symphony of electromagnetic radiation and signals we send to surrounding stars. Beginning with the near-Earth environment, filled with satellites and electromagnetic radiation of all kinds, humanity is filling a sphere surrounding Earth with television, radio and cell phone signals. The chapter explores how GPS satellites, radio and television fill a sphere with evidence of human civilization, and how our nearby stars might be able to view Earth. With the new science of extrasolar planets, it also is possible to specify which stars have planets that like our own, and the chapter explores how planets around other stars are discovered and how many can see our own civilization. Moving further out, we also consider the ultimate limits of our view of the past “light cone” as it views beams of light travelling billions of years through space to our Earth. Just as earlier centuries mapped the regions of the Earth for the first time, our modern telescopes are mapping large superclusters of galaxies, and reaching out to the far horizon of our universe, the cosmic microwave background radiation. The techniques for mapping the vast expanses of space, the clues that the cosmic microwave background radiation provide for the origins and evolution of our universe are described.