How far can you see? Everything you can see, and everything you could possibly see, right now, assuming your eyes could detect all types of radiations around you -- is the
observable universe. In light, the farthest we can see comes from the
cosmic microwave background, a time
13.8 billion years ago when the universe was opaque like thick fog. Some
neutrinos and
gravitational waves that surround us come from even farther out, but humanity does not yet have the technology to detect them. The
featured image illustrates the observable universe on an
increasingly compact scale, with the
Earth and
Sun at the center surrounded by
our Solar System,
nearby stars, nearby galaxies, distant galaxies, filaments of early matter, and the cosmic microwave background. Cosmologists typically assume that our observable
universe is just the nearby part of a greater entity known as "the universe" where the same physics applies. However, there are several lines of popular but speculative reasoning that
assert that even our universe is part of a
greater multiverse where either different physical constants occur,
different physical laws apply,
higher dimensions operate, or slightly different-by-chance versions of our standard universe exist.