The Hidden Reality: Parallel Universes and the Deep Laws of the Cosmos

by Brian Greene

all of the parallel-universe proposals that we will take seriously emerge unbidden from the mathematics of theories developed to explain conventional data and observations.

If you take a box that’s a hundred million light-years on each side and plunk it down here, take another such box and plunk it down way over there (say, a billion light-years from here), and then measure the average overall properties inside each box—average number of galaxies, average amount of matter, average temperature, and so on—you’ll find it difficult to distinguish between the two. In short, if you’ve seen one 100-million-light-year chunk of the cosmos, you’ve pretty much seen them all.

Cosmological Principle