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Inflation not only explains the uniformity that we see in the cosmic background radiation, but it also explains the statistical properties of the very faint nonuniformities that have been observed with instruments so sensitive that they can measure minute variations of less than 1/1000 of a percent.

       While inflation must be tested and judged on the basis of what it says about observable features of the universe, curiosity leads us to ask what inflation says about the universe as a whole. The answer is bizarre.

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Inflationary Theory

Cosmic Background Radiation

Big Bang Universe


Bubble Universe Illustration

       The gravitational repulsion of the false vacuum that is believed to have driven inflation is so strong that it would have launched a period of incredibly rapid expansion. The region would have doubled in size in about 10-37 (i.e., a decimal point followed by 36 zeroes and a 1) second. In the next 10-37 second it would have doubled again, and it would have kept doubling every 10-37 seconds for as long as the false vacuum survived. The false vacuum is unstable, however, so at some point it “decayed,” converting its energy to a hot soup of ordinary particles. From this point onward the scenario would coincide with the standard hot big bang picture. The dramatic expansion, however, strongly suggests that the universe would be far larger than one would have otherwise imagined, so the observed part of the universe would be merely a speck in a much larger space.

       But the whole story is much more complicated. The false vacuum is unstable, but in most versions of the theory it decays like a radioactive substance, such as radium. The decay is described by a half-life: half of the false vacuum will remain after one half-life, a quarter will remain after two half-lives, etc. However, unlike a radioactive material, the false vacuum would expand as it decayed, and the expansion would be faster than the decay. Although only half of the false vacuum would remain after one half-life, it would be larger than the initial region. The false vacuum would never disappear, but instead would continue increasing in volume indefinitely. Pieces of the false vacuum region would randomly decay, producing new “bubble” universes at an ever-increasing rate. Our universe would be just one of the universes on this infinite tree of bubbles.

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