Before Stephen Hawking Died, He Revised Multiverse Theory One Last Time
For Stephen Hawking, it seemed like altering humanity's view on life, the universe, and everything was just something to do on a Friday night: whether it was quantum theory or black holes or looking toward the extinction of humanity, the man seemed to have an endless stream of mind-blowing new ideas. And just before he died, he left us with one last theory to turn our heads inside-out: a revision of the multiverse theory known as eternal inflation.
Eternal inflation was first proposed in 1983, and goes something like this: when the Big Bang happened, it created an exponential expansion of space, which then slowed down in some areas, but not in other areas.
This created 'bubbles' in space that developed into miniature universes, some of which stopped growing and became universes similar to ours, and some of which continued to grow, creating universes that are fractally nested. Here's how Hawking described eternal inflation (and his problem with it):
"The usual theory of eternal inflation predicts that globally our universe is like an infinite fractal, with a mosaic of different pocket universes, separated by an inflating ocean. The local laws of physics and chemistry can differ from one pocket universe to another, which together would form a multiverse. But I have never been a fan of the multiverse. If the scale of different universes in the multiverse is large or infinite the theory can't be tested."
Hawking's final paper, published posthumously in the Journal of High Energy Physics, claims that one of the fundamental assumptions of the eternal inflation theory is that Albert Einstein's theory of general relativity would still work.
Not so, according to Thomas Hertog, Hawking's co-author:
"The problem with the usual account of eternal inflation is that it assumes an existing background universe that evolves according to Einstein's theory of general relativity and treats the quantum effects as small fluctuations around this. However, the dynamics of eternal inflation wipes out the separation between classical and quantum physics. As a consequence, Einstein's theory breaks down in eternal inflation."
Hawking and Hertog say the current version of an infinite, fractal multiverse proposed by eternal inflation doesn't work—but that doesn't mean there isn't a multiverse.
Instead, Hawking and Hertog propose a new model of the multiverse that's much smaller, based on string theory, and much more measurable.
Of course, that involves accepting the claim that the universe is a hologram.