Stephen Hawking’s final theory about multiverses, the Big Bang and “cosmic inflation” has just been published

The nature of our cosmos may be simpler than we imagine, argues the final theory from the late Stephen Hawking.

The renowned physicist’s last theory, published this week in the Journal of High Energy Physics, contends that, while there may be multiple universes, the reality of these alternate universes may be closer to our own than has been previously proposed.

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There is a number of theories about how our universe came into existence, with one of the most popular being that a rapid, brief burst of “cosmic inflation” created a number of hospitable “pocket universes” – when inflation stopped and stars and galaxies formed.  

“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,” Hawking said last year.

This model places our visible universe as the exception rather than the rule, with most of the multiverse continuing to experience “cosmic inflation”. Hawking’s paper, penned with Belgian physicist, Thomas Hertog, from the Catholic University of Leuven, challenges that perspective.

“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,” Hertog said in a statement. “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.”

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Hawking and Hertog build their case on string theory, as a means to reconcile relativity and quantum physics. In particular, they hinge their thinking on the holographic principle, which postulates that the universe is a complex hologram, with 3D reality able to be mathematically reduced to a 2D projection at its boundary.

The paper presents a variation of the holographic principle to deal with the time dimension of eternal inflation, reducing it to a timeless state defined on a spatial surface at the beginning of time. This creates a small range of possible universes, without the fractal-like multiverse structure postulated by other theories.

“We are not down to a single, unique universe, but our findings imply a significant reduction of the multiverse, to a much smaller range of possible universes,” said Hawking in an interview before his death.

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Hertog aims to take the research further by studying it at smaller scales, within the scope of existing space telescopes. If the theory is correct it may have left telling clues in gravitational waves, or the cosmic microwave background (CMB) radiation; a remnant from the birth of the universe.