Famed theoretical physicist Stephen Hawking’s last theory about our universe which he worked on with Professor Thomas Hertog from KU Leuven, is available at the peer-reviewed Journal of High Energy Physics. The theory is based on string theory and it suggests that the universe is finite and much simpler, as compared to many other current theories on the big bang.

Stephen Hawking. via – PBS

Modern Big Bang Theories

The modern big bang theories predict that the existence of the universe was caused by a brief burst of inflation. However, it is believed that the moment inflation begins; there are those regions that it never stops. The quantum effects can keep the inflation to continue on forever in other regions of the universe, globally making inflation eternal. The end of the inflation leads to the formation of stars and galaxies which makes our universe a hospitable pocket.

Eternal Inflation Theory

During an interview last autumn, Hawking said that “the theory of eternal inflation predicts our universe to be like a fractal,” with a mosaic of different pocket of universes separated by an inflating ocean. And these different pockets of universes form a multiverse as the laws of physics and chemistry differ among the universes and the theory of external inflation cannot be tested if the scale of the different universes in the multiverse is large or infinite.

Hawking and Hertog, in the new paper, dismissed the theory of eternal inflation as one of the big bang theories. They highlighted the problem with eternal inflation, is that it makes an assumption that there is a background universe which already exists and evolves according to Einstein’s theory of general relativity. This does not take into account the quantum effects and treats them as just small fluctuations. However, Einstein’s theory breaks down in the eternal inflation theory as the dynamics in external inflation extinguishes the separation that exists between classical and quantum physics.

Holography Concept Of The String Theory

Hawking and Hertog predict that our universe is not a fractal structure but reasonably smooth and globally finite on its larger scales. The eternal inflation theory forwarded by Hawking and Hertog is derived from the string theory which is a theoretical physics branch which tries to reconcile gravity and the general relativity with the quantum physics through describing the fundamental constituents that make up the structure of the universe as being tiny strings which vibrate. Their method puts to use the theory of the string holography concept, which presupposes that the universe is a hologram which is complex and large. The realities that are physical in some of the 3D spaces are able to be reduced mathematically to 2D projections on the surface.

A variation of the holography concept of the string theory was developed by Hawking and Hertog in order to pin point the eternal inflation in time dimension. This made it possible for them to describe the external inflation without necessarily relying on the general relativity theory by Einstein. The new theory reduced the eternal inflation to a timeless state defined on a spatial surface at the beginning of time.

Taming The Multiverse Theory

Hawking’s no boundary theory predicted that when you move back in time up to the universe beginning, the universe tends to shrink and later closes in a sphere manner, but the new theory does represent a huge step away from the work that was earlier conducted. He also added that in a simpler way to say, that there is a boundary to everyone’s past.

Hertog said that when we look at our universe evolution back in time, we tend to arrive at the external inflation threshold where the time notion becomes meaningless. Hertog and Hawking used their new theory to come up with more accurate predictions that can be relied upon regarding the universe’s global structure. They predicted that unlike in the old theory of the eternal inflation which predicted the universe as being an infinite fractal, the universe that emerges from eternal inflation on the past boundary is finite and much simpler.

Their theory is predictive and testable because their findings show a significant reduction of the multiverse to a smaller range of possible universes which if proven by further work, will have far-reaching implications of the multiverse paradigm.

Hertog believes that primordial gravitational waves ripples in spacetime generated at the exit of eternal inflation is the evidence needed to test this model. Such gravitational waves would have very long wavelengths that are outside the range of the available LIGO detectors due to the expansion of our universe. However, they might be seen in future experiments measuring the cosmic microwave background or heard by LISA which is the planned European gravitational wave observatory based in space. Hertog plans to study the implications of this theory on smaller scales visible through space telescopes.