5.2 The Cyclic Model

summary

The cyclic model makes distinctive predictions.

For a theory to be scientifically sound, it must make testable predictions. This is something that the cyclic model can do whereas the inflationary theory cannot.
With inflation occurring at high energies, and gravitational fields associated with these high energies, you can produce gravitational waves at rather large amplitudes.
However, in the cyclic model, the concentration of energy during contraction is actually very small, comparable to today’s energy density—and thus the contraction would not produce large amplitude gravitational waves.
Discovery of such primordial gravitational waves in our universe would disprove the cyclic model of the universe, making it a theory with testable predictions.
Although the BICEP2 team initially claimed discovery of gravitational waves in early 2014, it was later discovered by the Planck satellite data that the evidence was in fact the imprint of dust in the Milky Way. The cyclic model remains a compelling picture.

The vacuum of our universe is predicted to be metastable.

This is another direct prediction of the cyclic model.
In the standard inflationary picture, the simple outcome would be that the universe expands forever and ends in the “big chill.”
But that can’t be the outcome in the cyclic model. Our present vacuum must be unstable and the dark energy must decay into some sort of energy that will cause this contracting phase—that’s a requirement of the theory.
By studying the Higgs and symmetry-breaking, we might be able to learn something about the stability or instability of the vacuum state of our universe.

What if there's nothing beyond the Standard Model of particle physics?

So far, we’ve discovered the Higgs boson but no other evidence has been found of physics beyond the Standard Model.
For a moment, let’s consider that there is no physics beyond the Standard Model—no supersymmetric particles to be discovered.
We can actually learn a lot about the state of the vacuum by just measuring the mass of two particles—the Higgs boson and the top quark. Depending on the value of those masses, there are three possible regions for the vacuum state of the universe—regions of stability, instability, and metastability.
Fortunately, these masses have already been measured at the LHC—and the data points us to the metastable region.

Current data points toward metastability.

The energy curve we would see in a region of metastability would imply our universe has a small positive energy (dark energy), with a finite energy barrier.
If crossed, it would take us to a part of the curve where the energy would go down and become negative, driving us into a state of cosmic contraction.
Curiously enough, many of the unanswered problems in the inflationary picture are desirable in the cyclic model. Not only have we escaped dead ends presented by the standard inflationary model, we’ve made testable predictions that experiments can be designed for.
Ultimately, it will be the scientific method—testing theories that make definitive predictions—that illuminates more about the origin and future of our universe.