The Big Bounce Theory: What is it?


The Big Bang Expansion (Image credit: NASA).   The drawing is a schematic representation of the entire evolution of the universe, starting from the Big Bang (at left) and ending with the present day (at right), 13.7 billion years later.  Shown also are the cosmic microwave background (the echo of the Big Bang seen with radio telescopes), the dark ages when there was only gas and not stars, then the formation of the first stars leading to the formation and growth of galaxies, until the present day.  The expansion is now accelerating, driven by an unknown “dark energy”.


Over the past few weeks I have been hearing the term “The Big Bounce Theory,” quite a lot. At first I thought it was a sequel to the brilliant “The Big Bang Theory” TV show. When listening to the “Star Talk,” podcast by Neil De Grasse Tyson however I heard the Big Bounce mentioned again. It was mentioned in a topic regarding the multiverse theory, and that is a topic for a completely different article, but it got me thinking, and I would like to know more about this so called Big Bounce.

The Big Bounce Theory is a hypothetical scientific model of the formation of the universe. As you may know there are many theories about the formation of the universe, and again I could write several other articles about them, but for now the Big Bounce is at the forefront of much discussion. It was originally suggested as a property of the cyclic model interpretation of the Big Bang. If you’re not too familiar with what the Big Bang Theory is exactly, it is basically the theory that the universe was born out of a expansion from an infinitely dense state. Before this there was essentially nothing. However I know what you’re thinking, what is this cyclic model that was mentioned and how does this relate to this concept?

The cyclic model universe theory is a model of cosmic evolution according to which the universe undergoes endless cycles of expansion and cooling, each beginning with a “Big Bang,” and ending in a “Big Crunch.”  There are three underlying notions that go with this cyclic model, which differ from the conventional ”single” Big Bag theory.  Firstly, that the Big Bang is not the beginning of space or time, but a moment when gravitational energy and other forms of energy are transformed into new matter and radiation, and a new period of expansion and cooling begins. Secondly,  that the ”bangs” occurred periodically, repeating about every 1012 (one trillion) years.  Finally, that the sequence of events that set the large-scale structure of the universe that we observe today took place during a long period of slow contraction before the ”bang”.


Cosmic Microwave Background Radiation (CMB), the fossil record of the Big Bang which is imprinted on the universe today.  This picture marks the era that radiation and matter decoupled from one another in the early universe, approximately 370,000 years after the Big Bang.  At that time the universe became transparent to the passage of radiation.  This has now been redshifted by the expansion of the universe to emit most strongly in the microwave portion of the spectrum.  The radiation represents an almost perfect thermal spectrum at a temperature of just 2.7 Kelvin above absolute zero.  Small fluctuations from this temperature, represented by the red and blue “hot” and “cold” spots in this image, become the seeds that led the formation of structure in the universe.  (Image credit: NASA/WMAP)


It is also said that The Big Bounce is also a consequence of applying loop quantum gravity techniques to Big Bang cosmology, so need not be cyclic.

If you’re familiar with The Big Bang Theory TV show then loop quantum gravity (LQG) may sound familiar to you, as they often referenced it  in earlier seasons. It is a theory that attempts to describe the quantum properties of the universe and gravity.  It is also a theory of quantum space-time because, according to Einstein’s theory of general relativity, gravity is a manifestation of the geometry of space-time. LQG is an attempt to merge quantum mechanics and general relativity. There have been interesting advances in LQG in recent years and this has resulted in loop quantum cosmology (LQC), which applies the ideas of LQG to the study of the early universe and The Big Bang. From these notion came the concept of a cosmic ”Big Bounce”.

In 2016 physicists made some progress in backing up the hypothesis of the Big Bounce Theory. Researchers in both the UK and Canada have hypothesised that when the universe is at its smallest point, it is ruled by quantum mechanics instead of the normal physics of the everyday world around us. At this extremely small scale, the universe would be saved from destruction because the effects of quantum mechanics would, in essence, keep everything together. The team behind this research were able to build a computer model to help aid their hypothesis. Steffan Gielen from the Imperial College London stated:

“Quantum mechanics saves us when things break down…It saves electrons from falling in and destroying atoms, so maybe it could also save the early universe from such violent beginnings and endings as the Big Bang and Big Crunch?”

I don’t know about you, but this whole thought that the Big Bang wasn’t actually the start of space and time as a whole, really excites me! Could there have been a whole other universe before ours? What was it like? Were there planets and stars, alien races or even human like races? Is Star Trek based on one of these previous universes? Did Star Wars really happen in a galaxy far, far away in a completely different universe? Okay, now I know I’m getting out of hand, but you never know! Just imagine our universe like a giant lung, expanding out with an in breath and contracting back in on the out breath, and continuing on that way, bouncing backwards and forwards. To me it seems like a plausible theory.


Article by Heather Taylor, Education Officer

Heather Taylor, Education Support Officer