Cycles of Time

In a future post I’ll talk in detail about conformal cyclical cosmology (CCC). This is a model of the Universe where it passes endlessly through a possibly infinite number of cycles (or aeons) each of which starts with a big bang and ends with a rapidly expanding empty universe.

 This fascinating idea was proposed in a rather technical book titled Cycles of Time: An Extraordinary New View of the Universe written by British theoretical physicist and mathematician Sir Roger Penrose (1931-).  The book was first published in 2010 but Penrose had been developing these ideas for decades earlier. Although CCC has not been accepted by the vast majority of cosmologists, the idea has provoked some  fascinating discussions

Roger Penrose

 Now aged well into  his 90s, Penrose is one of the greatest living thinkers and during his lifetime he has made massive contributions to: cosmology, mathematical physics, and mathematics. He was awarded the Nobel Prize for physics in 2020 at the age of 89 for his work in the 1960s showing that in general black holes will form as the end result of the  gravitational collapse of sufficiently massive objects. Prior to Penrose’s work it was generally thought that massive collapsing objects would escape this ultimate fate.  He has  also written many “popular” science books which have become best sellers

I use the word “popular” with some reservations because the phrase popular science is usually taken to mean that the content can be understood without a  scientific background. Although many of Penrose’s books are popular in the sense that they have achieved relatively good sales they are fairly mathematical, and for some of them, the reader needs to have a degree-level knowledge of physics to fully understand the content. I wonder how many are sitting on bookshelves around the world never having been read? 😉

Outside the realm of theoretical physics and mathematics, Roger Penrose  is also famous for the Penrose triangle – an object impossible to construct in three dimensions.

The Penrose Triangle popularised by Roger Penrose and his father the psychologist Lionel Penrose, consists of three beams each of which joins the other two at an angle of ninety degrees. It is not possible to construct such an object in three dimensions although it is possible to draw it  in two dimensions.

Penrose tilings are the best-known examples of tilings where the pattern does not repeat itself (a tiling is covering a surface with an arrangement of non-overlapping shapes). Penrose tilings  use a small number of different shapes of tiles to cover an entire plane, without creating a pattern that repeats, producing an infinitely changing pattern.

Roger Penrose standing on a Penrose-tiled floor

Conformal Cyclical Cosmology

Penrose’s theory, which I’ll discuss in more detail later, addresses some of the questions which the original Big Bang theory does not answer.

Was the Big Bang really a singularity? A singularity is a place of infinite density where the laws of physics break down. Singularities are thought to occur at the centres of black holes.

What caused the Big Bang? What was before the Big Bang? Does the concept of “before the Big Bang”  even make sense?

“The horizon problem” Why do different regions of the Universe, which lie so far apart they haven’t had time to come into contact with each other since the Big Bang, look the same?

Why is the Universe spatially flat? I will talk about what is meant by spatial flatness in a subsequent post.

Why are there no exotic relics? Exotic relics are unusual particles which theories of particle physics, known as Grand Unified Theories, (GUTs) predict should have been created in the extreme conditions which occurred in the very early Universe. One type of  exotic relic, magnetic monopoles, are predicted to be stable and should be found in large quantities in the Universe today . However,  all experiments to find these particles have failed.

Some of these problems are also addressed by a theory called cosmic inflation which I’ll talk about in a later post.

And finally…

On a historical note, CCC is not the only theory in which the Universe cycles through time and is infinitely old. The steady-state model was popular in the late 1940s, 1950s and early 1960s until it was finally disproved by observations. This theory asserted that although the Universe is expanding, on a large enough scale it  does not change its appearance over time. The Universe has no beginning and no end.

The steady-state model requires that matter be continually created in order to keep the Universe’s density from decreasing as it expands. If you want to find out more there is a short video on the Explaining Science YouTube channel.

7 thoughts on “Cycles of Time”

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