Roger Penrose, one of the most influential mathematicians and physicists of the modern era, is well known for his work on black holes, spacetime geometry, and the foundations of cosmology.
Among his most provocative ideas is the claim that the Big Bang was not the absolute beginning of everything, but rather the ending of a previous universe.
This view challenges the standard picture of cosmology and invites a radically different way of thinking about time, entropy, and the large-scale structure of reality.
From Classical Cosmology to a Radical Proposal
In the conventional cosmological model, the universe began around 13.8 billion years ago in a hot, dense state known as the Big Bang. Space and time themselves are usually treated as emerging from this initial singularity.
Penrose accepts much of modern cosmology, including the expansion of the universe and the evidence for the Big Bang, but he questions the assumption that it represents an absolute beginning.
Penrose was particularly troubled by the extremely low entropy of the early universe. According to the second law of thermodynamics, entropy tends to increase over time, and yet the universe appears to have started in an extraordinarily ordered state.
For Penrose, this fact is not a minor detail but one of the deepest mysteries in physics. His alternative theory attempts to explain this order without invoking special initial conditions created from nothing.
Conformal Cyclic Cosmology Explained
Penrose’s framework is known as conformal cyclic cosmology. In this model, the universe is just one phase, or aeon, in an infinite sequence of universes. Each aeon begins with something that looks like a Big Bang and ends in a state of extreme expansion.
The crucial idea is that the very distant future of one universe can be mathematically reinterpreted as the Big Bang of the next.
As the universe expands, matter gradually decays, black holes evaporate through Hawking radiation, and massive particles disappear. What remains is a cosmos dominated by massless particles such as photons.
In this state, concepts like distance and time lose their usual meaning, allowing the infinitely expanded universe to be rescaled, or conformally transformed, into the dense beginning of a new one. In this sense, the Big Bang is not a creation event, but a transition.
Why the End of a Universe Can Look Like a Beginning
The key to Penrose’s idea lies in the difference between massive and massless particles. Massive particles define scales of time and length, while massless particles do not. When all mass is gone, the universe no longer has a built-in scale.
Penrose argues that this scale-free state can be mathematically matched to the scale-free conditions thought to exist at the Big Bang.
From this perspective, the cold, empty, and extremely large universe at the end of an aeon can be reinterpreted as the hot, dense, and extremely small universe at the start of the next.
The transition does not require a singularity in the traditional sense. Instead, it represents a smooth handover between cosmic epochs, governed by geometry rather than explosive creation.
Possible Evidence
Penrose has suggested that traces of a previous universe might be visible in our own. One proposed signal involves faint, circular patterns in the cosmic microwave background radiation.
He believes that this potentially left behind by violent events such as black hole collisions in the aeon before ours. He and his collaborators have argued that these features could survive the transition between universes.
These claims remain controversial. Many cosmologists argue that the data can be explained within standard models or that the statistical evidence is weak.
Nevertheless, the fact that Penrose’s theory makes testable predictions sets it apart from purely philosophical speculation. It invites astronomers to look at familiar data in unfamiliar ways.
What Does It Mean for Time and Reality
If Penrose is correct, time has no absolute beginning and no final end. Instead, it stretches endlessly through a succession of cosmic cycles, each one giving rise to the next.
This vision reframes humanity’s place in the cosmos, suggesting that our universe is both ancient and young, shaped by events far older than the Big Bang itself.
While conformal cyclic cosmology remains outside the mainstream, it reflects Penrose’s lifelong willingness to challenge assumptions using deep mathematical insight.
Whether ultimately proven or not, the idea that the Big Bang was the end of a previous universe continues to provoke debate and expand the boundaries of how we imagine cosmic history.
