3. Did the Universe Have a Beginning? And If So… Does It Have a Cause?
Since antiquity, a fundamental question has shaped both philosophy and science: has the universe always existed, or did it have a beginning?
Some thinkers, such as Aristotle, argued for an eternal universe—one without origin or end:
One may therefore, from all that has been said, clearly see that the whole heaven was not generated, nor can it perish, as some philosophers say, but is one and eternal, having neither beginning nor end throughout all eternity.
By contrast, other traditions have maintained that the universe has an origin, sometimes linked to a cause or a creative reality.
Today, this question is no longer purely philosophical—it has also become scientific. Advances in modern cosmology now allow us to seriously investigate whether the universe had a beginning.
In this chapter, we will take a step-by-step, critical approach:
- We will begin by presenting the Big Bang model and the observations that support it.
- We will then examine alternative models proposed to avoid the idea of a beginning.
- Next, we will explore the fundamental physical constraints—drawn from cosmology and thermodynamics—that limit the possibility of an eternal universe.
- Finally, we will broaden the discussion on a philosophical level: can an infinite past be coherently conceived? And if the universe has a beginning, what follows from it?
Two central questions will guide this inquiry:
- Did the universe have a beginning?
- If so, can we reasonably infer the existence of a first cause?
⚠️ Note to the reader: Sections 3.1 and 3.2 are primarily scientific, while sections 3.3 and 3.4 are more philosophical. If these parts feel demanding, you may wish to skip directly to the conclusion (3.6) for a clear and accessible summary of the main ideas.