Big Bang or Big Bounce?
There is still quite a bit of disagreement among cosmological theories about how our universe began. The Big Bang Theory stands as the most widely accepted explanation for the origin of the universe.
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The Big Bang Theory
According to this theory, the universe began as an infinitely small, hot, and dense point, inflating rapidly as a result of the Big Bang, and continuing to stretch and cool until it reached the shape we find ourselves in today about 13.8 billion years later. This initial period of rapid inflation set the stage for the vast and still-growing cosmos (cosmic inflation) we observe today.
Although astronomers cannot directly witness the universe's formation, much of what we know about the Big Bang Theory comes from advanced mathematical models and simulations. Evidence supporting this theory includes the cosmic microwave background, a faint "echo" of the universe's early expansion that scientists can study in detail. Today, the standard cosmological model based on the Big Bang and cosmic inflation is widely supported within the scientific community for its success in explaining the structure and evolution of the universe.
However, some researchers propose alternative ideas, such as eternal inflation or a cyclical, oscillating universe. These theories aim to address questions the Big Bang does not fully resolve, keeping the debate about the universe’s origins alive and dynamic.
The main criticism raised by opponents of the Big Bang Theory relates to the fact that it leaves some of the most fundamental questions unanswered, in particular the following:
The Big Bang model begins with a singularity – a point of infinite density where the laws of physics break down. This is a deep theoretical problem which, according to its critics, suggests that we do not really understand the beginning at all.
Further, to explain the universe’s large-scale structure, physicists introduced a brief phase of rapid expansion into the early universe (cosmic inflation), powered by an unknown field with unusual properties. Later, to explain the accelerating expansion observed today, another ‘mysterious’ component was added: dark energy.
In short, the critics of the standard model of cosmology assert that the Big Bang Theory only works well because ‘new ingredients’ that have never been observed were introduced while leaving the most basic questions unanswered, namely: where did everything come from? Why did it begin this way? The theory cannot describe the conditions of the singularity that existed before the inflation was kick-started, nor even what kick-started it.
The Big Bounce Theory
Instead of claiming that the universe was started by a Big Bang, some scientists have suggested that the universe has switched between periods of expansion and contraction (Big Bounce Theory). According to these views, the Big Bang is just one of an endless cycle of expansion and contraction ending with a “Big Crunch” and restarting with a Big Bang.
Cyclic universe theories have the important advantage that they are based on the premise that the universe would not need a beginning if it were genuinely involved in an ongoing loop of periods of expansion and contraction. It would stretch forever into the past and similarly into the future in an infinite sequence of universes.
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According to a fairly recent Big Bounce model, the formation of our universe is the result of a gravitational collapse that generated a massive black hole, followed by a ‘bounce’ inside, which means that our universe may have emerged from the interior of a black hole formed within a larger parent universe (Black Hole Universe Model). Supporters of this model assert that as its particular advantage, the Black Hole Universe Model offers a radically different view of cosmic origins which is grounded entirely in known physics and observation.
Versions of the Big Bounce Theory have been around since 1922, but they have been held back by the fact that bouncing universe models have a problem with disorder or entropy, which builds up in the universe over time, making each cycle different from the last one and – in essence – not truly cyclic.
A recent cyclic Big Bounce model gets around the entropy buildup problem by proposing that the universe expands as a whole bunch with each cycle diluting the entropy. This new bouncing universe model tries to stretch everything out to get rid of cosmic structures such as black holes, thus returning the universe to its original homogeneous state before another bounce begins.
Despite new hypotheses and new models, the Big Bang Theory remains the prevailing and most widely accepted explanation of how our universe was formed. This means that, for now, the mystery of what existed before the universe and time itself remains and will be hotly debated by cosmologists for some time to come.
Sources
Gaztanaga, Enrique. “Big Bang May Not Be the Beginning of Everything, New Theory Suggests.” ScienceAlert, 5 June 2025. ScienceAlert
“New Theory Challenges How Our Universe Was Born.” University of Portsmouth, 10 June 2025. University of Portsmouth
Bojowald, Martin. “Big Bang or Big Bounce?: New Theory on the Universe’s Birth.” Scientific American, 1 Oct. 2008. Scientific American
Ratner, Paul. “How Did the Universe Begin? Study Reveals Why the ‘Bouncing’ Theory Is Wrong.” Interesting Engineering, 24 Aug. 2022. Interesting Engineering
Lea, Robert. “‘Bouncing’ Universe Theory Still Can’t Explain What Came First.” Space.com, 12 Aug. 2022.
