According to them, if this theory is correct, there is definitely another universe on the other side of the Big Bang, where time runs backward compared to our universe.
Does this question hold any significance?
Another possibility that might be simpler to comprehend is that time itself began at the moment of the Big Bang. If that’s the case, there was nothing before it.
Renowned scientist Stephen Hawking stated this in his best-selling 1988 book, “A Brief History of Time.” In his book, he compared the idea that something existed before the Big Bang to the concept of the “South Pole.” There’s nothing beyond the South Pole; it’s where the Earth’s surface ends. It’s difficult to imagine there being something beyond that, just like imagining something beyond the South Pole, it’s highly likely that there was nothing before the Big Bang.
However, speculations will persist among physicists regarding which idea holds more credibility. Explaining that our universe is a product of a prior universe sounds intriguing, but the question remains: what caused the existence of that universe?
Renée Hložek raises the question, “If you have an expanding universe model, does it continue expanding forever, and if so, how did it start expanding, and when?” These ideas may be bold, but they lack persuasiveness, much like Stephen Hawking stated that you can’t pose such a question.
In the end, the universe has its own origin story: the Big Bang. However, there is no compelling evidence to explain what happened before the onset of time. Instead, we have various high-speculation theories.
Hložek remarks, “I’ve spent my whole life working to answer that question, but the answer is, I don’t know.”
We often hear that the universe began with the Big Bang. But what if the Big Bang wasn’t the start of the universe? Could there have been a previous version of the universe, with its own stars and galaxies, or did the universe have its “inhabitants” and questions of its own before our universe came into existence?
Or perhaps there is an endless array of universes continuously giving rise to new universes. If so, does it even make sense to question the order of these universes?
To address these questions, scientists have pushed the boundaries of the laws of physics. Current theories can explain the evolution of the universe from its primordial state, which is from the moment of the Big Bang onwards, but the question of “what happened before” remains the most challenging.
Renée Hložek, a physicist and astrophysicist at the University of Toronto, Canada, mentioned that he has participated in numerous debates on this topic for hours without reaching a clear conclusion.
“The Big Bang” or “The Big Bounce”?
Physicists find it relatively straightforward to discuss observable phenomena and the universe’s longest-lasting existence, which we observe through cosmic microwave background radiation (CMB). CMB is a kind of “echo” of the Big Bang and is a bright light across the entire sky, detectable and mappable using radio telescopes. It formed around 380,000 years after the Big Bang. However, what occurred before that is unknown.
Hložek explains that we can only speculate about what happened in the past based on what is observable, and we lack a basis for understanding the universe before the CMB.
However, if there are limits to what astronomers can see, there are no limits to what theoretical physicists can imagine. One of the most prominent theoretical physicists, Professor Roger Penrose from the University of Oxford, proposed the idea of a succession of universes evolving over time. He suggested that our Big Bang might be just a “bounce,” a transformation from a previous universe that decayed and transformed into our universe.
Last year, Penrose surprised many when he suggested that there could be evidence of the existence of previous universes. These signs could be found in the CMB, which we could detect through careful analysis of radio telescope data.
Other physicists reacted with skepticism (as they did when Penrose made a similar statement in 2010). “Clearly, if someone could show that there was something special about the CMB as evidence that the universe has gone through a series of cycles, that would be very exciting,” said physicist Douglas Scott from the University of British Columbia, “but Penrose’s material is not sufficient to prove that.”
Penrose is not the only one to propose that the Big Bang might not be the beginning of time and that there is much more beyond the universe we see. In 2001, two physicists, Paul Steinhardt and Neil Turok, introduced the “cyclic model” of universes. This model is based on a concept known as M-theory, an extension of string theory. M-theory posits that everything is composed of tiny vibrating strings rather than tiny particles. In the cyclic model, our universe is just one of many coexisting in a higher-dimensional space (beyond the typical three dimensions).
In Steinhardt and Turok’s model, the universes periodically collide, and each collision acts as a new Big Bang. The standard Big Bang model shows a singular moment of creation, while the model introduced by these two physicists suggests that we live in a universe that is continually formed and reformed.
Expansion, Multiple Universes, and Reversed Time
Steinhardt and Turok are not the only ones to suggest that we live in a multiverse, a collection of universes, with our universe being just a small part of a much larger and potentially timeless reality. Another similar idea comes from the “inflationary universe” theory, which emerged in the early 1980s. The central idea of this theory, now widely accepted by physicists, is that the universe underwent an extremely rapid expansion in its early moments, starting from a size smaller than a proton and growing to the size of a grapefruit.
Nobody knows what caused that expansion, but some physicists, including Andrei Linde from Stanford University, believe that whatever caused it could happen not just once but many times, giving rise to a collection of universes. If the “eternal inflation” theory is correct, new universes are constantly being produced in space, much like bubbles in boiling water.
In 2013, two British physicists, Julian Barbour and Tim Koslowski from the University of New Brunswick and Flavio Mercati, introduced a theory that also challenged traditional thinking. They conducted computer simulations of simple particle systems to observe their motion under the influence of gravity for a long time. The experiment entirely describes the universe’s expanding development that we observe, simultaneously acting as a reflection of reversed time streams.