Stephen Hawking famously compared asking what was before the Big Bang to asking what is north of the North Pole? It’s an intriguing question that has stymied theologians, scientists, and the cosmically curious for a long time. The Big Bang theory proposes that, 14 billion years ago or thereabouts, the entire universe as we know it today existed in a singular steady state known as ‘singularity’, a subatomic point of infinite heat, density and gravity. [source: Las Cumbres Observatory] The exact nature of this singularity, though, is still mysterious; it’s a point where known physics breaks down.  

The Primordial Question Mark

An influential Catholic theologian and philosopher in the fourth-century, Augustine of Hippo, struggled with the question of what existed, besides God himself, before he created the universe. Augustine settled on the firm belief that the literal Genesis phrase “In the beginning” implied ‘creatio ex nihilo’, creation out of nothing. He also argued that matter and time both were created simultaneously. [source: Trinity Evangelical Divinity School]. According to Buddhist belief, there is be no First Cause, and no creation ‘ex nihilo’ of the universe, as in the Big Bang theory. Since the universe has neither beginning nor end, the only universe compatible with Buddhism as with Hinduism is a cyclical one. The interdependence of matter with the flow of consciousness have co-existed for all time. [source: National Library of Medicine]. Hinduism uniquely teaches that the cosmos experiences endless cycles of death and rebirth, with time scales resembling those in modern scientific cosmology. [source: Sagan 1980] The Big Bang was the origin of space and time themselves, based on Einstein’s general relativity, making the question of what came ‘before’ essentially meaningless. Cosmologist Rev. Georges Lemaître in 1927 agreed with Einstein and proposed that the universe began as a primordial singularity and expanded toward its current shape and size through the Big Bang [source: American Museum of Natural History].

Cosmic Inflation – the initial phase of the broader Big Bang theory

Cosmic Inflation is considered the mechanism that powered the subsequent, slower, and continued expansion of the universe. An ultra-rapid, exponential expansion of space that occurred a tiny fraction of a second before or after the traditional hot Big Bang. Cosmologists do not have a single, universally agreed-upon definition for the “Big Bang,” which leads to different answers regarding whether inflation happened before or after it. The timing depends on which definition of the Big Bang is used. If the Big Bang is defined as the singularity, the absolute beginning of time and space, then inflation occurred after it. Many modern cosmologists now define the Big Bang as the moment inflation ended and the universe was filled with hot, dense matter and radiation, a process called “reheating”. Under this definition, inflation happened before the Big Bang. This perspective is increasingly favored because inflation essentially “wiped clean” any evidence of what came before it, making the end of inflation the earliest state we can actually observe or verify.[source: Physics] This ‘before’ cosmic inflation theory implies that instead of a definitive beginning, the universe was a cold, empty space with high-energy fields that expanded space-time exponentially, eventually faster than the speed of light for a fraction of a second triggering its energy converting into matter and radiation, a process known as “reheating,” which created the hot, dense, rapidly expanding state that we call the Hot Big Bang. The Big Bang theory alone cannot explain why distant parts of the universe have the same temperature (homogeneity). Inflation proposes these areas were once tiny and in close contact before being rapidly stretched apart, allowing them to reach a uniform temperature. Inflation stretched the curvature of the early universe so rapidly that it appeared almost perfectly flat, matching modern observations. Tiny quantum fluctuations during inflation were stretched to cosmic scales, providing the initial “seeds” of density variations that later grew into galaxies. [source: NASA Science]

Inflation is the current leading model because it highly accurately predicts the patterns seen in the Cosmic Microwave Background (CMB). Big Bounce models are gaining interest because they avoid the mathematical “breakdown” of a singularity and don’t necessarily require the complex “multiverse” outcomes that some physicists find problematic. [source: Scientific American]

Big Bounce

Some contemporary scientists believe that instead of a hot Big Bang, the Big Bounce theory proposes a cyclic universe that alternates between expansion and contraction, avoiding a singularity by “bouncing” when it reaches a minimum size. Instead of a single Big Bang, each cycle begins with a small, smooth, expanding universe that becomes clumpier, eventually collapsing and smoothing itself out to begin anew. The universe goes through endless cycles of expansion and contraction, driven by quantum gravitational effects that prevent the total collapse into a singularity. Instead of a Big Crunch resulting in a zero-volume point, the universe hits a minimum volume and reverses, triggering a new Big Bang-like expansion. The cycle starts with a smooth, small universe, expands as it grows, becomes clumpier, and subsequently smoothens out during the contraction phase. The Big Bounce is an alternative to the standard Big Bang theory, offering a model where the universe is potentially eternal and does not require a singular, beginning. Quantum gravity, specifically loop quantum cosmology, is often used to explain how the universe avoids singularity. [Source: Quanta]

For the Big Bounce idea to work, it has to find a way around the singularity theorems developed by British physicists Roger Penrose and Stephen Hawking. These theorems suggest that a contracting universe would shrink all the way down to a singularity, similar to a massive dying star condensing to form a black hole. Big Bounce models depend on the idea of negative energy counteracting gravity and reversing the collapse, driving the universe and space-time apart again and again [source: Quanta].

Scientists are currently looking for “fossils” or signals in the Cosmic Microwave Background (CMB) that might be leftovers from a previous universe. Some astrophysicists speculate that our universe is the offspring of another, older universe. This story, they believe, is written in the cosmic microwave background (CMB), the relic radiation left over from the Big Bang. Astronomers first observed the CMB in 1965, and it quickly created problems for the Big Bang theory. These problems were addressed (for a while) in 1981 with the inflation theory, which entails an extremely rapid expansion of the universe in its first moments. This theory accounts for temperature and density fluctuations in the CMB but dictates that those fluctuations should be uniform. [source: Scientific American]

While both the Big Bounce and Cosmic Inflation aim to explain why our universe is so smooth, flat, and uniform, they use fundamentally different mechanisms and timelines to achieve it. Both theories ‘Smooth’ the universe. Cosmic inflation postulates an expansion, a near-instantaneous, exponential burst of expansion immediately after the Big Bang. Like quickly blowing up a wrinkled balloon, this rapid growth “stretches out” any irregularities, making the observable universe appear flat and uniform. The Big Bounce (Contraction): Proposes a contraction, a smoothing that happens before the bounce during a long, slow period of contraction. As the universe shrinks, matter and energy have enough time to interact and equilibrate, naturally washing out irregularities before the next expansion phase begin. They two theories differ on the nature of the beginning. Cosmic inflation assumes a singular starting point—the Big Bang singularity—a state of infinite density and temperature. Inflation is an “add-on” to explain the conditions immediately following this start. The Big Bounce replaces the singularity with a “bounce” at a high but finite density. It suggests the universe may be eternal, cycling through infinite phases of expansion and contraction without a definitive beginning. [source: PBS]

Is the universe with or without an initial singularity as Einstein’s Theory of Relativity and the Big Bang Theory both postulate? Physical cosmology is a relatively young but very well-established discipline of science. Nevertheless, in one very important aspect it differs strongly from other scientific disciplines. Namely, it is about its uniqueness related to the following aspects: we cannot re-run the universe with the same or altered conditions; we cannot compare the Universe with any similar object; we cannot scientifically establish ‘laws of the universe’ that might apply to the class of all such objects; problems arise in applying the idea of probability to cosmology as a whole; we have an essential difficulty in distinguishing between laws of physics and boundary conditions. Does this mean that, from a scientific point of view, we will never know if the universe had any beginning at all? This is very likely to be the case indeed. [source: Cosmoverse]

“If you like, you can say the laws are the work of God, but that is more a definition of God than a proof of his existence,” Hawkings wrote. With the universe running on a scientifically guided autopilot, the only role for an all-powerful deity might be setting the initial conditions of the universe so that those laws could take shape — a divine creator who caused the Big Bang to bang, then stepped back to behold His work. “Did God create the quantum laws that allowed the Big Bang to occur?” Hawking wrote. “I have no desire to offend anyone of faith, but I think science has a more compelling explanation than a divine creator.” Hawking’s explanation begins with quantum mechanics, which explains how subatomic particles behave. In quantum studies, it’s common to see subatomic particles like protons and electrons seemingly appear out of nowhere, stick around for a while and then disappear again to a completely different location. Because the universe was once the size of a subatomic particle itself, it’s plausible that it behaved similarly during the Big Bang, Hawking wrote. [source: Live Science]