According to the Big Bang model, which enjoys consensus in cosmology today, the universe began to exist which was followed by a rapid expansion of matter from a state of extremely high density and temperature. The estimated age of the universe is roughly fourteen billion years.

Initially, the Big Bang theory was not well received. When Lemaître, a Catholic priest and astronomer, proposed a prototype of the Big Bang, critics countered that his hypothesis was based upon religious rather than scientific reasons. Lemaître denied these allegations claiming them to be unfounded and affirmed that his hypothesis was based on scientific, not religious, grounds. Previously it had been assumed that the universe is eternal, unchanging, and had always existed in a static form. But Lemaître’s hypothesis affirmed that the universe is expanding and that if its expansion was reversed one would arrive at a single “cosmic egg” or at an edge or boundary to space and time itself. 

The scientific evidence is believed to support the Big Bang model. First is the expansion of the universe. At the Mount Wilson Observatory, the astronomer Edwin Hubble not only discovered that the universe is significantly bigger than previously thought but also made observations that light from distant galaxies appeared red, at least much redder than expected, because of the stretching of light waves as galaxies progressively moved further away from us. This stretching was universal as everywhere Hubble peered, he observed this same redshift. Hubble’s discovery showed that we live in an expanding universe and that by rewinding this expansion we will eventually reach a beginning point in a singularity smaller than a pinhead,

“This has the astonishing implication that as you reverse the expansion and go back in time everything gets closer and closer together until finally the entire universe is contracted down to a mathematical point before which the universe did not exist” (1).

The second piece of scientific evidence for the Big Bang model is the Second Law of Thermodynamics. This law posits that a system will become increasingly disorderly unless energy is fed into it. This made cosmologists realize that at some point in the future the universe will reach equilibrium when energy will be evenly distributed throughout the universe. This is known as the heat death. That the universe will reach a heat death raised a further question: Why, if the universe has existed eternally, has it not already reached heat death? As philosopher William Lane Craig states, “If in a finite amount of time, the universe will reach equilibrium, then, given infinite past time, it should by now already be in state of equilibrium. But it’s not. We’re in a state of disequilibrium, where energy is still available to be used and the universe has an orderly structure” (2).

Third, the cosmic microwave background radiation (CMBR) supports the Big Bang theory. CMBR is electromagnetic radiation left over from the earliest cosmological epoch. It permeates the universe and formed roughly 380 000 years after the Big Bang. The cosmic microwave background was redshifted radiation emitted by a hot gas that filled all of space shortly after the universe began. The universe today evolved from a hot, uniform state. This indicates an evolving universe since the universe is cooler today than it was in the beginning. The CMBR thus matched the predictions of the Big Bang theory with precision. It offers evidence of the expansion of space and thereby supports the Big Bang model.

The Steady State Model

The Steady State theory was proposed by Hermann Bondi, Thomas Gold, and Fred Hoyle in 1948. It maintains that the average temperature and density of the universe are constant through the creation of new matter and energy as the universe expands. It accepts an expanding universe. However, the model attempts to account for the universe’s expansion by claiming that the density of the universe remains the same because matter is continuously created in the voids left by the retreating galaxies. The generation of new atoms and matter go on to form stars and galaxies,

“On this model we can think of the universe as kind of like a rubber sheet with buttons glued on it. As the sheet is stretched and the buttons recede from each other, new buttons come into existence out of nothing in the voids left by the retreating buttons. So the condition of the sheet will remain the same over time and therefore you don’t have to have any beginning of the process. As you trace the expansion back in time the galaxies never get any denser because as they approach each other the matter just vanishes. It just goes out of existence as you go back in time and the galaxies approach one another” (3).

Proponents of the Steady State model also believed that the universe is infinitely old and has always existed. It is worth noting that Hoyle proposed the theory because he strongly disliked the idea that the universe had a finite beginning in what, he called, a “big bang”. Ever since Hoyle used the “big bang” derisively in an interview, the name stuck and now refers to the consensus model in cosmology. Those like Hoyle who proposed the Steady State theory held metaphysical motivations for doing so; astrophysicist John Gribbin remarks how “The biggest problem with the Big Bang theory of the origin of the universe is philosophical–perhaps even theological–what was there before the bang? This problem alone was sufficient to give a great initial impetus to the Steady State theory…” (4).

Nonetheless, the Steady State theory has been discredited. This is partly because astronomical evidence shows that the universe is, in fact, changing over time and has an evolutionary history. Further, the theory “was overthrown in 1965 by the discovery of the cosmic microwave background radiation, which provided irrefutable evidence for an early, hot phase of the universe”. But on the Steady State model, no such earlier condition of the universe could have existed, hence this fact came to discredit the model. Simply put, it is indisputable that the universe has changed over time.

The Oscillatory Model

The Oscillatory Model posits that the universe has always been expanding and contracting, and always will be. It therefore, if true, avoids a finite beginning to the universe posited by the Big Bang model. On the oscillatory view, the Big Bang is just the latest explosion of the universe and there has been an infinite number of others before it. The universe expands but then slows to a stop before contracting all the way back into a singularity, which is a process called the Big Crunch. After having contracted, the universe heats up until it reaches a certain point before exploding and expanding again. There is no need to posit a finite beginning or an end of the universe.

There are several similarities and differences between the Big Bang and the Oscillatory Model. Both theories accept a beginning of the universe with the major difference that the Bing Bang posits a finite beginning whereas the oscillatory theory affirms an eternal universe. Both agree that the universe will continue to expand. But the Big Bang theory disagrees that the universe will contract; rather it will reach a state of maximum entropy where there will no longer be any movement of energy because all available energy will have been moved to areas with less energy. The Oscillatory Model, however, maintains that the universe will stop expanding before reaching the heat death state.

There has been motivation for some to accept the Oscillatory Model because “many cosmologists want to avoid the implication of the big bang theory that the universe came into existence in the finite past. How can we resolve this dilemma? Some scientists try to avoid the temporal finitude of the universe by introducing the so-called oscillating (or cyclic) universe theory…” (5). The theory is convenient for those who do not wish to be faced with a finite beginning to the universe because it avoids one having to ask the question: “What caused the Big Bang?” But few today accept the Oscillatory Model and the evidence is stacked against it,

“The pivotal point seems to be that there is not enough matter – and therefore gravitational attraction – in the universe to make it “close,” that is, to make it cease expanding and start contracting. According to our best evidence the universe is “open,” that is, will keep expanding forever – at an accelerating rate! Moreover, even if the universe did close and contract, that would not guarantee oscillation. There could just be a Big Splat rather than another Big Bang, or there could be a series of bounces that diminish into motionlessness – and then we would need an explanation as to how the series got started” (6).

As we noted already, most scientists agree that the empirical evidence favors the standard Big Bang theory, which is inconsistent with the Oscillatory Model. Additionally, there are no known laws of physics that allow the contraction of the universe (7),

“… there are no known physics which could cause a collapsing universe to bounce back to a new expansion. If, in defiance of the Hawking-Penrose singularity theorems, the universe were somehow to bounce back, this would require a whole new physics which is completely unknown. Physics predicts that a universe collapsing upon itself will not bounce back like a basketball hitting the floor. Rather, it would be like a lump of wet clay hitting the floor – it will just collapse down into a singularity and end” (8).

Further, the mass density of the universe is insufficient to generate enough gravitational attraction to halt and reverse expansion. Rather than reverse, the universe will just continue to expand which, as we know, is happening at an accelerating rate rather than slowing down.

A final issue with the Oscillatory Model is that each cycle of oscillation increases in length, which means a new cycle is always longer than the previous one. This must mean that if the Oscillatory Model is correct, there is no infinite past because each cycle becomes shorter and shorter as we go back in time.

References

1. Craig, William Lane. 2007. The Cosmological Argument (part 4). Available.

2. Craig, William Lane. n.d.[a]. The Kalam Cosmological Argument. Available.

3. Craig, William Lane. 2007. Ibid. 

4. Craig, William Lane. n.d.[b]. The Ultimate Question of Origins: God and the Beginning of the Universe. Available.

5. Nagasawa, Yujin. 2011. The Existence of God: A Philosophical Introduction. Taylor & Francis Group. p. 147

6. Creel, Richard. 2013. Philosophy of Religion: The Basics. Hoboken: John Wiley & Sons p. 94.

7. Craig, William Lane. n.d.[b]. Ibid. 

8. Craig, William Lane. 2007. Ibid.