Does Big Bang Cosmology Prove the Universe Had a Beginning?

There are a number of arguments for the existence of a creator which depend, at least in part, upon the notion that the universe had a beginning. Some apologists appeal to Big Bang cosmology to support that notion. For instance, according to Christian apologist Phil Fernandes:

The big bang model also teaches that the universe had a beginning. In 1929, astronomer Edwin Hubble discovered that the universe is expanding at the same rate in all directions. As time moves forward, the universe is growing apart. This means that if one goes back in time the universe would be getting smaller and smaller. Eventually, if one goes back far enough into the past, the entire universe would be what scientists call “a point of infinite density.” This marks the beginning of the universe, the big bang. (Fernandes 1997:96)

It is perfectly understandable that Fernandes and many others would make such an argument: as far as I can tell, similar expressions were commonplace among scientists and science writers long before religious apologists picked them up. However, the argument is in fact unworkable. In saying so, I am not saying anything novel or unorthodox; rather, I am just repeating what cosmologists have long known yet somehow failed to communicate adequately to the public, as much as they may have tried. I will try to explain myself in the rest of this paper. The details may sound technical on a first reading, since I will make reference to general relativity and quantum mechanics, but I ask the reader to bear with me: the main point is actually quite schematic, and I believe it should be understandable to anyone.

So what does Big Bang cosmology tell us?

As Fernandes correctly notes, the universe is expanding. Using the general theory of relativity, we can therefore infer from this data that the universe should be smaller and smaller as one looks back into the past. However, this works only up to a point.1 There is a point in time called the “Planck time” (after the late physicist Max Planck, one of the pioneers of quantum mechanics), before which our ability to infer the behavior of the universe on the basis of general relativity alone is destroyed. The problem is that prior to the Planck time, the universe is so small that quantum mechanical effects become very important. Hence, a correct description of the behavior of the universe prior to the Planck time requires a synthesis of quantum mechanics and general relativity, which is known as a theory of quantum gravity. Unfortunately, to this date, no theory of quantum gravity has attained the consensus status that post-Planck-time Big Bang theory enjoys. Without such a theory, we cannot draw from cosmology any conclusions about whether the universe had a beginning or not.2

University of Chicago physicist Robert M. Wald made this point nicely as early as 1977, although it was surely understood well before then:

Do we expect the theory of general relativity to break down in the extreme conditions near a spacetime singularity? The answer is yes. We know that on a microscopic scale, nature is governed by the laws of quantum theory. However, the principles of quantum mechanics are not incorporated into general relativity. Hence, we do not believe that general relativity can be a true, final theory of nature. Classical mechanics (that is, Newton’s laws of motion) provides us with an accurate description of the motion of macroscopic bodies, but it breaks down when we attempt to apply it on atomic distance scales. In a similar manner, we believe that general relativity provides an accurate description of our universe under all but the most extreme circumstances. However, near the big bang singularity when the scale factor a goes to zero and the density and curvature become infinite, we expect general relativity to break down. What is the new, fundamental theory of nature which incorporates the principles of both general relativity and quantum theory? What does this theory say about spacetime singularities? Even the most optimistic theorist can only hope for the beginning of an answer to these questions within the foreseeable future. (Wald 1977:53)

Advances have certainly been made since Wald wrote the above passage, but as of yet, there is no definitive theory of quantum gravity. Nevertheless, we can still ask what quantum gravity might say about the origin of the universe. According to Penn State physicist Lee Smolin, there are three possible scenarios:

  • [A] There is still a first moment in time, even when quantum mechanics is taken into consideration.
  • [B] The singularity is eliminated by some quantum mechanical effect. As a result, when we run the clock back, the universe does not reach a state of infinite density. Something else happens when the universe reaches some very high density that allows time to continue indefinitely into the past.
  • [C] Something new and strange and quantum mechanical happens to time, which is neither possibility A or B. For example, perhaps we reach a state where it is no longer appropriate to think that reality is composed of a series of moments that follow each other in a progression, one after another. In this case there is perhaps no singularity, but it may also not make sense to ask what happened before the universe was extremely dense. (Smolin 1997: 82; format altered)3

So it remains possible that once a theory of quantum gravity becomes established, Fernandes and like-minded apologists will be able to refer to cosmology as scientific proof that the universe had a beginning. In the absence of such a theory, however, that particular line of argument must be suspended.4


1 For anyone trying to anticipate my argument, I would like to stress that the objection I am making does not hinge upon the adequacy of such notions as “the past” in a relativistic framework.

2 One source of the public’s confusion about what Big Bang theory says about the origin of the universe may be the fact that the Planck time is typically referred to as something like “the first 10-43 seconds of the universe.” If the Planck time does in fact consist of the first 10-43 seconds of the universe, then the mere existence of Planck time obviously implies that the universe had a beginning. I presume that what cosmologists actually mean when they talk in such a manner about Planck time is that if you were to ignore quantum mechanical effects, and thus predict a beginning of the universe from general relativity alone, then the Planck time would be 10-43 seconds after that hypothetical beginning. This provides a convenient way to assign dates to everything, but tells us nothing about whether the universe really had a beginning.

3 Nicholas Huggett (University of Illinois at Chicago philosopher of physics) informs me that there is a fourth scenario. It relies upon technical considerations, but if they are too confusing you may safely ignore them for the purposes of this paper, since the viability of scenarios [B] and [C] alone are enough to establish the thesis of this paper. In any case, the fourth scenario is that [D] there is an initial singularity, but that it is cut out of the timeline, so that while the universe has a finite age, there is no first instant and hence no beginning—i.e. the set of times is a half-open set, like the set (0, 1] on the real number line. Surprisingly, this scenario is viable even in the pure general relativistic picture of the Big Bang—a point made, for instance, by Adolf Grünbaum (see Grünbaum 1989: 391). So even if quantum gravity did not come into play, Big Bang cosmology apparently would not demonstrate with certainty that the universe had a beginning.

4 I would like to thank Matt Lund, Nick Huggett, and Jon Jarrett for reviewing this paper.


Fernandes P. 1997. The god who sits enthroned: evidence for God’s existence. Bremerton, WA: IBD Press.

Grünbaum A. 1989. The pseudo-problem of creation. Philosophy of science 56(3).

Smolin L. 1997. The life of the cosmos. Oxford: Oxford University Press.

Wald RM. 1977. Space, time, and gravity: the theory of the Big Bang and black holes. Chicago: University of Chicago Press.