The Existence of God in Light of Contemporary Cosmology
William Lane Craig and Sean Carroll in Dialogue
William Craigâs Opening Speech
Good evening! It is an honor to be taking part in a forum featuring such distinguished scientists and philosophers. Thank you very much!
Introductory Remarks
In his recent book, Where the Conflict Really Lies, Alvin Plantinga distinguished three ways in which scientific theories and theism might be related: apparent conflict, genuine conflict, and concord.[1] I take it as obvious that there does not exist even apparent conflict between contemporary cosmogonic theories and theism. Contemporary cosmology would, therefore, seem to be an area of obvious concord between science and theism.
But, tonight, I want to defend an even stronger claimânamely, that the evidence of contemporary cosmology actually renders Godâs existence considerably more probable than it would have been without it: Pr (Theism | Contemporary Cosmology & Background Information) >> Pr (Theism | Background Information). This is not to make some sort of naĂŻve claim that contemporary cosmology proves the existence of God. There is no God-of-the-gaps reasoning here. Rather, Iâm saying that contemporary cosmology provides significant evidence in support of premises in philosophical arguments for conclusions having theological significance.
For example, the key premise in the ancient KalÄm Cosmological Argument that
2. The universe began to exist.
is a religiously neutral statement, which can be found in virtually any contemporary textbook on astronomy and astrophysics. It is, obviously, susceptible to scientific confirmation or disconfirmation on the basis of the evidence.[2]
Figure 1: The key premise of the KalÄm Cosmological Argument is religiously neutral.
So, to repeat, one is not employing the evidence of contemporary cosmology to prove the proposition that God exists, but to support theologically neutral premises in philosophical arguments for conclusions that have theistic significance.
In tonightâs discussion, Iâll focus on two such arguments: the KalÄm Cosmological Argument from the origin of the universe and the teleological argument from the fine-tuning of the universe.
The KalÄm Cosmological Argument
Consider first the KalÄm Cosmological Argument:
- If the universe began to exist, then there is a transcendent cause which brought the universe into existence.
- The universe began to exist.
- Therefore, there is a transcendent cause which brought the universe into existence.
By âthe universe,â I mean that reality which is studied by contemporary cosmology; that is to say, all of contiguous physical reality, which currently takes the form of space-time and its contents.
I take it that (1) is obviously true.[3] Rather, the truly controversial premise is (2). Traditional supporters presented philosophical arguments in support of (2),[4] which, for me, constitute its primary warrant. But theyâre not the subject of tonightâs debate. Rather, whatâs emerged during the twentieth century is remarkable empirical confirmation of the second premise from the evidence of astrophysical cosmogony. Two independent, but closely interrelated, lines of physical evidence support premise (2): evidence from the expansion of the universe and evidence from the second law of thermodynamics.
Figure 2: Two lines of physical evidence support the key premise of the KalÄm Cosmological Argument.
In saying that the cosmogonic evidence confirms (2), I am not saying that we are certain that (2) is true. Too many people mistakenly equate knowledge with certainty. When they say that we do not know that the universe began to exist, what they really mean is that we are not certain that the universe began to exist. But, of course, certainty is not the relevant standard here. The question is whether (2) is more plausible in light of the evidence than its contradiction. As Professor Carroll reminds us,
Science isnât in the business of proving things. Rather, science judges the merits of competing models in terms of their simplicity, clarity, comprehensiveness, and fit to the data. Unsuccessful theories are never disproven, as we can always concoct elaborate schemes to save the phenomena; they just fade away as better theories gain acceptance.[5]
Science cannot force you to accept the beginning of the universe; you can always concoct elaborate schemes to explain away the evidence. But those schemes will not fare well in displaying the aforementioned scientific virtues.
Even many who have expressed skepticism about premise (2) admit that it is more plausibly true than not. For example, in my recent dialogue with Lawrence Krauss, he volunteered, âIâd bet our universe had a beginning, but I am not certain of it. . . . based on the physics that I know, Iâd say it is a more likely possibility.â[6] This is to admit precisely what cosmologists such as Alexander Vilenkin have contended all along: that the evidence makes it more likely than not that the universe began to exist.[7]
Evidence from the Expansion of the Universe
Figure 3: The expansion of the universe supports premise (2).
Consider, first, the evidence from the expansion of the universe. The standard (Friedmann-LeMaĂŽtre-Robertson-Walker) Big Bang cosmogonic model implies that the universe was not infinite in the past, but had an absolute beginning a finite time ago. Although advances in astrophysical cosmology have forced various revisions in the standard model, nothing has called into question its fundamental prediction of the finitude of the past and the beginning of the universe. Indeed, as James Sinclair has shown, the history of twentieth-century cosmogony has seen a parade of failed theories trying to avert the absolute beginning predicted by the standard model.[8] Meanwhile, a series of remarkable singularity theorems has increasingly tightened the loop around empirically tenable cosmogonic models by showing that under more and more generalized conditions, a beginning is inevitable. In 2003, Arvind Borde, Alan Guth, and Alexander Vilenkin were able to show that any universe which is, on average, in a state of cosmic expansion throughout its history cannot be infinite in the past, but must have a beginning.[9] In 2012, Vilenkin showed that cosmogonic models which do not fall under this condition, including Professor Carrollâs own model, fail on other grounds to avert the beginning of the universe. Vilenkin concluded, âNone of these scenarios can actually be past-eternal.â[10] âAll the evidence we have says that the universe had a beginning.â[11]
The Borde-Guth-Vilenkin theorem proves that classical space-time, under a single, very general condition, cannot be extended to past infinity, but must reach a boundary at some time in the finite past. Now, either there was something on the other side of that boundary or not. If not, then that boundary is the beginning of the universe. If there was something on the other side, then it will be a non-classical region described by the yet-to-be-discovered theory of quantum gravity. In that case, Vilenkin says, it will be the beginning of the universe.[12]
Figure 4: The BGV theorem implies a boundary to classical spacetime in superspace.
Think about it. If there is such a non-classical region, then it is not past eternal in the classical sense. But neither can it exist literally timelessly, akin to the way in which philosophers consider abstract objects to be timeless or theologians take God to be timeless. For this region is in a state of constant flux, which, given the Indiscernibility of Identicals, is sufficient for time.[13] So, even if time as defined in classical physics does not exist at such an era, some sort of time would.[14]
Figure 5: The Vilenkin and Hartle-Hawking quantum gravity models exemplify temporal finitude.
But if the quantum gravity era is temporal, it cannot be extended infinitely in time, for such a quantum state is not stable, and so, would either produce the universe from eternity past or not at all. As Anthony Aguirre and John Kehayias argue,
It is very difficult to devise a systemâespecially a quantum oneâthat does nothing âforever,â then evolves. A truly stationary or periodic quantum state, which would last forever, would never evolve, whereas one with any instability will not endure for an indefinite time.[15]
Hence, the quantum gravity era would itself have to have had a beginning in order to explain why it transitioned just some 13 billion years ago into classical time and space. Hence, whether at the boundary or at the quantum gravity regime, the universe probably began to exist.
Evidence from Thermodynamics
Figure 6: Thermodynamics supports premise (2).
Consider now the evidence from thermodynamics. According to the second law of thermodynamics, entropy in a closed system almost never decreases. Given the naturalistic assumption that the universe is a closed system, the second law implies that, given enough time, the universe will come to a state of thermodynamic heat death, whether cold or hot. Given that the universe will expand forever, it may never reach a state of equilibrium, but it will grow increasingly cold, dark, dilute, and dead. But then the obvious question arises: why, if the universe has existed forever, is it not now in a cold, dark, dilute, and lifeless state? P. C. W. Davies gives the obvious answer: âThe universe canât have existed forever. We know there must have been an absolute beginning a finite time ago.â[16] The universeâs energy, says Davies, was simply âput inâ at the creation as an initial condition.[17]
By contrast, Professor Carrollâs solution to the problem confronts serious obstacles. He imagines that the overall condition of the universe is a state of thermal equilibrium (a sort of de Sitter space), but that random fluctuations spawn baby universes, which pinch off to become wholly independent space-times. We find ourselves in one such baby universe in a state of disequilibrium.
Figure 7: Carrollâs proposed solution to the universeâs low entropy conditi...
