Skydive Phil has released a new video in his "Before the Big Bang" series, Eternal Inflation and the Multiverse. In this video he interviews Alan Guth of BGV fame (there are also interviews with Anthony Aguirre, Yasunori Nomura and George Efstathiou).
The reason that Guth is of much interest to me is that he was one of the three who collaborated on the Borde-Guth-Vilenkin theorem (BGV) which WLC invariably refers to in support of his Argument from First Cause.
In order to recap, I will quote Alexander Vilenkin (who is quoting WLC, before taking issue with WLC's first premise):
The cosmological argument for the existence of God consists of two parts. The first is straightforward:
· everything that begins to exist has a cause;
· the universe began to exist;
· therefore, the universe has a cause.
The second part affirms that the cause must be God.
The BGV is used, by William Lane Craig, as evidence in support of the second premise - the idea that the universe began to exist. The problem, however, is that WLC explicitly assumes that the universe (all that for which we have evidence of existence) was brought into being, from nothing, by a spaceless, timeless, immensely powerful mind which he identifies as his god.
However, the beginning of our universe does not preclude the existence of something else prior to our universe, something that is not a mind, but instead is a multiverse - an eternal inflation that spawns universes such as ours. In doing so, Guth not only describes a mechanism by which our universe could begin without an intention directed cause, but also explains how our universe could be both contingent and as fine-tuned as it appears to be. (It's complicated, so I suggest that you look at the video to get the gist of it. I wrote a comment to the video that contains a link to Alan Guth's written explanation as to how inflation works which might be of assistance.)
Now, the power of WLC's argument, such as it is, is rooted in ignorance. We can't think of any other mechanism by which the universe might have begun, therefore it must be caused (which Vilenkin disputes) and therefore it must have a causal mechanism and the only possible causal mechanism we can think of is a god.
What is on show in the video is that the ignorance on which the argument rests is illusory. As a species at least, even if not as individuals, we can think of other mechanism by which our universe may have begun (Vilenkin's uncaused universe) and, in any case, we can think of other possible causal mechanisms (pocket universes from the decay of eternal scalar field inflation).
There are, of course, potential objections with the eternal inflation multiverse. Most obviously is the fact that it is, in a sense, not really a multiverse at all. The process results in one vast but nevertheless connected region of space-time, with the overwhelming majority of it in a state of inflation. This is not a major issue, however, since this would just mean that we are talking about a Tegmarkian Level II Multiverse in which there is an effectively infinite universe populated with an infinite array of pocket universes so the argument that it's "not really a multiverse" is merely betraying a misunderstanding about what constitutes a multiverse.
Another possible route that an apologist might take is to suggest that while the infinite array of pocket universes explains the apparent fine-tuning of our universe, some fine-tuning of the multiverse would still be required to permit our type of universe to fall within the range of possible universes. This would be justified if the range of possible values for physical constants in a pocket universe are limited to small variations from the values of physical constants in the precursor universe (from which inflation commenced).
This however ignores a feature of quantum mechanics on which much of this rests. If there is any set of values of physical constants that is possible then this corresponds to a non-zero probability of that set being instantiated, no matter what the original set of values of physical constants looked like in the precursor universe. And with an infinite number of pocket universes being spawned by that precursor universe, the likelihood of a universe with a set of values of physical constants like ours is unity - meaning that it is a necessary consequence. (Note that this strikes at the heart of WLC's trilemma: physical necessity, chance or design.)
And even if it were true that the set of values of physical constants that characterise our universe were not reachable from a possible set in a possible precursor universe, then all this means is that our universe did not derive from one of those types of precursor universe. We need to step back and think about how the initial precursor universe would have arisen, which means that we turn to Vilenkin:
Quantum tunneling can create a universe 'from nothing' [because] in quantum mechanics things that are classically forbidden by energy barriers can happen by tunneling through energy barriers. So a universe of zero size — that is, no universe at all — can originate spontaneously by 'tunneling through' an energy barrier and then expanding by inflation.
If that can happen naturally once, in other words if it is at all possible, then we have no reason to think that such quantum tunnelling is limited to happening only once (as might be the case with a supernatural origin of the universe). Therefore, quantum tunnelling like this could potentially happen an infinite number of times. As a consequence, we could have not only an infinite number of pocket universes in our multiverse, being spawned by inflation that was initiated in the original precursor universe but also an infinite number of original precursor universes being created by quantum tunnelling processes. Each of these precursor universes would assume a set of values of physical constants that falls within the possible range, including sets that allow the set in our universe to be instantiated.
If this is the case, then the apologist could still claim that her god is the author of quantum mechanics and this hugely wasteful process, generating an infinite number of precursor universes each of which generates an infinite number of pocket universes, is all part of the plan to create humanity.
She then runs, however, into the bunny problem.
WLC argues that if there is a possible world in which rabbits suffer unremittingly, then it follows that there is no maximally great being - that there is no god. But if god is a quantum engineer and has created this infinity of infinities, then a world in which cute fluffy creatures suffer unremittingly is not only possible, it must actually exist.
We can easily imagine scenarios in which rabbit analogues suffer without end - even on this planet in the future: a plague wipes out all other creatures including pests as well as predators, a couple of small genetic changes lead to the immunity of rabbits to all fatal viruses and bacterial infections and another to prevent the deterioration of telomeres beyond a certain point so that death due to old age is prevented but the ageing and deterioration of bones, ligaments and so on still goes on. Imagine the life of a rabbit (or any sufficiently cute animal) under these conditions, barring accident or starvation, it will live forever, crippled and in pain and constantly hungry because rabbit numbers will rise and fall with the availability of food - there will never be enough to support an increasing population of creatures that pretty much do not die unless they starve to death.
So, I accept that this might be unlikely. But impossible? No, I don't think so. The question then is how many variations of this universe do we need for the likelihood of this scenario to be quite high? The actual number doesn't really matter because, in a universe created by a god as quantum engineer, we would have an infinite number of them, making the likelihood is unity. Following WLC's own argumentation, we find that a maximally great being does not and cannot exist.
The apologist must therefore back away from the multiverse, away from the evidence, and rely ever more heavily on argumentation from (false) ignorance.