Are Vacuum Fluctuation Models Dead?
In 1973, a new model for the origin of the universe was born when physicist Edward Tryon published a paper (pdf) asking the question, “Is the Universe a Vacuum Fluctuation?” This model suggests that the universe as a whole is something like a long-lived virtual particle; a random (and extremely large) fluctuation of energy in the quantum vacuum. And although William Lane Craig refers to Tryons proposal as a “bizarre speculation,” it sparked a buzz for the better part of a decade with many physicists proposing different variants on the model (Ex. 1, Ex. 2, Ex. 3).
The problem with all the above models is that they presuppose a background space from which our universe arose. But where did this background space come from? It could have begun in the past – an unsatisfying answer which only pushes back our question of origins another step – or we could say that it is simply eternal. Craig, however, doesn’t like this second answer and raises two objections:
Within any finite interval of time there is a positive probability of such a fluctuation occurring at any point in space. Thus, given infinite past time, universes will eventually be spawned at every point in the primordial vacuum, and, as they expand, they will begin to collide and coalesce with one another. Thus, given infinite past time, we should by now be observing an infinitely old universe, not a relatively young one.
The second objection, that we should be observing an infinitely old universe, seems easily answered by the anthropic principle – an infinitely old universe would have infinite entropy where observers cannot exist. However, the first objection does make sense – given an infinite past of this meta-space, there should be universe-sized fluctuations occurring all over (i.e. our universe should be colliding with other universes, but we don’t see that).
Craig then drives his objections home by quoting physicist Christopher Isham:
According to Isham this problem proved to be “fairly lethal” to Vacuum Fluctuation Models; hence, these models were “jettisoned twenty years ago” and “nothing much” has been done with them since.
The citation for these fragmented quotes points to a 1990 paper by Isham titled “Space, Time, and Quantum Cosmology,” which I have been completely unable to locate in any book or journal – and according to Google Scholar, this paper has only ever been cited by Craig and various other religious apologists.
Luckily, I was able to find two other papers by Isham which were on the same subject: “Creation of the Universe as a Quantum Process” (1988) published in the book Physics, Philosophy, and Theology and “Quantum Theories of the Creation of the Universe” (1993) published in the book Quantum Cosmology and the Laws of Nature – both of these papers are highly critical of Tryon’s proposal.
. . . Except there is one variation of Tryon’s model which are immune to both Craig’s and Isham’s criticisms: Alexander Vilenkin’s model (pdf). This model, unlike the others, does not propose any sort of background space. Rather, Vilenkin suggests that the universe was a quantum tunneling event “from nothing” – though not “absolutely nothing” (this will be discussed further in a future post). In fact, Isham writes in his 1993 paper that, “a scheme like Vilenkin’s might have some approximate validity.” Although, Isham cautiously goes on to say that we won’t know for sure until the theories of quantum mechanics and general relativity are unified.
So, are vacuum fluctuation models dead? Well, Tryon’s model has some serious problems – there’s no doubt about it. On the other hand, Vilenkin’s variation on Tryon’s theme is still alive and kicking.
On a final note, I’d like to quote a bit of Isham’s 1993 paper (page 50) which seems relevant to this discussion (though you’ll never see Craig using it):
A variety of reactions is generated by the idea that the universe may be temporally finite . . . For example, a rather naive reaction is to posit a God who performs creation at the precise point where the theory breaks down but who is such that the subsequent development of the universe is described exactly by the existing theoretical structure. The invocation of such a Deistic creator is psychologically understandable even if it cannot be justified logically.