“Universe,” Kalam, and Equivocation
The second premise of the Kalam Cosmological Argument states, “the universe began to exist,” where William Lane Craig defines “universe” as “the whole of material reality.” This definition is important to the Kalam argument because it serves as a linchpin for Craig to argue that the universe must be caused by something which is “uncaused, changeless, timeless, and immaterial.” In other words, if the universe isn’t the whole of material reality, then it’s possible that some other part of material reality caused it.
To be fair to Crag, his definition of the universe is traditional, but it also might be outdated. In the book The Hidden Reality (Pg. 4) physicist Brian Greene writes:
There was once a time when ‘universe’ meant ‘all there is.’ Everything. The whole shebang. The notion of more than one universe, more than one everything, would seemingly be a contradiction in terms. Yet a range of theoretical developments has gradually qualified the interpretation of ‘universe.’ The word’s meaning now depends on context. Sometimes ‘universe’ still connotes absolutely everything. Sometimes it refers only to those parts of everything that someone such as you or I could, in principle, have access to. Sometimes it’s applied to separate realms, ones that are partly or fully, temporarily or permanently, inaccessible to us; in this sense, the word relegates our universe to membership in a large, perhaps infinitely large, collection.
In A Universe from Nothing (Pg.125-126), physicist Lawrence Krauss echos the same sentiment:
Talking about many different universes can sound like an oxymoron. After all, traditionally the notion of universe has become synonymous with ‘everything that exists.’ More recently, however, universe has come to have a simpler, arguably more sensible meaning. It is now traditional to think of ‘our’ universe as comprising simply the totality of all that we can now see and all that we could ever see.
Craig, however, often cites the work of physicist Alexander Vilenkin to buttress his claim that “the whole of material reality” began to exist. So I emailed Dr. Vilenkin the following question:
Could you briefly define your use of the term “universe,” as you use it in the context of your work on the beginning of the universe? I’m just curious to know whether you use the term in the traditional sense, “all of physical reality,” or if you use it in the more modern sense of “those parts of ‘everything’ that we could, in principle, have access to.”
. His response:
It is certainly more than what we can have access to. Regions beyond our cosmic horizon are included. But if there are other universes whose space and time are completely disconnected from ours, those are not included. So, by “universe” I mean the entire connected spacetime region.
So, it seems to me that there is some equivocation going on between Craig’s definition of the word “universe” and that of the physicists he uses to support his claim.