“How to Think About God” by Mortimer Jerome Adler,1981

The universe as we know it today is not the only universe
that can ever exist in time.

...

In his 1981 book “How to Think About God”, Adler attempts to demonstrate God as the exnihilator of the cosmos.

The steps taken to demonstrate this are as follows:
1. The existence of an effect requiring the concurrent existence and action of an efficient cause implies the existence and action of that cause
2. The cosmos as a whole exists
3. The existence of the cosmos as a whole is radically contingent (meaning that it needs an efficient cause of its continuing existence to preserve it in being, and prevent it from being annihilated, or reduced to nothing)
4. If the cosmos needs an efficient cause of its continuing existence, then that cause must be a supernatural being, supernatural in its action, and one the existence of which is uncaused, in other words, the Supreme Being, or God.

Two of the four premises, the first and the last,
appear to be true with certitude.
The second is true beyond a reasonable doubt.

If the one remaining premise, the third, is also true beyond a reasonable doubt, then we can conclude beyond a reasonable doubt that God exists and acts to sustain the cosmos in existence.

The reason we can conceive the cosmos as being radically rather than superficially contingent is due to the fact that the cosmos which now exists is only one of many possible universes that might have in fact existed in the past, and might still exist in the future.

This is not to say that any cosmos other than this one ever did exist in the past, or ever will exist in the future.

It is not necessary to go that far in order to say that other universes might have existed in the past and might exist in the future.

If other universes are possible, than this one also is merely possible, not necessary.

In other words, the universe as we know it today is not the only universe that can ever exist in time.

How do we know that the present cosmos is only a possible universe (one of many possibilities that might exist), and not a necessary universe (the only one that can ever exist)?

We can infer it from the fact that
the arrangement and disarray,
the order and disorder,
of the present cosmos might have been otherwise.

That it might have been different from what it is.
There is no compelling reason to think that the natural laws which govern the present cosmos are the only possible natural laws.

The cosmos as we know it manifests chance and random happenings, as well as lawful behavior.

Even the electrons and protons, which are thought to be imperishable once they exist as the building blocks of the present cosmos, might not be the building blocks for a different cosmos.

The next step in the argument is the crucial one.

It consists in saying that whatever might have been otherwise in shape or structure is something that also might not exist at all.

That which cannot be otherwise also cannot not exist; and conversely, what necessarily exists can not be otherwise than it is.
Therefore, a cosmos which can be otherwise is one that also cannot be; and conversely, a cosmos that is capable of not existing at all is one that can be otherwise than it now is.

Applying this insight to the fact that the existing cosmos is merely one of a plurality of possible universes, we come to the conclusion that the cosmos, radically contingent in existence, would not exist at all were its existence not caused.

A merely possible cosmos cannot be an uncaused cosmos.

A cosmos that is radically contingent in existence, and needs a cause of that existence, needs a supernatural cause, one that exists and acts to exnihilate this merely possible cosmos, thus preventing the realization of what is always possible for merely a possible cosmos, namely, its absolute non-existence or reduction to nothingness.

Adler finishes by pointing out that the conclusion reached conforms to Ockham’s rule (the rule which states that we are justified in positing or asserting the real existence of unobserved or unobservable entities if-and only-if their real existence is indispensable for the explanation of observable phenomena) because we have found it necessary to posit the existence of God, the Supreme Being, in order to explain what needs to be explained-the actual existence here and now of a merely possible cosmos. The argument also appeals to the principle of sufficient reason.

Adler stressed that even with this conclusion,
God's existence cannot be proven or demonstrated,
but only established as true beyond a reasonable doubt.

However, in a recent re-review of the argument, John Cramer concluded that recent developments in cosmology appear to converge with and support Adler's argument, and that in light of such theories as the multiverse, the argument is no worse for the wear and may, indeed, now be judged somewhat more probable than it was originally.