**Warning**: this post is rather longer than my usual postings.

One popular pseudo-scientific argument used by religious believers
to justify their faith in a guiding deity is based on probability, or more correctly, the abuse of probability. The use of probability in science is
common, but unfortunately even some scientists have misconceptions about it.

The believer argument goes something like this: that the existing universe could have
come about by chance is so extremely unlikely as to have an infinitesimal
probability of having happened.
There must have been a guiding hand in the creation of the universe, in
the form of the believer’s favorite anthropomorphic deity.

The primary flaw in this crude attempt at a justification
for belief in a supernatural deity is its mischaracterization of the
unbeliever’s argument. Yes, if all
of the matter in the universe were simply crammed into one location and was
unaffected by anything other than random happenings at the subatomic level, it
indeed seems unlikely that anything coherent would emerge. Unfortunately, this argument hinges on completely
random behavior for all the contents of the universe.

The fact is that there’s a guiding “hand” in creating the
universe from the “soup” of matter that emerged from the putative “big
bang”. But that hand need

*not*be some conscious being that happens to look like a human being but is actually an infinitely capable deity. The universe’s organization is not completely at the mercy of randomness, and hence, the “calculations” (Most believer apologists haven’t a clue how to estimate probabilities, of course, so they don’t offer any such calculations at all!) must account for non-random processes. In the real universe, the behavior of matter and energy isn't completely random and self-organizing processes go on all the time, but believers for the most part seem not to know anything about that. For example, the weather self-organizes into storms, rather than being just a chaotic foam of random fluctuations.
For a general audience, I can’t go into too much detail
without resorting to mathematical concepts, but the laws of the natural world
are generally

*nonlinear*, which makes predicting the evolution of matter from one state to the next rather challenging – weather forecasting is a perfect example of this. All the natural laws are fundamentally nonlinear because any linear process goes on in a straight line for infinite time. The equations used to describe atmospheric motion are “deterministic”: for a given set of initial conditions, they make a clear and unambiguous prediction for a future state. Unfortunately, even a tiny change in the initial conditions (which can’t be known with infinite accuracy) can result in a large change in the predicted future state. This is why the weather is notoriously difficult to predict far into the future.
The same principle applies to ‘hindcasting” – that is, the
task of running the equations backward from some point to try to deduce
conditions at an earlier time.
Thus, we can’t simply take things as we know them at present and run the
clock backward to calculate what conditions were 15 billion years ago when the
universe began. The laws of
nature, however imperfectly we understand them at the moment, describe what
amounts to a deterministic control over the natural world, but we can’t employ
those laws to account for everything that went on during the last 15 billion
years. All we know is that the
development of the universe from the primordial ‘soup’ was distinctly

*not*random. Matter condensed from pure energy as the universe expanded. Under the influence of gravity, matter collected into clouds and some of them collapsed to form stars. Star groups became galaxies under the influence of rotational inertia. Planets formed within solar systems. Somehow, life began (we don’t yet understand how) and evolved following the laws of evolution. And so on. It wasn’t random, but it also was unpredictable in its details. Hence, the argument that a completely random assembling of the universe is probabilistically impossible is pretty much irrelevant – t**hat process wasn't random**!
Another logical fallacy in this argument is the assumption
that we’re only concerned with the specific path by which the universe as we
know it developed. Yes, it
certainly could be argued that if we could follow the exceeding large number of
events that led to the present, that exact sequence would be only one amongst a
very, very large number of alternative paths, the end result of each of these different paths would depart from the present to a widely-varying degree.

If we could somehow “rewind the tape” to go back to that
primordial soup at some instant in the deep past, and then let the system go
forward again, it would indeed be rather unlikely that all those events would ever
occur in exactly the same way as it did to produce the universe we know.
But given the laws of the universe, the universe simply would
evolve differently. It's a virtual certainty that

*some*sort of universe would evolve, but it wouldn't be an exact fit to the one we inhabit. Our finite knowledge of the detailed disposition of all the matter and energy in the universe would be inadequate to describe its state at some moment long ago, so we could only guess at those properties of our universe at the moment it universe began 15 billion years ago. What’s remarkable is that science has come so far in understanding these processes. It does so by, among other things, by not postulating unnecessary supernatural interventions in that evolution.
Given the “guiding hand” of the natural laws governing the
universe, something sort of resembling the present could emerge 15 billion
years after rewinding the tape, but it likely wouldn’t be precisely what things
are now, as we know them. Humans
might not exist, or if something humanoid was inhabiting a new Earth-like planet, they
certainly wouldn’t be us. Under
the non-random processes associated with those natural laws, an exceedingly large
number of distinct outcomes is still possible of course. But the fallacy of the believer’s use
of the probability argument is it's insistence that we must account quantitatively for the likelihood of the exact state of the universe as
it now is known. We can't be sure that all the possible outcomes are

*equally*likely, but this seems like a plausible assumption, in the absence of information to the contrary. The probability of the exact universe as we know it is indeed exceedingly small, but there's a 100% probability there would be a universe that would resemble the current one more or less, under the natural laws of the universe! Thus, this "probability argument" fails utterly to establish a need for a deity. I don't care what theists choose to believe in the absence of logic and compelling evidence, but their use of this argument is simply specious.
Of course, this begs the question of why the laws of the
universe are as they are. That’s
an entirely different topic and theists have their usual “pat” explanation for
that – again, their favorite deity is their “logical” explanation. I’m not going to go into that one here
– it can wait for another time.