In A Return to Sweet Probability, I
argued that the resurrection does not increase the likelihood of William Lane
Craig's god, largely because the credibility that you give reports of the
resurrection depends very heavily on your predisposition to believe that his god
(or some very similar god) exists.
Let
o = intelligent observers exist
f = a finely tuned universe
exists
b = background information.
NID = a non-terrestrial
intelligent designer exists.
…
I can admit that “p(finely tuned
universe | observers exist) = 1” and still conclude that
p(NID | f.o.b) >> p(~NID |
f.o.b)
Now this argument between Richard Carrier and Luke Barnes
was about Bayesian probability, so we know that:
P(NID | f & o & b) =
P(NID & f & o & b) / P(f & o & b)
Holding f and o together (for reasons which should become
apparent shortly) this eventually becomes:
Now we need to define our terms. I think it’s reasonably clear what the term o
means, the intelligent observers in question are us. By “intelligent”, we are not implying that
the universe in question must be crammed with Albert Einsteins. We merely need to be intelligent enough to
observe the universe and note that the universe contains observers who are
intelligent enough to observe their own existence. Tick.
The term f is a little more contentious. I’m going to use the definition that Carrier uses (see Part Deux), in part because
it’s something that Barnes appears to have consistently overlooked:
If fine tuning is necessary
for life, and there is no God, then necessarily life will
only ever exist in correlation with fine-tuning. This is because all universes
without fine tuning (sic) will thus by definition not contain life.
Note that this does not say anything about the hypothetical case
in which there is a god. A
god may choose to fine tune the universe for life, or it may choose to magically
create and sustain life even in universes which are not at all tuned for life,
or it may choose to create a universe in which the range in which life is
possible is very wide indeed. Carrier
appears to be conceding a point to apologists (such as Barnes) for the sake of
the argument. The fine-tuning argument
will only work in a universe which is apparently fine-tuned for life, if there
are observers in a hypothetical universe which is not fine-tuned for life then
the fine-tuning argument fails (and, hypothetically, the pseudo-scientific, apologetic
denizens of that universe will deploy the “non-fine-tuning argument” for
whatever god they have imagined into existence).
So, in the instances in which there are observers, the
universe will either be fine-tuned (either naturally or as the result of the
intervention of a god) or non-fine-tuned (as the result of the invention of a
god). There is the possibility that some
universes will be fine-tuned for life but, for some reason, life doesn’t
manifest. I don’t think we are
particularly interested in those universes but in any event, those universes
won’t have observers. I think we can get
around this scenario by strengthening the concept of fine-tuning – if a
universe is sufficiently fine-tuned for intelligent life, then there will be,
at some point, intelligent life. Any tuned
universe which doesn’t manifest intelligent life simply isn’t sufficiently tuned
to consider it fine-tuned.
It certainly could be excluded from the set of universes that our
universe fits into (also known as the reference class – that is: what is it
about our universe that is pertinent to our consideration in this
instance? It would appear to be the fact
that it contains not only life, but also intelligent observers).
So fine-tuning is defined as the sort of fine-tuning in our
universe, that may or may not have been due to the intervention of a god, and
resulted in intelligent life, life that was intelligent enough to observe that
the universe is sufficiently fine-tuned to produce intelligent observers.
This is an extremely long and convoluted way to say what
Carrier had been saying, P(o|f)=1 and, therefore, P(f&o)=P(f). Or, in other words, once you have fine-tuning
(as defined) you necessarily get observers, so the probability of fine-tuning
and observers resolves down to the probability of fine-tuning. This allows us to change all the (f&o)
terms to f:
Perhaps you might want to weaken the definition of
fine-tuning, but I don’t think that apologists want to. If they do, I think they merely weaken their
fine-tuning argument as a consequence but that can be an argument for another
day if any apologist wishes to take that route.
We know that NID is the “non-terrestrial intelligent
designer”. I’m not as coy as some
others, so I am just going to call this the god of people like William Lane
Craig, Plantinga and (almost certainly) Barnes (but certainly
many of Barnes’ adoring fans). For the
sake of the argument, let’s change NID to R as in “cReator” or “Representing
god” or “what the apologists are Really arguing for”.
Fine-tuning (f) is, of course, the evidence in this
argument, so let’s call it E. If you are
reluctant to roll o into f per the argument above, we could instead say that
E=(f&o).
Then there’s our background, b (which we will capitalise and
call B). Background is a little vague in
its definition. What exactly constitutes
background? Fortunately, we can rely on
Barnes again, who has written a piece on precisely this topic.
Background is everything we know, with the
exception of the evidence that we are currently looking at, so in this case
everything we know with the exception of fine-tuning (and thus observers). However, this in effect resolves down to
everything we know that is relevant. I suspect that we have to be very careful
about doing this step manually – because that which is relevant might not be
immediately obvious and eliminating relevant data will skew the result.
I think we have enough to be getting on with. We’ve renamed NID, b and f (or (f&o)) to
R, B and E, respectively, so we have:
For anyone who has read A Return to Sweet Probability recently, this equation
should be familiar. On the right hand
side of this equation we have four terms to consider:
P(E|R&B) – this is asking us: Given the
hypothesis that there is a cReator, and our background information (everything
we know, bar fine-tuning), what is the likelihood of our evidence (fine-tuning)?
P(R|B) – this is asking us: Given our
background information (everything we know, bar fine-tuning), what is the
likelihood of there being a cReator?
P(E|^R&B) – this is asking us: Given the
hypothesis that there is not a cReator, and our background
information (everything we know, bar fine-tuning), what is the likelihood of our
evidence (fine-tuning)?
P(^R|B) – this is asking us: Given our
background information (everything we know, bar fine-tuning), what is the
likelihood of there not being a cReator?
On the left of the equation is P(R|B&E), which asks us: Given our
evidence (fine-tuning) and our background information (which is, cumulatively, everything
we know), what is the likelihood of a cReator?
The value of this equation relies very heavily on two questions having
already been answered, namely the likelihoods of there being a cReator and not being
a cReator, given what we know, apart from fine-tuning. It also relies, rather heavily, on the
assumption that fine-tuning doesn’t follow necessarily from what we already
know. If we were, in the future, to
discover that B→E (if B then (necessarily) E), then B&E would equal B, so
the left had side of the equation would become P(R|B). This would naturally follow because P(E|R&B)
= P(E|^R&B) = 1 and P(R|B)+P(^R|B)=1.
Therefore, there is an assumption that fine-tuning is consistent with
our background (everything we know, bar fine-tuning) but our background is insufficient.
Now, we should make clear something about “background”. Barnes’ says, of background, “tell me everything” and warns that
information should not be arbitrarily ignored.
So, my question is this: is it arbitrary, given that no time related
caveat is placed on the cReator hypothesis, to limit “background” to that which
we know now? How extensive is this “everything”
of which you speak? Is it possible that,
in the future, we will discover that the fine-tuning we observe is a necessary consequence
of relatively simple, yet entirely natural laws? It would seem that the answer to that
question, according to an apologist, should lie somewhere between “maybe” and “I
don’t know” – perhaps somewhat closer to “maybe” given that “I don’t know” is
saying that it isn’t necessarily impossible, and is therefore
possible, making the answer an unambiguous “yes, it is possible”.
So, it seems to be unreasonable to assume that our background is always
going to be insufficient to explain fine-tuning. The assumption might be valid if we presupposed
an interventionist god, or if there is some natural limit on the information that
we can glean about the universe. In the
case of the latter, the argument by apologists is unacceptably stacked in
favour of their god (assuming the existence of god, what is the likelihood of
god?) In the case of the latter, such a
limit would imply that the question of the existence of a god may never be resolved,
a god may never be proved but it may also never be disproved.
This is, I guess, a wonderful conclusion for apologists. Potential job security until the end of time!
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I think that I am now ready to assign tentative probabilities to each of
the terms in the equation. I’m going to
be as charitable as I can to the apologetic cause.
P(E|R&B) – we don’t know
P(R|B) – we don’t know
P(E|^R&B) – we don’t know
P(^R|B) – we don’t know
Plugging those values in, we arrive at P(R|B&E) = P(R|B) = we don’t know.
So, we could argue endlessly about how to manipulate the identities in
the Bayesian calculations, and how likely or unlikely fine-tuning itself is,
but at the end of the day, we merely arrive at “we don’t know”. Sure, an apologist may immediately transmute
that “we don’t know” into “god exists” via the subtle alchemy of an appeal to
ignorance. The more intellectually
honest among us, however, are left with a mystery to investigate – why does the
universe appear to be fine-tuned? – without any real need to worry about the
superstitious wretches who continue to dog our investigative heels.
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It’s vaguely possible that someone is going to be upset that there were
no jellybeans in this article. I’m
sorry, but the probabilities are so nebulous that I didn’t see any point in assigning
any, even tentatively.
If someone else is keen to do an analysis using the jellybean model,
feel free.