Timeless Decision eory
I have said that this strange singularity at the heart of decision theory is where the
confusion lurks. Not least did I refer to that related debate, often associated with dis-
cussion of Newcomb, called the problem of free will and determinism. I expect that most
of my readers will have already come to their own terms with this so-called problem.
Nonetheless I wish to review it, because the central appeal of causal decision theory
rests on human intuitions about change, determination, and control.
It seems to me that much confusion about free will can be summed up in the causal
diagram depicted in Figure 14. Suppose our decisions are completely determined by
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Figure 14
physics—given complete knowledge of the past, our present choice is thereby deter-
mined: p(decision
i
|PHYSICS) = 1 for one particular value of decision
i
, and all deci-
sions have p(decision
j
) = 0. If so, then p(DECISION|PHYSICS) =
p(DECISION|PHYSICS, AGENT). For if PHYSICS determines DECISION with
certainty, then there is nothing left over to be determined by the variable AGENT, and
the alleged causal link from AGENT to DECISION is extraneous. We have no inu-
ence at all over our own choices; they are determined wholly and entirely by physics. e
feeling we have,of being in control of our own thoughts and actions, is but an illusion—it
is really physics that is in control the whole time.
Before the invention of mathematical physics, a similar fear was expressed by earlier
philosophers who asked if the future were already determined (see Figure 15). If all the
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Figure 15
future is already recorded, a book unread but already written, then what use decision?
104