Reference Material:
I
wanted to take some time to engage with a (relatively) current conversation
about determinism among a couple public intellectuals, mostly as a kind
calibration of the view I’ve set out in the previous two posts. Sean Carroll
published a blog post several years ago entitled “On Determinism”, primarily in
response to Massimo Pigliucci’s related post on the Rationally Speaking blog. Both
authors delve into the inevitable free will debate in their pieces, but I want
to remain focused on the narrower topic at hand – determinism. Many of
Carroll’s points seem to corroborate my view – the world evolves (events
unfold) according to two distinct processes: deterministic evolution according
to the laws of physics, and purely random, acausal events.
Classical
Mechanics
Carroll agrees
that, under a fairly strict interpretation, CM is not deterministic. However,
he refers to the examples from the SEP article (space invaders, Norton’s Dome,
etc.) as “loopholes”, and apparently doesn’t find them super impressive. His
reasoning: the examples are “highly non-generic”, i.e. they are in some sense
contrived and almost inconsequentially improbable (technically, they form a set
of measure zero in the larger space of all possible system configurations). This
contrasts with Earman’s more principled philosophical position that the cases
in question, though rare, constitute important departures from determinism. My
view seems insensitive to the outcome of this debate. We can argue about how
much attention should be paid to certain systems whose future behavior is not uniquely determined by CM, but as long as that behavior exhibits a random, arbitrary
quality, my view is preserved.
General
Relativity
I
haven’t dealt with General Relativity (GR) yet, partly because it’s the theory
I understand the least, but I thought it would be worth at least mentioning what
Carroll has to say here. Like in CM, determinism breaks down in certain
solutions to the governing equations in GR. There are several ways in which
this can happen, but, as Carroll explains, the basic idea is that whenever
information can “flow in” to a system from somewhere that cannot be included in
the description of the system (e.g. a singularity or a boundary at spatial
infinity), determinism breaks down. Earman seems to think these cases worthy of
our attention. Carroll admits their existence, but deems them unimportant
because a more limited local determinism is still preserved. Again, my view
seems unaffected. From an observers point of view, any indeterministic
information flow into a system would manifest itself much like a space invader
in CM – random, arbitrary, and acausal.
Quantum
Mechanics
An
interesting first point from Carroll here is that the evolution of a quantum
system according to the Schrodinger equation is in some sense more deterministic than the evolution of
an analogous classical system. The reason is rather technical – the
mathematical space of all configurations of a quantum system (Hilbert space)
does not allow the “loopholes” to enter into a solution like in the state space of
classical systems.
When
it comes to quantum measurement, Carroll’s summary of the Copenhagen
interpretation is similar to mine – thoroughly indeterministic, but
unsatisfying and ill-defined. He also categorizes the many-worlds approach as
indeterministic, which caught my eye. In his words, “this approach… restores
determinism at the level of the fundamental equations, but sacrifices it for
the observational predictions made by real observers”. I think I agree, and
when phrased this way, I don’t view that tradeoff as worthwhile, while Carroll
embraces it. At the risk of repeating myself, the above disagreement can and
should be taken up by physicists and philosophers, but its potential resolution
doesn’t really affect my view. Indeed, the outcomes of quantum measurements are
the epitome of true randomness in the physical world.
I’m
left feeling relatively secure in my view of determinism’s status among today’s
best theories of the physical world. Where to go from here?
