Chemistry Reference
In-Depth Information
McLaughlin finds the kind of emergentism espoused by Broad “enormously
implausible”. According to McLaughlin, the fall of British emergentism was not
caused by some philosophical difficulties, but by advances in science:
[Q]uantum mechanical explanations of chemical bonding in terms of the electro-magnetic
force [
] render the doctrines of configurational chemical [
] forces enormously
...
...
implausible. (McLaughlin
2008
, p. 49)
s view has been widely embraced by philosophers. It would not be
too exaggerated to say that it has become the orthodoxy amongst contemporary
philosophers. But this orthodoxy has been challenged by Scerri (
2012
)who
questioned the idea that progresses in theoretical physical chemistry have dealt a
death blow to Broadian emergence. Scerri argues that today
McLaughlin
'
s theories of bonding still
do not allow us to predict in advance the properties of compounds based on the
properties of the components. Indeed, in all but the simplest cases, the theoretical and
computational difficulties are enormous. But Scerri does not believe that this warrants
one to draw the conclusion that emergence as conceived by Broad is a genuine
phenomenon. Rather, Scerri distinguishes between what he calls “apparent emer-
gence” (i.e., epistemic emergence, which might occur because of the limitations of
our current theories) and “ontological emergence” (i.e., a deeper kind of emergence,
which might occur because of the reasons presented by Broad). It is not hard to argue
that chemistry does exhibit some sort of epistemic emergence, but according to Scerri
it is an open question whether it exhibits ontological emergence as well.
Broad
'
s account of emergence has inspired a prominent contemporary account
of ontological emergence in chemistry, due to Hendry (
2003
,
2006
,
2010a
,
b
,
2012
).
Instead of employing configurational forces, Hendry employs “configurational
Hamiltonians” - non-resultant Hamiltonians governing the behaviour of the
molecule. Hendry gives as an example the CO
2
molecule. One can view the parts
of this molecule as quantum mechanical harmonic oscillators and rigid rotators. But
one can do this only after one assumes the linear structure of CO
2
. Where does this
assumed molecular structure come from? Hendry argues that rather than deriving
this structure using resultant Hamiltonians, the linear structure of CO
2
is put in “by
hand”. For Hendry, this is tantamount to assuming “configurational Hamiltonians”.
Since the overall molecular structure constrains the motions of the parts of the
molecule, this would count as an example of downward causation.
Now, the reductionist may agree that the molecule as a whole constrains the
motion of its parts. But he may still disagree that this is a genuine case of downward
causation; the reductionist may say that the powers of the molecule to constrain the
motion of its parts come ultimately from the parts themselves, and their inter-
relations. We use the configurational Hamiltonians, the reductionist may argue, just
because the real (resultant) Hamiltonians are just too hard to obtain. Thus, the
configurational Hamiltonians are just approximations to the real (resultant) Ham-
iltonians, and their adoption does not make much of a difference. But Hendry
argues this answer won
'
t work. Hendry starts by pointing out that in the calculation
of the wavefunction of the molecule one makes use of the Born-Oppenheimer
approximation, which allows the molecular wavefunction to be broken into its
electronic and nuclear components, and in which the nuclei are considered
'
