Eric Scerri, who is a lecturer in chemistry
and the history and philosophy of science at the University of California, Los
Angeles, asks a very basic question in last week’s New Scientist (24 Nov. 2012, pp.30-1): how do we know what’s real?
In the world of physics and chemistry, scientists
deal with lots of unobservables like electrons and photons (we see their
effects) not to mention all the varieties of quarks that can never be seen in
isolation, even in theory. Now an electron, and even a positron, will leave a
track in a cloud chamber which can be photographed, but quantum phenomena are
so anti-intuitive that people are sure to ask: is it real? Where ‘it’ is the
Schrodinger wave function that no longer plays a role once the event in question
is ‘observed’. In fact, an earlier issue of New
Scientist dared to address that very question (28 Jul. 2012, pp.29-31), and
it goes to the heart of the longstanding debate as to what quantum mechanics
really means epistemologically. The truth is that no one really knows.
The fact is that since so much of modern
science, especially the fundamentals that underpin physics and chemistry, is
based on unobservables, it leads people to argue for a form of relativism
whereby anything is valid. This point of view is supported by the belief that
all scientific theories are temporary, given their historical perspective.
The gist of Scerri’s article is a
discussion on the philosophical approach proposed by John Worrall in 1989 (Philosopher
of Science at the London School of Economics) called “Structural Realism”. To quote Scerri: ‘For Worrall, what survives when scientific theories change is not so
much the content (entities) as the underlying mathematical structure (form).’
Scerri gives the example of Fresnell’s
theory of light (involving an aether, 1812) being replaced by Maxwell’s
electromagnetic theory. Worrall
argues that some of Fresnell’s mathematics can be found in Maxwell’s theory,
therefore ‘structurally’ Fresnell’s theory is still sound even if the aether is
not. The same criterion can be applied to Einstein’s theory of relativity
compared to Newton’s mechanics. Newton’s inverse square law for gravity is
still intact in Einstein’s theory and all of Einstein’s equations reduce to
Newton’s when the speed of light becomes irrelevant.
Scerri’s own field of expertise is
chemistry and he’s written books on the periodic table, so, not surprisingly,
that becomes a point of discussion. Dmitri Mendelev published his paper in
1869, when the structure of atoms and all their components were unknown. Most
people are unaware that it wasn’t until the 1920s when Bohr, Heisenberg,
Schrodinger and Pauli were pioneering quantum mechanics that the periodic table
suddenly made sense. It reflects the orbital shells that quantum theory
predicts.
At my country high school, we had a
farsighted science teacher (Ron Gunn) who taught us what all these quantum
shells were (without telling us that it was quantum mechanics) so that we could
make sense of all the properties that the periodic table predicts. As Scerri
points out, the periodic table literally embodies the quantum mechanical
structure of the atom. This is something that Mendelev could never have known
about, in the same way that Darwin didn’t know in 1859 that DNA underpins his entire
theory of evolution.
In fact, Scerri also references Darwin and
DNA as another example of mathematical structure underpinning a theory and
ensuring its continuity a century and a half later. To quote again:
‘But
DNA only takes things so far: to go deeper we need to take a mathematical
direction. DNA determines the sequence of bases, A, T, G and C. This becomes a
question of mathematical combinations… played out during the human genome
project.’
Of course, this does not mean that all
mathematical models determine reality, as Ptolemy’s epicyclic solar system
demonstrates; only the ones that survive scientific revolutions. In this context,
no one knows if string theory will follow Ptolemy or Einstein.