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.