Do atoms, genes, electrons,
fields, and other theoretical entities in the physical sciences actually exist?
Excerpt from THE
PHILOSOPHY OF SCIENCE An Introduction, by STEPHEN TOULMIN, (London:
Hutchinson’s University Library, 1953), pages 135-137:
A child who had read that the
equator was 'an imaginary line drawn round the centre of the earth' might be
struck by the contours, parallels of latitude and the rest, which appear on
maps along with the towns, mountains and rivers, and ask of them whether they
existed. How should we reply? If he asked his question in the bare words,
"Do contours exist?", one could hardly answer him immediately:
clearly the only answer one can give to this question is "Yes and
No." They 'exist’ all right, but do they exist? It all depends on
your manner of speaking. So he might be persuaded to restate his question,
asking now, "Is there really a line on the ground whose height is
constant?" ; and again the answer would have to be "Yes and No",
for there is (so to say) a 'line', but then again not what you might call a
line. . . . And so the cross-purposes would continue until it was made clear
that the real question was: "Is there anything to show for contours
anything visible on the terrain, like the white lines on a tennis court? Or are
they only cartographical devices, having no geographical counterparts?"
Only then would the question be posed in anything like an unambiguous manner.
The sense of 'exists' in which a child might naturally ask whether contours
existed is accordingly one in which 'exists’ is opposed not to 'does not exist
any more’ or to 'is non-existent’, but to 'is only a (cartographical) fiction’.
This is very much the sense in
which the term 'exists’ is used of atoms, genes, electrons, fields and other
theoretical entities in the physical sciences. There, too, the question
"Do they exist?" has in practice the force of "Is there anything
to show for them, or are they only theoretical fictions?" To a working
physicist, the question "Do neutrinos exist?" acts as an invitation
to 'produce a neutrino', preferably by making it visible. If one could do this
one would indeed have something to show for the term 'neutrino', and the
difficulty of doing it is what explains the peculiar difficulty of the problem.
For the problem arises acutely only when we start asking about the existence of
sub-microscopic entities, i.e. things which by all normal standards are
invisible. In the nature of the case, to produce a neutrino must be a more
sophisticated business than producing a dodo or a nine-foot man. Our problem is
accordingly complicated by the need to decide what is to count as 'producing’ a
neutrino, a field or a gene. It is not obvious what sorts of thing ought to
count: certain things are, however, generally regarded by scientists as
acceptable for instance, cloud-chamber pictures of a-ray tracks, electron
microscope photographs or, as a second-best, audible clicks from a Geiger
counter. They would regard such striking demonstrations as these as
sufficiently like being shown a live dodo on the lawn to qualify as evidence of
the existence of the entities concerned. And certainly, if we reject these as
insufficient, it is hard to see what more we can reasonably ask for: if the
term 'exists’ is to have any application to such things, must not this be it?
What if no such demonstration
were possible? If one could not show, visibly, that neutrinos existed, would
that necessarily be the end of them? Not at all; and it is worth noticing what
happens when a demonstration of the preferred type is not possible, for then
the difference between talking about the existence of electrons or genes, and
talking about the existence of dodos, unicorns or nine-foot men becomes
all-important. If, for instance, I talk plausibly about unicorns or nine-foot
men and have nothing to show for them, so that I am utterly unable to say, when
challenged, under what circumstances a specimen might be, or might have been
seen, the conclusion may reasonably be drawn that my nine-foot men are
imaginary and my unicorns a myth. In either case, the things I am talking about
may be presumed to be non-existent, i.e. are discredited and can be written
off. But in the case of atoms, genes and the like, things are different: the
failure to bring about or describe circumstances in which one might point and
say, "There's one!", need not, as with unicorns, be taken as
discrediting them. Not all those theoretical entities which cannot be shown to
exist need be held to be non-existent: there is for them a middle way. Certainly
we should hesitate to assert that any theoretical entity really existed until a
photograph or other demonstration had been given. But, even if we had reason to
believe that no such demonstration ever could be given, it would be too much to
conclude that the entity was non-existent; for this conclusion would give the
impression of discrediting something that, as a fertile explanatory concept,
did not necessarily deserve to be discredited. To do so would be like refusing
to take any notice of contour lines because there were no visible marks
corresponding to them for us to point to on the ground.
[...]
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