Philosophy Now-Aug-Sept 2019

(Joyce) #1
What Aristotle actually believed, to be more precise, is that
the terrestrial (non-spirit) elements move towards or away from
the centre of the universe, and the Earth, being mostly earth,
was therefore in the middle. Since it had already reached its des-
tination, Aristotle argued that the Earth wasn’t moving. His evi-
dence for this claim was that when you drop a stone it lands at
your feet. If the Earth were moving, it should land as far away
from you as the Earth had moved in the time it took to fall. His
explanation for why the Sun, Moon, planets and stars move round
the Earth is that they are set in a series of concentric spheres
that are spinning around an axis that goes through the Pole Star.
The spheres are made of aether, the fifth element, which unlike
the terrestrial elements moves in circles. This Aristotle explained
by claiming that there are only two types of basic motion, linear
and circular. All motion can be described as a combination of
those two; and since earth, water, air and fire all move in straight
lines, there must be an element that moves in circles.
The premises are a bit shaky, but if you accept them, it’s a log-
ically coherent explanation. Aristotle’s model was developed by
Ptolemy into a mathematical description that was reasonably
successful at predicting the positions of the heavenly bodies. So
it was supported by the available evidence too; and if the posi-
tion of the stars is important to you (say for navigation or for reli-
gious observance), it’s a useful model as well.
We now know that practically everything Aristotle said about
gravity is wrong, but his explanation taken as a whole made so
much sense that for two thousand years it resisted all chal-
lenges. In the century after Aristotle, Aristarchus of Samos
argued that the Sun rather than the Earth is the centre of the
universe; but this idea wasn’t fully revived until Copernicus in
the sixteenth century AD. When it did finally triumph, it also
undermined Aristotle’s explanation of gravity. If the Earth isn’t
at the centre, and is moving, then Aristotle’s explanation for
why stones always fall straight down, and indeed, why they fall
at all, must be wrong, and a new explanation is needed.
After Copernicus’s death, responsibility for the publication of
his book De revolutionibus orbium coelestium (On the Revolu-
tions of the Celestial Spheres, 1543) was given to Andreas Osian-
der. Osiander added a Preface in which he argued that different
explanations can be supported by the same evidence. It doesn’t
matter to the calculations whether people choose the explana-
tion they find most plausible or the one they find most useful to
work with. As Osiander said, “If they provide a calculus consis-
tent with the observations, that alone is enough.” And although
Copernicus’s mathematics wasn’t as developed as Ptolemy’s,
bits of it were easier to work with. So some mathematicians and
astronomers adopted Copernicus’s model; not necessarily
because they believed the Sun-centred explanation, but because
it was useful.

W


ith which of these three propositions do you most agree?
A scientific theory must be:

1) A logically coherent explanation.
2) Supported by evidence.
3) Useful.

If you are firmly of the opinion that one of these is the defining
feature of science, then in philosophical terms you are either (1) a
rationalist, (2) an empiricist, or (3) a pragmatist. Moreover, if you
happen to be a scientist, then it is likely that your main interest is
(1) Theoretical, (2) Experimental, or (3) Instrumental. More generally,
you might just like to (1) Have an idea about how something works,
(2) Find out how it works, or (3) Just make it work.
When philosophers of science are doing what they are paid for,
one of the key things they consider is what blend of the above
elements makes an activity a science. On the face of it, it should-
n’t be all that difficult to work out. There are only three variables;
how hard can it be?
Rather than think in terms of abstract ideas, it’s probably easier
to copy many philosophers of science and look at examples from his-
tory. The story of gravity is a useful example of the development of
scientific understanding, because it’s something we all experience,
its science involves all of the above points, and it’s still a mystery.
There’s a simple story about how ideas about gravity developed up
to the twentieth century, according to which it’s a hop, skip and a
jump from Aristotle to Galileo to Newton, to Einstein; from an expla-
nation to a demonstration to a useful equation or two.


Aristotle (384-322 BC)
If longevity were any measure, then by far the most successful
theory of gravity is Aristotle’s explanation, or rather his two expla-
nations, of it. One of those ideas is based on the behaviour of the
Greeks’ four elements, earth, water, air, and fire (Aristotle himself
was to add spirit or aether, to make five elements). We all know
that stones sink in water; that air bubbles to the surface, and
flames leap upwards, because we have seen the evidence. Aris-
totle explained that it is the nature of the different elements to
seek their natural place: earth and water move down, air and fire
move up. In other words, there is something about the elements
that makes them move the way they do. But does calling it a
‘nature’ make it science?
Aristotle went on to make a rudimentary quantitative claim:
that the more of a particular nature an object contains – the more
earth or air it is made of, for instance – the faster or slower it will
fall. In other words, freefall velocity is proportional to mass. This
is an hypothesis that can be measured relatively easily, and would
be useful to know, if true. So does that make it science? Aristotle
never tested the idea.


6 Philosophy Now ●^ August/September 2019

Philosophy of Science


The First 2½ Millennia


Will Bouwman asks what really matters when studying matter.


Science


SP

AC

E
FO

LD

SA

RO

UN

D
EI
NS

TE

IN

©^

KE

N
LA

ID
LA
W

20

19

P

LE
AS

E
VIS

IT

KE

NL

AID

LA

W.
CO

M
TO

SE

EM

OR

E
OF

HIS

AR

T
Free download pdf