[...]
BH:==
>>
>> "If you let fall from the same height two weights,
>> of which one is many times as heavy as the other,
>> you will see that the ratio of the times required
>> for the motion does not depend on the ratio of the
>> weights, but that the difference in time is a very
>> small one" -- Philoponus
>>
>> The question naturally arises: How did Aristotelian
>> physics manage to survive for several hundred more
>> years in the face of this empirical refutation?
>
Greg:==
>! While there was a long period of time before 600BC, this
>is still 2000 years before I'd suggested :-). As to how?
>I have no idea. I guess Aristotle's famous feminine dentition
>theory may give an indication :-).
>
Perhaps I was sloppy in my dates, it was 6th century AD instead
of BC, but still quite a few centuries before Galileo. This
seems to have been well known in Galileo's day which
heighten's the mystery. I've thought quite a bit about this,
which probably seems pretty weird to a lot of folks :). But
I find this period really interesting with many valuable
lessons.
If I were to bend over backwards to give the A's (I'm tired
of typing Aristotelean) the benefit of the doubt then I
would emphasize that A physics was successful in some ways,
for example if weights are dropped through liquids instead
of air then A physics does a reasonable job. So we might
say that air represented an anomaly that would someday :)
be explained.
But I think the main reason is what you allude to above.
The A's thought that nature could be understood through
logic and reason alone (guided by the "scriptures",
Aristotle's writings) without relying on vulgar experience.
One important lesson from this is that Galileo did not rely
on negative argumentation such as the results of this
experiment. He had the task of showing that the earth
could move without violating the laws of physics!
One thing he did along these lines was to show that the
motion of a projectile could be divided into two independent
parts. A horizontal motion that was uniform and a vertical
motion that was uniformly accelerated. The independence of
the two is the critical point. In this way he showed that it
was not absolutely impossible for an object to fall straight
towards the earth even if it were moving. Now, the really
odd situation wherein the horizontal component would exactly
match the velocity of the earth, even though they were not in
physical contact, he could not explain. Talk about your fine
tuning! The explanation for this would have to await the
extremely counter-intuitive law of inertia.
At the risk of boring everyone silly (there's always the
delete key :), let me give another example which illustrates
the difference between the A's and Galileo and which also
corrects a common myth about the Galileo affair.
Galileo's first serious conflict with the A's had to do,
believe it or not, with hydrostatics. Galileo developed
a new theory of hydrostatics which totally outraged the
A's. In that time it was common for rich fellows with
an interest in science to arrange for debates between
scientists on controversial new issues. One of these guys
arranged a debate between Galileo and some Aristotelean
university profs. The Aristotelean view here, as everywhere
else, was logic and common sense. Whether a heavy body would
float depended upon its weight and also its shape. Bodies
with smooth "sharp" edges could cut through the water
better thus having greater tendency to sink. Bodies with
large flat surfaces would resist sinking. There's a funny
story about how some engineers tried to build some floating
bridges based on these ideas :).
Anyway, Galileo came prepared for the debate with a clever
experiment. He had designed a cone that, when placed in
the water flat side first, would sink to the bottom. Turning
it around and placing it in point first it would float.
Can you imagine? The A's are going on and on with their
logic and their quotations of authorities and Galileo
pulls this cone out of his pocket and puts it in the water,
much to the amusement of Galileo's rich friend and much
to the embarrassment of the A's.
As you can imagine, this is a good way to make enemies
and Galileo made some bitter enemies this day. The A's
determined to destroy Galileo anyway they could. Unfortunately,
this included getting the church riled up over Galileo's
pro-Copernican views. This is not to say that the church
would not have gone after Galileo anyway. The commonly
held view that the secular academics were innocent bystanders
in the whole affair is, however, definitely a myth.
Brian Harper
Associate Professor
Applied Mechanics
The Ohio State University
"It is not certain that all is uncertain,
to the glory of skepticism." -- Pascal