[Phys-l] 2 +- 1 new sciences

[John Denker <jsd@av8n.com>]

The other day I quoted the following passage

>      The present does not seem to me to be an opportune time to enter
>      into the investigation of the cause of the acceleration of
>      natural motion, concerning which various philosophers have
>      produced various opinions ....
>      Such fantasies, and others like them, would have to be
>      examined and resolved, with little gain. For the present, it
>      suffices .... to  say that in equal times, equal
>      additions of speed are made.

I got that from Galileo, _Two New Sciences_ (1638).

In particular, I got that from page 159 of the English translation by
Stillman Drake, 2nd edition.  Drake is far more than a translator;  he
is an historian who has studied Galileo's unpublished notes and other
records, in the effort to understand the background and the methods
of Galileo's work.

I was particularly taken by Drake's footnote on page 159: "Rejection of
causal inquiries was Galileo's most revolutionary proposal in physics,
inasmuch as the traditional goal of that science was the determination
of causes."

Drake discusses that point at more length in the Introduction.

      What was lacking in physics, from the time that Aristotle coined
    that word to name the science of nature, was the idea that
    actual measurement could contribute anything of real value to /any/
    science.  The object of /science/, as set by Aristotle, was to find
    out the hidden causes of events in nature.  Measurement could not
    reveal underlying causes of the kind required by philosophers, so
    measurement had no place in physics.
    ....
    No mathematician stated that fall exemplified uniformly accelerated
    motion.  Medieval natural philosophers decided that it did not, and
    could not.  Until about 1550, no one suggested it even as a possibility.

I find this really quite remarkable.  We give Galileo credit for establishing
two new sciences.  But here is this big-shot history-of-science professor
telling us that neither of those two sciences, strictly speaking, is the
most important thing.  You would think that establishing two new sciences
would suffice to make the book off-scale important, but the book offers
us something even more important:  it tells us we should concentrate on
quantifying the motion, rather than squabbling about the "causes" of the
motion.

Let me say it again:  This is the epoch, i.e. this is the defining moment,
defining physics as we know it:  the realization that we don't need to
know whether F causes ma or vice versa or both or neither;  for a wide
range of purposes it suffices to know that F _equals_ ma.

==========

There are a large number of follow-up remarks that could be made.

For one thing, it is remarkable how much of Galileo's work is attributed
to other people.  Many of the ideas we refer to as "Newton's laws" go back
to Galileo.  And Newton is famous for saying "hypotheses non fingo" but
the idea clearly goes back to Galileo, as you can see from the passage I
quoted.


Also:  Please don't think I am making an appeal to authority.  I am not
arguing that F _equals_ me because Galileo said so, or that this is
epochal because Drake said so. I have spent the last week giving my own
explanations of what is right and why it is important.

What I *am* doing here is giving credit where credit is due;  I wouldn't
want people to credit me with originating an idea that is really ~400 years
old.


I will put additional remarks in another message.