Re: [Phys-l] F causes a

[John Denker <jsd@av8n.com>]

Hugh Haskell wrote:

> But it also 
> seems to me that one might, in principle, conduct an experiment that 
> could distinguish between the symmetry of a mathematical equality and 
> the causal implication, and that is to look for the inevitable time 
> delay that must exist between a cause and its effect. Admittedly, for 
> close encounters detecting this time delay may be beyond our current 
> technological capability, but certainly if one thinks about it for a 
> while it may be possible to come up with a suitable experiment. If 
> so, and if it does demonstrate a causal relationship, then that would 
> imply that we have been writing NSL wrong all these many centuries.

IMHO this is EXACTLY the right way to think about it.

I look at this the same way I look at Eötvös experiments:  Nobody
has ever gotten a non-null result, and a non-null result would be
shocking and amazing ... but I am quite willing to entertain the
possibility, and the experiments are worth doing.

In the Eötvös case, years of null results have led us to trust the
equivalence principle ... but the principle could, for all we know,
be overthrown tomorrow.

The asymmetric notion that "F causes ma (and not vice versa)" is
analogous to a non-null Eötvös result.  Years and years of no
evidence leads us to write the symmetric law "F equals ma".  The
F=ma law _could_ be overthrown tomorrow.  I would be shocked and
amazed, but I am willing to entertain the possibility.

>  But that impulse to infer causality is very strong 
> in humans, for better or for worse. 

That's quite true.  But it doesn't mean we should let the inmates
run the asylum.

"For better or worse" should not be our motto.  We should strive
for "better".

As an anthropological tangent, note that there are some socio-religious
systems that carry pseudo-causation to an extreme.  If somebody trips
and breaks his leg, the shaman will be called to investigate.  Typically
the conclusion will be something like "Aha!  Look!  He wore mismatched
socks today.  That's against the natural order of things, and this is
nature's vengeance.  The socks caused the fall that caused the broken
leg."

As you can imagine, "explanations" like this are a powerful way of
encouraging people to conform to the established way of doing things,
since even mild non-conformity can "cause" terrible things to happen.

As another example, the book _I, Claudius_ tells of an incident where
someone died by choking on a fruit.  Any halfway-alert reader would
conclude that the guy was almost certainly murdered by having the
fruit shoved into his mouth ... but the official imperial explanation
was that it happened "because" of the fruit, and the response was to
chop down the tree that was responsible.

It is the business of science to seek explanations.  Explanation is
*not* equivalent to causation.  The difference is often very important.
As I said previously:

   It turns out that judgements about cause-and-effect often lead to
   real-world actions. For example, you might find that certain locations
   are associated with a high number of weird diseases. If you think
   there is something about the location (e.g. Love Canal) that is
   causing weird diseases, you might well decide to take drastic action,
   such as moving everybody out. On the other hand, it may turn out that
   the location (e.g. the Mayo Clinic) is not causing the diseases, and
   it would be a really bad idea to move everybody out.

   These are not made-up examples: The people who lived near Love Canal
   would have been better off almost anywhere else, while the people in
   the Mayo Clinic would be worse off almost anywhere else.

   http://www.av8n.com/physics/causation.htm

I really don't think we should train our students to assign causation
"for better or worse".  We should train them to do it right.  It's
important.