delusions / illusions

[Hans Blom, 970715d]

(Bill Powers (970714.1822 MDT))

Ultimately, all rules of physics are descriptive. They can be
called "explanatory" only in sofar as they describe one level in
terms of a different, lower level which we think we understand
"intuitively".

There's another kind of "lower level" that's not just an intuitive
matter, but is based on definitions involving measurements. As an
example, the concept of mass involves two measurements: applied
force and measured acceleration. Inertial mass is defined as the
ratio of force to acceleration. Mechanics is built on such basic
definitions. Even relativity uses this definition.

Such definitions are not hierarchical; they are essentially circular.
They are also not based on observations but on a theory. Only if
given the complete "theory" F = m * a, for instance, one can define
any of the three concepts in terms of the other two:

F = m * a
m = F / a
a = F / m

It appears that one has to accept the theory as a whole in order to
be able to define its individual terms and concepts; there is no way
to build up a theory starting from elementary a priori givens,
although it may appear that way, because the concepts of Newtonian
theory have become "second nature" to (some of) us.

But why is so "self-explanatory" that no two physical bodies can
occupy the same space? In mathematics, for instance, it is
perfectly admissible for two points to have exactly the same
coordinates. We think we "understand" where we simply accept an
"obvious truth", it appears to me.

It may seem self-explanatory that two material objects can't occupy
the same space, but we can at least say why this is true, in terms
of a model based on more fundamental notions.

No, we cannot, because it is not true. It is only approximately true
under some circumstances: add, for instance, a volume of salt to a
volume of water and check whether the water volume is displaced by
the salt. It is not: to a good approximation, the water and the salt
will be observed to occupy the same space simultaneously. Archimedes,
also, certainly did not have more fundamental and indubitable notions
to fall back on.

If we treat this idea as a philosophical truth it has little
justification, but if we think in terms of physical operations and
interactions, it has a great deal of practical -- i.e., experimental
-- truth.

But that is exactly what I wanted to pinpoint: your intuition that
two material objects can't occupy the same space is a _philosophical_
truth! It is only sometimes, and then only approximately true. There
are experiments -- just take water and salt -- that will falsify it.

It appears to be our human condition that there are so many of what
you call experimental truths that we never get around to discovering
them all. We simply have to live with a few incorrect or approximate
or context-dependent philosophical truths or "models", although these
are valuable in practice even though simple experiments will prove
them not to be "true".

To paraphrase: Archimedes' law is a perfect example of what I mean.
Some guy said, "What if there's a rule that says no two material
bodies can be in the same space at the same time?"

The difference is that we can offer an explanation for why two
objects can't be in the same space at the same time: we can't push
hard enough, without destroying the objects. The reason that objects
displace water is not that there's a rule saying they do, but that
the interaction of the objects and the water is such as to push the
fluid water aside. There is a simple mechanical explanation, or if
you like, a more sophisticated one involving electrostatic fields or
other interatomic forces. And the rule comes out of interactions
between the objects.

It seems you forgot at least one possible interaction ;-).

Without an explanation that invokes an underlying model, a rule of
nature is like a rule of a game: it's given, and we play by it, but
it stands alone, unrelated to anything else. It isn't "true" in any
sense.

That is correct, regrettably. But neither is any explanation "true"
in any sense. If you want to explain the world to somebody, you must
necessarily do so in terms that are already understood. That makes
every explanation an analogy. And because nothing is already
perfectly understood, that makes every explanation fuzzy. Just look
around and see how people have "understood" PCT!

What frustrates me is that nobody but a full-fledged physicist could
possibly understand all these things well enough to see whether the
entire logical-mathematical system really hangs together. But people
with that much knowledge also have a considerable committment to
physics as it exists today; they are willing to expend considerable
time and energy to convince doubters that physics is on the right
track, but very little of either to see if it is really just a giant
systematic delusion.

Come on, Bill, there's no alternative. It's all illusion, says
Buddha. It's all perception, says PCT. It's all projection, says
Freud. It's all explained in terms of your own idiosyncratic private
internal model, says model-based control theory. And, as Buddhists
know so well, it is impossible to do away with that illusion: our
life depends on it. But it's helpful, at least once in a while, to
acknowledge that we live in a self-created "reality".

True Believers are not likely to be looking for a way to negate
their beliefs!

One of my gripes, too ;-).

Anyway, I doubt whether my own problems with physics will have any
impact on that science.

I don't. Even -- or especially? -- the most knowledgeable physicists
often acknowledge that the world is incomprehensible beyond even our
wildest imagination. And you want it explained to you in simple terms
so you can understand it? Why? To create more "philosophical truths"?

To repeat: It appears that one has to accept the theory as a whole in
order to be able to define ("understand") its individual terms and
concepts; there is no way to build up a theory starting from
elementary ("already understood") a priori givens.

Sorry if I have shattered any illusions ;-).

Greetings,

Hans

[From Bill Powers (970715.1010 MDT)]

Hans Blom, 970715d --

There's another kind of "lower level" that's not just an intuitive
matter, but is based on definitions involving measurements. As an
example, the concept of mass involves two measurements: applied
force and measured acceleration. Inertial mass is defined as the
ratio of force to acceleration. Mechanics is built on such basic
definitions. Even relativity uses this definition.

Such definitions are not hierarchical; they are essentially circular.
They are also not based on observations but on a theory. Only if
given the complete "theory" F = m * a, for instance, one can define
any of the three concepts in terms of the other two:

F = m * a
m = F / a
a = F / m

Algebraically this is true, but with respect to observations it is not. It
is possible to measure F and a independently, but not m.

It may seem self-explanatory that two material objects can't occupy
the same space, but we can at least say why this is true, in terms
of a model based on more fundamental notions.

No, we cannot, because it is not true. It is only approximately true
under some circumstances: add, for instance, a volume of salt to a
volume of water and check whether the water volume is displaced by
the salt. It is not: to a good approximation, the water and the salt
will be observed to occupy the same space simultaneously. Archimedes,
also, certainly did not have more fundamental and indubitable notions
to fall back on.

I could quibble that an object made of rock salt would have to be destroyed
to dissolve it in water, but the truth is that I didn't think of this example.

But that is exactly what I wanted to pinpoint: your intuition that
two material objects can't occupy the same space is a _philosophical_
truth! It is only sometimes, and then only approximately true. There
are experiments -- just take water and salt -- that will falsify it.

Right. I should have caught the fact that the term "object" is an informal
and subjective one.

It appears to be our human condition that there are so many of what
you call experimental truths that we never get around to discovering
them all. We simply have to live with a few incorrect or approximate
or context-dependent philosophical truths or "models", although these
are valuable in practice even though simple experiments will prove
them not to be "true".

True. I think there is a range of "truthfulness", in that some proposed
truths have so many exceptions that I wouldn't consider them very useful,
while others have so few that one would be hard-pressed to think of ANY.

That is correct, regrettably. But neither is any explanation "true"
in any sense. If you want to explain the world to somebody, you must
necessarily do so in terms that are already understood. That makes
every explanation an analogy. And because nothing is already
perfectly understood, that makes every explanation fuzzy. Just look
around and see how people have "understood" PCT!

I think there are different kinds of statements that people use as
explanations. Those that refer to observables are disprovable; those that
invoke hypothetical entities are not. If I say your car stopped because
it's out of gas, you can look in the gas tank to see if my explanation is
believable. But if you say you robbed a bank because of a trauma that
occurred when you were young, there is no way to check to see if the trauma
occurred (that is, an effect inside of you, not the circumstances that
supposedly created it).

Best,

Bill P.