Re: Incommensurability of Mathematical Logic and Scientific Logic
- From: surrealistic-dream@xxxxxxxxxxx
- Date: 2 Nov 2005 07:24:16 -0800
AllYou! wrote:
> "jem" <xxx@xxxxxxx> wrote in message news:Hn3af.112$ii.85@xxxxxxxxxxxxx
....
> >> Models are completely distinct from real-world measurements because there's
> >> no way to ascertain what the real world is, or even whether or not it exists.
> >
> > A real-world exists. Physics defines it as the collection of all measurable
> > phenomena.
>
> Physics is only about building models of what we observe. Reality is a
> philosophical issue, not a scientific one.
A physicist may stipulate a minimal meaning to the term "reality,"
which includes at least the existence of observers, reference frames,
measuring devices, and measurements (others may want to include the
so-called laws of physics). True, physics is not the correct platform
to discuss the *ultimate* nature of reality.
To avoid needless arguing, both posters could refuse to use the word
"reality" stipulated as such, but for convenience you would just have
to invent some other term to replace it. Maybe the term "physicality"
would do?
>
>
> >> To claim, as you do, that there are two sets of
> >> measurements (i.e., that of the defined hypothetical measurements and that of
> >> real world measurements) is pure folly. Please provide an
> >> example of two such meansurements and how we'd match them.
The dicotomy is between the theory predictions and the actual
measurements.
> >
> > A weather model indicates that real-world devices called thermometers will
> > register 20 degrees Celsius when other real-world devices called clocks
> > register noon. Hold a clock and a thermometer side by side so that both
> > readings are visible simultaneously. When the clock reads 12:00, check to see
> > whether the thermometer reads 20.
> >
> > Can you identify what's from the model and what's from the real-world?
Yes. The prediction is "from the model" and the actual measurement is
"from the real-world" so-called (or say it is from "physicality"). But
the theoretical cause of a phenomena need not be the "real" cause of
the phenomena. It is NOT the job of physics to map theoretical causes
from the theory to reality, though both physicists and non-physicists
love to do this anyway.
>
> Now I see what you meant. You think physics is about building models of what
> will happen in the future, but that physics can determine what the real world is
> in the present. Well, I hate to break this to you, but that's not what's meant
> by physics being used to build models. As I've said, all we have at any given
> present time are observations. Physics isn't concerned about if what we
> observed really happened or not. We have no way of knowing if our lying eyes,
> or any devices we've invented *really* happened as we observed them.
The notion of a physical measurement includes the possibility that it
is "in error" for whatever reason. But at some point you have to say
that this is what we measured and if you think that measurment is in
error, it must be because you have some theory that tells you how to
"identify that error" and possibly "correct the measurement."
> To claim
> that we do is to close off a whole set of possibilities. Even AE claimed that
> no observer has a valid claim over any other observer about what *really*
There must be something in common when comparing the measurements made
by various observers in different reference frames. That commonality
exists in the laws of physics that governs the behavior of measuring
instruments. Einstein said that every frame of reference is as good as
any other frame of reference to reveal the general laws of physics
because he believed that there exists a form of the laws of physics
such that they have the same form for all reference frames: the
principle of general covariance (which he used as a heuristic). Thus,
the measurements made on a certain phenomena may give different values
in different frames of reference, but the laws governing those
measurements satisfy the general laws of physics for EACH frame of
reference.
Jem has tried to tell you that he stipulated a very narrow meaning to
the term "reality" to mean "measurements actually taken."
> happened.
>
> We make observations, and we build a model of what reality is. Now, we can use
> that model to make the sorts of predictions you spoke of, but as far as physics
> is concerned, all we have is the model, and reality has nothing to do with
> anything.
Reality as stipulated by Jem does have something to do with physics.
This is purely a semantic argument being passed-off as having deeper
physical or philosophical content. Where Jem used the term "reality"
substitute the word "physicality."
>
>
> >> All we have are observations, and we use those observations to build a model
> >> of what we believe might be an accurate reflection of a real world, should
> >> one exist.
> >
> > Where "accurate reflection of a real world" means that predicted measurements
> > match actual measurements (within suitable tolerances).
>
> No. We can only hop our model is accurate.
I presume you are referring to the "problem of induction." If so, you
are right. But in science we take comfort in the knowledge that some of
our models (theories) have worked well for a long time in a domain of
applicability. This gives us confidence for the future value of the
model as a good predictor. In that regard, SR is no different than
Newtonian mechanics or classical thermodynamics.
> But there's no way of knowing that
> at all. All we can do is build the mot reliable model possible.
That's what Jem was saying too. You two disagree on the right to employ
the term "reality" in this physics setting.
>
> > The real-world *is* the measurements - of course it exists.
>
> Maybe, maybe not, but that's a philosophical issue, not a scientific one.
If there is no existence to observers, reference frames, and
measurements then science has no practical or theoretical foundation to
even get started, much less progress. If that requires us to allow a
little a priori ontology into physics, then so be it.
>
>
> >> The worth of the model lies in it's abiltiy to
> >> reliably predict future
> >
> > and retrodict past
> >
> >> observations, and those predictions are based
> >> upon past observtions,
> >
> > Those predictions/retrodictions are based entirely on a model. The extent to
> > which the formulation of the model relied on past observations is irrelevant.
>
> Ignoring the past to make predictions is nothing more than sheer random
> guessing. I base my prediction that the rock will hit the Earth, how fast it
> will get there, and the force with which it will impact, when I let it go based
> upon past observations. Those observations are in no way irrelevant to those
> predictions.
>
> > > and speculations as to the causes of those
> >> observations. IOW, we observe the Earth in orbit around the Sun,
Do we? Or is that just what our best theories tell us we "observe"?
> >
> > We've observed certain affects on certain measuring instruments (e.g. eyes,
> > clocks, sextants, etc.), and built a model containing entities called Sun,
> > Earth and orbit.
>
> There's nothing in what I've said that's contrary to this. So why'd you post
> it?
>
> >> we
> >> predict that this orbit will continue along a certain path,
> >
> > We've *defined* the paths of the Earth and Sun (model entities), and
> > translated those paths into numerical results that are expected to match the
> > readings on particular real-world instruments.
>
> We can define a path all we want, but the observation will be the observation,
> and natural phenomena will ignore any definition created by man. It will be
> what it will be, and all we can do is match our prediction of what it will be to
> what it is in order to value the worth of our model.
So far, Jem has not suggested that a successful model is a true model.
In GR, gravity is theoretically "caused" by spacetime curvature, which
is caused by the presence of matter. That doesn't mean that in
"reality" there is something called spacetime as a thing, which can be
either flat or curved. The "reality" of GR is no different than the
"reality" of classical thermodynamics: it is the set of actual
measurements and the "things" that make them. Theoretical causes are
not necessarily "real" causes.
>
> >> and we base
> >> this prediction upon the observations we've made which result in speculation
> >> as to the cause.
> >
> > The prediction is based solely on the model; no speculation is needed in order
> > to designate a cause within the model.
>
> Well, of course we base all of this upon the model. There's nothing in that
> proposition that's contrary to what I said.
>
>
> >> The worth of our model lies in the
> >> reliability of those predictions.
> >
> > It lies in the correctness of the predictions.
>
> And the *correctness* is determined by matching the predictions which were made
> using the model to the observations.
A philosophical comment?
.
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