P3D Re: projection (part 2 of 2)

[roberts@xxxxxxxxxxxxxxxxx (John W Roberts)]

>Date: Fri, 26 Feb 1999 20:32:07 -0700
>From: jacob@xxxxxxxxxxxxxx (Gabriel Jacob)
>Subject: P3D Re: projection

>A question for you!
>Should we re-classify light as invisible because a blind person
>(sorry, visually-impaired) can't happen to see it?

No need to apologize - "blind" and "visually impaired" are related but
not identical terms.

While ultimately everything humans discuss is in terms of human thought and
human experience, there has been a strong tendency (since the time of the
Renaissance, at least) to develop a model of a community of thought and
experience, and to put a considerable degree of acceptance on this model,
unless there is a strong reason to suspect that the model is incorrect.
Input to this model can come from other persons, animals, and instruments
to extend our sensory perception. If I successfully use a bloodhound to
track a person, I generally accept that the dog is following a scent trail,
even though *I* can't smell it. Most people totally blind from birth,
living among the sighted, accept that there's such a thing as visible
light, even though they have never seen it.

I do not believe it's necessary to have direct personal experience of
each thing in the universe in order to incorporate it in one's world model,
and to impose such a restriction is needlessly and wastefully limiting.
The "tree falling in the woods" question really has no end. If 500 human
witnesses tell me the falling tree made a sound, and the scene was captured
on a video with sound, but I wasn't there in person, did the falling tree
make a sound? If the tree fell yesterday, and I was there, but all I have
to go on is chemical memories of a sound being made, was there really a
sound? If I'm witnessing the tree falling right now, and I'm hearing it
making a sound, is it possible that I'm just imagining that it makes a
sound?

There may not be a way for a human to absolutely "know" anything. But it
is possible to say "available evidence supports the hypothesis that the
falling tree made a sound".

>John, you'd better read my posts more carefully! :-)

I apologize if I missed or misread any of your posts (or was excessively
sharp in any comments).

>Gabriel (me!) wrote:
>>>As for equations applying to UV and IR as well as the visible 
>>>spectrum this is correct, but since they have different physical
>>>effects on matter (or 3-D slides!) the classifications (IR, light,
>>>UV, etc.) are important to keep distinct.

>>But do those different physical effects (relatively minor compared with
>>X-ray/microwave differences) have wavelength boundaries that necessarily
>>line right up with the threshold of sensitivity of the human eye? 

>Yes these wavelength boundaries are significant enough, especially
>the visible.   

There may be light-assisted chemical reactions for which the boundary between
550nm and 551nm is "significant". The question is whether there are boundaries
for non-visual physical effects which are *right at* the ~400nm and ~700nm
boundaries of human vision, which are clearly much more "significant" than
any other boundaries in the IR, visual, or UV ranges, which make 400nm and
700nm worthy of being considered as major points of demarcation, aside from
the fact that they happen to be significant to human vision?

>There are no problems. These are clearly defined by the CIE curves
>and tables. 

Could you please be more specific? The only CIE curves I see on a regular
basis are those relating to *chromaticity*, which is not a definition of light.

>The reason
>I brought this all up is because of the rather strict definitions
>of infrared and it not being heat, heat absorbing filters not 
>absorbing heat, etc. 

I tend to agree with whoever posted it, that "infrared absorbing filter"
seems to be more descriptive of the function of the device than
"heat absorbing filter".

Further nitpicking corrections to recent posts:
 - "heat" is the form of energy that passes from one body to another as
   a result of a temperature difference between them. The stuff that's
   inside a body may be "loosely" called heat, but is more correctly called
   "internal energy".
 - "specific heat" is the amount of heat required to raise the temperature
   of a unit mass of a substance by a specified amount (in SI, that's
   J / (K x kg)).

I think John Toeppen made another excellent point:
> It is important to have a wholistic understanding of this kind of
>stuff if you want to make effective use of it.  Otherwise, we degenerate
>into bickering fools and become obsessed with seeking specific
>definitions for intrinsicly fuzzy terms.  Language can never accuratly
>embrace reality, it is only a symbolic code. 

John R


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