NetNews Usenet Archive 1992 #16/NN_1992_16.iso/spool/sci/physics/11376

Text File | 1992-07-22 | 3.4 KB | 76 lines

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From: [e-mail] (Daniel E. Platt)
Subject: Re: Blue Sky
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Date: Wed, 22 Jul 1992 18:06:59 GMT
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In article <[e-mail]>, [e-mail] (Mike White) writes:
|> Andrew Mullhaupt writes:
|> > Why is the sky blue?
|>
|> You'll get lots and lots of answers, and I'll bet my tenure that not one
|> of them will address the question "Why?"; they'll all address the question
|> "How?".  They'll go on and on about scattering of light from Nitrogen
|> molecules, but the question of "Why?" is much harder.  The mechanism that
|> makes the sky blue is well understood, but why does that mechanism exist,
|> instead of one that makes the sky, say, green?  This rapidly gets into
|> metaphysics; I think the answer has to do with conditions that make it
|> possible for us to exist to ask the question in the first place.

Let's see...

    1)    mechanism of light scattering in the atmosphere (Rayleigh
        scattering, if I remember my Jackson correctly).  This has
        more to do with the properties of light scattering from
        small objects compared to the wavelength than it does
        with what the objects are, if I remember rightly...

        2)    composition of atmosphere... has to do with the evolution
        of our atmosphere.

    3)    Why our planet had the initial conditions it did (nucleo-
        synthesis, etc, astronomy).

    4)    Why elements, chemicals, nucleii, etc have the structure they
        do (quantum physics, chemistry, nuclear/particle physics).

ALL of those questions are mechanistic at some level (that is, they talk
about 'how').  At this level, there are connections between the 'how' of life
and the 'how' of why the sky is blue (same kinds of chemistry/physics
involved at some level, as well as the natural history of our planet to
produce the correct conditions).  As far as conditions, we can ask 'how not,'
and look at other planets for examples.  As far as mechanism, it is much
harder to ask 'how not,' in that its like asking 'how would it be if
electrons behaved differently... how would life look like, or what color
would the sky be?'  In a way, I think that kind of question is getting closer
to the 'why'...

As an undergrad, I remember something about 'causes' being described this way,

"Why is this a 'table'?"

1)    It is a table because it has for legs supporting a flat top.
    (it is shaped like a table)
2)    It is a table because you can put things on it.
    (it acts like a table)
3)    It is a table because someone made it.
    (it was created to be a table by someone)

There were two other 'causes' in this context that I don't recall.  However,
I think they all tie in with the question of what one can mean by the
question 'why.'  The above description of why the sky is blue covers several
facets of the above meanings of 'why' while only handling mechanistic 'hows.'

You don't want to get stuck in the position of the little child who asks
'why' in response to every explanation...  Ultimately, it has to reduce to
some basis of common experience (agreed standards...).

Dan