Re: [asa] New fruit fly threat in Southern California

George:

I was on my way to church when I posted my first comment.
Now I have some time to try to actually think more carefully.

I was simply struck by the leap of imagination that went from subsets of
class to an historical process that linked them all.
This appears to be a fairly modern (say post-evolutionary mindset) presumption.

I tend to agree that the process is "helical" (or hermeneutical).
I think, however, that we pass over this too quickly.
It would do us all good to try to map out this progress.

thanks,

bill

On Sun, 2 Aug 2009 17:15:04 -0400, "George Murphy" <GMURPHY10@neo.rr.com> wrote:
> "Same type of system" in the sense that they're all stars. & they're "set
> up" in different ways - different masses, sometimes different compositions
> &
> environments - when we start to observe them. Of course we can't know for
> sure how they were in the past but we can make reasonable inferences.
>
> E.g., it's standard practice to assume that the stars in a cluster were
> all
> "born" at roughly the same time. That seems reasonable in the case of a
> cluster in which all the stars are moving toward about the same point
> because that suggest that they were formed from a cloud of material that
> was
> moving that way & aren't just a random collection of stars (like the
> Hyades). In cases of that type we can measure distance by cluster
> parallax
> & thus get absolute luminosities (& thus absolute magnitudes). Spectra of
> course give us info on surface temperature, composition & other properties
> &
> if there are binaries we can get masses (or we can use even more indirect
> methods involving pressure broadening of spectral lines &c for mass
> estimates). Then we can see if & how different variables are correlated.
>
> We can construct the H-R diagram ( magnitude vs. spectral type) for the
> cluster & then compare such diagrams for different clusters. There are
> significant differences that can be interpreted in terms of differences in
> cluster ages. This is obviously a non-trivial step & I'm leaving a lot
> out.
> That's clear from the fact that 70 years ago or so it was thought that
> stars
> evolved from red giants to the main sequence instead of the other way
> around, as we think now. But once we get it right (!) we can get some
> understanding of stellar evolution. There is certainly a good deal of
> theoretical inference in this but that's the case with all experiments. &
> note that much of what we're doing is applying physical principles that
> have
> a great deal of experimental & theoretical support in terrestrial physics.
>
> Now is this, as you suggest, a circular argument? Are we assuming that
> all
> the stars in a cluster were formed at about the same time in ordet to
> "prove" that they all have the same age? No. We assume - & not without
> some good reason - that they were formed from the same interstellar cloud
> at
> about the same time. From that & other input we are able to work out
> things
> like the mass-luminosity relation, ideas about stellar energy sources &
> stellar evolution &c, some of which we can check against further
> observations. This eventually does give us an estimate for the age of the
> cluster we started with - but also a lot more. It's not a circular but a
> helical argument - we go in a circle but also make progress.
>
> The parallel here with what geophysicists do with radioactive dating
> should
> be fairly clear.
>
> Shalom
> George
> http://home.roadrunner.com/~scitheologyglm
>
> ----- Original Message -----
> From: "Bill Powers" <wjp@swcp.com>
> To: "George Murphy" <GMURPHY10@neo.rr.com>
> Cc: "Cameron Wybrow" <wybrowc@sympatico.ca>; "asa" <asa@calvin.edu>
> Sent: Sunday, August 02, 2009 9:55 AM
> Subject: Re: [asa] New fruit fly threat in Southern California
>
>
>> George:
>>
>> You say:
>>
>> " Start with astronomy. There are 2 things to note about this science.
>> 1st,
>>> we can't do experiments on stars or galaxies - it would be completely
>>> beyond the physical ability of any foreseeable technological
> civilization
>>> to manipulate the conditions of even our closest star. & 2d, this
>>> science is historical - all the stars & galaxies we observe are in the
>>> past, & in most cases the distant past. It's an historical science.
>>> However, there are billions of stars & of galaxies. We can observe
> stars
>>> of varying masses, chemical compositions & ages, in different
>>> environments. (Of course all those things are inferred but so are all
>>> our observational data.) In a quite real sense, the experiments on
>>> stars have been done for us. It's as if we walked into a huge lab &
>>> found billions of experiments on the same type of system set up under
>>> different conditions."
>>
>> How do you know that it is the same type of system *set up* under
>> different conditions? This appears to be a conclusion that is beyond
> the
>> data, one that we "naturally" make today.
>>
>> I suppose we might view it as abductive. We try the presumption out for
>> size. We hope to find confirming or supportive evidence that is
>> consistent with the presumption. How does that work and not be
> circular?
>>
>> Got to go.
>>
>> bill
>>
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>>>>>
>>>>>
>>>>> To unsubscribe, send a message to majordomo@calvin.edu with
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>>>>>
>>>>
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>>> To unsubscribe, send a message to majordomo@calvin.edu with
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>>>
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>
> To unsubscribe, send a message to majordomo@calvin.edu with
> "unsubscribe asa" (no quotes) as the body of the message.

To unsubscribe, send a message to majordomo@calvin.edu with
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Received on Sun Aug 2 19:41:52 2009