Re: Roberts versus Lazio on "Overaveraging"
From: Androcles (dummy_at_dummy.net)
Date: 01/29/05
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Date: Sat, 29 Jan 2005 23:20:02 GMT
"Bill Rowe" <readnewscix@earthlink.net.invalid> wrote in message
news:readnewscix-F3934A.12071329012005@news1.west.earthlink.net...
> In article <7gJKd.10374$B5.3390@fe1.news.blueyonder.co.uk>,
> "Androcles" <dummy@dummy.net> wrote:
>
>> "Bill Rowe" <readnewscix@earthlink.net.invalid> wrote in message
>> news:readnewscix-A21103.21481428012005@news1.west.earthlink.net...
>> > My comment was far too strong and careless as Tom Roberts correctly
>> > points out.
>
>> > For a simple example of systematic error that cannot be eliminated
>> > consider a temperature measurement. For the measurement to take
>> > place
>> > there must be heat transfer from the object whose temperature you
>> > are
>> > trying to measure to the instrument you are using. That will
>> > clearly
>> > cool the thing being measured, an unavoidable systematic error.
>
>> How do you measure the temperate of a star, and how does your
>> measurement affect the star?
>
> I would measure the temperature of a star by doing a spectral analysis
> of the radiation being emitted by that start. And yes, since the star
> is
> continuously emitting radiation, my capture of some small fraction of
> the total doesn't alter the stars characteristics. But the star is
> emitting energy, is cooling in that sense.
Hold on... What I want to know is why measuring the star's temperature
is a systematic error, not whether it is cooling or not.
>
> But more to the point, I had in mind a more ordinary direct
> measurement
> of something in a typical laboratory using say a thermocouple. To get
> the temperature, energy is transferred to the thermocouple.
Which junction, the hot or the cold? Doesn't work without both. How
about I reverse them and transfer energy FROM the thermocouple? Just by
heating the cold junction, really. Now, I'll agree I'm introducing
error, but I'm not taking energy out of the system, and look, if I get a
null current and measure the temperature of the cold junction, wasting
energy as I do so, I'm not affecting the system I'm measuring. I'm
looking into this idea of yours that systematic errors cannot be
eliminated. Maybe they cannot, but you've yet to give an example of why
they cannot, let alone a proof for every case.
> A new
> equilibrium temperature is achieved since the thermocouple has mass
> and
> ir takes a finite non-zero amount of energy to bring it in equilibrium
> with the thing whose temperature is being measured. A direct
> consequence
> is the temperature of the thing being measured is altered unavoidably
> by
> the measurement.
>
> I simply didn't feel it was necessary to be this detailed in my
> original
> comment.
Why on earth not? This is a sci.* newsgroup, we promote thought here
(or try to) so few can get away with willy-nilly assertions. Make a
statement, be challenged. Defend it, withdraw it or insult someone. Its
all part of the fun.
As I told Draper when he complained of feeling demoralized:
If you feel demoralized, I can only advise you this way.
"If you can't take the heat, stay out of the kitchen" - Harry Truman
After a mere three months I think he's gone back to scraping potatoes.
But really, would you want to just be adored as the great scientist and
be right all the time? That would be pretty boring, I think.
Androcles.
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