[Avodah] Geocentrism

[Micha Berger]

On Tue, Jul 30, 2013 at 11:11:40AM -0400, David Riceman wrote:
> And their objection to geocentrism is precisely that it denies the value  
> of that deep explanation.

I'm not sure this objection is real. Yes, they don't use geocentrism when
it's the harder way to model things. But here are examples. And if you
compute movement relative to the galaxy as a whole, heliocentrism isn't
much better than geocentrism. And the galaxy too is in motion, etc...

>From wiki, EMPHASIS mine:
https://en.wikipedia.org/wiki/Heliocentrism#The_view_of_modern_science
    In modern calculations the terms "geocentric" and "heliocentric" are
    often used to refer to reference frames. In such systems the origin
    in the center of mass of the Earth, of the Earth -- Moon system,
    of the Sun, of the Sun plus the major planets, or of the entire
    solar system can be selected; see center-of-mass frame. This leads
    to such terms as "heliocentric velocity" and "heliocentric angular
    momentum". In this heliocentric picture, any planet of the Solar
    System can be used as a source of mechanical energy because it moves
    relatively to the Sun. A smaller body (either artificial or natural)
    may gain heliocentric velocity due to gravity assist -- this effect
    can change the body's mechanical energy in heliocentric reference
    frame (although it will not changed in the planetary one). HOWEVER,
    SUCH SELECTION OF "GEOCENTRIC" OR "HELIOCENTRIC" FRAMES IS MERELY A
    MATTER OF COMPUTATION. iT DOES NOT HAVE PHILOSOPHICAL IMPLICATIONS
    AND DOES NOT CONSTITUTE A DISTINCT PHYSICAL OR SCIENTIFIC MODEL. From
    the point of view of General Relativity, inertial reference frames
    do not exist at all, and any practical reference frame is only an
    approximation to the actual space-time, which can have higher or
    lower precision.

Or the aforementioned Discovery column
http://blogs.discovermagazine.com/badastronomy/?p=20845#.Uff2oKzGDf0 ,
"Geocentrism is a valid frame, but not the /only/ one."

Or http://prl.aps.org/abstract/PRL/v61/i8/p903_1 , "Effect of
General Relativity on a Near-Earth Satellite in the Geocentric and
Barycentric Reference Frames". (Barycentrism is what we /really/ mean
by heliocentrism, centered on the center of mass, which is pretty
close to the center of the sun. But our orbit is really baycentric,
not heliocentric.

Googling "barycentric geocentric relativity" will turn up a number of
hits for systems for converting between the two frames of reference
among the first pages of hits.

Tir'u baTov!
-Micha

-- 
Micha Berger             A wise man is careful during the Purim banquet
micha at aishdas.org        about things most people don't watch even on
http://www.aishdas.org   Yom Kippur.
Fax: (270) 514-1507                       - Rav Yisrael Salanter