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Q & A: space isotropy in gravity

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Most recent answer: 08/31/2012
Q:
Are the scales of the three XYZ dimensions of space all equivalent in a gravitational field or are Latitude, Longitude, and height(orthometric) more representative of reality on earth?
- David Philip (age 64)
Newburgh, Aberdeenshire, UK
A:
To an excellent approximation, space near the earth is just Euclidean, the same in all directions, so there's almost no fundamental reason to prefer some particular set of axes. To a very small extent, thanks to general relativity, the space deviates from that simple form. Laying identically made rulers in circles around the earth gives a slightly smaller (~ 1 inch) circumference than you would calculate from the number of rulers needed to go through the earth along a diameter. So in that regard it makes slightly more sense to use height as one of the axes, since it's the special direction. There are also some extremely subtle effects of the earth's spin (recently measured by the Gravity Probe B experiment) so perhaps (I'm weak on general relativity) there would be some tiny reason to prefer latitude-longitude to other choices of surface coordinates.

Mike W.

(published on 08/31/2012)

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