Expert: Tom Whiting - 9/27/2010

Question
In Einstein’s theory where time and space is bending around earth my understanding is we are being pushed down to the earths surface by this and not pulled to earths surface by gravity. Yet everybody keeps talking about gravity pulling this or that.
I’m missing something here either reading it or understanding it. Can you straighten me out here or clarify any of this for me?


Answer
Hi Steve,
Yes, we and every other mass (including the atmosphere) is being kept on the surface by the curvature of space around the Earth... and not "pulled down" by some mysterious gravitational - so called "force".  I think YOU have an excellent understanding of it, and its true nature, from your first statement.

The average person will still continue to use the words "force" and
pull because 1. It's easier to picture, and 2. Newton's view of gravity is much easier to picture and calculate, and the force calculations will come out the same as Einstein's General Relativity, unless you increase the mass up to White Dwarf, Neutron star, or black hole mass.

This is why the GPS satellites have to include special "clocks" onboard
which run at a different time passage speed compared to time on the surface of the planet, because time runs at a different rate at 200 miles above the surface of the Earth.  If that wasn't accounted for, Einstein's Relavistic effect of gravity and space-time curvature, then our super-accurate GPS system would be useless in a matter of a few days.  
Clear Skies,
Tom Whiting
Erie PA

FOLLOW UP:
Opps.. check that; I guess GPS satellites are much higher at 20,000 km high, and here is an article explaining how special and general relativity have to be taken into account, at
http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit5/gps.html
tom