What if they make it so that people who don't have the software can't connect to the Internet at all? For example, they could have the software add a header to each packet, and drop packets that don't have the header (in the same way that they already drop packets that match certain keywords).

Actually, IIRC, gravitational field inside a solid sphere increases linearly with r for r less than R and drops off with 1/r^2 for r greater than R. In this case the field would be 50% of the field at the surface. I don't know where you got "logarithmic" from.

Of course this is assuming the earth is a perfect sphere of uniform density--if anyone has an even more accurate calculation, feel free to add it too ;)

Broken link in parent

Mathcamp