I thought it was because
the inside of the Earth is a big magnet and everything has varying amounts of iron in it. That's why things that have lots of iron like a car are really heavy.
( sandettie light vessel automatic New Twitter - @bollocksreally, Sat 5 Mar 2011, 17:18, 1 reply)

Nope, it's inertia.
Everything is expanding at a constant rate, including the space between everything, so what you feel as the "pull" of gravity is actually the "push" of the earth's surface against your feet as it gets bigger.

You don't notice things expanding as you're expanding too, as is the space between everything, which is why the universe is not getting more crowded. Trains notwithstanding.
( argyleblanket The man on the roof works for me, Sun 6 Mar 2011, 12:50, closed)

partly true
there's also the pull from quantum strings.
( Ring Of Fire A petty, drooling belming butthurt retard., Sun 6 Mar 2011, 22:19, closed)