Say, gravitational potential energy is always negative (gravity is attractive force), so two (or more) attracting bodies separated by some distance and NOT moving have NEGATIVE net energy. Moving and NOT attracting bodies have net POSITIVE energy. Moving And attracting each other bodies may have net energy to be negative (say, orbiting each other bodies), or positive (say, moving with more than escape velocity) or exactly zero (moving with escape velocity).

It turns out, that universe is moving with exactly "escape velocity" so to speak - negative gravitational potential energy of Universe is equal to all positive energies in it (dominating by its motion plus rest-mass energy mc^2), so net balance is zero.

• Ok thanks - highvoltage - June 28, 2001 - 20:50 UTC