We all know that what goes up must come down, unless escape velocity has been achieved. We also know that whatever escapes the tug of gravity loses some speed in its effort to resist the pull of gravity. But, what happens when the thing can't slow down? What if the thing that was launched into space was a beam of light? As you would expect, even though the beam of light cannot lose any of its speed, it does lose energy. It loses energy by slowing its frequency. This loss of frequency can be viewed as a slowing of the flow of time. Let's hold on to that thought, we'll come back to it later. So, how do we calculate just how much energy is lost? In order to do that we have to switch to considering what happens to a particle with mass. The amount of energy lost leaving a gravity well is just the negative of the kinetic energy gained by a particle falling to the surface from infinity. That energy is equal to the work it took for gravity to bring the particle...