When reading "one of whom is moving at close to the speed of light compared to the other" in the explanation I'm reminded of the (non-)joke "What's the difference between a duck? One of its legs is not the same." Because of frames of reference both of them are moving at close to the speed of light compared with the respective other. Which doesn't affect the disagreement about the simultaneity of observed events, of course. That still potentially/inevitably happens. 220.127.116.11 13:36, 28 May 2013 (UTC)
You don't have to move close to the speed of light to create this effect, you just need to go close to the speed of light to make a noticeable difference.
Any amount of movement would cause this difference in perception, it would just be so small you would not notice it. In fact very accurate clocks have demonstrated this simply by flying one in a jet around the world while the other sat still.
Even if you walked around the world there would still be some effect. So there is no need to assume the there was any near speed of light sex, just a disparity in the amount of movement made by the two partners. 18.104.22.168 19:37, 7 July 2013 (UTC)