I just came across this video today with Brian Greene talking about how time slows down for an observer near a black hole relative to an observer who is farther away. See the first two minutes: It reminded me of another video I saw recently by David Butler where he states that the twin paradox can be resolved by looking at the time dilation factor of the traveling twin as being essentially fully a result of the turnaround acceleration effect producing more the equivalent of a gravitational time dilation effect (see 24:40): Edit: I forgot to add this video, which is where he explains the resolution (see 17:17 in): Such an effect would be similar to the one in the Brian Greene video. Thus, David Butler's position is that the twin paradox is not explained by Lorentzian time dilation due to relative velocity differences but rather to the acceleration effects of the turnaround. However, having read numerous threads in this forum on the twin paradox over the years, the consensus here seems to be that acceleration effects of the turnaround are not a significant factor in the time dilation effect but rather that it is simply the longer world line of the traveling twin that accounts for the paradox. To be honest, the acceleration resolution makes more conceptual sense to me than the world-line solution does. If you look at the Brian Greene video and replace the black hole with a long, strong turnaround with high acceleration, it seems to make great sense. To this day I can't put my head around the world-line solution only to say that it seems to work mathematically and I'll have to take it on faith. Is David Butler wrong? Please explain how. More generally, the question is what is responsible for or what makes a greater contribution to the age differences in the classic twin paradox experiment, gravitational time dilation or SR-velocity related time dilation?