I never claimed that it would. My point is: what does Charlie measure about his time at stand-still, now that he has been travelling again and received the information about what Alice's clock was doing at the time. Yes, obviously. But what does Charlie now measure "really" happened back there, now that he's moved on? That's exactly what I meant. I don't see how what I said can be interpreted in another way? At what other point earlier than that does "the information about Alice's clock reach[es] him?" I know the second half of the scenario is your blind spot, so I'm glad you managed to remember it this time! And what would you call that, the fact that Charlie changing frames changed what DVR is relevant to him, and his conclusions about Alice's clock? I'm still open to a better word that "overwrite". The calculations, yes. But Alice's clock never ticked backwards; that was the whole point. Yes, obviously. But you've dodged the whole point: is Charlie now justified in saying Alice travelled back in time? My answer: no. No, I don't find ignorance offensive. Go back a couple of sentence in your own post just now. You have, in order: 1) t=10 2) t=40 3) t=10 Any object or clock going from t=40 to t=10 is travelling back in time. However, everybody knows that currently, we haven't got any evidence travelling back in time is possible. So, it can't be travelling back in time. Thus, Charlie must not be able to draw the conclusion that Alice's clock ticked backwards, even though the (correct) calculations suggest it. How do you address this? Same here. Well, I've learned that the best way to really get to know a theory like SR, is to play with it, and address any questionable answer you get. For example, obviously the travelling backwards in time cannot be real, so I try to answer that question. I feel sorry for you that you don't experience such journeys anymore. I on the other hand have an internal drive to understand. Any questionable answer in a theory so obviously self-consistent and worked-out as SR must have a resolution, so I go looking for it. I really do feel sorry for you that you've lost that curiosity. Do you think travelling backwards in time is possible through this method? Erm, you've just stated that Charlie calculates t=10, then t=40, and then t=10, and that those calculations are correct, but in the very next line you say that's not possible. Don't you see the problem? If travelling backwards in time isn't possible, then how it t=10, followed by t=40, and then followed by t=10 possible? I'm not sure if it does; it doesn't "feel" right, but I can't come up with a better one at the moment. "Invalidates" would be better, but that sounds like the old calculation was wrong in some way. "Supersedes" perhaps? In science, it's actually quite important to use the right words. Right, and neither of those show Alice travelling backwards in time at any moment. Correct. You keep ignoring the second half. How can t=10 be followed by t=40 be followed by t=10, if travelling backwards in time isn't allowed? Charlie's measurements also show that Alice at no point in time travelled backwards in time. However, t=10 followed by t=40 followed by t=10 suggests otherwise. It's really weird... You were just a few posts ago making all kinds of silly statements like me not understand that 40>10, but here you are, doing that exact thing. If time (t) starts at 10, then takes a value of 40, and then a value of 10, how did time not decreasing in that last step? And since it's the time on a clock; how is that not travelling backwards in time? Really, you say there's a clock going from t=40 to t=10, but it's not ticking (or jumping) backwards? No, I didn't ask about Charlie or his calculations. Show on Alice's worldline where she does it. Show me where her worldline changes direction, and starts flowing downwards. Nothing more that I've already explained to you multiple times. It's just that you often ignoring half of it.