Hi, I found this 'paradox' which supposedly says that SR is incorrect, I have a hunch why it may be a flawed argument, but can't personally get the numbers right. Perhaps it's a fun exercise for some of you to destroy the argument. Here it is: So my hunch why this is incorrect: Spoiler This is ignoring length contraction, because of it, d will appear differently in the different reference frames, this changes the calculations for the expected times, making the problem disappear. Unfortunately I couldn't get the numbers right myself, giving me different results for t1 and t2 in the different reference frames regardless. So I'm not entirely sure if that's the correct counter.