Yeah looking at the problem from the perspective of Minkowski spacetime clears up a lot of things.Thanks.
The problem I have with textbooks is that they use a thought experiment with a mechanism involving light to explain time dilation and then extrapolate it to ALL mechanisms in that IF.
Could someone please explain to me both technically and intuitively why the heart slows down as one nears the speed of light relative to an arbitrarily defined stationary observer? I feel rather silly for asking this because I've read the special relativity chapters in 5 different books...