This is probably a bad question, but can it be transformed away? Say Alice is on Earth and Bob is far away in outer space. Bob would think that Alice's clock is running slow. Alice would think Bob's clock is running fast. A third observer, say Carl, anywhere in spacetime would have to observe this as well. Or can Carl somehow transform away the difference he observes between Alice and Bob? Say Carl is somewhere between Bob and Alice. If Carl is in a rocket and tries to accelerate towards bob and away from Alice, he could claim that he isn't moving and that it's Bobs mass that is increasing, and Bob from Carl's frame of reference would be blue shifted. He could similarly claim that Alice is moving away in the opposite direction with the same acceleration. But we know that space is expanding radially in all directions. So Carl should be seeing Bob slightly more blue shifted than normal and he should see Alice slightly more red shifted than normal, which gives a slight bias in favor of Bob. Also, I'd imagine that the path between Carl and bob would be slightly length contracted and opposite for Alice. So from Carl's frame of reference, would he not see the difference in spacetime curvature between Alice and Bob to be slightly different than he would have if Carl didn't accelerate at all? Or would the Lorentz contraction/expansion cancel out the effect of the expanding universe? Would the expansion of the universe to instantaneously follow Carl so that it wouldn't even be a factor?