ABCD

[[A bereaved person and his friend are talking.]] Bereaved: The moment my brother died, I felt a searing pain in my heart. Right: Friend: I'm so sorry. Wrong: Friend: Was it instant, or was there a speed-of-light delay? Very Wrong: Friend: If it was instant, with the right arrangement of moving reference frames, we could use this to send signals back in time and violate causality! How many remaining siblings do you have? {{Title text: Excellent recovery: ... which we could try to use to somehow save your original brother!}}