The doc makes no mistakes; what looks like a mistake at first plays out in such a way he's right. Tachyons have that effect... and no he doesn't care if you believe it or not; he has so much time and you are so inconsequential he's only here because some of the few people he ever cared about are still alive and he feels obligated. In a few more years, when his attachment to "humanity", whatever that is, is gone, so he will be.
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