Judgment Day July 11, 2010Posted by Dwight Furrow in Dwight Furrow's Posts, Philosophy, Science.
Tags: science-fiction, time travel
I don’t find thought experiments about the nature of God very interesting—but throw in time travel and I perk up a bit.
Mike Lebossiere poses the following puzzle:
Sally is working on a time travel project and during one experiment, her own smartphone appears in the lab. Startled, she checks her pocket and finds that her phone is there. Yet it also appears to be on the table. Picking it up, she finds that video has been recorded on it. Much to her horror and dismay, it seems to be a video of her saying that she has killed her husband for having an affair with her friend, only to find out after that she was wrong. In the video, she can she the body of what seems to be her dead husband. The video closes with her future self saying that she is sending back the phone to tell her past self to not kill her husband; future Sally then shoots herself in the head as the phone is being sent into the past.
Being something of a skeptic, Sally checks the phones carefully and finds that (aside from some blood on the future phone that matches her husband’s blood type) the two are identical. This convinces Sally and she does not kill her husband.
Now, let God be brought into the picture, at least hypothetically. If one prefers to leave God out of this game, then an omniscient observer who judges people for their deeds and misdeeds can be used in His place.
In this scenario, what would God actually “see” and how would He judge?
On one hand, the future Sally did kill her husband and send the phone back. After all, without those events, then the phone would not have the video recorded on it and would not have been sent back. As such, God would judge that Sally was guilty of suicide and murder, hence worthy of divine punishment. Also, both Sally and her husband would be dead and thus would have gone off to the relevant afterlife (assuming there is such a thing).
On the other hand, the time traveling phone prevented Sally from killing her husband and committing suicide. Thus, Sally would not be judged for these deeds. Also, neither Sally nor her husband would be dead. In effect, that future event never will be, although it must have been (otherwise there would be no phone).
One classic view of God and time is that God perceives all of time “at once.’ To use an analogy, God’s perspective is like being able to see the entire filmstrip of a movie at once. The past, present and future are just positions on the strip relative to a specific film cell. Hence, He does not see any changes in the past-He merely sees as the events that did occur, shall occur and are occurring all “at once.” So, God would “see” the phone appear from a future that never was to save Sally from committing a murder that never will be.
I think this just points out that the idea of time travel is logically incoherent. The whole idea of going back in time to “undo” an event that has occurred requires that the event both did happen and did not happen. That is a logical contradiction. The future event would have to have happened in order for it to be caused to not happen. Since the “undoing” event is in a cause effect relation with the undone event which must exist for the undoing event to occur we have backward causation going on.
And it is not obvious that backward causation is a coherent idea. It would seen that the outcome of an event must happen only after the event. Although quantum mechanics seems to allow for backward causation (if I understand it correctly) surely there is no experimental result that depends on that idea.
So what would God see? It is a widely accepted view that God is a rational being and thus can neither see nor coherently think contradictory states of affairs. If time travel is logically impossible then trying to imagine how an omniscient being would view it doesn’t help.
Of course, if Sally is the sort of person who would murder her spouse for infidelity then God may have all the justification God needs.
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