Strong downvoted. This article raises a concern of apparently extremely large scale (what happens during time travel) but supports it with invalid reasoning. I believe you should explore this direction more carefully.
In the Everettian multiverse, this action would create a new branch of reality where the 2019 version of ourselves receives this message.
That does not precisely match MWI which states that our uncountably infinite amount of branches splits&merges constantly, with no other reason for new states to appear; do you perhaps mean that a certain bunch of branches would receive more measure?
There are two main theories of time, eternalism and presentism. In the presentism theory, only the now moment of time actually exists, and in the externalism there is a timeless universe, in which past, present and future coexist simultaneously.
The validity of eternalism is a necessary condition (but it is not enough) for time travel, as the past still exists in it.
Paradoxically time travel requires that time doesn’t exist: past and future should exist similarly to the objects in space dimension in the same modal status as now.
From perspective of presentism: if there is a moment where they remember that some object/information had suddenly appeared out of thin air, and at this moment the same object disappears into the thin air, then that is time travel. I do not see any paradox here.
This may mean that subjectively inhabitants of such a loop may experience it infinitely many times – even if they were not sent back in time in the time machine and only a few bits of information were sent.
That requires that experience of an inhabitant is unrelated to their brain matter which had changed at most finitely many times. In particular, it must make it impossible to report on such an experience or to witness it in someone other.
The main claim of the article does not depend on the exact mechanism of time travel, which I have chosen not to discuss in detail. The claim is that we should devote some thought to possible existential risks related to time travel.
The argument about presentism is that the past does not ontologically exist, so “travel” into it is impossible. Even if one travels to what appears to be the past, it would not have any causal effects along the timeline.
I was referring to something like eternal return—where all of existence happens again and again, but without new memories being formed. The only effect of such a loop is anthropic—it has a higher measure than a non-looped timeline. This implies that we are more likely to exist in such a loop and in a universe where this is possible.
Strong downvoted. This article raises a concern of apparently extremely large scale (what happens during time travel) but supports it with invalid reasoning. I believe you should explore this direction more carefully.
That does not precisely match MWI which states that our uncountably infinite amount of branches splits&merges constantly, with no other reason for new states to appear; do you perhaps mean that a certain bunch of branches would receive more measure?
From perspective of presentism: if there is a moment where they remember that some object/information had suddenly appeared out of thin air, and at this moment the same object disappears into the thin air, then that is time travel. I do not see any paradox here.
That requires that experience of an inhabitant is unrelated to their brain matter which had changed at most finitely many times. In particular, it must make it impossible to report on such an experience or to witness it in someone other.
The main claim of the article does not depend on the exact mechanism of time travel, which I have chosen not to discuss in detail. The claim is that we should devote some thought to possible existential risks related to time travel.
The argument about presentism is that the past does not ontologically exist, so “travel” into it is impossible. Even if one travels to what appears to be the past, it would not have any causal effects along the timeline.
I was referring to something like eternal return—where all of existence happens again and again, but without new memories being formed. The only effect of such a loop is anthropic—it has a higher measure than a non-looped timeline. This implies that we are more likely to exist in such a loop and in a universe where this is possible.