The Copenhagen interpretation never defined an observer that way. It's a non-interpretation basically, just shut up and calculate, which is still the most widely accepted approach among scientists, since there are no other falsifiable interpretations.
I'm reminded of learning about the grandfather paradox as a kid. I recall hearing shit about scientists saying if you were to travel back in time, you would be compelled by a universal force to do things that don't alter the future and create a paradox. Even as a kid, that sounded so idiotic. In retrospect it was almost certainly the reporting that was wrong.
Is that really so weird? That's a very common version of time travel in SF, perhaps the most common. You can travel back in time, and you think you're changing history, but through a series of unlikely coincidences you end up being the person who created the history you were trying to change.
Come to think of it, maybe that's more common in short stories, where the "gotcha!" format works. It's probably harder to spin that unchangeable-history gimmick out to novel length, whereas "you can change history and it has endless weird side effects" can work well in long form. I can't think off-hand of any time travel novels with unchangeable history.
But it's stupid as a serious time travel proposal. Things like "travel in back in time 5 seconds unless you see your future self is already there" create a hard paradox that this logic cannot solve. Time loops are easily broken by anyone interested in testing them.
I found that link via a blog post that excoriates it for its supposed logical fallacies: https://loopingworld.com/2019/07/13/debunking-ted-chiang-rec.... I don't necessarily agree or disagree with that, but I do disagree that it's "obviously" logically wrong or inconsistent.
It's really just on them for trying to alter the future in large ways before conducting small experiments to understand the mechanics of the universe imo.
Time loops are only a problem if you insist on being able to simulate reality by computing the next time step from previous ones, without discarding any. Or if you for some reason insist on total free will.
> Or if you for some reason insist on total free will.
Like, the free will to do something other than what you saw your future self do? Yeah, you do have that. You have that ability even as a completely deterministic brain.
Heck you could send a machine to go back in time 5 seconds that displays a number 1 greater than the number it just saw its future self display from the previous travel and your time loop has infinitely increasing state with no human in the process. Or the mundane, send a bomb back in time to destroy the time machine and your past self. It's very easy to think of examples.
> Time loops are only a problem if you insist on being able to simulate reality by computing the next time step from previous ones, without discarding any
If you frame the system as "the universe conspires to create a series of coincidences such that no paradox exists", then it makes perfect sense that nobody chooses to run that experiment, because the simplest coincidence that prevents the paradox is for the characters in question to simply not think to run that particular experiment. This raises the obvious question of how the time machine got invented in the first place, which seems like a great story.
