An introduction to timetravel
Now you're thinking with portals!
We provide three axioms for our introduction to timetravel1. All of these are axioms. I am not certain any of them are true in real life, and am not asking you to believe they are true. For the purposes of argument, we will assume they are true, and see what conclusions they lead to.
Quantum mechanics allows for FTL communication. This is, roughly, Bell’s theorem. Some of you who are familiar with quantum physics will claim that Bell’s theorem doesn’t require FTL communication, particularly in some many-universe interpretations. As a different objection, unlike much of quantum mechanics, I’m not personally 100% convinced Bell’s theorem is true, there is an entire Wikipedia article on loopholes in Bell tests.
FTL communication allows for timetravel. The argument here is that because of special relativity, FTL communication in one frame will look like reverse-causality in a different frame. There are also arguments that special relativity doesn’t do anything of that sort. Anyhow, we are simply assuming that the FTL communication can be “chained” in a way to get timetravel communication as well.
Timetravel creates השם (2) as a pseudo-force. Very roughly, because humans can create arbitrarily-complicated time puzzles, the universe must be able to solve them in arbitrarily-complicated ways. As a less religiously-themed version (which is roughly but not entirely equivalent), we can say that the potential to interact with timetravel will have unpredictable consequences for any conscious entity. It is important to note that this is not saying “when ancient people experienced השם, it was actually time-travelers from the future”, but if you want to believe that, it won’t lead you too far astray.
We also sometimes rely on a lemma - any paradox that can be accomplished with a timemachine that takes a person into the past can also be demonstrated with a collection of time machines that each send a single bit of information into the past (that is, roughly, by using Ted Chiang’s Predictor machine). I leave the proof as an exercise to the reader. While the axioms above don’t allow for you to timetravel into the past physically, some thought experiments may do so for the sake of simplicity. Other thought experiments are much simpler if you only allow for the Predictor.
But how does timetravel work in this model? We start to give two explanations at (code pending), roughly "we don't know" and “it’s a secret”. Unfortunately, neither explanation is complete, and the available information will likely leave you with more questions than you started with. A third explanation, that the answer resides “on the far side of chapel perilous”, is one I have not yet even started to try to explain.
Up next here: more on prophecy and secrecy, followed by “how do you get a consistent model of timetravel”.3
We prefer “timetravel” and “timemachine” as a compound word, rather a two-word or hyphenated phrase.
We leave readers to their own theology. Whether השם is the God of the Hebrews, or some other God that insists tade name not be spoken, is of no concern to us. The code-switching is part of the point, though.
If you want to do the legwork yourself, about 75% of those answers are in Eliezer Yudkowsky’s Harry Potter and the Methods of Rationality, conveniently abridged at http://hpmora.com/ . But there are a few important gaps as well.