Sure, but then why do you expect memory and experience would also behave in a common sense manner? (At least, that’s what I think you did in your first comment.)

I interpreted the OP as “I’m confused about memory and experience; let’s try a thought experiment about a very uncommon situation just to see what we think it would happen”. And your first comment reads to me as “you picked a bad thought experiment, because you’re not describing a common situation”. Which seems to completely miss the point, the whole purpose of the thought experiment was to investigate the consequences of something very distinct from situations where “common sense” has real experience to rely on.

The part about torturing children I don’t even get at all. Wondering about something seems to me almost the opposite of the philosophy of “doing something because you think you know the answer”. Should we never do thought experiments, because someone might act on mistaken assumptions about those ideas? Not thinking about something before doing it sounds to me like exactly the opposite of the correct strategy.

The problem with that is that life on Earth appeared about 4 billion years ago, while the Milky Way is more than 13 billion years old. If life were somewhat common, we wouldn’t expect to be the first, because there was time for it to evolve several times in succession, and it had lots of solar systems where it could have done it.

A possible answer could be that there was a very strong early filter during the first part of the Milky Way’s existence, and that filter lessened in intensity in the last few billion years.

The only examples I can think of are elemental abundance (perhaps in a young galaxy there are much fewer systems with diverse enough chemical compositions) and supernova frequency (perhaps a young galaxy is sterilized by frequent and large supernovas much more often than an older one’s). But AFAIK both of those variations can be calculated well enough for a Fermi estimate from what we know, so I’d expect someone who knows the subject much better than I would have made that point already if they were plausible answers.

Your rephrasing essentially says that you torture an identical copy of a person for a week.

If you read it carefully, my first rephrasing actually says that you torture the original person for a week, and then you (almost) perfectly erase their memories (and physical changes) during that week.

This is not changing the nature of the thought experiment in the OP; it is exactly the same experiment, plus a hypothetical example of how it could be achieved technically, because you implied that the experiment in the OP is impossible to achieve and thus ill-posed.

Or, at least, that’s how I interpreted “Of course I'm fighting the hypothetical thought experiment. I think the notion of experience without being affected doesn't make any sense.” I just gave an example of how one can experience something and not be affected. It was a somewhat extreme example, but it seems appropriate when Omega is involved.

It seems rather silly to argue about that, when the thought experiment starts with Omega and bets for amounts of a billion dollars. That allows glossing over a lot of details. Your position is like objecting to a physics thought experiment that assumes frictionless surfaces, while the same thought experiment also assumes mass-less objects.

As a simple example: Omega might make a ridiculously precise scan of your entire body, subject you to the experiment (depending on which branch you chose), then restore each molecule to the same position and state it was during the initial scan, within the precision limits of the initial scan. Sure, there’ll be quantum uncertainty and such, but there’s no obvious reason why the differences would be greater than, say, the differences appearing during nodding off for a couple minutes. Omega even has the option of anesthetizing and freezing you during the scan and restoration, to reduce errors. You’d remember that part of the procedure, but you still wouldn’t be affected by what happened in-between.

(If you think about it, that’s very nearly equivalent to applying the conditions of the bet, with extremely high time acceleration, or while you’re suspended, to a very accurate simulation of yourself. The end effect is the same: an instance of you experienced torture/ultra-pampering for a week, and then an instance of you, which doesn’t remember the first part, experiences gaining/loosing a billion dollars.)

perhaps costly, but worth the price

How about extending the metaphor and calling these techniques "Rituals" (they require a sacrifice, and even though it’s not as “permanent” as in HPMOR, it’s usually dangerous), reserving “Dark” for the arguably-immoral stuff?

The nice thing about hacking instrumental goals into terminal goals is that while they’re still instrumental you can easily change them.

In your case: You have the TG of becoming fit (BF), and you previously decided on the IG of going to the gym (GG). You’re asking about how to turn GG into a TG, which seems hard.

But notice that you picked GG as an instrument towards attaining BF before thinking about Terminal Goal Hacking (TGH), which suggests it’s not optimal for attainging BF via TGH. The better strategy would be to first ask yourself if another IG would work better for the purpose. For example, you might want to try lots of different sports, especially those that you instinctively find cool, or, if you’re lucky, that you’re good at, which means that you might actually adopt them as TGs more-or-less without trying.

(This is what happened to me, although in my case it was accidental. I tried bouldering and it stuck, even though no other sport I’ve tried in the previous 30 years did.)

Part of the trick is to find sports (or other I/TG candidates) that are convenient (close to work or home, not requiring more participants than you have easy access to) and fun to the point that when you get tired you force yourself to continue because you want to play some more, not because of how buff you want to get. In the sport case try everything, including variations, not just what’s popular or well known, you might be surprised.

(In my case, I don’t much like climbing tall walls—I get tired, bored and frustrated and want to give up when they’re too hard. One might expect that bouldering would be the same (it’s basically the same thing except with much shorter but harder walls), but the effect in my case was completely different: if a problem is too hard I get more motivated to figure out how climb it. The point is not to try bouldering, but to try variations of sports. E.g., don’t just try tennis and give up; try doubles and singles, try squash, try ping-pong, try real tennis, try badminton, one of those might work.)

It doesn’t work if you just click the link, but if you copy the link address and paste it in a browser then it works. (Because there isn’t a referrer header anymore.)

Medical issues that make life miserable but can be fixed with ~1M$ would be a (bit more concrete) example. Relatively rare, as you said.

I have a rare but recurring dream that resembles very much what you describe.