@stveje
> as long as we're being speculative, can we ever truly be sure that a death or any other event couldn't ultimately be traced back to some entanglement somewhere? At least a contributing one.

Still considering (Everettian) many-worlds, quantum entanglement is something happening constantly: it just means that you can't describe certain groups of "particles" independently. Like, electrons being entangled is why we have to describe them with orbitals, etc.

I'm absolutely not a physicist, but I think statistical mechanics comes into play here because we want to determine whether the microscopic events that create new "branches" of non-interacting universes have macroscopic outcomes. In other words, does the difference at the small scale make a difference in the large scale. My understanding is that, yes our best theories of how the universe works do allow for cases where a particle decohering into one state or another, and thus "branching the wave function of the universe, results in a person dying or not dying, but outside of humans making detectors and hooking them up to death machines (which mostly just happens in thought experiments) we don't think that happens most of the time.

> It's more about infinity. If you believe there are (truly) infinite universes, then a universe with a "you" will exist where that "you" didn't die at that exact moment

Honestly, I just don't know the physics here. I don't think just because there are infinite universes, that implies there are enough degrees of freedom in the state of the universe that a person with my same life history on a different branch of the wave function lives eternally.

(all above is based on my casual reading of Sean Carroll's book, "Something Deeply Hidden", and listening to Carroll's podcast, so by no means do I claim any real authority on this.)

P.S.:
For anyone who thinks thinking about this kind of thing is fun, there's a Wikipedia article on it: https://en.wikipedia.org/wiki/Quantum_suicide_and_immortality

@2ck I'm no physicist either, but I do love speculative ideas. My point about infinity is perhaps best illustrated with a simpler example: suppose you start counting even numbers. It's true that you'll never reach an uneven number, or a number like pi, so there are indeed limits to what can happen within this system. But since the even numbers are infinite, you will eventually reach any given number, no matter how big you make it.

@2ck Applying this to universes: if there are infinite universes, and a universe such as ours with a person such as you *can* exist within this infinity of universes ... then they will exist. And if a person can exist who is exactly like you, except they happen to live a little longer ... then they too will exist. It's true, none of these "you" may live forever, strictly speaking. There may be an upper limit, but I'm quite sure it's not 120 years, at least.

@stveje I don't disagree in principle, but with this kind of thing, the fact that something could be isn't particularly interesting unless I can also say how likely it is. I don't really even need to invoke "infinite universes" for this though. unless I want to say that the universes interact, I might as well just talk about the observable universe we're in.