The reason I post this is that in as few words as possible, I think, that the Many Worlds Hypothesis renders Kripke semantics as redundant. No wavefunction collapse, no necessity. Everything goes so-to-speak.

How much intersectionality between Kripke semantics and theories like the Many World Hypothesis lend to each other? — Wallows

None, it seems to me, since they're describing very different things. "Possible worlds" is a tool for modeling abstract hypotheticals or counterfactuals. Whereas Many Worlds is an interpretation of a physical theory (i.e., what actually occurs, according to Many Worlds).

Compare, for example, a classical coin toss with a quantum coin toss. The possible classical coin toss outcomes could be modeled as "possible worlds", yet no Many World's branching occurs. Conversely, the quantum coin toss outcomes would likely count as a single "possible world" (since both branches are actual and potentially interfere or even eventually merge on a Many Worlds view).

None, it seems to me, since they're describing very different things. "Possible worlds" is a tool for modeling abstract hypotheticals or counterfactuals. — Andrew M

Yes, I understand that; but, what are we to make of claims made in physics as counterfactual definitiveness? Don't they derive from Lewis' work on possible worlds or Kripke?

what are we to make of claims made in physics as counterfactual definitiveness? Don't they derive from Lewis' work on possible worlds or Kripke? — Wallows

No. Everett developed his interpretation prior to Lewis' and Kripke's work. And the earlier Copenhagen Interpretation rejected counterfactual definiteness from the beginning (as do almost all interpretations - see the comparison table).

The Many Worlds interpretation is additionally factually indefinite in the sense that a quantum coin toss lands on both heads and tails (in their respective branches).

Do you believe in the MW interpretation of I may be so bold?

Do you believe in the MW interpretation of I may be so bold? — Wallows

"Believe" is too strong. However MWI and Rovelli's RQM are my preferred interpretations.

Rovelli's RQM — Andrew M

Thank you for introducing me to this. It sounds more or less like how I've always interpreted MWI (which, more on topic, strikes me as very similar to Lewis' notion of actuality being indexical), but the RQM formulation of those ideas seems even more clear and elegant.

FWIW, my take on the relationship between MWI and modal realism is that they can be considered equivalent if we take a "possible world" to be something slightly different from what Lewis takes it to be, which also meshes better with Kripke's semantics about accessibility, which always struck me as really bizarre from a Lewisian perspective (e.g. the notion that something might be necessary from one possible world but contingent from another, when "necessary" should rightly mean "true in all possible worlds").

Instead of taking possible worlds to be time-spanning, each with their own pasts and futures, I take them to be identical to points in the configuration space (or phase space) of the universe, which in turn has its obvious connections to quantum mechanics and the universal waveform. I take time itself to be identical to extension across that configuration space, with one point in the configuration space being in the immediate past or future of another adjacent one on the basis of something equivalent to Kripke's notion of accessibility: if you can "get to" one "world" (point in the configuration space) from another, it's a possible future (and thus "possible" in Kripke's relative sense, while still preserving room for the more absolute sense of possibility across all worlds), and conversely worlds from which you can get to the present world are in the past of this world.

The deciding factor in why you can or can't get from one world to another is entropy: if you take a random walk around the configuration space, you're inevitably (because of the statistical nature of entropy) going to end up wandering into higher and higher entropy states (because there are just more of them, by definition), so higher-entropy worlds than the present one are more readily accessible, "more possible", or in other words more probable. Futures thus diverge over time (i.e. over travel distance in the configuration space), while pasts converge, giving us our notion of the past being one fixed thing and the future being open to alternative outcomes (although on extremely short time scales, there are actually multiple pasts, they just quickly converge over any significant amount of time; compare to e.g. Feynman's work).

If we imagine the configuration space two-dimensionally for conceptual simplicity, and then extrude each point in it "downward" proportional to its entropy, we get an image of rolling hills, with the peaks of each hill being points of locally (in the configuration space) minimal entropy, from which points any direction in the configuration space is "downhill", i.e. into the future. Such points are thus seen as the "beginning of time" by those downhill from them, and even though there are things further in the same direction in the configuration space, those aren't "further back in time" but rather into the future in a different direction (down a different side of the hill), just like every direction is south from the north pole and if you keep going in the direction that was "north" past the north pole, you just end up going south down a different line of longitude.

As a modal realist and MWI proponent, I say that all points in the configuration space are equally real, and thinking beings like us existing at any one point in the configuration space can only have memories of the past because memory formation, like all processes, increases entropy; and from those memories we construct a notion of linear time, projected into an uncertain future, "perceiving the flow of time" inasmuch as we have an immediate, instantaneous perception of that series of memories and expectations and a sense of our place in that construction. But we, strictly speaking, only exist instantaneously in this moment. But beings in worlds slightly in the future of us will have memories of this world, memories shared across the multiple future worlds because their pasts all converge through this world, and so will feel, in their instantaneous moment of existence, like they are all continuations of ourselves, each feeling like they are the only continuation of ourselves because they cannot have memories of each other since they are not in each other's pasts; though as I'm demonstrating right now, we can infer each others' existences in the same way we can infer things about the future.

It sounds more or less like how I've always interpreted MWI (which, more on topic, strikes me as very similar to Lewis' notion of actuality being indexical), but the RQM formulation of those ideas seems even more clear and elegant. — Pfhorrest

Yes, RQM is a high-level abstraction that preserves nice features like locality, theory completeness (i.e., no hidden variables or ad hoc changes) and treats all physical systems as fundamentally quantum (including observers). The downside is that it is not explanatory in the sense that MWI is.

FWIW, my take on the relationship between MWI and modal realism is that they can be considered equivalent if we take a "possible world" to be something slightly different from what Lewis takes it to be, which also meshes better with Kripke's semantics about accessibility, which always struck me as really bizarre from a Lewisian perspective (e.g. the notion that something might be necessary from one possible world but contingent from another, when "necessary" should rightly mean "true in all possible worlds"). — Pfhorrest

Fair enough. I agree that accessibility is important, e.g., Alice seeing heads (from a quantum coin toss) in her world means it is impossible for twin Alice to see heads in her world. But it seems to me that interference effects between worlds also need to be factored in which is a function of probability amplitudes, not merely classical possibilities. For example, it might seem possible for a particle travelling through a Mach-Zehnder interferometer (with equal path lengths and no sample) to arrive at Detector 2, but it isn't.