If you can construct a certain line of reasoning about observed world using MWI, you should be able to do the same if you assume that only this single world "exists".
If the two theories make the same predictions, what is the point? Why not just stick with the old fuddy duddy one reality? Is MWI just a fashion statement? Just a theory that falls under Quine's "inscrutability of translation"?
Note that a hidden variable theory does make a prediction - that there are hidden variables we may one day discover and use to make better predictions than we can now, and do more powerful things, while theories that make randomness ontological say that we will absolutely never do that - the unpredictability and uncontrolability are inherent in reality.
I'm a fuddy duddy sticking with other fuddy duddies like Einstein (and I believe Jaynes) until the the detector efficiency and fair sampling loopholes are closed.
Would someone in the know tell me what the MWI supposedly buys? What's the payoff? Even conceptually, ignoring the identical predictions, what's the payoff? What problem does it supposedly solve? And then, what problems does it introduce that fuddy duddies don't already have?
I don't see that branching has gained me anything over wave function collapse - and now I have to deal with being killed by an asteroid strike last week in some parallel universe. Who needs it?
The positives I see are: wavefunctions being real, and not statistical statements about point objects; measurements are actually quantum interactions of joint wavefunctions.
My prescription for physics is to accept that (some) wave functions are real, they can interact in ways that we don't currently understand (wave function collapse, branching, etc.) and let's get on with doing some real physics and figuring out how they interact, how we can measure it, and how we can control it.
Physics seems awash in mathematical wanking that I explain through evolutionary theory. Measurements are expensive, and give a zillion uninteresting and unpublishable failures before an interesting publishable success. Mathematical wanking is cheap, and allows "successful" papers to be published, and phds to be had. Run a couple iterations of that, the measurers go extinct and the wankers have inherited the physics departments.
If the two theories make the same predictions, what is the point? Why not just stick with the old fuddy duddy one reality?
For example, Lagrangian and Hamiltonian mechanics make the same predictions and are completely equivalent in most cases, but have different uses. There is nothing wrong with picking the formalism more convenient for a specific problem. Granted, MWI does not have a specific formalism, but I allow that it can still provide an inspiration or an intuition in certain problems, which then has to be checked by doing the calculations.
As for ...
Today's post, Living in Many Worlds was originally published on 05 June 2008. A summary (taken from the LW wiki):
Discuss the post here (rather than in the comments to the original post).
This post is part of the Rerunning the Sequences series, where we'll be going through Eliezer Yudkowsky's old posts in order so that people who are interested can (re-)read and discuss them. The previous post was Why Quantum?, and you can use the sequence_reruns tag or rss feed to follow the rest of the series.
Sequence reruns are a community-driven effort. You can participate by re-reading the sequence post, discussing it here, posting the next day's sequence reruns post, or summarizing forthcoming articles on the wiki. Go here for more details, or to have meta discussions about the Rerunning the Sequences series.