it appears the physicists who have happened to run across his argument found it severely flawed
The criticisms at those links have nothing to do with the argument for MWI. They are just about a numerical mistake in an article illustrating how QM works.
The actual argument for MWI that is presented is something like this: Physicists believe that the wavefunction is real and that it collapses on observation, because that is the first model that explained all the data, and science holds onto working models if they are falsified. But we can also explain all the data by saying that the wavefunction is real and doesn’t collapse, if we learn to see the wavefunction as containing multiple worlds that are equally real. The wavefunction doesn’t collapse, it just naturally spreads out into separate parts and what we see is one of those separate parts. A no-collapse theory is simpler than a collapse theory because it has one less postulate, so even though there are no new predictions, by Bayes (or is it Occam?) we can favor the no-collapse theory over the collapse theory. Therefore, there are many worlds.
This is informal reasoning about which qualitative picture of the world to favor, so it is not something that can be verified or falsified by a calculation or an experiment. Therefore, it’s not something that a hostile physicist could crisply debunk, even if they wanted to. In the culture of physics there are numerous qualitative issues where there is no consensus, and where people take sides on the basis of informal reasoning. Eliezer’s argument is on that level; it is an expression in LW idiom, of a reason for believing in MWI that quite a few physicists probably share. It can’t be rebutted by an argument along the lines that Eliezer doesn’t know his physics, because it is an argument which (in another form) a physicist might actually make! So if someone wants to dispute it, they’ll have to do so, just as if they were intervening in any of these informal professional disagreements which exist among physicists, by lines of argument about plausibility, future theoretical prospects, and so on.
ETA One more comment about the argument for MWI as I have presented it. Physicists don’t agree that the wavefunction is real. The debate over whether it is real, goes all the way back to Schrodinger (it’s a real physical object or field) vs Heisenberg (it’s just a calculating device). The original Copenhagen interpretation was in Heisenberg’s camp: a wavefunction is like a probability distribution, and “collapse” is just updating on the basis of new experimental facts (the electron is seen at a certain location, so the wavefunction should be “collapsed” to that point, in order to reflect the facts). I think it’s von Neumann who introduced wavefunction realism into the Copenhagen interpretation (when he axiomatized QM), and thereby the idea of “observer-induced collapse of the wavefunction” as an objective physical process. Though wavefunction realism was always going to creep up on physicists, since they describe everything with wavefunctions (or state vectors) and habitually refer to these as “the state” of the object, rather than “the state of our knowledge” of the object; also because Copenhagen refused to talk about unobserved realities (e.g. where the electron is, when it’s not being seen to be somewhere), an attitude which was regarded as prim positivistic virtue by the founders, but which created an ontological vacuum that was naturally filled by the de-facto wavefunction realism of physics practice.
The criticisms at those links have nothing to do with the argument for MWI. They are just about a numerical mistake in an article illustrating how QM works.
The actual argument for MWI that is presented is something like this: Physicists believe that the wavefunction is real and that it collapses on observation, because that is the first model that explained all the data, and science holds onto working models if they are falsified. But we can also explain all the data by saying that the wavefunction is real and doesn’t collapse, if we learn to see the wavefunction as containing multiple worlds that are equally real. The wavefunction doesn’t collapse, it just naturally spreads out into separate parts and what we see is one of those separate parts. A no-collapse theory is simpler than a collapse theory because it has one less postulate, so even though there are no new predictions, by Bayes (or is it Occam?) we can favor the no-collapse theory over the collapse theory. Therefore, there are many worlds.
This is informal reasoning about which qualitative picture of the world to favor, so it is not something that can be verified or falsified by a calculation or an experiment. Therefore, it’s not something that a hostile physicist could crisply debunk, even if they wanted to. In the culture of physics there are numerous qualitative issues where there is no consensus, and where people take sides on the basis of informal reasoning. Eliezer’s argument is on that level; it is an expression in LW idiom, of a reason for believing in MWI that quite a few physicists probably share. It can’t be rebutted by an argument along the lines that Eliezer doesn’t know his physics, because it is an argument which (in another form) a physicist might actually make! So if someone wants to dispute it, they’ll have to do so, just as if they were intervening in any of these informal professional disagreements which exist among physicists, by lines of argument about plausibility, future theoretical prospects, and so on.
ETA One more comment about the argument for MWI as I have presented it. Physicists don’t agree that the wavefunction is real. The debate over whether it is real, goes all the way back to Schrodinger (it’s a real physical object or field) vs Heisenberg (it’s just a calculating device). The original Copenhagen interpretation was in Heisenberg’s camp: a wavefunction is like a probability distribution, and “collapse” is just updating on the basis of new experimental facts (the electron is seen at a certain location, so the wavefunction should be “collapsed” to that point, in order to reflect the facts). I think it’s von Neumann who introduced wavefunction realism into the Copenhagen interpretation (when he axiomatized QM), and thereby the idea of “observer-induced collapse of the wavefunction” as an objective physical process. Though wavefunction realism was always going to creep up on physicists, since they describe everything with wavefunctions (or state vectors) and habitually refer to these as “the state” of the object, rather than “the state of our knowledge” of the object; also because Copenhagen refused to talk about unobserved realities (e.g. where the electron is, when it’s not being seen to be somewhere), an attitude which was regarded as prim positivistic virtue by the founders, but which created an ontological vacuum that was naturally filled by the de-facto wavefunction realism of physics practice.