Remember, the key suppositions of MWI are just that [...] Hence why it’s claimed here that MWI wins by Occam’s Razor.
You can’t get the probabilities from those suppositions. And without the probabilities, MWI has no predictive power; it’s just a metaphysics which says “Everything that can happen does happen”, and which then gives wrong predictions if you count the worlds the way you would count anything else.
But even if you can justify the required probability measure, there is another problem. John Bell once wrote of Bohmian theories (see last paragraph here):
As with relativity before Einstein, there is a preferred reference frame in the formulation of the theory…but it is experimentally indistinguishable.
In a Bohmian theory, you take the classical theory that is to be quantized, and add to the classical equations of motion a nonlocal term, dependent on the wavefunction, which adds an extra wiggle to the motion, giving you quantum behavior. The nonlocality means that you need a notion of objective simultaneity in order to define that term. So when you construct the Bohmian counterpart of a relativistic quantum theory (i.e. of a quantum field theory), you will still see relativistic effects like length contraction and time dilation (since they are in the classical counterpart of the quantum field theory), but you have to pick a reference frame in order to make the Bohmian construction—which might be seen as an indication of its artificiality.
The same thing happens in MWI. In MWI you reify the wavefunction—you assume it is a real thing—and then you divide it up into worlds. To perform this division, you need a universal time coordinate, so relativity disappears at the fundamental level. Furthermore, since there is no particular connection between the worlds of the wavefunction in one moment, and the worlds of the wavefunction in the next moment, you don’t even have persistence of a world in time, so you can’t even think about performing a Lorentz transformation. Instead, you have a set of disconnected world-moments, with mysterious nonstandard probabilities attached to them in order to make predictions turn out right.
All of that says to me that the MWI construction is just as artificial as the Bohmian one.
You can’t get the probabilities from those suppositions. And without the probabilities, MWI has no predictive power; it’s just a metaphysics which says “Everything that can happen does happen”, and which then gives wrong predictions if you count the worlds the way you would count anything else.
Sorry, yes. I took weighting things by squared-norm of amplitude as implicit, seeing as we’re discussing QM in the first place.
You can’t get the probabilities from those suppositions. And without the probabilities, MWI has no predictive power; it’s just a metaphysics which says “Everything that can happen does happen”, and which then gives wrong predictions if you count the worlds the way you would count anything else.
But even if you can justify the required probability measure, there is another problem. John Bell once wrote of Bohmian theories (see last paragraph here):
In a Bohmian theory, you take the classical theory that is to be quantized, and add to the classical equations of motion a nonlocal term, dependent on the wavefunction, which adds an extra wiggle to the motion, giving you quantum behavior. The nonlocality means that you need a notion of objective simultaneity in order to define that term. So when you construct the Bohmian counterpart of a relativistic quantum theory (i.e. of a quantum field theory), you will still see relativistic effects like length contraction and time dilation (since they are in the classical counterpart of the quantum field theory), but you have to pick a reference frame in order to make the Bohmian construction—which might be seen as an indication of its artificiality.
The same thing happens in MWI. In MWI you reify the wavefunction—you assume it is a real thing—and then you divide it up into worlds. To perform this division, you need a universal time coordinate, so relativity disappears at the fundamental level. Furthermore, since there is no particular connection between the worlds of the wavefunction in one moment, and the worlds of the wavefunction in the next moment, you don’t even have persistence of a world in time, so you can’t even think about performing a Lorentz transformation. Instead, you have a set of disconnected world-moments, with mysterious nonstandard probabilities attached to them in order to make predictions turn out right.
All of that says to me that the MWI construction is just as artificial as the Bohmian one.
Sorry, yes. I took weighting things by squared-norm of amplitude as implicit, seeing as we’re discussing QM in the first place.