I know almost no physics so this might be a stupid question, but aren’t “makes no testable predictions” and “contradicts general relativity” contradictory? Wouldn’t contradicting another theory imply some kind of a prediction?
That’s a good point! I was definitely unclear, and even sloppy in my claims.
My first statement, “makes no testable predictions” refers to “pure” quantum physics, specifically quantum mechanics and quantum field theory on a fixed spacetime background, where what the matter is doing does not affect, in the first approximation, what happens to the spacetime itself (which is the subject of general relativity). We know it is not a good assumption in general, because it leads to contradictions like the various black hole evaporation paradoxes. But it works within certain limits. Within those limits, many worlds add absolutely nothing new and predictable.
Sadly, the extrapolation of QM to the realm where gravity is still weak but already matters, is still an uncharted territory, over 90 years later. The generally accepted claim (but only a claim) is that the unitary evolution part of the QM scales up into the macroscopic world in some way, and the measurement postulate emerges from this upscaling eventually. Many worlds make a more specific claim, that we live in many worlds, decohering (splitting) all the time, and that there is nothing new happening beyond the basic decoherence. However, there is still the gravitational footprint of those worlds, unless you figure out how they split the spacetime itself, as well. In that sense, many worlds make a claim in the domain where QM has never been observed that is incompatible with the theory that rules that domain. it is still just an ontological claim though, without any predictive power in it.
while i can’t actually understand what your saying because I don’t understand physics well enough. As far as I know its not controversial to use the multi world model in the less wrong forums and that most people I respect use it fully. Is what your writing relevant to my question or to the entire lesswrong that believe that the many worlds explanation is correct
its not controversial to use the multi world model in the less wrong forums and that most people I respect use it fully
the key word is “in the lesswrong forums”. This is because Eliezer Yudkowsky, the founder and the main contributor for a long time, promoted both MWI and Bayesianism as cornerstones of rationality. Neither is necessary for either epistemic or instrumental rationality, but they are useful reasoning devices. No one really “uses” those directly to make decisions in life, even though most people pretend to. In actuality, they use those to justify the decisions already made, consciously or subconsciously. The reason is that the Bayes theorem relies on evaluation of probabilities, something humans are not very good at. At least not until you spend as much time as Eliezer, Scott and some others on self-calibration. And MWI is generally used as a fancy name for “imagine possible outcomes and assign probabilities to them”, which has nothing to do with physics whatsoever, when it is not misused for discussing quantum suicide/immortality, or, well, to justify anthropics.
I know almost no physics so this might be a stupid question, but aren’t “makes no testable predictions” and “contradicts general relativity” contradictory? Wouldn’t contradicting another theory imply some kind of a prediction?
That’s a good point! I was definitely unclear, and even sloppy in my claims.
My first statement, “makes no testable predictions” refers to “pure” quantum physics, specifically quantum mechanics and quantum field theory on a fixed spacetime background, where what the matter is doing does not affect, in the first approximation, what happens to the spacetime itself (which is the subject of general relativity). We know it is not a good assumption in general, because it leads to contradictions like the various black hole evaporation paradoxes. But it works within certain limits. Within those limits, many worlds add absolutely nothing new and predictable.
Sadly, the extrapolation of QM to the realm where gravity is still weak but already matters, is still an uncharted territory, over 90 years later. The generally accepted claim (but only a claim) is that the unitary evolution part of the QM scales up into the macroscopic world in some way, and the measurement postulate emerges from this upscaling eventually. Many worlds make a more specific claim, that we live in many worlds, decohering (splitting) all the time, and that there is nothing new happening beyond the basic decoherence. However, there is still the gravitational footprint of those worlds, unless you figure out how they split the spacetime itself, as well. In that sense, many worlds make a claim in the domain where QM has never been observed that is incompatible with the theory that rules that domain. it is still just an ontological claim though, without any predictive power in it.
Not sure if this makes sense.
while i can’t actually understand what your saying because I don’t understand physics well enough. As far as I know its not controversial to use the multi world model in the less wrong forums and that most people I respect use it fully. Is what your writing relevant to my question or to the entire lesswrong that believe that the many worlds explanation is correct
the key word is “in the lesswrong forums”. This is because Eliezer Yudkowsky, the founder and the main contributor for a long time, promoted both MWI and Bayesianism as cornerstones of rationality. Neither is necessary for either epistemic or instrumental rationality, but they are useful reasoning devices. No one really “uses” those directly to make decisions in life, even though most people pretend to. In actuality, they use those to justify the decisions already made, consciously or subconsciously. The reason is that the Bayes theorem relies on evaluation of probabilities, something humans are not very good at. At least not until you spend as much time as Eliezer, Scott and some others on self-calibration. And MWI is generally used as a fancy name for “imagine possible outcomes and assign probabilities to them”, which has nothing to do with physics whatsoever, when it is not misused for discussing quantum suicide/immortality, or, well, to justify anthropics.