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> Similarly, the equations of quantum mechanics predict multiple "worlds" No they don’t. If I roll a dice it’ll land on one of 6 faces. That’s a model, in that

> Similarly, the equations of quantum mechanics predict multiple "worlds" No they don’t. If I roll a dice it’ll land on one of 6 faces. That’s a model, in that model I might assume equal probability due to the geometrical symmetry, that’s an assumption. So now I have a problem if all outcomes are equally likely how do I resolve that only one occurs? Well obviously every dice roll must spawn 6 parallel universes... Now nowhere in that model or that assumption does “so there must be 6 parallel worlds spawned when you roll the dice” get predicted by my model. The multiverse/many world is an interpretation, not an outcome of, or even prediction from the model. There is nothing “right there in the math”. QM makes predictions about probabilistic outcomes, accurate predictions, but there is no requirement for those accurate predictions to be right that there must be multiple parallel worlds.

simiones 6y ago
> There is nothing “right there in the math”. QM makes predictions about probabilistic outcomes, accurate predictions, but there is no requirement for those accurate predictions to be right that there must be multiple parallel worlds. While I mostly agree with you, the discussion is much more complex than this. First of all, most of QM is completely deterministic, just like classical and relativistic mechanics. The Schrodinger equation is a linear partial differential equation, it gives you an exact prediction of the state of any system of particles. However, that prediction turns out to be so wrong on the face of it, it's almost meaningless: the Schrodinger equation predicts that "particles" (wave-packets) have some complex amplitudes of many different mutually-exclusive states, such as being here with amplitude 1+i and being there with amplitude 1-i. BUT, it turns out that if we interpret these amplitudes of the wave function (well, the squares of their absolute values) as being probabilities of the particle being in those states when measured, then you get extremely accurate predictions. The final problem then is that the amplitudes -> probabilities step is only correct when predicting the result of a measurement. At the particle level (before the measurement) the particles actually exist in all those states at the same time, and interact with each other in all those states (e.g. particle A may interact with particles B and C at the same time in two different places, modifying both their trajectories). So, the laws of motion for QM that you need to use are: 1. Particles move and interact according to the Schrodinger equation (e.g. causing interference patterns, interacting in multiple places at the same time), fully deterministically and linearly 2. When you want to predict the outcome of a measurement on a system that has evolved according to 1, you will get a single value with some probability computed as the square of the absolute values of the amplitudes of the possible states. After the measurement, the amplitude of any other state than the one measured will be 0, and this can be plugged in to make further predictions about how it will interact with other particles. It is this 2nd postulate that feels very artificial, the main subject of the measurement problem. MWI seeks to explain QM without the 2nd postulate - that is why people say that it "derives from the math" (the 2nd postulate can obviously not be derived from the first, as it is a nonlinear change to the system).
GoblinSlayer 6y ago
But math does cover the evolution of quantum state entirely. And that evolution doesn't resemble "lands on one of 6 faces", it resembles "6 orthogonal states", and this picture is accurate and quantitative. "The universe stops when I look at it" - that's what math doesn't predict even remotely.

simiones 6y ago

> There is nothing “right there in the math”. QM makes predictions about probabilistic outcomes, accurate predictions, but there is no requirement for those accurate predictions to be right that there must be multiple parallel worlds. While I mostly agree with you, the discussion is much more complex than this. First of all, most of QM is completely deterministic, just like classical and relativistic mechanics. The Schrodinger equation is a linear partial differential equation, it gives you an exact prediction of the state of any system of particles. However, that prediction turns out to be so wrong on the face of it, it's almost meaningless: the Schrodinger equation predicts that "particles" (wave-packets) have some complex amplitudes of many different mutually-exclusive states, such as being here with amplitude 1+i and being there with amplitude 1-i. BUT, it turns out that if we interpret these amplitudes of the wave function (well, the squares of their absolute values) as being probabilities of the particle being in those states when measured, then you get extremely accurate predictions. The final problem then is that the amplitudes -> probabilities step is only correct when predicting the result of a measurement. At the particle level (before the measurement) the particles actually exist in all those states at the same time, and interact with each other in all those states (e.g. particle A may interact with particles B and C at the same time in two different places, modifying both their trajectories). So, the laws of motion for QM that you need to use are: 1. Particles move and interact according to the Schrodinger equation (e.g. causing interference patterns, interacting in multiple places at the same time), fully deterministically and linearly 2. When you want to predict the outcome of a measurement on a system that has evolved according to 1, you will get a single value with some probability computed as the square of the absolute values of the amplitudes of the possible states. After the measurement, the amplitude of any other state than the one measured will be 0, and this can be plugged in to make further predictions about how it will interact with other particles. It is this 2nd postulate that feels very artificial, the main subject of the measurement problem. MWI seeks to explain QM without the 2nd postulate - that is why people say that it "derives from the math" (the 2nd postulate can obviously not be derived from the first, as it is a nonlinear change to the system).

GoblinSlayer 6y ago

But math does cover the evolution of quantum state entirely. And that evolution doesn't resemble "lands on one of 6 faces", it resembles "6 orthogonal states", and this picture is accurate and quantitative. "The universe stops when I look at it" - that's what math doesn't predict even remotely.