Born rule for macroscopic objects

[durant35]

There is one thing that I don't understand when considering quantum mechanics for macroscopic bodies. It is said that classical mechanics is a valid approximation and that macroscopic bodies that we encounter on everyday basis have a small uncertainty in position and momentum.

So far, so good.

But when the many-worlds interpretation is invoked, there are suggestions that the branching in the macroscopic world is occurring. The problem with this is the probability. If we just consider things from a probabilistic perspective, there is an enormous chance that the things around us will behave approximately classicaly and follow classical paths without some miracoulous deviations, like my monitor suddenly turning left without any force applied to it. So if we strictly try to give probabilities for macroscopic behaviour, one outcome has something like 99.9999..% probability and sudden deviations have very, very small amplitudes.

But in MWI, all outcomes occur. In fact it is ridicoulous to say all, it's better to say one that we would expect (high amplitude branch) and many, many low probability branches. So does quantum mechanics actually give probabilities for macroscopic behavior like I mentioned and do MWI supporters really believe that the branching occurs on this weird way, where one branch is always extremely probable and others are negligible?

 

[A. Neumaier]

it is ridicoulous

MWI is ridiculous if you take it to mean that everything that can happen happens.

In the only world we see only one thing happens, and the other worlds are irrelevant since we cannot say the slightest thing about them. All probabilities we measure are probabilities about the single branch we have a memory about - only that counts. No branching ever happens as all branches are already present in the wave function, at any time. The branches are just a label attached to terms in the wave function when expressed in a particular basis. Lots of irrelevant blabla accompanies this to make it sound interesting and explanatory.