According to the Many Worlds interpretation of quantum mechanics by Hugh Everett, taking the double slit experiment as an example, every possible outcome that can happen does happen. And the chances of any specific interaction occuring in our universe is based on its probability. Imagine that we do the double slit experiment a million times. If this interpretation is correct, then shouldn't we get an irregular or different observation in at least one of those experiments? What gives us a perfect observation every time?
closed as unclear what you're asking by Aaron Stevens, Emilio Pisanty, ZeroTheHero, user191954, John Rennie Nov 11 '18 at 16:23
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Many worlds is an interpretation. It is not a separate theory. It is a story we tell about the theory. The actual predictive part of the theory is in the mathematics. Thus, it does not, and cannot, make any predictions that are different from standard theory.(*) Any controversy is over whether it is the "right" story to tell and whether or not it fully agrees with the picture in the mathematics.
Also, in theory, you are right, if you repeat a quantum-probabilistic experiment a huge number of times you will see very unlikely events. But that has nothing to do with what interpretation of quantum mechanics you are using - it's purely how probability works. If some event has a fixed probability $P$ of occurring on any given trial, then probability and statistics alone tell us that if we repeat that trial $N$ times, there is probability $1 - (1 - P)^N$ to observe the event during those $N$ trials, which approaches $1$ as $N \rightarrow \infty$ so long as $P > 0$.
For any individual double slit experiment, there is a probability density $p(x)$ for an agent (i.e. you, watching the experiment) to acquire the information "It hit spot $x$ on the target". Actual probability is, of course, the integral to hit within a particular region: $P[R] := \int_R p(x)\ dx$. This comes from the mathematics of quantum mechanics itself, so it holds on ALL interpretations. I believe what you're asking is that "is it possible that, if we do it enough, we observe something extremely unlikely, like that all the electrons or photons end up in one narrow area"? The answer is yes - at least insofar as we are willing to be that quantum mechanics is a totally valid theory, of course. If we fire $N$ particles, the probability to see them end up all in the one small area $R$ is $1 - (1 - P[R])^N$, just as before. If $R$ is very thin and $N$ very large, this will be VERY small (makes the lottery look like fate by comparison). But not zero.
(*) There is one caveat here: Some "interpretations" do try to alter the mathematics, esp. with an aim toward simplifying it, like trying to derive the Born rule that relates wave functions to probability amplitudes, from some more elementary principle. But these really, then, should be called separate "quantum-like" theories, not interpretations.