That blog post associates for me with the indirect observation of branching that I mentioned. Double slit experiment with one detector has a seemingly impossible phenomenon when the interference pattern disappears without measurement in our branch, so without branching this phenomenon can't be explained as "pattern disappears due to measurement", because measurement didn't happen. In MWI in this case the pattern disappears due to measurement in the other branch, that branch splits from our with the measured part of the photon and the pattern disappears in our branch. Our branch isn't privileged in this case, actually it's affected by the other branch, and the situation is symmetric: when measurement happens in our branch, pattern disappears in the other branch without measurement there. Well, technically if the other branch is destroyed by measurement there, the result for our branch is the same I guess. And if this phenomenon can't be explained without branching, then it's almost direct evidence for branching.
> Double slit experiment with one detector has a seemingly impossible phenomenon when the interference pattern disappears without measurement in our branch
Then you don't understand quantum mechanics at all. You should read this:
The TL;DR is that measurement and entanglement are the same phenomenon. A particle can become entangled with a detector even if the detector doesn't register anything.
But that is neither here nor there. Why do you get interference with no detectors? Your theory is that a detector at one slit is somehow paired with a "virtual detector" in a parallel branch at the other slit. But why would that "virtual detector" go away when the real detector is removed? Why is it never the case that there is a "virtual detector" at either slit unless there is a real detector at one of them?
Before measurement it's one detector, then it interacts with half photon, which is superposition |photon>+|no photon>, and the detector's state splits, the first state interacts with the |photon> state and measures it, nothing happens to the second state, because there's nothing to measure in the |no photon> state, but the first state splits away from the second state and leaves it alone, that's how the second state ends up alone with pure |no photon> state, but this really was done to it by the first state, the second state can't do it by itself. For this to happen in the second branch you need measurement to happen in the first branch, so when you are in the second branch, the first branch still needs to exist even though you don't see it, otherwise your branch won't be able to be as it is.
When you remove detector and start next measurement, you start with your one branch, branches from previous measurements don't affect it, the phenomenon happens during decoherence, nothing happens after it.
Your article explains this with branching without saying the word.
It's a part of photon's state at the slit with detector, the other part is at another slit. It's superposition of photon near detector and no photon near detector.
