For instance, the fact that we know about the other world and also measure some "signals" from there, but how can we get there to see what's really going on?

Actually, we must say "we could know" instead of "we know". We have a way to probe the mirror world, but so far there is no sign of it in data. Consequently, this will constraint the theory. Inversely, if we have a signal of something, you can be sure there will be in no time hundreds of theoretical interpretation of it. Then we need time, more data and more global analyses (investigating many channels and signatures) to see which one of these theories could hold and which one is just wrong.

The un-famous 750 GeV excess of the LHC is a good example of this: 400 theory papers explaining an excess who disappeared after a year [fun fact, I only wrote one and I was claiming that either our knowledge of the strong interaction is wrong, or the excess is fake; I was right!] :)

Thanks for stimulating my mind in this way.

I am glad to read this! Have a nice week-end!