The ‘Fermi Paradox’ has turn into familiar fodder for theories on the nature of life in the cosmos, so I’m not going to repeat it in any excessive detail here. Instead, take a look at this nice explanation by Adam Frank, and think of that the basic principle is: if life in the cosmos is not extremely rare, it should have already shown up on our familiar doorstep. The fact that is hasn’t is hence attention-grabbing. Groups of physicists are telling us that our actuality, our universe, may not be the only one – somewhat that we live inside a multiverse. This could be organized in a range of forms: from pocket worlds formed by cosmic inflation, to quantum mechanical deviations and ‘many-worlds’, to ‘membranes or branes’ in higher dimensional M-theory, and so on. Moreover, all of these options may not surely be variants at all, they could all be mushed together into one astonishing range of realities. So many realities, actually, that anything that can take place will (and must) happen, and will happen a huge (dare I say, countless) number of times.
Some other groups of physicists (well, possibly not groups, but an important and sober part of the physicist species) roll their eyes and point out the aroma of ridiculousness in some of this talk. In the end, they say, theories that can describe categorically anything you throw at them by just saying ‘anything is possible,’ are not precisely theories according to the proper scientific method, since they can’t be reasonably falsified. Touché. Now, before you criticize me on behalf of one or the other side of this argument, take one more slurp of your sweet cocktail (if you are having one) and consider the following. Let’s assume that the most generous of multiverse notions are correct. In this circumstance, a modern-day Fermi might find themselves creating exactly the same proclamation that was made back in the 1950s: ‘Where is everyone?’
Except for this time the query is not about where the interstellar travelers are, or why gigantic civilizations haven’t been spotted. The new riddle is ‘Where are all the pan-multiverse travelers and civilizations?’
Well take another sip, and let’s unload that question a little. If reality is truly composed of a huge, huge number of actualities, and if ‘anything’ can, does, and must happen, and happen several, several, times, this apparently has to comprise the likelihood of living things (whatever they’re composed of) hopping between universes willy-nilly. In any case, just because physics in our universe makes that look kind of complex, it doesn’t stop the physics of a vast number of other universes from saying ‘sure, go right ahead!’
Disregarding our all-to-human ability for self-delusion, there is categorically no solid evidence that we are being, or ever have been, visited by things or peoples from other realities. So what’s the solution? Why isn’t this happening? It might be that roaming between parts of the multiverse is unmanageable (excluding it shouldn't be unmanageable everywhere, almost by definition) or very, very hard.
It might be that no entity who touches a point where they could jump between universes truly wants to (excluding, there has to be somebody somewhere who does. Again, nearly by definition).
It might be that we're alone, the only type of life in any actuality (except, once more, almost by definition, a multiverse will contain other life). It could also be, very simply, that there is no multiverse at all. Go on, drink up, that’s what I’m doing.