Do parallel worlds exist ?
First, my advice is to define - fully - what this concept called a parallel world is. Is it one in which you can see, smell, touch, taste, feel something remarkably different than you would in the 'normal' waking reality? If so, then these worlds have been accessible via hallucinogenics and lack of sleep and well documented by many explorers throughout history. Is it one in which you can see a world just like yours - only opposite? All you need to do then is to understand basic physics and the possibility that that mirror you're looking at is a mirror reality. Is it one in which the laws of physics or the flow of time is substantially different or non existent? All you need to do is look at video games to understand that humans are capable of creating, which includes other worlds which quite possibly - to the sentient inhabitant should sentient life arise in these world - are as real as yours is to you. Personally, I think it's naive to believe parallel worlds don't exist. So my advice is to define what your idea of a parallel world is. And then investigate whether said world exists.
Quite possible.. "Solidity" is an illusion of opposing forces. Matter, is ultimately waves. If the wave attributes of "particles" match relative to each other then they are said to be interactive or "solid". Universes are those SETS of wave/particles whose wave attributes match each other.----Thus many universes can exist in the same space, just like the signals from different radio stations share the same air. the only real universe to us is the one we are "Tuned "to ---that matches the particles of our bodies. Many universes, then would exist in the same space just as real in the absolute sense, but each with its own history, stars, planets and galaxies.----but only real to itself being non interactive with others.
The answers prove they do
Dunno. Theoretically there's not really any good reason they wouldn't, but since we can't observe them, it's pure conjecture.