Somewhere Over The Rainbow - Magical Lands
A Level 4 parallel universe is the strangest place (and most controversial prediction) of all, because it would follow fundamentally different mathematical laws of nature than our universe. In short, any universe that physicists can get to work out on paper would exist, based on the mathematical democracy principle: Any universe that is mathematically possible has equal possibility of actually existing.
The Theory of Parallel Universes
The multiverse is a theory in which our universe is not the only one, but states that many universes exist parallel to each other. These distinct universes within the multiverse theory are called parallel universes. A variety of different theories lend themselves to a multiverse viewpoint.
Not all physicists really believe that these universes exist. Even fewer believe that it would ever be possible to contact these parallel universes.
Go Far Enough, You Return Home
The idea of Level 1 parallel universes basically says that space is so big that the rules of probability imply that surely, somewhere else out there, are other planets exactly like Earth. In an infinite universe there would be an infinite number of planets, and on some of them, the events that play out would be virtually identical to those on our own Earth.
We don’t see these other universes because our cosmic vision is limited by the speed of light, the ultimate speed limit. Light started traveling at the moment of the big bang, about 14 billion years ago, and so we can’t see any further than about 14 billion light-years (a bit farther, since space is expanding). This volume of space is called the Hubble volume and represents our observable universe.
The existence of Level 1 parallel universes depends on two assumptions:
If Level 1 parallel universes do exist, reaching one is virtually (but not entirely) impossible. For one thing, we wouldn’t know where to look because, by definition, it is so far away no message can ever get from us to them, or them to us. (We can only get messages within our Hubble volume.)
Go Far Enough, You’ll Fall Into Wonderland
In a Level 2 parallel universe, regions of space are continuing to undergo an inflation phase. Because of the continuing inflationary phase in these universes, space between us and the other universes is expanding faster than the speed of light and they are, therefore, completely unreachable. Two possible theories present reasons to believe that Level 2 parallel universes may exist: eternal inflation and ekpyrotic theory.
In eternal inflation, recall that the quantum fluctuations in the early universe’s vacuum energy caused bubble universes to be created all over the place, expanding through their inflation stages at different rates. The initial condition of these universes is assumed to be at a maximum energy level, although at least one variant, chaotic inflation, predicts that the initial condition can be chaotically chosen as any energy level, which may have no maximum, and the results will be the same.The findings of eternal inflation mean that when inflation starts, it produces not just one universe, but an infinite number of universes.
Right now, the only noninflationary model that carries any kind of weight is the ekpyrotic model, which is so new that it’s still highly speculative.
In the ekpyrotic theory picture, if the universe is the region that results when two branes collide, then the branes could actually collide in multiple locations. Consider flapping a sheet up and down rapidly onto the surface of a bed. The sheet doesn’t touch the bed only in one location, but rather touches it in multiple locations. If the sheet were a brane, then each point of collision would create its own universe with its own initial conditions. There’s no reason to expect that branes collide in only one place, so the ekpyrotic theory makes it very probable that there are other universes in other locations, expanding even as you consider this possibility.
The ultimate vision of eternity is the Black Hole which consumes everything, including light, and to which we have no knowledge of its end. Its power is so great that it crushes everything it consumes, but we don’t know if what it does consume is destroyed. We know that the Black Hole takes from one place but we don’t know where it goes, or if it even goes anywhere at all. It could be a channel from one point to another or it could be an ending place that recycles all it consumes for other purposes. Astrophysicists conjecture, calculate, and theorize daily, but the answers continue to evade them.
Some theorize that Black Holes are the openings and exits of wormholes and that these connect different parts of the universe. In the “Dune” novels there was a concept of traveling without moving by “folding space.” Essentially this was using wormholes to travel from one place to another by moving space instead of the traveler.
The wonder of not knowing is the joy of imagining what might be. The reality of knowing the truth is very often a disappointment. This is a human condition.