Scientists can only see so far before they run into the edge of the universe. Will we ever know if anything lies beyond? We can only guess what lies beyond the edges of the observable universe. It is possible that our universe is just one of many in a much larger multiverse. Movies cannot get enough of exploring these possibilities and science fiction stories are full of creative interactions between alternate realities. And depending on which cosmologist you ask, the concept of a multiverse is more than pure fantasy or a handy storytelling device. Human ideas about alternate realities are ancient and varied. In the middle of the nineteenth century Edgar Allan Poe wrote a prose poem in which he fancied the existence of a limitless succession of Universes. But the multiverse concept really took off when modern scientific theories attempting to explain the properties of our universe predicted the existence of other universes where diverse events take place outside our reality. Stanford University physicist Andrei Linde says that reality exists independently of us. If they exist, those universes are separated from ours, unreachable and undetectable by any direct measurement. And that makes some experts question whether the search for a multiverse can ever be truly scientific. The multiverse is a term that scientists use to describe the idea that beyond the observable universe, some other universes may exist as well. Multiverses are predicted by several scientific theories that describe different possible scenarios  from regions of space in different planes than our universe, to separate bubble universes that constantly spring into existence. The only thing all these theories have in common is that they suggest the space and time we are able to observe is not the only reality. Perhaps the most scientifically accepted idea comes from what is known as inflationary cosmology, which is the idea that in the minuscule moments after the big bang, the universe rapidly and exponentially expanded. Cosmic inflation explains a lot of the observed properties of the universe, such as its structure and the distribution of galaxies. This theory at first looked like a piece of science fiction, although a very imaginative one. But it explained so many interesting features of our world that people started taking it seriously. One of the predictions is that inflation could repeatedly, perhaps even infinitely, happen creating a constellation of bubble universes. Not all of those bubbles will have the same properties as our own  they might be spaces where physics behaves differently. Some of them might be similar to our universe, but they all exist beyond the realm we can directly observe. Another compelling type of multiverse is called the many-worlds interpretation of quantum mechanics, which is the theory that mathematically describes how matter behaves. The many-worlds interpretation, by Hugh Everett, predicts the presence of branching timelines, or alternate realities in which our decisions play out differently, sometimes producing wildly different outcomes. Hugh Everett says that there is actually an infinite number of parallel Earths, and when you do an experiment and you get the probabilities, basically all that proves is that you live on the Earth where that was the outcome of that specific experiment. But on other Earths, there is a different outcome. According to this interpretation, versions of you could be off living the many different possible lives you could have led if you had made different decisions. However, the only reality that is perceptible to you is the one you inhabit. All those other Earths are all overlapping in dimensions we cannot access. It is a type of multiverse, where multiple scenarios are playing out in branching realities. In the many-worlds interpretation, you still possess an atomic bomb, you just do not know exactly when it is going to go off. And maybe in some of those realities, it will not. By contrast, the multiple universes predicted by theories of cosmic inflation are such types of universes, where fundamental physics can be totally different across the different universes. In an inflationary multiverse you do not even know if, in some parts of the universe, things like atomic bombs are even possible in principle. Unfortunately, you cannot meet yourself. Scientists do not think it is possible to travel between universes, at least not yet. However, in a thousand years time from now, who knows. 
