There is an idea in contemporary physics that the universe is one of an infinite number of parallel universes. I do not believe this to be correct, but the idea has grains of truth in it.
Firstly let us dispose of infinity, for one infinity anywhere will inevitably lead to infinity everywhere. There is no instance in the real universe of infinity, although reality can often move as close to it as possible. Mathematics creates models of infinity (infinity doesn't exist in mathematics, as such, we could never count forever) but its models of infinity and a perfect universe work to describe ours. We can say that space is infinite, in that there is no limit to the nothing that particles can move into, but the size of the universe can still be finitely specified as the range between the particles at its most extreme; this is, and will always be, finite. One may say that the expansion of the universe will continue forever, but as forever is infinite, this cannot be the case. I am aware that this is logical fallacy and so state this jokingly; I am doubtful of the existence of forever, as, like infinite space, time can be measured as the difference between the start and end of the universe in its dimension. If time were infinite, such a measurement would be impossible. Would time exist in those circumstances? No. Remember that time is relative, and indeed, so is existence itself, which brings me on to the crux of this argument.
Some simple logic will conclude that multiple universes exist, but not that the observable universe is one of an infinite number of possibilities. Instead we have one each; there is necessarily one universe per observer.
Each of us has a unique viewpoint of the universe; you have a different view than I. This also applies to every particle and atom. Because of this, we each build up a unique picture of what the universe looks like. Our views may overlap; we might agree that the moon is over there, that the sky is blue etc. but our views can never be identical, there will always be an instance of knowledge that one of us knows that another doesn't. This means that the knowledge about the universe that we each have is unique to us.
This might sound obvious and lacking in serious implications, but actually its implications are extraordinary. I might not know anything about the dark side of Jupiter, but that doesn't affect whether it exists or not, does it? Actually, it does. The existence of the dark side of Jupiter, or of anything at all, depends on our observation and knowledge of it. That is a crucial fact in philosophy, and quantum mechanics. Our knowledge of the universe actually defines reality. Only what we know exists for us. Essentially, existence is relative to us, not absolute.
Of course, we can learn by communication and thus gain knowledge. Light particles communicate the existence of distant stars to our eyes, but at the same time, it is our unique knowledge that defines the reality of our universe.
So, there are multiple universes, but we are each in our own unique one. These are not infinite in number, but dependent on the number of particles and therefore viewpoints in the universe. Particles can combine; I myself, like you, are a summation of particles, so do I have a unique viewpoint, different from any of the particles or groups of particles that constitute me? Perhaps. If so then the number of viewpoints in the universe is the total of any combination of all of the particles in the universe; a gigantic number, but not infinite.
We will always have a unique perspective, and thus exist in a unique universe of our own. Perhaps, as a result of this perspective there is an aspect of it which cannot be shared, and perhaps this is what we call consciousness. It seems that consciousness cannot be defined in absolute terms, only relative, and then only experienced by ourselves and not proven to exist elsewhere. If consciousness is the result of our unique perspective in our universe, then all things, even atoms and sub-atomic particles, experience what we perceive as consciousness; a perspective, which is separate from thought.
What we call the objective universe is an overlap of a vast number of others; a common, but not definitive or perfect, reality.
