There are one of two possibilities:
1. the universe is infinite
2. the universe is finite.
This is based on the ideal that the universe is infinite. A lot of people settle with option 2 because option 1 is too difficult to conceptualize.
This principle is based on a number of existing principles.
Let's start with a simple 2-option variable. An unbounded figure is made up of black pixels and white pixels. You can not only zoom in infinitely; you can also zoom OUT infinitely; this concept is similar to the central theories behind fractals, but much simpler than something like the Mandelbrot set. Because only a finite amount can be viewed, only a finite number of pixels is seen at any given time. Let's say that the resolution of our view is limited to 4x4. We thus see 16 pixels at any given point in time. Because these pixels are composed of black pixels and white pixels, they appear in greyscale. Unlike our resolution, this greyscale is defined infinitely.
THE PIXELS WILL NEVER BE BLACK OR WHITE.
This holds true because even a figure with a ratio of infinite white to 1 black is still greyscale. However, because each pixel has an infinite number of randomly generated pixels within it, the actual ratio is infinite to infinite. This winds up somewhere between black and white, but never equal to either. As infinite is extended again infinitely, we wind up with something quite peculiar:
Delving further, we can try to simplify this by dividing out infinite. However, we do so only to find that this does not change the figure. This is because infinite cannot be treated as a figure because it's a rate.
Thus, we have 16 grey pixels which are the average values of an infinite number of black and white pixels and an infinite rate of finite arrays of grey pixels. We will assume that there is a 50% chance of each pixel being either black or white. Logically, one would assume that our 4x4 screen would appear true grey (a perfect balance of white and black) the further you zoom out, and since there is neither a beginning nor an end, it would make sense that every screen would appear true grey, because every pixel is the result of and infinite amount of pixels being averaged. However, this is quite far from true. Not only would every screen not always appear true grey; an infinitely small percentage of possible screens would be true gray.
However, some screens
would be true grey. In fact, you could state any
rational (mathematical definition) input for our 4x4 screen and zoom in OR out infinitely and encounter that screen not once, but an infinite number of times. You will also encounter
every other rational input for our 4x4 screen an infinite number of times. In addition, you will encounter an infinite number of irrational inputs an infinite number of times more often than you encounter rational inputs.
What this all means in an infinite universe is that unique is irrelevant. Because there is a finite inward viewport (subatomic structures), this is actually simpler than the 4x4 concept because we only have rational figures. Let's say that we have an infinite universe where every object is defined by 10 factors, either a or b (like DNA). We thus have 1024 possibilities. When this situation is extended to infinite, we have a ratio of 1:1023 for each object to each other object. However, our ratio is infinite, and thus our value is actually infinite to infinite, like in the 4x4 concept.
Thus, there is an infinite amount of each of our 1024 objects. Let's say that each environment is composed of 30 objects. Thus, there are 1024^30 (approximately 2037000000000000000000000000000000000000000000000000000000000000000000000000000000000000000) different possible environments. 1024 of these possible environments are just the same object; 30 of them. 1024 out of 2.037x10^30 are environments made of all the same thing. But, because of the infinite nature of this hypothetical universe, there are not only an infinite number of uniform environments like this, there are an infinite number of infinitely large collections of these uniform environments.
But we aren't made of 10 genes; we're made of 80,000 or so, plus environmental factors. Despite this, if our universe is infinite, or finite but so large that it outstrips the vast amount of factors that make us unique (2.510x10^24082 from genetics alone), there is someone who is EXACTLY LIKE YOU IN EVERY WAY. If the universe is, in fact, infinite, there are an infinite number of people who have the exact same life as you; this document is being typed in an infinite number of places by an infinite number of DancingTofu's. It is simultaneously being finished, started, pondered, and disregarded by an infinite number of DancingTofu's. This is not a theory of parallel universes; it's a principal of infinite recurring rationals.