There are two options: either the universe is finite and has a size, or it is infinite and stretches forever. Both options are thought provoking. How big is our universe? It all depends on the answer to the above questions. Have astronomers tried to figure this out? Of course we tried. We can say they are obsessed with finding answers to these questions, and through their search we are building sensitive space telescopes and satellites. Astronomers are peering into the cosmic microwave background, the relic radiation left over from the Big Bang. How can you test this idea just by watching the sky?
Scientists have tried to find evidence that features at one end of the palate are associated with features at the other, such as the way the edges of the bottle wrapper connect to each other. So far, no evidence has been found that the edges of the sky can be connected.
Humanly speaking, this means that over 13.8 billion light years in all directions, the universe does not repeat itself. Light travels back and forth across the entire 13.8 billion light-years and only then leaves the universe. The expansion of the Universe pushed the boundaries of light to leave the Universe by 47.5 billion years. You could say our universe is 93 billion light-years across. And this is the minimum. Perhaps this number is 100 billion light years, or even a trillion. We do not know. Perhaps we won't know. Also, the universe may well be infinite.
If the universe is truly infinite, then we will get an extremely interesting result that will make you seriously puzzle.
So, imagine. In one cubic meter of space (just spread your arms wider) there is a finite number of particles that can exist in this region, and these particles can have a finite number of configurations, taking into account their spin, charge, position, velocity, etc.
Tony Padilla of Numberphile calculated that this number should be ten to the tenth to the seventieth power. This is such a large number that it cannot be written down with all the pencils in the universe. Assuming, of course, that other life forms have not invented eternal pencils, or that there is no extra dimension filled entirely with pencils. And still, there probably won't be enough pencils.
There are only 10 ^ 80 particles in the observable universe. And this is much less than the possible configurations of matter in one cubic meter. If the universe is truly infinite, then moving away from the Earth you will eventually find a place with an exact duplicate of our cubic meter of space. And the further, the more duplicates.
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Just think, you say. One hydrogen cloud looks the same as the other. But you should know that as you walk through places that look more and more familiar, you will eventually come to a place where you find yourself. And finding a copy of yourself is perhaps the strangest thing that can happen in an infinite universe.
As you continue, you will find entire duplicates of the observable universe with exact and inaccurate copies of you. What's next? Possibly an infinite number of duplicates of the observable universe. You don't even have to drag in the multiverse to find them. These are repeating universes within our own infinite universe.
Answering the question whether the universe is finite or infinite is extremely important, because any of the answers will be mind-boggling. So far, astronomers do not know the answer. But they do not lose hope.
Ilya Khel