Though reports and studies have suggested that the universe is constantly expanding, no consensus has been reached on where it ends.
When we refer to the term universe, we’re actually excluding an integral part of it. In other words, the universe that we think we know is actually just a fraction of the whole universe. This is because as inhabitants of earth, we consider earth as the central point of the universal sphere. The radius of this sphere is given by the amount of distance that light traverses in the 13.7 billion-year age of the universe. The rest of the universe is simply unknown or invisible to us.
Another theory often associated with the universe that it is understood to be infinite. However, no concrete evidence has been established in support of this statement. Instead, space research bodies and authorities like NASA have collected enough proof to state that the universe is indeed expanding constantly. This fact could actually substantiate that the universe is infinite, but it isn’t so. A counterintuitive logic says that even if an infinite universe is shrunk to a degree, it would still remain infinite, as infinity cannot be measured or bounded.
Coming back to the question of where the universe actually ends, some people opine that it doesn’t end at all, while some opine that the universe would end in an exactly opposite reaction of the big bang. That is, during the big bang, all matter and celestial bodies spread out from a central point to far ends of space, probably to infinity, whereas at its end, the universe would shrink back to the same central point, where all the bodies and matter would get sucked back in that had come from it in the first place.
The other faction of astronomers and scientists who believe that universe is never ending, present the following analogy as an explanation for their belief:
Think of the whole universe as a big balloon, on the surface of which live two ants. These ants can’t move up and down, but they can move along the surface of the balloon. In essence, they can figure out how big the balloon really is. However, one ant gets stuck in a spot of honey on the balloon and can’t move ahead, but the other ant is insistent on finding out where does the balloon end. So the other ant continues its journey and while doing so continually comes across the ant that got stuck in a spot of honey.
This analogy actually implies that the universe has no end at all, and that one would always come back to the point where he’d started off on his journey.
Furthermore, the universe is expanding all the time, and the rate at which it’s expanding is constantly changing as well. According to the results of the Wilkinson Microwave Anisotropy Probe (WMAP) mission and the Supernova Cosmology Project, the universe is constantly expanding at an exponential rate. In other words, the rate at which universe is growing is itself rapidly accelerating. In retrospect, the fact that light has traversed for 13.7 billion years would then have to mean that light actually traveled for about 46 billion years, as the universe was constantly expanding when light was in motion through the years that it originally had to travel.
Therefore, the question of where does the universe end is probably as open-ended as the universe itself!