When we talk about the universe we are referring to the observable universe, the part that we can ‘see’. It has a horizon of sorts, from our point of observation and it is called the cosmic light horizon. It is approximately 46 billion light years away. This calculation is based on us being the centre of the universe (which we are not) and is restrained by the shape of the universe (of which we are unsure).
Taken literally though, this would mean that if we travelled at the speed of light (29,9792 km/s) we would arrive at the edge of the observable universe in about 46 billion years.
However, the universe is constantly expanding. The rate at which it expands has varied over time and is still a topic of debate. It is estimated that the universe is currently expanding at 67 km per second. So in the 46 billion years it would take to get to the point where the edge is now, it would be further away.
As to what we would see when we get to the edge, we are back to a number of theories. It is possible that there is literally only what we can see and nothing more. However, it is hard to find any science to back this up, the theory to predict such a universe just does not seem to exist.
There is a theory that the universe is infinite, which would mean we could literally see anything beyond the observable universe, including another galaxy like ours, another planet Earth, even another version of ourselves. In fact, if we take this infinite universe theory to its full conclusion, we could find many versions of ourselves, each perhaps slightly different, due to different life choices made at various decision points in time.
Alternatively, the universe may be contained within a cosmic bubble of sorts with other universe bubbles floating around too, called. The multiverse theory does itself hold many possibilities. For example, we could be living in the only universe ‘bubble’ that allows life to exist. The laws of physics within the others may not support life as we know it. Or each universe in the multiverse could be separated by time, generating a different universe at every option, a bit like a mother universe spawning daughter universes at various junctions in time.
There is also the possibility of something beyond the observable universe called the, a massive structure exerting gravitational influences on everything beyond our observable limit and creating different laws of physics to those our own universe is governed by.
I will leave you one more possibility, that of theeverything we observe in 3D is in fact contained within a 2D surface at its boundaries; like holographs, except we can touch everything within them, at least from our perspective, which, ultimately is the only way we can observe the universe… from where we stand!