To understand where this limit lies, we must first understand the limits of the human mind. Our minds were designed to handle tactile form - to exist within a universe governed by the observable laws of physics. Sensory dominant minds can see, accept and understand what is right in front of them. Intuitive minds can see the more abstract concepts around them, but still require that those concepts, however abstract, exist within a physical universe.
What happens, then, when our minds are confronted with that which has no reality to exist within - absolute nothing. We inevitably imagine empty space - at best a vacuum between two somethings. But that is still something. That gap is not nothing - it is a space between two points. How, then, can we perceive nothing? How can we visualise something which does not exist? We can't. We have to understand it without visualisation. But I will try to explain in terms we can all visualise.
When we learned of the expansion of the universe in elementary/primary school, we inevitably pictured matter expanding into empty space. Things moving further away from each other and an apparently infinite empty space beyond that. But then we learn that this is not the case. The space time continuum itself is expanding along with matter - but we need to visualise it expanding into something. At some point, however far away, there must be an edge to the universe. The edge of the sphere of all that is.
Inside this sphere, not only does all matter exist but all laws of physics exist. Beyond this, there is nothing. Not because it is empty space or because it is a void, but because beyond this, there is no physics. There is no distance, no time, no mass. These things that our minds can process exist only within our little 93bn light year bubble. Outside of that is the nothingness that our minds cannot visualise because there is nothing our minds could process as anything to visualise beyond that limit. And so, the universe still continues into infinity even if it has a limit because it continues as far as there is anything to continue into.
If you cannot see this, try thinking about time. We can agree that time is a dimension that is expanding much as space expands, and that expansion of time is what our minds see as it's passage. Therefore, when we look forward in time we can see possibilities of it's existence but can reasonably well understand that it does not yet exist because it has not happened yet. So in essence, we are caught in the wake of the expansion of time and held at the edge of it's infinity. Likewise, if the universe is expanding into nothing it is simply expanding into what space has yet to exist. It expands into nothingness.
But what would you see if you were to travel all that distance to the edge of the universe? What would you see beyond that precipice? We cannot see forward in time because we haven't any means with which to peer through this dimension and traverse it in anything other than a truly linear fashion. we see only the presence - the point at which we now exist. But distance is another matter - if we look forward into nothing, what would we see? What would that barrier at the edge of the bubble look like? There would be nothing for our eyes to see, so would we simply look at it and see absolute darkness, no different to the void that we can see when we look at space because our minds and our eyes could not process it any differently?
What would happen if you tried to cross it? I can think of a few possibilities, but my imagination says that if you tried to pass that barrier, nothing would be there and you would simply cease to exist and become nothing with it.
The limit of infinity is that it continues until there is nothing to continue into - it is eternal because beyond it there is nothing.
