In this Universe, just because you can see it doesn’t mean you can reach it. Conversely, just because you can’t see it today doesn’t necessarily mean that its light won’t arrive tomorrow. Because the fabric of the Universe itself is expanding, and because the maximum speed at which any signal — whether massive or massless — can travel through that fabric of space is finite, there are both:

places that we can currently see that we could never reach or communicate with,

and places that we cannot currently observe today, but whose light is on the way and will someday reach us in the future.

Today, there’s a well-understood limit for how far we can observe in any direction in space: 46.1 billion light-years.…