We can see light that was emitted from it billions of years ago, before we split apart. Similarly, they can see light that ours emitted billions of years ago.

We can see light that was emitted from it billions of years ago, before we split apart. Similarly, they can see light that ours emitted billions of years ago. They can never be affected by anything we do now, or vice versa. This doesn't make it "read-only", though -- we can't read it either. All we're seeing is their distant past, back when we were mutually able to reach each other.