In fact, we know that IPv4 lives in the observable universe. You can travel at the speed of light towards IPv6, but the expansion rate of space time-itself (you can think of space-time as a series of tubes) is not limited by the speed of light. Thus, IPv6 is only theorized to exist, in order to explain other physical phenomena. Worse, even if it was proven to exist by a distant observer, there no way for them to relay that information back to us because our routers here at earth would drop the packets.