I stand by my point though, for the purpose of totally ordering blocks, the difficulty is not intergalactic because a solution on mars is much less useful than a solution on earth. The problem here is time-delay preventing simultaneity. This is the same problem that block chain time-stamping hopes to solve. Thus it seems unfair to me to ignore this problem.
I wonder how tight the 10 minute mark is at the moment. I imagine there might be nodes that are 5 seconds apart on the network. Maybe even more when we have backhoe outages. How much lower could the 10 minutes be before we start seeing to many orphans even on earth?