I wonder if there's some way to do proof of location based on the latency of light.
Edit: It would clearly require some pretty complex network interactions. You can't be able to precompute a proof and send it to another place.
I'm thinking something like every node broadcasting a public key, which every other node then uses to sign an identifier and sends back. From this, you can generate local maps of the network. While nodes could collude to seem close to each other or lie and claim other nodes are far away, there's presumably some density of truth at which you can construct a reliable global map.
I was thinking of an activity called "mapping the stars". Essentially users with telescopes all around the world map as much stars coordinates as they can, and create a block with such info. Next blocks does the same and so on.
Users verify the validity of the chain by making sure those stars exist at those coordinates.
It's hard for any single entity to create a copy of this chain as they would have to map all the stars themselves.
Of course the whole endeavor ends when all the stars have been mapped - but maybe there are so many that this can be viable, and more importantly, cheaper than energy consumption.
EDIT: another idea would be using supernovas, which may actually be infinite since they're constantly exploding. Similar to mapping the stars, users signal the coordinates of the found supernova. Users validate the block based on whether or not it's a supernova - I think there are specific traits which remain in the sky for a long period of time that proves whether there was a supernova there.
You can always introduce more latency artificially. So the only thing you could prove is a "no farther than" property, because you can't be farther than the speed of light, but you could be arbitrarily closer.
Edit: It would clearly require some pretty complex network interactions. You can't be able to precompute a proof and send it to another place.
I'm thinking something like every node broadcasting a public key, which every other node then uses to sign an identifier and sends back. From this, you can generate local maps of the network. While nodes could collude to seem close to each other or lie and claim other nodes are far away, there's presumably some density of truth at which you can construct a reliable global map.