I've heard claims that the game is multiplayer, but the universe is so huge you will almost certainly never encounter another player.
That seems unlikely. It's a lot of work to make a game multiplayer, so I doubt they would go through all that effort for a feature they didn't expect anyone to ever actually use.
So, what happens when two players are on the same planet? Can they see/interact/communicate with each other?
Best Answer
Update:
As of the "1.5 NEXT" update, there is 4-player multiplayer. Players can see each others' buildings/ships, interact and trade with each other, and fight together. Quests are still separate.
If you're here to see the list of all the ways the players were lied to about multiplayer, see this answer's history.