The Universe is the "world" (server) in which the game takes place. There are currently 50 different universes. There are no inter-universe links and no interaction between different universes. All the universes are hosted on different servers, so if one breaks down, the rest of the game and forums don't go down with it.
Each universe consists of 9 galaxies; each galaxy consists of 499 solar systems; each solar system consists of 15 Planets and one Outer Space slot. Since each player can have multiple planets (depending on the level of astrophysics), this means that a universe can hold many more planets than players. The player cap is in most cases 15,000, most often about 2000 to 5000 players are active. With each having 4+ planets, there can be about 20,000 planets in one universe. Browsing the universe in the galaxy-menu costs some deuterium, 10 units per solar system, at least in some universes.
It is worth noting that the set of features available to players can be different in each universe. For example, at ogame.org Alliance Combat System is implemented only in Universe 5 and recently in Universe 18 and onwards (including the 100s ie. Andromeda etc.); in the rest of the universes it is currently not available. Also some universes have defenses included in the debris field, 40% resources, and some in other versions of ogame have Deuterium in the debris fields.
Travelling between planets, systems, and galaxies takes time. The time taken to travel depends on the speed of the ships in the fleet and the Distance between the departure point and the destination.
Older and Redesigned Universes Edit
Before 7 June 2010 Universe numbers 41 and below had an older, basic HTML design.
Universe 42 was the first universe to have the new, more interactive design. It has updated graphics and a better feel to it. Universe 43 also had this redesign. Both of these universes were "testing" the new design before being fully implemented as Version 1.0.
Nowadays all Universes use redesigned layout, but universe 41 and below still have old rules of gameplay (ie. the Expedition Technology instead of Astrophysics).
See Redesigned Universe for more information.