Minecraft is a 3D sandbox game that has no specific goals to accomplish, allowing players a large amount of freedom in choosing how to play the game. However, there is an achievement system, known as "advancements" in the Java Edition of the game, and "trophies" on the PlayStation ports. Gameplay is in the first-person perspective by default, but players have the option for third-person perspective. The game world is composed of rough 3D objects—mainly cubes and fluids, and commonly called "blocks"—representing various materials, such as dirt, stone, ores, tree trunks, water, and lava. The core gameplay revolves around picking up and placing these objects. These blocks are arranged in a 3D grid, while players can move freely around the world. Players can "mine" blocks and then place them elsewhere, enabling them to build things. Many commentators have described the game's physics system as unrealistic. The game also contains a material known as redstone, which can be used to make primitive mechanical devices, electrical circuits, and logic gates, allowing for the construction of many complex systems.