A gravity gun is a type of device in video games, particularly first-person shooters using physics engines, whereby players can directly manipulate objects in the world, often allowing them to be used as projectiles against hostile characters. The concept was popularized by the gravity gun found in Valve's Half-Life 2, as well as the Temporal Uplink found in Free Radical Design's TimeSplitters: Future Perfect; although a similar concept was used by id Software during the production of the earlier game Doom 3, eventually leading to the introduction of a physics-based weapon in the expansion pack Resurrection of Evil. Later games, such as Portal, BioShock, Crysis, Dead Space, and Garry's Mod have been influenced by the success of these physics-based weapons, adopting their own styles of comparable abilities or weapons.
Half-Life 2
Valve's Half-Life 2 made significant use of physics, powered by the Source engine. The physics engine within Source is derived from Havok, which opens up a wealth of possibilities for object interaction – particularly when later in the game, Freeman receives an energy-beam weapon that lets him move huge objects. Although the player can pick up and throw objects early in the game, this ability is somewhat limited in scope. Around a quarter of the way through the game, the player acquires the gravity gun, properly named as the "Zero-point Energy Field Manipulator". Alyx Vance explains that the gravity gun is designed for handling hazardous materials, but is mostly used for heavy lifting. She explains to Gordon that she once found it useful "for clearing minefields". The gravity gun significantly increases the player's ability to manipulate objects in the game. Like most other weapons in the game, the gravity gun has two trigger functions. The primary trigger causes the gun to emit a small discharge which emits energy to the targeted object. The distance which the object is forced is dependent on its weight and distance from the gun. The secondary trigger attracts the targeted object to the gun and holds it in midair a few inches away, negating its weight and allowing the player to carry it with them. Using the secondary trigger again will drop the item, while the primary trigger will launch it with considerable force.
By combining these functions, players can use the gravity gun to scale barriers and obstacles, create cover against enemy characters, or launch the objects at enemy characters, causing them considerable damage. Certain types of objects, such as saw blades, fuel barrels and hydrogen tanks are intentionally designed by Valve to be used as "gravity gun ammunition". The gravity gun, however, cannot manipulate heavier objects and enemy characters until the late stages of the game, when the device becomes temporarily infused with dark energy meant to destroy it.
The gravity gun was very well received by critics, who considered it one of the defining features of Half-Life 2s entertainment value. Planet Half-Life called the gravity gun "the next level in interactive gaming." Electronic Gaming Monthly described Half-Life 2s gravity gun as the "thinking man's death tool," which lets players "toy with gravity to kill foes with everyday objects." Call of Duty series military adviser Hank Keirsey stated that "the weapon is not very practical". He did, however, discuss its historical precedents, further stating that "The ancients learned very early how to use gravity to their advantage — but this usually involved rolling rocks down hills or pouring boiling oil down the castle walls. Those that failed to respect gravity suffered."
Influence on later games
Half-Life: Alyx
Valve's 2020 virtual reality game Half-Life: Alyx is set as a prequel to Half-Life 2. The player controls Alyx Vance who during the events of the game gains a pair of "gravity gloves", which provide function similar to the gravity gun with the ability to lift and throw objects, though tailored to work as standard VR in-game hand controls.