The holodeck appears in most Star Trek episodes as an ordinary chamber on a spacecraft. The user can choose from a number of options on a panel outside the door to customize their experience or choose a program.
When a program is not running, the inside of the holodeck is often depicted as a medium-sized, empty room. Different representations of the floor and walls have been used, such as a metallic grid in Star Trek: Voyager, a brilliant yellow grid on a dark background, or numerous other techniques.
The environment vanishes and is replaced with a lifelike, interactive replica of the actual world when the holodeck is turned on. Until the program is finished or the user orally requests to leave, the door also vanishes. Voice instructions can be used to operate the holodeck, or a computer terminal dubbed the “Arch,” which can be invoked with a vocal command can be used for manual operation. Some simulations are preprogrammed, while others are created as they go by the user giving the computer descriptions of the items to be simulated.
Participants can wander about freely and as far as they want in the virtual area, which can be of any size imaginable. The holodeck is depicted in certain instances to produce an interior environment that is at least as big as a spacecraft. In the first scene of the 1994 movie Star Trek Generations, a holodeck simulation of a sailing ship with an ocean backdrop is shown.
Projected light, force fields, and replicated matter are used to construct the environment, objects, and people (using the same technique as the food replicators). Within the holodeck, holographic projections are solid and can be interacted with as if they were real. However, they vanish instantly as the program stops or quickly deteriorate if taken out of the holodeck. Some episodes do, however, depict simulated matter remaining after exiting the holodeck, like in “Encounter at Farpoint,” in which Wesley Crusher plunges into a virtual stream and continues to feel wet after doing so.
Different levels of intelligence can be assigned to living characters inside the holodeck, ranging from the complete absence of animation to fully interactive representations of people and other sentient species that even include self-awareness. Users have the option of watching a situation passively while being invisible to the simulated characters or actively participating by taking on the role of a certain character.
In many episodes of Star Trek: The Next Generation, Captain Jean-Luc Picard participate in storylines in which he assumes the character of fictitious detective Dixon Hill, one of his childhood idols. “Holonovelists” create programs with actual or imaginary scenarios for amusement.
Some holodeck users turn into pathological addicts, a condition the characters refer to as “holo-addiction.” Aliens known as photonic lifeforms are also introduced in Star Trek: Voyager, and they think holodeck programs are actual events rather than artificial simulations.
Many Star Trek series contain plots where the holodeck malfunctions and poses real threats or if the safety measures have been overridden, which requires the approval of two senior officers. The holodeck is meant to be safe, protecting users from harm, even from realistic violence.
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