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I can understand how the holodeck creates virtual environments. But I don't see any mechanism that prevents people from walking into walls. Are the floors moving? Are they in a different dimension that has more space? Do they simulate the feeling of movement while keeping you stationary?

Some simulations appear to take up far more physical space than the holodeck would allow (as in people are physically all over the virtually created world - like Voyager's 24/7 running Irish city).

Molag Bal
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Aaron Klap
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2 Answers2

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From the TNG Technical Manual;

Matter conversion subsystem creates physical props using replicators. Replicated props are generally created when an object is likely to be touched by the participant. Some props are animated under computer control by precision-guided tractor beams.

Holographic imagery subsystem creates three-dimensional images of simulated environments. Shaped forcebeams give physical substance to foreground objects so they have the illusion of being solid.

Substrate forcefield creates "treadmill" effect, permitting participant to remain stationary while the simulated environment "scrolls" by within the limits of the simulation program.

TNG Technical Manual

Valorum
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    What happens if two people in the holodeck try to walk away from each other? Will they eventually hit the walls? – Tim S. Feb 16 '14 at 23:42
  • That sort of makes sense about the "treadmill effect". Perhaps something like that would allow the participants to walk with a different stride, relative to the environment moving around them, so that they never hit the walls? – MDMoore313 Feb 16 '14 at 23:56
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    @TimS. if I remember correctly, that's addressed elsewhere in the same section of the technical manual: the holodeck creates separate sections of the moving forcefield under each person, so that neither one of them truly moves very far, but it also manipulates the propagation of light and sound between them so that they appear to each other to be far away. Maybe someone who has the book handy can confirm. – David Z Feb 17 '14 at 00:55
  • Aaron, there are plenty of types of force-field in the trek universe. On at least one occasion we see dax walking on top of one. – Valorum Feb 17 '14 at 07:47
  • Not only that, but it does not explain how multiple levels work in a holographic simulation that does not all reside on the same floor. If the floor you are on is above a floor a person below you is on, then does the physical floor movie with you? Not only that, but if the simulation ended wouldn't you fall to the floor and the person below you be on the "real" floor? If this is not the case, then how is the sensation of walking up stairs accomplished? You could also climb up a tree which would mean you are definitely not on the floor. – Aaron Klap Feb 17 '14 at 07:52
  • Treadmill explanation also does not explain if you swing from vines from one tree to the next. With the explanation above, you would definitely hit a wall because you are physically interacting with the vines which would have to exist in material form. This also would not explain if you were on a fast moving train and another person is on the stationary ground. (Many, many, more examples, which prove the above answer is obviously wrong). – Aaron Klap Feb 17 '14 at 08:07
  • @Richard Thank you for letting me know about the different types of force fields. The type you mention is far less commonly shown in the Trek universe but would work for flat floor simulations. – Aaron Klap Feb 17 '14 at 08:14
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    @AaronKlap: I always assumed that the "treadmill" was more complex than just moving the floor from under you, as that would create noticeable inertial effects but also couldn't create certain other kinds of inertial effects (Like constant acceleration). Presumably the holodeck makes use of a lot of force fields for positioning, holographics to draw even other participants, and artificial gravity to make the movement unnoticable. This way each person only needs to be just out of arm's reach of every other person and their actual positions need not change at all during the entire simulation. – Phoshi Feb 17 '14 at 13:21
  • @Phoshi localized gravitational fields strong enough to effect you would also effect other people in the holodeck who are nearby. I don't believe forcefields nullify gravitational effects - they are different phenomenon. If gravitational fields can be controlled so precisely then why isn't it used more often? For example, carrying wounded crew members and other heavy objects. – Aaron Klap Feb 18 '14 at 04:00
  • Does the holodeck manipulate your mind as well? I feel myself jumping off the ground and would definitely notice if my feet never lifted off the ground. In one episode a crew member reached down and touched another. How could this be done if one crew member was not physically higher than another? – Aaron Klap Feb 18 '14 at 04:11
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    @AaronKlap: Their anti-gravity technology is clearly very mature, given that it never fails and is not even a concern on even the smallest ships they have. This is an utterly wild guess that I know of no evidence for, but I can only assume antigrav generators can only generate one field. The ship's is down, the holodeck has hundreds, and the corridors have none. Why would they? If they want to use high technology to move things around they have a teleporter! – Phoshi Feb 18 '14 at 09:21
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    @AaronKlap - As much as I hate to give an "out of universe" answer but the reality is that certain aspects of the technology are genuinely nonsensical; sci-fantasy rather than sci-fi. – Valorum Feb 18 '14 at 17:16
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    @AaronKlap--Presumably if two people are within touching distance the then their actual relative positions in space will match their relative positions in the simulation (if one is elevated above the other, one can be standing on a force field). Only if they are supposed to be far apart, but still in visual range, would the holodeck need to use the technique Phoshi mentioned where each person is looking at a holographic image of the other rather than the real thing. – Hypnosifl Aug 14 '15 at 03:01
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    @AaronKlap -- Also, on your comment that "If gravitational fields can be controlled so precisely then why isn't it used more often? For example, carrying wounded crew members and other heavy objects", in the TNG episode "The Naked Now" Wesley showed off a mini tractor beam he built for a science project which could lift a chair, see images in the middle of this page. And it's mentioned in the DS9 episode "Captive Pursuit" that tractor beams use a "graviton field" to take hold of objects. – Hypnosifl Aug 14 '15 at 04:33
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    There's a Voyager episode in which B'Elanna is skydiving in the holodeck. She kills the simulation upon being ordered to the bridge (if I remember correctly) and as the simulation ends, there's a scene where the holodeck visibly alters her perceived velocity along with the effects of gravity. –  Aug 14 '15 at 06:03
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    The text in this image is completely unreadable on my phone. Adding a transcript might be prudent. – ApproachingDarknessFish Jul 04 '17 at 15:28
  • @ApproachingDarknessFish - Wouldn't it be easier for you to get a better phone? – Valorum Jul 04 '17 at 15:32
  • What about the bullets from Picard’s Tommy Gun in First Contact with the safeties turned off to kill the Borg dude? Wouldn’t that have shot the walls all to hell? – iMerchant Oct 28 '17 at 20:27
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    @iMerchant: Not if the matter from any bullets that would reach the wall would be "recycled" in time before impacting, while the visual effect of the bullet flying and hitting would just be recreated as an optical illusion by the holodeck. – O. R. Mapper Oct 28 '17 at 20:34
  • That treadmill wouldn't work because that would mean everyone on the holodeck is on the same treadmill, and if you look in Voyager's Season 5 Episode 11 "Latent Image" in the end you will see the floors of just the bare holodeck and there's no such treadmill, and if there were, if one person was walking, the treadmill would move everyone else too even if they weren't moving. – lights Jul 04 '17 at 13:09
  • @lights It's a holo-treadmill. We know that the holodeck can create solid holographic projections, and we know that it can create them at any location. Each person can have their own little forcefield that acts as a treadmill, right under their feet. And it projects it invisibly. – Michael Jul 04 '17 at 17:58
  • Easy. A holodeck uses Time Lord technology and is bigger on the inside, at least while a program is running. When the program ends the transcendental dimensions are disconnected and any real occupants are returned to the normal space of the holodeck. – Wallnut Sep 17 '18 at 15:02
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With an omni-directional treadmill! They can already do that today!

Chloe
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    +1. Certainly not Trek canon, but it's a freakin cool technology, and certainly a low tech proxy of whatever a real holodeck would use. – Dacio Feb 17 '14 at 01:56