I’m rewatching TNG, and twice have noticed that objects from the holodeck are able to exit the holodeck. Wesley gets wet and stays wet when leaving; and also has a snowball fight, throwing a snowball which exits the holodeck and hits Captain Picard. How?
1 Answer
Holograms can't exit the holodecks on the Enterprise-D, since they require holo-emitters to exist, and there aren't any in the corridors of that vessel.
Holodecks are apparently capable of transporting and/or replicating real matter, however; Data intimated as much in one of the scenes you cited (the one with Wesley Crusher, from Encounter at Farpoint):
Riker: "I didn't believe these simulations could be this real."
Data: "Much of it is real, sir. If the transporters can convert our bodies to an energy beam, then back to the original pattern..."
Riker: "Yes, of course; then these rocks and vegetations have much simpler patterns."
Data: "Correct, sir."
So apparently, the water Wesley was drenched with was real, non-holographic matter (and I'm guessing the same thing applied to the snowball).
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2There are also numerous scenes where people eat and drink in holographic bars and restaurants, which would lend weight to the "replicator" theory. Commented Aug 24, 2020 at 22:06