As “Ooh!” and “Aah!” the Holodeck was in The Next Generation. It has no more chance of becoming a reality in the sense in which it was presented then the economy of the Star Trek universe of the same series.
Generating the smarts, the intelligence to drive the story logic and problem creation for mysteries or training programs is not an issue as long as the writers actually create good scripts, a lost art in The Next Generation.
Holographic projection in real time is not a technological impossibility either. It won’t have the smoothness, at least not in our lifetimes.
The problem comes when one wishes to simulate hard surfaces and, more importantly, inertia. Hard surfaces require resistance, a reaction to force. There must exist a field that can sense and respond to a movement to oppose the action. Magnetic fields won’t work unless you have a high iron diet!
And there are no physical fields of which I am aware that will, under machine control, resist your movement without some form of aversive punishment. I think the idea is for a little push back. If you touch a person, tactile resistance to skin makes sense. Of course, a retributive slap makes sense in other situations, you masher!
Inertia, the ability to maintain motion against a resisting force, requires mass. A holodeck is empty. No mass just laying around to use. Mass must be found to give the characters designed for interaction for the living users some semblance of reality. They must feel real to the spacemen on leave in the Holo-House of Ill Repute, or the wrestler working out for the Sector 7 Olympics with a simulacrum. Either of these cases must resist forces placed on it by the user. When the wrestler lunges, the user must feel it’s force in proportion to its mass and force of its musculature. It must work as expected.
The Holo-deck is a tool, not just entertainment. In fact, it’s purpose is at least eighty percent of the mission and the rest, morale.
So how do you get mass out of thin air? Simple. Einstein gave us the formula in Special Relativity, E=Mc², Energy is equal to mass times the square of the speed of light in a vacuum. Once we decide how much mass we need, we can calculate the energy requirements. How simple!
A famous episode was a Holmes-Watson show where Moriarty appeared and took flight beyond the bounds of the Deck! Ignoring that oddity, let us calculate the energy cost of creating that amount of mass. Let us say Moriarty weighed in at 175 lbs. Yes, English, that would be 12.5 Stone. 1 Stone = 6.37 Kg. Moriarty weighs 79.54 Kg. C = 300,000,000 m/s. The mass, in this case, is the rest mass, M∅.
E = 79.54 x 9 x E16 Kg m²/s² = 7.16 x 10^18 Joules.
The Hiroshima bomb was 15 Kilotons which is equivalent to 63 Terajoules, that is, 63 x 10^12 Joules. Moriarty requires roughly 72 x 10^17 / 63 x 10^12 which is appr. equal to 10^5. In other words, the starship Enterprise would need to generate the energy of 100,000 Hiroshima bombs just to create enough mass in order that Moriarity feels like Moriarty when Picard as Watson punches him. A lot of match heads just for some recreational sleuthing!
We can’t stop with the body. The puppet must be motivated. Subcutaneous musculature, blood pumping, skin flushing, heart beating, breath panting, sweat dripping, everything must fit the image of a man that acts the part. Seated and contemplatively intellectual or loquaciously manic, any mood must satisfy the illusion of reality. The inert mannequin must live.
And to do that, more energy. But the rest is a paltry sum compared to the amount needed to create. Applying it, however, will be more difficult. Active fields, as discussed above, will be required not just to resist humans but to move inorganic matter. This is all technology not even in the sights of science, merely the dreams of futurists.
Sorry to be your buzz kill Betty, but facts are facts. There are too many important things to do in this world for the unwashed to imagine that things happening in a Virtual World are the same things that happen in a Holodeck. Aside from the fact that a Holodeck comes with a green screen and a CGI staff, VR gives no tactile feedback of the type experienced on the pretend starship Enterprise.
By far, the best way to enjoy a Holodeck in this day and age is to learn Improv.