Question about holograms (Star Trek related)

I was reading a joke about Star Trek the other day and for some reason it got me thinking about the film where the Borg and over running the Enterprise (I think it is First Contact) and the go back in time. Anyway, that is not important.

In this movie, Picard kills two of the Borg on the holodeck using a tommy gun from a story about a gangster. He says (I’m paraphrasing cause I can’t remember exactly) “If you disable the safety protocols, even a holographic bullet can kill”.

Can it? How?

If this just another example of ST making something up as a plot device, or is there some real science behind this? Also, how is it possible for holographic people to interact with humans (touching them as the doctor does on Voyager)? Again, is this possible or just made up?
Rick

In our real world, there’s no such thing as a free-standing hologram (yet, and maybe there never will be); you can’t project light onto empty air.

And in the world of ST, the holograms on the holodeck are solid (in a sense); the technology is supposed to be related to the transporter and the replicator, so yes, a solid projected object could do harm (but it’s fiction.

I do realise it is fiction.

I just wanted to know if it was based on any tiny little shred of fact.

Star Trek physics: The holodeck uses a combination of “free standing” holograms (light projected from the walls that somehow appears to be reflected from nonexistent objects in the room), force fields (invisible forces that seem to be exerted by nonexistent objects in the room), and replicator/transporter technology (actual objects created from vats of raw molecules). The “safety protocols” are rules in the holodeck computer that prevent force fields and replicated objects from hurting the human participants - when disabled, a bullet (whether replicated or simulated by force fields and holograms) can tear right through you.

Real physics: Real 3D holograms are simply light interference patterns recorded as a physical pattern on a surface (glass plate, embossed metal/plastic). When light hits the surface, it forms back into the original pattern of light that recorded the hologram. Since the light reflecting from each angle of the object was recorded when the hologram was created, you can see a 3D image of the object when you view the hologram. Different techniques record light from different angles, so you may not be able to see the object from a full 180 degrees.

However, the image isn’t real. When you look at a hologram it seems like you’re looking through a window at the object, a bizarre window where you see things on your side instead of the opposite side; break the hologram in half, and your window is half the size. But you can’t touch the object because it’s just light, all you can touch is the material it’s been recorded or embossed into.

Free standing holograms, force fields, and replicator technology are all fictional.

Maybe we’ll be able to do it someday using atom holograms instead of light holograms?
http://www.academicpress.com/inscight/03252002/graphb.htm

Free-standing holograms are impossible?

Well, have you ever seen a real-image hologram?

Rather than seeming to exist behind glass, this type of hologram appears free-standing. The only requirement is that the hologram plane be somewhere behind the “floating” image as viewed from your location. For example, if the walls of a room were some kind of advanced flat-screen holographic display, then you certainly could fill that room with 3D holographic objects. Real hologram generators aren’t like little slide projectors. Instead they look like huge LCD panels.

Real-image hologram walls would give some weird effects though. When a real person walked “behind” one of the objects, then from the observers viewpoint, that object would develop a large, human-shaped hole. In other words, a “real-image” holographic object cannot block your view of a genuine solid object. If you reach behind that holographic apple, the apple will vanish and you’ll wind up looking at your empty hand.