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In the Voyager episode: "Future's End, Part II" the doctor rescues B'elanna and Chakotay.

PORTER: They've got lasers! A black man and some bald guy. (The EMH enters. Porter and Butch's bullets go straight through him.)

PORTER: God in heaven help us.

EMH: Divine intervention is unlikely. (The EMH phaser stuns them, then unties Torres and Chakotay.)

In an earlier episode of Voyager, "Phage":

PARIS: But a hologram is just a projection of light held in a magnetic containment field. There's no real matter involved. (The EMH slaps Paris.)

EMH: Now, you hit me. (Paris's hand passes through the EMH's head.)

EMH: The magnetic containment field that creates the illusion of my body can be modulated to allow matter to pass through it or be stopped. I might be able to modulate the holographic lungs in the same way, allowing oxygen and carbon dioxide to pass from the lungs to the blood stream.

In order to make the above adjustments the doctor had to touch several buttons on a control panel. I realize the time I refer to above he was using the hollow emitter instead.

How does it work exactly that the doctor can have bullets pass straight through him but he's able to hold on to a phaser without it falling out of his hand? Can he simultaneously have part of his body be transparent and the rest be more like matter at the same time? What if the bullets hit the hand holding the phaser? I think one had a shotgun as I recall so there probably would have been pellets going all over the place.

  • 1
    We could make the same argument in both those instances as to why the doctor was still walking on the floor... – Robotnik May 25 '15 at 4:45
  • @Robotnik Not quite. The "not falling through the floor" requires no physical interaction - it can be entirely simulated by the computer handling the EMH (although e.g. sound of footsteps would stretch that a bit). Holding a phaser, on the other hand, requires a physical interaction (even if you handwave that as being due to electro-magical force generator, it's still a physical interaction between the generator and the phaser). – Luaan May 25 '15 at 13:09
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    There's an assumption here... that the doctor actually has hands. He doesn't. He's a projection, they just look like hands. There's a forcefield and/or tractor beam that's part of the entire holographic system that keeps the phaser positioned where it should be so it appears he's holding it. It's actually just floating there with an image projected around it. The Paris scene with The Doctor requiring a control panel is very early in the show. Throughout the series, it is established that the Doctor is tinkering with his program. His limitations in S1:E5 may not exist later. – T.J.L. May 27 '15 at 12:58
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The EMH is a solid hologram, which is designed to have the same solidity and haptic appearance as a human; this is done by the use of tractor beams.

If the doctor touches you, it is supposed to feel like a human touch. If he grabs a phaser, the phaser is supposed to be lifted as if a human hand had grabbed it.

So logically, if a bullet hits the doctor, the default programmed response is to offer as much resistance to the bullet as human flesh, which is not that much.

(The specific incident occurs at 34:10 in the episode. It is not visible whether the bullets pass trough the doctor or fragment upon contact. Certain bullet types are specifically designed to break up on contact with human flesh, but a full jacket bullet will pass right through.

Additionally, safety precautions and power limitations may impose an upper limit of resistance that the hologram emitters will generate, lower than the average resistance of human flesh.
After all, if the doctor collides with a human it is better to be a bit squishier than the human.
)

So why do the bullets not leave holes or other visible damage? Probably because no one bothered to implement a "show damage" routine for the EMH. I cannot recall any incident where the doctor is visibly damaged; the hologram emitters are most likely only capable of displaying an undamaged version of the doctor. Having your doctor look injured or damaged would be quite upsetting for the patient after all.

It has been pointed out that the doctor can choose to be solid or not solid by changing settings on a control panel (see Thomas' answer); He may even be capable of selectively changing the solidity of individual parts without the use of such a panel, thought the evidence is not entirely clear.

However, why bother? Physical objects are not capable of harming his projection, he does not feel pain, so he can simply ignore the bullets penetrating his simulated flesh.

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    With an in-universe explanation, the Doctor even shows this. He has Paris try and hit him after pressing a button on a control panel to alter the force field system that holds his photons into place and allows him to interact with items. It's also been said by the EMH that he can regulate the force fields that hold his matrix in place and allows tactile interaction, to allow matter to pass thorugh or be stopped like if he were solid. It stands to reason that can be selectively modified for portions of his matrix/body as well independently from other sections. – Thomas Ward May 24 '15 at 13:46
  • Season 1, episode... Heroes and Demons? Not sure about the name, but it involves problems on the holodeck during a program about the Beowulf epic. The EMH goes on his first "away" mission and at one points ends up losing a significant portion of his arm. The hologram emitters are quite capable of displaying a damaged doctor. – 8bittree Oct 24 '16 at 16:31
  • @8bittree The interactions of the Doctor's software with the hardware on a holodeck and hardware in sickbay are not implicitly the same. There's more than one episode where they talk about how difficult it is to make them work properly together. – T.J.L. Oct 6 '17 at 17:54
5

We have instances in the show where the Doctor even shows how he can manipulate the force fields which hold him in place and allow him interaction with objects.

On one occasion (Star Trek Voyager, Season 1, Episode 5) (thanks to Kyle Kanos for the link), the EMH has Paris try and hit him after pressing a button on a control panel to alter the force field system that holds his photons into place and allows him to interact with items. Paris' hand flies right through the photonic projection of the holographic matrix, and then when the doctor changes it again to its original method of operation and interacts with objects it shows the variance of the force field and its intensity. It's also been said as such that the EMH can regulate the force fields that hold his matrix in place and allows tactile interaction or not, to allow matter to pass through or be stopped like if he were solid.

Using that logic, it stands to reason that the force fields which allow for tactile interaction with objects or to allow objects to pass through him can be selectively modified and controlled over different areas of his matrix/body independently from other sections, which would allow bullets to pass through portions of him while allowing him to hold a phaser. (We see examples of force fields such as this during other episodes of Voyager where prisoners are held behind force fields that can have the field modified to shape a hole for passing through food to the prisoners)

(This does not necessarily apply to directed energy weapons, however, as it has been said elsewhere in the Star Trek Universe that a phaser beam at the correct setting would outright disrupt the matrix of a holographic projection, so at that point regardless of the force fields containing the matrix the directed energy weapon would disrupt the matrix entirely. Physical evidence of this being possible is seen in Star Trek: Insurrection when a phaser is fired at different parts of a holodeck projection and 'disrupt' those portions of the projection)

  • YouTube has the Paris scene from S01E05 of Voyager. – Kyle Kanos May 24 '15 at 23:34
  • @KyleKanos Thanks I'll add the link after my computer boots up (updates are a pain sometimes) – Thomas Ward May 24 '15 at 23:52
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    That youtube video, while funny, kinda makes you ask how he managed to press the panel again, after having made himself intangible... - although since he pressed quite a few buttons maybe he just made his face intangible. – BMWurm May 25 '15 at 12:40
  • @BMWurm that's my logic, actually. The idea, as I interpret it, is that he can control what areas are actually 'solid' vs. what areas are not. In theory his hands would then be invariably solid as a result of needing to interact with objects. The same logic would apply to the original question as to how a bullet could go through the EMH's holographic matrix while he holds a phaser. – Thomas Ward May 25 '15 at 13:05
2

The Doctor has regularly manipulated his solid nature at will, most notably in the penultimate episode Renaissance Man where he casually vaults, phased, through a window then immediately picks up his mobile emitter and runs off.

This is clearly simply something that he can do. There is no reason to assume a requirement that his solid nature is an "all or nothing" proposition.

0

The EMH is the same exact thing as a typical holodeck hologram, but more advanced in depiction (smaller emitters, no need for a grid). On various occasions it has been shown that the holodeck has options to adjust the holograms, mainly, safety protocols. A Holographic bullet could just as easily kill if the safety protocols are turned off, allowing the force field used to project the illusion of its surface to force its way through a person. As Jean-Luc so vividly explained:

The same has been shown for the EMH. He (or others) can control essentially at will when and how the hologram can physically interact with various objects.

  • The EMH still needs a "grid" or network of holoemitters to work, although not restricted to the "grid" of a holodeck – Thomas Ward May 24 '15 at 17:09
  • @ThomasW. In the end the Mobile Emitter is a single emitter (or array at best). That's what I meant. – user16696 May 24 '15 at 17:13
  • Ah, OK, I misunderstood your intent with the statement. Sorry! – Thomas Ward May 24 '15 at 17:32
  • The mobile emitter is also about 500 years more advanced technology compared to that onboard Voyager (and what the EMH was originally designed to work with). It stands to reason that it is considerably more advanced than anything onboard any VOY-era Starfleet vessel or facility. Yes, a slight bit of handwaving here, but just look at where computers were in 1965 compared to now 50 years later. – a CVn May 25 '15 at 7:29
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Just a thought. Everyone is treating this question as he has to be either solid (can hold phaser) or allow matter to pass through him (can't hold phaser).

This could be simple: Objects passing through him is a result of a force field surrounding his body (Fact), force fields have different levels, he could have simply weakened the field to allow bullets to pass through without turning it off entirely. He could have merely selected the minimum field setting required to hold the phaser.

Essentially turning his force field strength down, so instead of as strong as skin it's as weak as cardboard (but still able to hold the phaser).

And why bullets pass through but don't leave any holes? That's easy too, his physical appearance is just light, it's the force fields that control his physical tangibility. So why would an EMH be programmed to simulate damage, that's not what he was designed for.

He doesn't even have to weaken the force field either, by default it's supposed to have the texture and strength of skin (as a doctor), so the bullets would pass through anyway (there's no reason for the force fields to simulate bone after all), and there's no reason for his program to simulate damage (as a doctor, he's not programmed to be in the wild west on a holodesk like recreational characters).

0

I'd like to point out another difference: in the episode "Phage" the EMH had to use the control panel, as he was created by the ship's holo projectors; in "Future's End" he was using the portable holo projector, which being from the future and more advanced, could allow him to do more, like being solid to hold the phaser but pass-thru for bullets.

-1

Out of universe: looks cool, convenient for the story, pay no attention to the man behind the curtain. In universe: no explanation given. Hand-waving: the EMH was actively interacting with the phaser, his program was directing the tractor beams which give any part of him substance to act as his hand with regard to the phaser. The bullets were irrelevant; his program either failed to take them into account or actively chose to ignore them. It is not unreasonable, as such things go, to suppose that Starfleet holograms only project substance where that substance is relevant to the hologram's purposes/actions; tractor beams cost energy.

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