Plausible explanation for lack of reflection in a mirror

Question

Thanks to the commenters in the question sandbox for helping refine this question before posting.

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In many vampire stories the vampires do not have a reflection in a mirror. This is generally not explained beyond simply being a supernatural phenomenon. Is there any plausible way for something to be visible directly but invisible in a mirror?

I'm assuming this will have to be magic, as I am unaware of any way this could be possible physically. If there is a physical method I'd be very interested to hear about it, but what I'm expecting is ways to make the magical approach consistent and understandable. For instance, what about the vampire's shadow, and any objects the vampire may be carrying (and clothes for that matter).

Even with magic as the explanation, there still seem to be opportunities for inconsistencies, or at least odd consequences. Imagine someone crouching to drink from a pool, and a vampire leaning over them. Will there be a shadow cast onto the water? Or will this person just see a shadow on the bank that abruptly stops at the water's edge?

How can I design the rules so that they are in keeping with familiar vampire mythology, and still self-consistent when exploring consequences?

Answer 1

Alternative answer to keep the spirit of "mirrors as vampire detectors" for a very futuristic setting:

In a high-tech world, mirrors could be obsolete and replaced with smart 3d screens which show a reflection of the environment. When such a screen displays a human, it identifies the person and projects some information about them around their reflection in form of floating text panels. Due to a quirk in the biometric recognition system, it doesn't recognize vampires as humans. So they might show in the mirror-screen, but the lack of information panels around them gives them away.

The inability of vampires to trigger biometric sensors could also be used to transfer other common vampire weaknesses into a futuristic scenario. Like:

• Being unable to enter a building unless being invited. Doors just won't open for them, so they always need to follow other people. However, when they are invited, the system registers them as a pet or robot which is welcome and the vampire can then enter on their own.
• The inability to cross running water. All bridges over rivers are biometric checkpoints, so vampires can not pass them without being identified. Why only the bridges? The political debate of privacy vs. security ended in a compromise: The police can have biometric checkpoints, but only a very limited number per city and they must be visible. They of course place them in a way that they are impossible to avoid, which in a city like New York would be the bridges crossing the Hudson- and East-river.
• Being unable to enter churches. When entering a church, the biometric system recognizes you and automatically takes a small tithe from your bank account (voluntary donations just no longer cover the running cost of churches). Vampires don't register, so they are denied entrance. Alternatively, the catholic church is still holding up the ancient tradition of fighting vampires and reprogrammed the biometric sensors at all churches to recognize them. When a vampire is detected at a church entrance, a team of vampire hunters is dispatched immediately.
• Holy water. Replace with medical nanite solution. It might even be called Holy Water™ when that is the brand name it is sold as. While the medical nanites are able to automatically detect and cure many ailments of a normal human, the nanites totally misinterpret the biosigns of a vampire and inadvertently cause severe harm to them.

Answer 2

When your world allows psychic powers (for which you can often find a pseudo-scientific explanation), you could say that vampires are actually completely invisible and their physical appearance is just a hallucination induced into the observers mind through telepathy. Whatever mechanism is responsible for causing this hallucination is not smart enough to take reflective surfaces into account. It might or might not also manage shadows. Any clothings or accessories which are part of the vampires projected self-image would not show up in a mirror, but anything they picked up from the environment would. When a vampire invites you as a drink to a drink, their cup would be a part of their projected self-image while only yours is real (try switching them around and see what happens).

When vampires can control this effect consciously, it would also give them the ability to change their appearance at will or become invisible. Shape-shifting and invisibility are common abilities of vampires in many vampire stories.

However, the end result would be that your vampires would be more like ghosts than like living corpses.

Answer 3

The original explanation was that mirrors reflected the soul, and since vampires didn't have a soul there was nothing to reflect. If you don't like that you can still do something similar by saying the magic is no in the vampire, but the mirror. Perhaps certain mirrors are specially enchanted as vampire-detectors. Or perhaps it's simply a basic principle of magic that mirrors behave that way.

Many worlds have varying degrees of clap you hand if you believe style magic, where magic works the way it does simply because everyone expects it to. If you go with a system like that then you can simply say that because people expect the mirrors to not reflect vampires that's how they work.

If you only want mirrors to reveal vampires, and aren't committed to how they do it, one option I personally like is that the mirror still reflects the vampire, but it reflects a rotting and disgusting corpse. The vampire actually is undead and rotting, but he uses some form of magical suggestion to make you see a beautiful creatures (and presumptively not smell it); however, he can't use the same powers to keeping you from seeing his real reflection. This gives some fun potential to have someone be disgusted when they realize what the elegant or even sexy looking vampire they had been talking to really looks like; which helps bring a very viscerale sense of how wrong a vampire really is. Insert joke at expense of twilight sparkling vampires here

You could take this one step further by suggesting that if a vampire is very skilled and focused he may be able to control your perception of his reflection in a mirror as well, but it's very difficult and he has to do it for each person who sees the reflection. Thus he may be able to occasionally appear in a reflection if he knows he has to walk in front of a mirror where someone may notice; however, he can't do the trick if caught by surprise, if he doesn't know of someone who might see the reflection (he fails to consciously control what that one sees), or there are many people that would see the reflection (he can't consciously screen his reflection for that many at once). Perhaps when he is doing this it is such a strain he may be distracted or act odd in a way that may give subtler hints that something is wrong. Due to the difficulty of doing this though most avoid mirrors entirely, for fear they will not be able to control what everyone sees, and perhaps only the oldest and most powerful vampires can do it (thus you can show a vampires strength by having him casually walk in front of a mirror). This option gives you a little more control over when a vampire's glamor may break, at any point one person may see his reflection is wrong while others don't etc.

Answer 4

Vampires are often weak to silver. It could be that that silvered glass mirrors actually destroy the reflection (and maybe even injure, weaken, or unsettle the vampire). In that case, the logical result is that vampires could be seen in other reflective surfaces, just not typical mirrors.

Answer 5

As has already been said, mirrors show the soul, and vampires have no soul. It is perhaps worth mentioning that there are a whole bunch of superstitions which all play together here. Using all of them would make your magic system more self-consistent.

• Breaking a mirror brings seven years of bad luck, because you have done damage to your soul.
• When a person has died, a window must be left open overnight, to allow their soul to escape, and all mirrors in the house must be covered, lest you catch a glimpse of their soul passing by.
• Vampires (and the unseelie, I believe) have no reflection, as they have no soul.
• Photos capture a section of your soul too, of course.

  All across the multiverse there are backward tribes* who distrust mirrors and images because, they say, they steal a bit of a person’s soul and there’s only so much of a person to go around. And the people who wear more clothes say this is just superstition, despite the fact that other people who spend their lives appearing in images of one sort or another seem to develop a thin quality. It’s put down to over-work and, tellingly, over-exposure instead.

  _{* Considered backward, that is, by people who wear more clothes than they do.}

  Terry Pratchett, Witches Abroad.

If you tie all these beliefs together, as they are tied together in our world, you can develop a complex, interlocking, and self-consistent system of magic. And, of course, it’s not too hard to add a few new elements to this system.

• A smashed mirror can be a powerful object in itself. The Snow Queen managed to capture Kay when a fleck of her mirror entered his eye and his heart.
• Mirrors can be used in magic to enhance a practitioner’s power: the reflections build up. Using one mirror is one type of magic; using two or more, causing infinite reflections, stretching your single soul out over infinite space, gives far more power but is damaging to you. (You may want to read Witches Abroad before adopting this idea, to make sure you don’t follow too closely in Terry Pratchett’s footsteps, because that’s where I’m getting the idea from.)
• Mirrors in mirrors, Spiegel im Spiegel, are strange and powerful things generally, actually.
• Mirrors as windows to other parts of the world, which a practitioner of magic can use to view other parts of the world, is a common device in fiction. Mirrors are objects of mystery.
• What is a mirror? Is it any reflective surface, or is it specifically a flat surface, a flat glass surface with silver backing, or what? If mirror magic can be used to see out of another mirror, does the far mirror have to be specially prepared, or can you use ice in a puddle, flecks on a standing wave in a stream, a waxy leaf?
• Culturally, if mirror magic is widely known and understood, what is the attitude to mirrors? Is the king’s throne surrounded by them, or are they not to be found in the palace? Do people use shaving mirrors? Maybe people want mirrors around, as vampire detectors. Maybe they want to avoid them, as things which would damage their own soul. Or perhaps, like Terry Pratchett’s witches, people are happy with mirrors but uncomfortable with the idea of getting between two of them (which might make that bit at the end of a visit to the barber a little awkward).
• Photos too are suspect. We want them, of course, but not too many. People might have a limit on appearing in a maximum of one photo a month, or so. What would the attitude be to CCTV? If the footage is autodeleted after a week or so, as most CCTV footage is, is the damage to the soul restored?

Answer 6

Mirrors reflect the visible light which has bounced off of the objects in front of it. Perhaps a vampire absorbs all visible light that hits it but emits a currently unknown form of energy which excites the human optic nerve much like visible light does but is absorbed and not reflected by silver. If all of this were true, modern mirrors and standing water might show a vampire's reflection, while an old fashioned silver-backed mirror (and maybe a video camera) wouldn't.

Putting a poetic spin on the light absorbing properties of a vampiric corpse, you might say that the hungry spirit which animates the flesh eats the light in the same way it drinks human blood.

Some will say that I am cheating by including a "currently unknown form of energy" in my answer. "Currently unknown" is just a fancy way for saying "magic". To that unspoken complaint, I would offer that science is the study of change. It is an observational art. If vampires are the only earthly source of my "currently unknown" energy, and if no vampire has ever been observed in a scientific setting, then that energy could easily be missed by deductive science. Similarly, if my "currently unknown" energy did not play a major role in the cosmological creation story which is the almost exclusive focus of current inductive reasoning, it could easily have been overlooked by even the most intuitive investigators. "Unknown" is not synonymous with "Magic", despite the fact that both words equally challenge the arrogance of many scientists.

Answer 7

Really late answer, but I thought it was a fun one...

Vampires do have reflections, and are always visible, as visibility is just a result of light bouncing off something and striking your eye.

The myth of Vampires not having a reflection is actually a side effect of another of their abilities, namely Glamour. When you look at a vampire you are actually seeing the glamour that they have in place that they want you to see. This is why vampires are always beautiful and suave. They can also use this glamour to make you not see them.

The problem with mirrors is that the glamour only works when you see it directly. If you look at a vampire in a mirror then the glamour won't affect you, and you'd see the vampires true form. And that is the real problem, for a vampires true form is so horrible that the human mind simply rejects it because to do otherwise would lead to madness.
And so, as a coping mechanism, your mind just edits the reflection out.

Answer 8

Ah, I have thought about this myself in the past for a short story. Here's the best I could come up with, feel free to use it if you like it. Note that these are not exactly your old-fashioned vampires, but perhaps that's for the best, no?

The setting will have immersive Augmented Reality (i.e. almost everyone is wearing Virtual Reality Lenses, almost all the time). My vampires were pieces of predatory software, taking on the appearance of friendly strangers, then later (after gathering more information) close friends and even family. The victim would think these projections were real. The goal was to trick the victim into revealing useful information which they could then sell in the underworld. If threatened or discovered, they could project a set of strongly customized visual and audio patterns that could incapacitate, induce illness, confusion, short-term memory loss or sometimes even kill the victim (think the equivalent of blinking lights for inducing seizures, but massively up-teched).

PS: Only a careless or rushed vampire would forget to add their projection rendering onto reflective surfaces (as filtered by the VR lens), but depending on how far away the vampire's phylactery is, there might be a few dozen miliseconds' delay before the image is rendered and sent to the lens, enough to sometimes make them appear to blink a bit onto the mirror. The real objects would show no such reflections, of course. My character figures this when he accidentally takes out one of his lenses.

PPS: I had my vampires smoothly avoid being touched, but you could get around that if you add haptic gloves and the like.

Answer 9

Is there any plausible way for something to be visible directly but invisible in a mirror?

You could say that there's an alternate universe, that's exactly like reality, except that there are no vampires in it; And mirrors have the curious property to reflect light from one alternate universe to the other. (You can hand wave towards quantum superposition or Schrödinger's Cat to make this sound more physical. If there could be a dead cat and a living cat superimposed in Schrödinger's box, why couldn't there be an undead vampire and a dead body superimposed in your world? Of course it's not really physically possible, but it sounds more plausible than "magic".)

This would help clear a lot of inconsistencies: For example, if is a dead person rises as a vampire, and you watch the scene through a mirror, you'd see a decaying corpse lying there (clothes, shadow and all), even after the vampire went elsewhere, because that's what would happen in a world without vampires. More precisely: That's what happens in the alternate universe without vampires. If you'd look in a mirror while a vampire picks up a glass, the glass would still be standing on the table in the mirror, because that's what happens in the alternate universe without vampires. (This also explains why the vampire's clothes aren't visible in the mirror, even if she changed after she rose from the dead. In the mirror, the clothes never left the shop.)

You'd have to have some effect that "moves" the glass and the clothes in the alternate universe later, when no one is looking in the mirror, to make sure the world in the mirror looks just as our world without vampires. (You could again hand-wave towards the effects of measurements in quantum mechanics, to make this sound plausible. The idea that something would disappear if you don't continuously look at it sounds strange, but in quantum physics, there are actually strange effects like that!)

Sidenote: If you use this in a story, you have to have at least 3 separate references to Through the Looking-Glass! (Because that's obviously where I've got the idea from.)

Answer 10

One way would be polarization, if the mirrors were tuned to only reflect light with a certain polarization and the vampires reflected light with a different polarization then the mirror would not reflect their image. Some special property of the vampire would cause this polarization. The problem with this idea is that you would get a black shadow where the vampire should be though.

In fact that would be a common problem with most possible solutions, it's already not easy to make a vampire disappear from the mirror. Making what is behind the vampire appear in the mirror though is far harder still.

There are only two real ways I can see to do this:

1. The first is as suggested by Philipp, to have the vampires actually invisible, so light is passing through them, and then have humans viewing them directly somehow perceive them.

2. The second is to have the the vampires using a glamour to hide their true appearance, a side effect of that glamour may be to hide their presence in reflections. It's advanced enough to be able to hide their true form in the mirror, but not advanced enough to replicate the form they are projecting in the mirror.

Answer 11

I've pondered this ever since I was a child. It is almost impossible for a solid object to be truly invisible. The idea of only reflections being invisible, as though such an amazing feat could be an accident, pushes the idea even further into fantasy.

About a year ago, though, I realized that it is possible to create an interesting explanation. I considered writing a story as a vessel for the explanation, but I may as well describe my idea before I get around to it, as it will be borrowed anyway. Here's what you need:

• https://en.wikipedia.org/wiki/Blindsight
• https://en.wikipedia.org/wiki/Riddoch_syndrome

First of all, it is obvious that vampires are a constructed race and that they did not arise naturally. They must have been created by the ancients using magic (or very advanced technology). They are intended as predators. Ideally, they should be invisible. And the easiest way to make yourself invisible might be to interfere, telekinetically, in the visual cortices of nearby human brains, so that your prey sees you but doesn't see you.

Now we come to the interesting bit. Conceivably the effect was imperfect, and did not work as well on animals; but, worse, the effect was originally limited to a "blind field", so the vampire was visible in reflections. Therefore, once humans caught on, a separate spell was needed to mask the reflections as well. But in the early Middle Ages, there was a great war between human magicians and vampires, and by means of great effort the humans succeed in destroying the original invisibility spell. The best that modern vampires can do now is to create brief illusions when they are in danger: "turning into bats", etc.

But the second spell is still there.

Answer 12

You could have vampires without a mirror reflection if the world is actually a simulation, like the Matrix. In this scenario a vampire would be a specific kind of program construct within the simulation.

Answer 13

The most plausible explanation I can come up with would be mirrors reflecting most of the visible spectrum, but a few very specific wavelengths being absorbed.

Under normal circumstances we wouldn't notice that, because the reflected light would only lose the tiny amount of energy contributed by the few photons matching the absorbed wavelengths.

If we assume that when you shine light on a vampire, it doesn't emit light of the same frequency as you shine on it, rather it only emits one of the specific wavelengths absorbed by the mirror. Due to the physics of how it works, the emitted light would be lower energy than the light you shine on the vampire.

The outcome in this case is that if you look directly on the vampire, they will be visible. They will however appear a bit red. (To see their true colors, you need an ultra-violet light source.)

If you look at them in the mirror, you will instead see a black spot. Essentially you will see their silhouette filled with black and no nuances.

The explanations usually given would of course have given you the impression that when observed through a mirror they would appear transparent rather than black. But maybe that could be explained as a simple misunderstanding due to the wording of no reflection being interpreted slightly different from how it was meant in the first place.

Any objects including clothes worn by the vampire would have to only emit the same wavelengths in order to exhibit the same property when viewed in a mirror. Which mean the lack of reflection would be a property of those objects regardless of who were wearing them.

Answer 14

Mirrors and cameras are instruments of scientific measurement. They can only detect things that exist in nature, and they are incapable of detecting anything 'supernatural', which is something that only human minds can do.

So as far as mirrors and photographs are concerned vampires don't exist, and the information we get from them will reflect the natural or scientific explanation for the 'vampire' event.

Answer 15

There was a TV series many years ago called Ultraviolet by Joe Aherne that tried to explain everything vampiric as if it were real, though with plenty of "we don't know". It was very good - worth digging out a copy.

One of the ideas is that, because a vampire has no reflection, it follows that there is no light reflecting off its body, and therefore has no physical presence that we'd recognise. So, no reflection in a mirror also means no image in a CCTV camera, or a photograph, and no ability to use other electronic devices such as a telephone. The idea is that a vampire doesn't truly exist in this world as physical matter.

So why can humans see and interact with them? Possibly its a metaphysical thing, 'spiritual' forces that we can detect that physics cannot, similar to how ghosts work in the world but with a bit more power behind them. TBH it doesn't really matter exactly why, but the effects of such a situation go beyond mirrors.

Answer 16

Why a vampire is invisible from mirror can be explained this way.

Vampires are actually made up of the atom equivalent of dark matter. As dark matters, they are actually completely invisible to electromagnetic radiation. However, since the atom equivalent of dark matter, they are massive enough to radiate barely-visible electromagnetic radiation.

When the photons of these radiation bounces of the mirror (or any other reflective surface), they lost some of their energy and their frequency drops to the infrared radiation spectrum.

Now, since human optical nerves can only detect visible light and not infrared, vampires are invisible after reflection.

Of course that means that some very sensitive camera or heat-sensing devices can still detect vampires and it doesn't explain the lack of warmth of vampires. Also, some animals may be able to detect it from the mirror reflection itself.

I hope this worked for your question.

Answer 17

Could this be done technologically, assuming the mirrors are completely normal ones and there are no psychic powers in this universe? Maybe, with one of these options:

Option 1:

First, take a look at this article a hypothetical near-future invisibility suit. The suit would be covered with tiny omnidirectional light sensors and light emitters, all in contact with a computer. A diagram of such a sensor/emitter pair from the article:

To achieve true invisibility, optical camouflage must capture the background from all angles and display it from all perspectives simultaneously. This requires a minimum of six stereoscopic camera pairs, allowing the computer to model the surroundings and synthesize the scene from every point of view. To display this imagery, the fabric is covered with hyperpixels, each consisting of a 180 x 180 LED array behind a hemispherical lens.

When a certain wavelength and intensity of light strikes a sensor in a particular direction, the computer can calculate the trajectory that light ray would take along a straight line if the person were totally transparent, and where that line would intersect the opposite side of the body. Then, it can instruct the emitter at the intersection point on the opposite side of the body to emit a light ray in the same direction with the same wavelength and intensity, which we might call a "masking ray". If this is done at every point along the body for light rays coming in every direction (even if it's not perfectly fine-grained so the emitted light is a bit pixellated), you can have a form of practical invisibility.

I think it should be possible to modify this so that if you look at the person in the suit directly they are visible, but they will appear invisible in mirrors. My idea here is just that the image-processing software interpreting the data from the sensors can distinguish human eyes, and once the suit has identified all the human eyes in its surroundings, it can selectively instruct all emitters not to send masking rays in the direction of any human eyes. You may also want to have the software be able to distinguish camera lenses if you want the vampire to be visible on camera, and also be able to distinguish the eyes of various kinds of non-human animals along with humans (although you might not want to do this if you want these technological vampires to creep out animals because they can hear and smell them but not see them).

The only problem with this is that if the software sees someone's eyes in a reflective surface like a mirror, and interprets that as another set of eyes, then if it fails to send the masking rays in the direction of the reflected eyes, the person will be able to see them in a mirror. But with sufficiently sensitive sensors and smart software it may be possible to differentiate reflections of eyes from regular eyes which lie directly in the line of sight of the suit, since any real-world reflective surface is going to have some combination of specular and diffuse reflection (also, the software could be continually trying to build a model of the environment based on sensory information, so it could notice when the image on a surface seems to be a duplicate of some mapped region of the environment in the opposite direction).

Also, note there would be one side effect of this technology which isn't usually part of modern vampire lore (though it was apparently a feature in some older vampire myths): besides having no visible reflection, the vampire will also cast no shadows. I suppose if you want to avoid this, if the software can distinguish eyes in mirrors and other reflective surfaces from regular eyes directly in the line of sight, it could be designed to only send the masking signal in the direction of reflections of eyes, and then it would have a normal shadow. But this would have the disadvantage that if the system failed to notice a pair of reflected eyes because the reflection was far away, distorted, and more diffuse than specular (say, a faint reflection on a dull metallic teapot) then a person near the reflected surface could notice the vampire, whereas sending the masking signal everywhere except non-reflected eyes would avoid this error.

This option has the drawback that it requires the vampires to not only have this sort of detector/emitter system lining every surface of their body, but also to have it lining the surface of whatever clothing they wear. But if you imagine the vampiric "infection" was created by some civilization with advanced technology in the past (perhaps native to Earth of that time, or perhaps involving aliens or time travelers), it could involve a swarm of nanobots that envelop each new vampire, and it could be smart enough to form an envelope that extends to clothing as well as the vampire's body, with the nanobots forming tiny light sensors and emitters on the surface of both. Such nanobots could perform other plot-relevant functions like repairing damage to the body (aside from stakes to the heart and beheadings), preventing decay and keeping neurons and muscles functional even if the cells are not really alive, distinguishing sunlight from other forms of light and causing an explosive reaction when sunlight is detected, etc.

Option 2:

If you let the tiny robot swarm get very advanced, perhaps involving femtotechnology rather than nanotechnology or perhaps some particles unknown to current physics, there could also be an alternate solution that doesn't involve selectively detecting nearby eyeballs. Imagine the tiny machines absorb all incoming light, but the machines are designed to mimic the optical properties of the bit of the vampire's body or clothing directly underneath them, sending out light-like signals that match whatever light the bit of body/clothing underneath would emit under the same lighting conditions. However, instead of the emitted signals actually being light, imagine the signal is itself a subatomic-scale machine, or perhaps an exotic particle unknown to current physics, sent out on the same path the light ray would have taken (if you want to bring exotic particles in, I suppose you could ditch the idea of tiny machines and imagine the vampire's body is surrounded with some kind of field which is also unknown to current physics, which has the property that any photon exiting the boundary of the field is transformed into an exotic particle with the same momentum and energy).

Being smaller than an atom, this machine or exotic particle (which I will abbreviate M/EP to avoid having to keep saying 'machine or exotic particle') is designed to mimic the behavior of light in the sense of passing through transparent materials like water or glass, and even having its path refracted by them. If the M/EP comes to a bit of matter that would absorb or scatter photon, like an electron in a photosensitive molecule in the human retina, then we can imagine the M/EP imparts the same amount of energy and momentum to the bit of matter as that bit of matter would have gotten from the photon (if it's an exotic particle we can just imagine the particle itself has the same energy and momentum as the corresponding photon, if it's a tiny machine we can imagine the machine emits a photon of that energy and momentum when it detects a bit of matter that would naturally absorb or scatter a photon). And if the molecules in your retina react the same way, you will be able to see the vampire if you look at it straight-on.

But assume the M/EP behaves differently than a photon would when it encounters to some bit of matter that would reflect a photon--at this point the M/EP will just get absorbed or otherwise destroyed by that bit of matter, rather than travel on a reflected path (if it's a tiny machine it could just break up at that point). This will ensure that no M/EP can take a path that goes from the vampire to a reflective surface and then to a human retina (or camera lens or animal retina). Finally, if the M/EP encounters a bit of matter that has some probability $P_1$ of reflecting a photon, like a piece of glass which reflects some incoming light but lets the rest pass through, then the M/EP particle should have the same probability $P_1$ of being destroyed/absorbed, and otherwise will interact with this bit of matter the same way a photon would. This ensures that even though a person's eyeball is partially reflective, the photosensitive molecules in the retina will be imparted with the same energy/momentum by the M/EPs as they would get from photons if the vampire wasn't surrounded by this advanced technology and was just emitting light normally. But even if you were standing right next to a vampire and looking closely into the eyes of another person standing across from both of you, with this technology you wouldn't see the vampire reflected in the person's eyes (this wouldn't work with the more realistic invisibility suit technology I discussed in option 1). Also, with this method the vampire will cast a shadow normally, and the shadow will even extend over reflective surfaces like water even though the reflection itself will be absent.

Of course, this second option is well in the realm of technology indistinguishable from magic, so if you're going to pick a solution of this kind, it might be simpler just to assume that our apparent physical world is a Matrix-style hyper-detailed simulation, and whatever beings are running the simulation have just programmed in special alterations to the laws of optics for light rays emitted or reflected by vampires (an option already mentioned in user100487's answer).

Answer 18

Divine Intervention

Vampires don't have reflections due to the interference of a god or gods.

Perhaps the goddess of beauty is the friend of humanity, and she prevents mirrors from reflecting vampire buth to punish vampires (as they cannot see themselves and fix their appearances) and to give humans a way to see the undead.

Alternately, the god of shadows absorbs the reflections of his servants the vampires to feed his own powers. That is why vampires don't avoid mirrors more than is necessary, and might even keep them in the mansions. Their dark lord commands them to give him his due.