The Optical Behaviour of Vampires

[simont]

Vampires don't have reflections; everybody knows that. But how do they not have reflections? What's the mechanism? And what useful applications are there for that mechanism?

I think it goes like this. When a photon strikes a vampire, it separates into two different types of semiphoton, which I'm going to call an R-photon and an S-photon. The R-photon continues along the original photon's path, as if the vampire hadn't been there; R-photons disappear if they touch a sensor (such as an eye, or a camera), but if they touch a reflective object they reflect off it and turn back into ordinary photons. (Most noticeable with a mirror, but I think it applies to diffuse reflection off ordinary surfaces too.) The S-photon, meanwhile, reflects off the vampire as if it had been an ordinary body; S-photons disappear if they touch a reflective surface (again, ordinary diffuse surfaces as well as mirrors), but things like the photoelectric effect work just fine, so S-photons interact with sensors exactly like normal photons do.

Hence, if you're in the room with a vampire, you see it by means of the S-photons scattering off it; but if you look in the mirror, you don't see the reflections of the S-photons, but only those of the R-photons which went straight through the vampire.

There are a couple of fiddly corner cases: what happens if the first object struck by an R- or an S-photon is another vampire? After drawing a thought-experiment diagram or two on paper, I conclude that R-photons go straight through additional vampires and remain R-photons only, while S-photons bounce off vampires and remain S-photons only. Any other behaviour would sometimes enable you to see a vampire in a mirror, by putting another vampire either between the first one and the light or between the first one and the mirror.

So now we have a sound theoretical basis for the optical behaviour of vampires, what are its applications? Well, distressingly, no application I've been able to think of quite works.

You'd like to be able to use a wide flat vampire as a one-way wall: angle a mirror at the wall and you can see through the vampire as if it wasn't there, but people on the other side don't know you're watching. Except that doesn't work if they have mirrors too, and in a world where people used this as a means of covert surveillance, anyone remotely paranoid would have a small mirror about their person at all times.

A vampire itself would have the useful ability to wear a pair of glasses with one lens mirrored on the inside, and thus be able to see people sneaking up behind it with stakes. Unfortunately, a vampire so equipped would no longer be entirely invisible in mirrors – there'd be a mirrored lens hovering in mid-air. I'm sure that would turn out to be inconvenient.

A superficially impressive military application requires a vampire which itself has a mirror finish. If you take a laser beam and reflect it off a vampire, you split it into an R-laser and an S-laser. The R-laser is useless as far as I can see, but the S-laser has definite possibilities: it has the same effect on a target as ordinary laser weapons, but without the risk of mirror-carrying enemies reflecting it back at you. Except that even that doesn't work, because vampires reflect S-photons; so if the enemy also has a mirror-polished vampire, they can use that to send your beam back at you. Arrgh!

You'd also have to avoid using a laser working in the ultraviolet frequency range, or else your vampire would develop a completely different optical problem…

(Thanks to several people in the pub for helping me discuss this very silly idea :-)

Comments

[valkyriekaren.livejournal.com]

Me, I'm mostly disappointed that there aren't more uses for the phrase 'a wide flat vampire'.

[ewx.livejournal.com]

I suspect it would usually be “a wide, flat and very annoyed vampire”...

[feanelwa.livejournal.com]

There's got to be some sort of interesting diffraction-related thing here. I am going to think about it for a bit.

[mooism.livejournal.com]

A vampire itself would have the useful ability to wear a pair of glasses with one lens mirrored on the inside, and thus be able to see people sneaking up behind it with stakes. Unfortunately, a vampire so equipped would no longer be entirely invisible in mirrors – there'd be a mirrored lens hovering in mid-air.

But as we can’t see a vampire’s clothes in the mirror, why should we be able to see a vampire’s glasses in the mirror?

[simont]

Hmm. Well, it is possible that by wearing clothes and glasses a vampire can temporarily lend them the vampire-nature. But in that case, the mirrored glasses are even less useful: once the glasses become vampiric, they reflect S-photons, so the vampire can't use them to see behind it any more – it'd just see a closeup of its own left eyeball.

[pseudomonas.livejournal.com]

So vampires shouldn't show up in light that's been bounced off a reflector beforehand, such as most of the beam of car headlights?

[feanelwa.livejournal.com]

No, because that's ordinary photons, reflectors only affect it once it's been reflected from the vampire.

It must be a right bugger to be a vampire cyclist, though. Sorry mate I didn't see you.

[emperor]

I now want to go and look at episodes where Angel is carrying shiny weaponry and see if they remembered to CGI out his reflection on the blade!

[lionsphil.livejournal.com]

Well, it makes more sense than quantum superposition.

It also explains the Reverse Vampire Trousers worn by most first-person computer game characters: they have simply adapted the material to bounce R-photons and pass through S-photons.

[simont]

I'm not sure what you mean by that one. You can see your trousers in a mirror but not directly? Surely in most first-person games your trousers aren't usually in your direct line of sight anyway?

[simont]

Hang on, now I see a foolproof application. Having carefully determined by drawing diagrams that vampires must reflect S-photons, this means that the obvious application for a mirrored vampire is that – unlike a normal mirror – another vampire can use it to shave in!

[meihua.livejournal.com]

*falls about laughing!!*

[uisgebeatha.livejournal.com]

I have no useful contribution to make other than vampires program in C# (http://thedailywtf.com/Comments/22-The-Offshore-Coordinator.aspx?CommentReplies=202585).

Oh, and saw this and thought of you (http://www.bunniestudios.com/blog/?p=253)... ;)

[cartesiandaemon.livejournal.com]

vampires program in C#.

ROFL! That's great. And somehow just feels right. I bet vampires do program in C#[1].

[1] That is, if a vampire programs, they probably do it in C#. I'm not asserting the existent of a vampire :)

[shadowphiar.livejournal.com]

You should submit this to Physics Review - it reminds me of an article I read in there many, many years ago about the thermodynamic properties of ghosts. It concluded they would make an excellent filling for storage heater systems.

[(Anonymous)]

Vampires don't show up on cameras. Neither does their voice travel over the telephone: the only machine that can detect them, is us.

Now: sombras que corta.

[senji.livejournal.com]

Hey, wait, what happens if you put a vampire in a hologram imaging machine?

[simont]

Hmm. As I understand holography, it's done by illuminating the target object with a laser, and directing half of the original laser beam directly at a photographic plate while the other half bounces off the target object and from there on to the same plate, leading to an interference effect.

I think that given my model as specified above, I would have to say that it would make no difference if the target object is a vampire. The R-photons going through the vampire would miss the plate, and wouldn't affect it even if they reached it; the S-photons bouncing off would hit the plate and affect it as normal, since the plate changes state in response to photons and hence clearly qualifies as a sensor. Hence, you can take holograms of vampires in exactly the normal way.

[gerald_duck]

What happens to the energy in a photon incident upon a vampire?

I see three possibilities:

1. Both the R-photon and S-photon carry all the energy of the plain ol' photon.
   
2. The R-photon and S-photon each carry some proportion of the energy.
   
3. The energy goes Quantum (hand-wave) and is found by the first person to go looking for it.

(1) has the obvious problem that it violates conservation of energy; (2) has the problem that objects viewed in a mirror through space occupied by a vampire will look dimmer and/or vampires will themselves look dimmer when viewed directly; (3) avoids that objection, but only until both the reflection through the vampire and the vampire are simultaneously observed.

Thinking about it further, the only option that makes sense is (1), with the vampire acting as an energy source — maybe that's why vampires can't cope with sunlight? But even then, where does the energy go when an R-photon hits a sensor or an S-photon hits a mirror?

[simont]

Yes, this came up in the pub. My best answer was that the vampire must heat up or cool down as required: if both the R- and S-photons end up interacting with something then the vampire must lose energy, and if neither does then the vampire must gain energy. Unfortunately that gives rise to an obvious thermodynamics problem (shine bright light on a vampire such that most of the generated R- and S-light actually ends up being used, and the vampire must eventually chill to absolute zero in defiance of 2LoT – and then what happens if you continue to shine light on it?), and also a worrying action-at-a-distance effect. Though the latter at least might have interesting applications in long-distance communication; hmm.

[angoel.livejournal.com]

You can set up unevesdroppable communication key by sending polarised photons to a receiver. You could do the same using a vampire to block or not at one end, and using a mirror or not to observe at the other end.

Reflective vampires could be used as a power source. Sending a beam of light at them, and absorbing the light that bounced off them, and (by use of a mirror) the light that went through them would give, assuming >50% solar panel efficiency, a greater power output than input. Indeed, stick a reflective vampire in the lasing compartment of a laser minus the laser hole, and you'd get energy out with minimal input energy.

The latter probably means that reflective vampires don't exist; in order to exist without violating the law of conservation of energy they'd have to wear non-light-absorbing black clothing. This would probably be sufficient, provided they avoided reflective surfaces such as items of silver and bodies of water...

[gerald_duck]

Ooh — I've thought of an application!

Provided we are agreed that an optical fibre behaves as a mirror for the purposes vampirism, shining R-photons into a fibre make photons come out the far end.

Therefore, you can perform a vampire-in-the-middle attack on quantum cryptography: the endpoints see no difference with an interposed vampire, but you observe the stream of S-photons reflected off the vampire.

[simont]

Ooh, yes, I think I believe that. Nice one!

[cartesiandaemon.livejournal.com]

I thought of an application on the way back. Communication. Assuming you have some sort of time synchronisation, there are four sorts of photon you might send: photon, no photon, R-photon, and S-photon. These fulfil both possible axes of "visible directly" and "visible in a mirror".

Thus you can use the standard quantum polarisation cryptography technique of sending bits according to a randomly chosen axis, the other chosen randomly, and the receiver determining the value on a random axis, and then later collaborating, publicly to work out which half of the bits were sent and measured on the same axis, which are known to sender and recipient, and then comparing a small proportion of them to determine none have changed. (As any eavesdropper will lose information, due to eg. looking directly, and then not knowing if the photon would have been visible reflected off a mirror or not.)

I couldn't work out why this was better than the quantum angle, but gerald_duck helpfully provided that :)

[gerald_duck]

But does the No-Cloning Theorem pertain? I think not: you can simultaneously detect all four possible states by using a mirror-vampire. That would give you a reflected R-photon iff an R-photon or photon was incident and a passed-through S-photon iff an S-photon or photon was incident.

[ptc24.livejournal.com]

Eeep! Why did you have to call them R- and S-photons? Throughout the whole post I was wondering what this all had to do with chirality.

[simont]

I called them R and S because one interacts only with reflecting things and one only with sensors. In the pub I had briefly tried calling them A and B, but found that made it far too hard to remember which one I'd called what.

Oddly enough, I did briefly have a completely different thought which was related to chirality: supposing vampires' invisibility in mirrors was fundamentally a consequence of the mirror reversing chirality, so that a vampire reflected in any odd number of mirrors was invisible but in an even number it was there again. I think that would need an entirely different explanation at the photon level, though, and I haven't sat down and worked one out. (Also, I admit to having blatantly pinched the chirality idea from China Miéville.)

[atreic.livejournal.com]

I have nothing more to say, but this discussion is _fabulous_

[oedipamaas49.livejournal.com]

Fantastic. Also, If somebody built this into a computer game engine, they could enable some really neat tricks.

[cartesiandaemon.livejournal.com]

Very portalesque. Especially in the last scene, where you suddenly realise your reverse vampire trousers are a clue, not a bug :)