So what goes into a good dose of invisibility?
It’s the stock-in-trade of countless fantasy and not a few sf books and stories. But what is it? I got into a discussion over at the vision list and replied in such a fashion that I thought worth repeating here.
One of the posters said “The problem with invisibility is that it also makes you totally blind. Since your eyes’ photoreceptors work by light impacting on them and triggering an electrical response in the nerves, an invisible eye would allow the light to pass right through, thus rendering the photoreceptors useless. An invisible person is also blind”
Hmm. Only for certain values of ‘invisible’ Only if you conflate entirely transparent with invisible.
Let’s start by defining just what we mean by invisibility
🙂 I assumed – seeing as the discussion is of the physics of making something which should in plain sight that we were all referring to the physics definition of transparent (as opposed to translucent) which would be to allow the unreflected passage of at least certain wavelengths of the EM spectrum (although this would still permit refraction). Something which is perfectly transparent to the EM frequencies we humans see, would de facto be invisible, and many glass doors which are walked into prove we find this to be true. Your contention that the invisible eye would allow light to pass through it would seem to indicate that this is type of ‘invisibility’ to which you referred. However, this is only a small part of the set of possible reasons a human wearing an invisibility ring could remain unseen. One would have to start with what sight is, what was being seen and by whom. What sight is, is a translation to an image of a message transmitted by the nervous system to the brain from photoreceptors in the eye. What being seen is largely reflected light (as most humans don’t appear to emit much visible light, the luminaries of sf excluded) which passes through air (or possibly liquid) to the photoreceptor. That reflected light has bounced off the skin hair and/or clothing of the visible person. To create a situation (purely for the purposes of writing about it, natch) in which the person is unseen, the simplest is to coat that human in writerum (or even just give them a small part-time ring of it) and to have the person trying to see them (in order to pay outstanding royalties or turn in monies) in traditional publishing industry. This has been proven to render the parties owed money invisible and de facto non-existent for years, and always for months. However, in the absence of writerum paint, we could start with each of the steps. Firstly the simplest is the brain where something like a SEP field can make the image rendered invisible. In slightly more technical terms we can force the brain to lie to itself. This is possible by physics and or magic, which could be the same thing. It’s also possible by psychology, which could not. Then there are the nerves and photoreceptors themselves. There are possible ways of interfering with these to make them carry false information, or remove information. Then there is the medium through which the reflected light is transmitted, which could be affected in various ways – some of which could effect light traveling in one direction differently to to the other (thereby making the human who is invisible able to see but not be seen). Simple distortion of light transmission would make it impossible to see anything let alone the invisible person. Then there is the surface of the ‘invisible’ person or object which has to reflect light so that it may accurately be seen. Both chameleon and scattering effects could be used to varying degrees of effective. So could illusionary effects – ‘that’s not a person it’s a bush’. So could transparency (which would leave the the invisible person blind).
And those are just a few possibilities. Then we get onto dimensionality and size… And bankerbunkum which can make unexplained billions just appear in said banksta’s accounts, and they have NO idea how that happened.
Or we could just say ‘what make fire?’ “Aha, MAGIC.” ‘Same thing make invisible’. 🙂