Could we transmit smells electronically?

Question

We can encode sound and images in radio waves and send them, but presumably there's some physiological reason that we can't easily make a picture or video of a smell. Could we realistically break smells down into "primary scents", in analogy with "primary colors" and encode the information for easy reproduction?

Answer 1

There are only three kinds of optical receptors in the eye, but more than 900 kinds of olfactory receptors. Thus you can encode pictures with the three primary colors, but there is no small set of primary scents.

To transmit a smell via "primary scents", you'd have to create an artificial nose that monitors the response of each of the olfactory receptors, and then at the other end release a chemical mixture that has the exact same response pattern. (You won't find a one-to-one mapping of chemical compound to receptor.)

Answer 2

In expansion to biocs' excellent answer, I would like to highlight some practical limitations of this. Suppose we did manage to create a huge database of exact chemical mixtures which produce all smells recognisable by humans. You would still meet some complications:

• The output device (analogous to headphones or screen) would either need to be able to produce those substances on demand or have a large enough stack of them.
  • The former would require a whole lab built into one device - even with our miniature technology this would probably end up rather large.
  • The latter would require you to regularly stock up on all of the substances. You could sell these in an all-in-one package (again size becomes a problem) or in smaller "smell sets" (possibly practicable - but it would take a long time until people would understand what this is about)
• The "smell substances" have to get to your nose somehow. At the same time, you probably don't want them in the rest of the room: While sound boxes are no problem because sound disappears rather quickly after being produced, smell can stick around for longer. The solution would be an apparatus that you insert into your nose. Not very practical, but people might do it.

I can't think of more at the moment but there probably are :)

Answer 3

In my view, the reason we can't transmit smell is that we don't understand it. That is, we don't have a solid understanding of how odor information is coded, so it is hard to imagine how to build a system that could reproduce that information.

This is sometimes discussed in terms of a multi-dimensional "odor space," where each odor could be described by its location along each dimension. The problem is that we don't really know what any of the dimensions are. By contrast, we know that visual space can be described by the intensity of a set of colors in a two-dimensional plane; auditory space is described by frequency and amplitude. It is clear that odors are comprised of chemicals, but we don't yet know where those chemicals fit in odor space. Understanding the odor space is a prerequisite to building a system that could transmit messages from it.

Also, to a great extent, how to engineer a smell transmission system is only partly a biological question. For instance, a CMYK printing system does a fine job at generating images that our RGB photoreceptors understand just fine. A telephone wire can transmit sound without a care about how the cochlea actually works. Transmitted pictures and transmitted sounds work because they activate our photoreceptors and auditory hair cells in the same pattern that the original images and sounds would. We can build systems to do this because we understand the nature of the information sensory systems decode, and we don't need a really deep understanding of the physiology to do that. (Of course, I think figuring out that physiology is great fun, but that's another point.) That is, to build a smell system, it's probably not really necessary to know what every one of the many olfactory receptors does. That's a detail of the way the mammalian olfactory system evolved. The important thing is to understand the nature of odor information. Then it really may be theoretically feasible to create a system to transmit odors.