I swear I saw this question elsewhere. Let me know if this is a dupe.

Photons are great. They're little bundles of energy that

  • Reflect off of nearly everything, allowing us to see faraway objects that don't necessarily produce their own light
  • Are practically everywhere, allowing us to see most of our world
  • Are somewhat easy to detect
  • Don't kill us (most of the time)
  • Provide detail (in the form of colors/different wavelengths)

I'm interested in replacing them with a different particle for a fictional species - but I don't know if anything else matches the above qualities.

What particles, real or theoretical, would meet the above criteria well enough to provide adequate vision, besides photons?

My thoughts so far have been about neutrinos (although they are hard to detect), positrons (annihilate themselves) and gravitons (hard to detect).

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    $\begingroup$ So, are sound waves out? They're not really a particle, but they have no mass like photons. $\endgroup$ Dec 25, 2016 at 14:53
  • $\begingroup$ @XandarTheZenon I suppose waves can be workable even if no particle is associated with them - but something besides sound would be ideal for the whole "alien" affect $\endgroup$
    – Zxyrra
    Dec 25, 2016 at 15:02
  • $\begingroup$ Well, while not really based on perceiving a particle, hyper and sub-sonic echolocation, as well as electroreception are viable options to seem alien. $\endgroup$ Dec 25, 2016 at 15:21
  • $\begingroup$ Electric field like the hammerhead shark, so electron maybe. Magnetic field like MRI scan, so charged particle like isotopes and electron again... $\endgroup$
    – user6760
    Dec 25, 2016 at 16:55
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    $\begingroup$ When it comes to tools like echolocation, we often talk about "phonons" which are wave packets of sound energy. In many situations, it is actually effective to think of the sound wave as a bunch of particles! $\endgroup$
    – Cort Ammon
    Dec 26, 2016 at 21:42

5 Answers 5


If it quacks like a duck...

Have you heard of The Duck Test, or so called Duck Typing?

The Duck Test is a type of abductive reasoning, and it works like this:

If it looks like a duck, swims like a duck, and quacks like a duck, then it probably is a duck.

...in other words the appearance and behavior of something determines what we say it is.

Now this may sound silly when it concerns something like waterfowl because one glance at it and we can say if it is a duck or a goose or something else that quacks, waddles and/or looks similar to a duck.

But in the case of something like photons, this becomes decisive, because when it comes to elementary particles it is near impossible to determine if it is a photon or anything else. I mean, have you ever seen an elementary particle and on first glance been able to say "Oh, that's a photon right there... not an electron or a neutrino or a neutron... that is a photon, I am certain by the looks of it"? No you have not, and neither has anyone else.

Phrased slightly differently you asked the question: "what can I have that behaves like a photon, but is not a photon?"

Well... you cannot. Because if it behaves exactly like a photon, then for all intents and purposes, it is a photon. And even if it was not actually a photon, there is no way we can say that it is not, so you might as well treat it exactly like you would a photon.

For all we know, "photon" might actually be two, ten, a thousand, or billions of different types elementary particles. But we cannot tell them apart, so we just say they are "photons", all of them.

In short: we define particles by their behavior, because truth be told: no-one knows what a photon or any other elementary particle actually is. We only know how it works and behaves. And so we say that anything that behaves like a photon, is a photon

So is there any other particle that can behave exactly like a photon while not being a photon? No, there is not.

Hence the question becomes: what other particle could produce something like vision? Well, probably none at all really.

  • Electrons... are out of the question because they do not go very far in any kind of atmosphere, and they are hard to emit.

  • Neutrinos... do not interact with (nearly) anything so even though they are more omnipresent than photons they are useless as vision.

  • Protons... is even worse than electrons because they are stopped very quickly by air. Also they are highly ionizing (i.e. the mechanism that makes radiation very harmful) so you do not want to try to use that.

  • Neutrons... are even worse because not only are they ionizing, they also transform atoms they hit into other elements, some of them very unstable, and therefore radioactive.

  • ...and so on, down all of the list.

So in short: of all the known particles, none do the job of photons as well as photons themselves.

...and then there is Chekhov's Gun.

Remove everything that has no relevance to the story. If you say in the first chapter that there is a rifle hanging on the wall, in the second or third chapter it absolutely must go off. If it's not going to be fired, it shouldn't be hanging there.

— Anton Chekhov

What do you need this alternate vision for? Is it something that is relevant to the story, or is it just a fun gimmick you are throwing into the story for the heck of it?

If so: do not do that. Do not throw in stuff that are not actually important for the setting, the flavor or the elements of the story. Readers will quickly see through that and recognize it as a bolt-on filler that does not actually add to the experience.

If you do need it for the story however, then you can make up anything you want. But then you need to make it behave different then photons, because if they radiate like photons, refract like photons, reflect like photons, and make you see like photons do... then they are photons.

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    $\begingroup$ I appreciate the answer but the question does not say "exactly like a proton"; it asks for particles that can do most of the same things that we have identified to be separate from a proton. That eliminates the need for "if it quacks for a duck" because I have made it clear that it should be a bird that's not a duck that still honks. $\endgroup$
    – Zxyrra
    Dec 25, 2016 at 16:39
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    $\begingroup$ ...and I explained that no elementary particle we know of make a very good job of being a bird either. And then I went on to say that maybe you do not need this story element at all. And if you do, then just hand-wave it, making up any particle you like... but if you do that then you need to make it behave different than photos, because otherwise they are photons. $\endgroup$
    – MichaelK
    Dec 25, 2016 at 16:42
  • $\begingroup$ The catch here is that humans have managed (with the aid of appropriate technology, of course) to use all of your list except for neutrinos for various forms of "seeing". But the OP's question is poorly specified: what environment does the species live in, and what exactly are the requirements for "seeing"? $\endgroup$
    – jamesqf
    Dec 25, 2016 at 19:18
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    $\begingroup$ @jamesqf I am sorry but did you miss that handy bullet list that OP provided? If you apply that to these other methods of "seeing" you will quickly find that they do not fulfill even that simple list. $\endgroup$
    – MichaelK
    Dec 25, 2016 at 20:36
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    $\begingroup$ You forgot the most important part of the duck test: if it weighs the same as a duck, then it's a witch! $\endgroup$
    – Mrkvička
    Dec 27, 2016 at 20:44


Since this question is tagged with "Xenobiology" and "science-based" it is best to keep in mind that possible solutions don't equate with plausible solutions and that using real science terms to explain unplausible science-fiction doesn't really do anything to help with suspension of disbelief. (e.g. saying "the alien vision relies on entangled neutrinos" isn't much less hand-wavey than "the alien vision relies on flubulated tachyons".)

Making aliens extremely unique in their biology in order to avoid inventing more fictional aliens that "look like us" is a good habit, as assuming that all aliens (especially the sentient ones) are humanoid bipeds is a laughably anthropocentric of us. However, it is possible to overshoot the mark and make aliens too weird to exist by all logical accounts of what we do thus far know about physics and biology.

Photons: If it ain't broke, don't fix it.

If you have life you have heat, and if you have heat you have photons. Therefore, if you have life you must have photons. There is no escaping this. Photons also interact with the building blocks of matter: the protons, neutrons, and electrons that compose all biological life.

Because photons are so ubiquitous, it is very likely organisms develop some way(s) to interact with them. On Earth this is mostly evident in plants which are able to use the energy for photosynthesis, and most higher-level organisms which posess occular organs which are used to collect directionally-specific photo-sensory stimuli.

While most higher-level organisms posses eyes which grant them varying degrees of occular prowess, the fact is that most such creatures detect only certain wavelength bands covering different sections of the visible photon spectrum. Some creatures are rather primitive only having one color-discriminitory sensor, whereas humans have three, and others like the mantis shrimp have as many as 16 types of photoreceptors. Yet other creatures have other forms of photon detection; pit vipers and many related reptiles have infrared-detecting abilities which effectively allow them to "see heat" in a useful way.

The visible spectrum, as we call it, is actually a rather narrow section of the entire electromagnetic spectrum. Even if you include the infrared heat sensors of pit vipers and the UV sensors of the mantis shrimp, the range of perception for all Earth creatures is still quite limited. Creatures with visual acuity in wavelengths to either end of our chunk of the spectrum (either higher energy like hard-UV and X-ray, or lower energy like far-infrared and microwave) would likely see the world quite differently than us, and feel quite alien, while still possessing a type of directional vision very comparable to what we're used to encountering- and all without evoking any sort of exotic, non-interactive, or exceedingly rare particles.

Additional Options

Echolocation (Back-scatter)

Of course, you might be very loose with your definition of vision in the original post. If you're simply asking for another sense similar to vision without needing that sense to be particularly long-ranged, then echolocation is one possibility employed by Earth creatures which could be sci-fi adapted to other methods of propagation.

Rather than the usual auditory clicking noises used by bats and dolphins, any combination of particles could be used in a similar "ping-then-listen manner to help understand an area. If the particles in question were photons of X-ray wavelength, then the alien would essentially work like an X-ray backscatter machine found in airports. Unfortunately, the return-trip timeframe for electromagnetic signals is extremely fast, so 3D imaging is unlikely to arise from photon-based detection, though a series of 2D images can create a good guess if you have enough differently-positioned eyes generating pictures to compare/contrast.

Electrons or neutrons could be similarly used, though these pings would potentially cause a significant amount of damage (as the animal basically would be shooting electrons out it's eye sockets like a scanning electric microscope, ditto neutrons). Furthermore, the backscatter is unlikely to be any significant fraction of the output beam. Either way these would be problems. (Let alone describing how a neutron-gun organ developed through natural selection.)

Charge Sensitivity / Magnetic Sensitivity

These abilitys occur to varying degrees among Earth creatures, but creating an alien that sees a nearby object by looking at its electric charge or mapping it's magnetic fields. To really investigate a surface would involve moving the sensors around to feel the maxima and minima of the fields- which starts looking more like touch than sight, however.

  • $\begingroup$ Good answer! Though, since you only mention the danger with having an electron/neutron gun in the eye socket, I would like to point out that x-ray backscattering vision would require an x-ray source. While the airport one uses so low intensity thay it is essentially negligible, the aliens would still need to be able to shoot x-rays with their eyes. I suspect I would be the cause of some breast cancer if I had that ability, even with a low intensity ray... $\endgroup$
    – Mrkvička
    Dec 27, 2016 at 11:01
  • $\begingroup$ @Mrkvička Rather than add to the already large wall of text I did gloss over the details a bit. I think biologically-generated electron beams are probably most plausible, followed by bio x-rays (triboluminescence of sticky tape comes to mind) as somewhat plausible, with neutron beams (and other exotic particle beams) being very hard to explain in biological terms. $\endgroup$ Dec 28, 2016 at 8:12
  • $\begingroup$ As for dangers, I would actually consider an xray system more safe than electrons or neutrons. Neutrons randomly transmuting some target atoms presents a problem of turning things into fissile material. Electrons pose a less long-term risk, but I imagine the flux needed for a vision system would just be quite high. Xrays are ionizing radiation, but depending on the energies and exposure amounts it may not be horrible; especially if the creatures' DNA-like-structures are more evolved to deal with random errors caused by xray damage. $\endgroup$ Dec 28, 2016 at 8:22

The great Hal Clement came up with something.

In his story Uncommon Sense, the animals have eye-like structures that are globes with pinholes.

In a vacuum, any molecules given off by something will travel in straight lines, so smell works like sight! The pinhole provided image forming of the scents coming from objects just as reflected light does for us.


Vision is interchangeable with other sensing faculties, it's well known in the Buddhist teaching. Apart from using light/reflection/eyes to gain information, audio, smell, taste, touch are also working in the same way, but just the channel for the input is different. Thus in Vimalakirti Sutra it described a world made by smell/scent, even the buildings and clothes, all are made by scent, so is the language they used to talk to each other. There is another world called Realm of Brilliance of Sound. In it the language is communicated via light, not sound; the food is thought, not milk or bread :).

However, it maybe sexier to think up a term belongs to the physics' terminology or like. It's interesting scientists used "flavors" to attribute neutrinos.

  • $\begingroup$ Let's ignore that the thread is as ancient as Buddhism, I think this is the closest thing to an answer so far. When altering perception in a story, one has to always ask what perception actually is first. I see too many questions here where people think inside the box and not enough people questioning if what they are asking is even defined. I hope Mishu will answer more questions. $\endgroup$
    – Raditz_35
    Jul 3, 2017 at 10:53
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    $\begingroup$ @Raditz_35 Happy is one being understood by another :). Fresh perspective enriches the world, professional/expertise is respected but polymath is one step closer to genius. We shall cultivate all knowledge but empty the mind. $\endgroup$ Jul 3, 2017 at 12:22

I could imagine Neutrinos being used by something HUGE that needed to "see" things on an interstellar scale. This might be out of scope of your question, though, if your alien species is more analogous to earth-life than, say, a lovecraftian planet-sized space-whale.


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