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A sense is something that provides an organism with information about its surroundings. Humans have the five senses, sight, hearing, smell, taste, and touch (sensing pressure). However, some creatures also have electrolocation, where they are able to detect electrical fields.

I'm trying to come up with different senses to give my alien races to make them seem more, well, alien.

What other senses are there, if any, that I have not already named? Are there any other ones possible?

Note - Echolocation I am considering as simply very good hearing. Also, I don't want answer about some kind of "sixth sense" like knowing someone is watching you, or telepathy, or anything like that.

Edit - I am looking for external senses, that tell about your environment, as opposed to senses that tell you about your own body, like thirst or the sense that tells you were your body parts are.

Edit 2 - I'll concede that sonar is different from hearing, since it gives you a kind of image of what you're screaming at instead of just listen ending to tell the location of things.

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Would you consider subdivisions separate senses? Like a species that had two kinds of eyes, one that can see spectrums from yellow up to infrared, and the other can see from blue down to UV. Or a sense of temperature that is separate from sense of touch? – Xavon_Wrentaile Feb 29 at 4:53
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Well, I linked to it because you talked about the "five senses" in your question. So, you want external senses only? – sumelic Feb 29 at 5:33
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If echolocation is just "good hearing", wouldn't smell just be "good tasting"? I think it's kind of silly to assume an alien would have the same delineation of senses we do. I doubt a sapient bat would consider echolocation and hearing to be the same sense. And hearing is just a different kind of touch. So we really just have EM sense, pressure sense, and chemical sense, with pressure and chemical separated into near and far detectors. – MichaelS Feb 29 at 7:33
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Humans have about twenty senses, not five. There's pressure, itch, thermoception, proprioception, tension, pain, balance, hunger, thirst, etc., etc. – Mike Scott Feb 29 at 12:22

12 Answers 12

I think we can go two ways with the question.

Perceived Senses
The first way is to assume "sense" refers to a set of inputs that we perceive and process as some type of information. So vision would be considered a single sense, smell a different sense, etc. In this case, humans have sight, touch, taste, smell, hearing and balance as base senses, along with the possibility of electric and magnetic senses most of us don't pay attention to (if they exist at all). And all the subdivisions of those senses, such as touch giving us sensations of temperature, texture, pain, pressure, stroking, etc.

This way, the question becomes too broad, as there's really no limit to things. An alien could sense magnetic fields in a way comparable to our sense of vision, while EM radiation could just be felt as some kind of environmental pressure. This alien might see a server room, with all it's tiny little magnetic fields forming and dissipating at high frequency, as a disco dance floor, while only being mildly aware of the difference between a brightly-lit field and a dark cave.

Underlying Physics
Another way is to look at what we're actually perceiving, regardless of how we perceive it. So sight is some method of perceiving EM radiation, touch is a method of perceiving direct pressure, sound is a method of perceiving mechanical pressure waves, etc.

In this case, the question is still going to be broad, as there are a lot of grey areas. Sound is ultimately just a form of touch, for example. But we could list a few basic things to detect:

  • EM radiation.
  • Direct pressure.
  • Vibration.
  • Acceleration.
  • Chemical interactions.
  • Electric fields.
  • Magnetic fields.
  • Temperature.
  • Radiation. (Shamelessly stolen from Bryan McClure's answer.)

Of course, these things could be perceived in any number of ways, affected by the spatial, frequency, and amplitude resolutions of the sense in question. An alien who has multiple vibration sensors touching the ground could sense the phase difference between the incoming vibrations to determine the direction and distance of the vibration's origin, for example. With enough sophistication, it could make a 2D map of the ground in a wide radius by inferring reflections, frequency shifts, etc.

And the senses aren't stand-alone. Our sense of spatial awareness pulls information from both sight and sound on a regular basis, while having negligible input from our sense of taste. An alien could potentially smell the "color" of a tree as being distinct from that of a rock, and combine it with some type of echolocation to paint a picture of its environment more detailed than either sense alone could give.

And I think this is how you would make an alien seem alien. It's not that an alien is going to see using some mystical magic field we've never heard of, but that the alien senses its environment using the same senses we have, in ways we wouldn't normally think about.

On Earth, all the magnetic sensors we know of use our planet's magnetic field as a means of north/south orientation. If the alien lives on a world with rapidly changing magnetic fields, it could use the fields to track prey, determine the time of day, communicate with friends, intimidate foes, decide a cold front is coming in, etc. And the possibility of a world with a globally-aligned magnetic field used for direction sensing could elicit a response of "Whoa dude, what kind of alien world would that be?"; "I know, right? We should lay off these mind-altering light patterns."

Mystical Magic Fields
Of course, if you want to introduce magical effects, there's no real problem. It's your story, after all. Just try to keep them consistent. And a good way to do that is to start with human senses, and figure out how they work.

You want a magic field that tells your aliens when other aliens are angry? Well, make it so certain chemicals that cause the "anger" emotion release magic "photons" of certain frequencies. Of course, it's probably more complex than that, since there's unlikely to be one, single catalyst for anger. Instead, the aliens would see (feel/smell/whatever) a combination of magic photons of different intensities and wavelengths. Just like "sky blue" is a fairly even mix of green and blue with about half as much red but humans just see a color, "anger" could be some particular mix of adrenaline, various endorphins, and so forth.

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Temperature (or more correctly, heat) is also a base sense since it isn't related to touch. You can feel that something is hot without touching. In a sense, our heat sense is a sort of radiation sense: sensing infrared radiation. – slebetman Feb 29 at 10:53
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@slebetman: What we feel is that our skin is getting warmer or colder. This could be related to incident EM radiation, but it's most often related to the temperature of the air around us or an object we're touching. Even when you put your hand near a burner to detect heat, you're mainly just feeling the warm air, not EM radiation. Also note that any radiation absorbed makes us warmer, not just infrared -- in fact, walk outside and most of the heat you feel from the sun is visible light. So I called it part of "touch", because I think that's how most people perceive it. – MichaelS Feb 29 at 11:05
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But, it does illustrate how "underlying physics" is a grey area. In some ways "temperature" is just really high frequency vibration, which itself is high frequency direct pressure, which itself is sensing the electric fields of a billion billion electrons. In other senses, temperature might well be EM radiation. For that part, I was just trying to come up with some baseline things we would typically consider different on a macro scale. – MichaelS Feb 29 at 11:08
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Actually, we cannot sense temperature. We can only sense heat - which is a different thing. A table and a spoon in a room both have exactly the same temperature (you can test this with a thermometer) but the spoon feels cold and the table is not cold. – slebetman Feb 29 at 13:56
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"An alien who has multiple vibration sensors touching the ground could [..] determine the direction and distance of the vibration's origin" - Elephants do this already, in the real world. – BlueRaja - Danny Pflughoeft Feb 29 at 17:03

Humans actually have 9 senses, not 5. The first 5 are the traditionally recognised senses:

  1. Sight
  2. Hearing
  3. Smell
  4. Touch & pressure
  5. Taste
  6. Heat
  7. Balance, acceleration & gravity
  8. Kinesthetic (the sense of where our arms, legs and various body parts are)
  9. Pain

In animals and plants here are the other recognised senses:

  1. Electricity
  2. Magnetic field

I honestly can't think of any other senses that may exist. However, some of the senses above may be refined further to extraordinary levels:

  • Sense radio waves (sight?)
  • See into the extreme ultraviolet and infrared (sight)
  • Sense presence like a sixth sense (touch or sound - it could develop from either since both are pressure senses)
  • Sense heartbeat/life like a vampire/zombie (electricity - dolphins and some sharks actually have this)
  • Sense tremors/earthquakes (touch)
  • Sense health/disease (smell)
  • Hear infrasound (hearing)
  • "See" in the dark (sight/infrared or hearing/echolocation)
  • See through walls (sight/xray)
  • Sense mass/gravity sensitive enough to feel objects around you (acceleration)
  • Smell water
  • Taste poisons (we've partially evolved this - it's why we hate bitter foods: most natural poisons are bitter)
  • See polarized light (sight)

Radio waves is a bit odd. While a radio antenna might be technically labeled a photoreceptor we don't normally think of them that way. So one might imagine a completely different sense for radio waves. Imagine an animal with a built-in passive radar.

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The problem with sensing radio waves is that the sensory organ must be a significant fraction of the wavelength of the energy to be sensed. (I don't know the specifics in optics, but in radio, approximately half a wavelength is a very good rule of thumb for simple dipole antennas.) This isn't a major issue when the energy to be sensed has a wavelength in the several hundred nanometers range, but it becomes a problem when the energy to be sensed has a wavelength in the several decimeters range or longer. (30 MHz is a wavelength of 10 meters; 300 MHz is a wavelength of 1 meter.) – Michael Kjörling Feb 29 at 8:57
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@MichaelKjörling: I'm thinking 2.4GHz -- radar, wifi, bluetooth etc = 3cm for a quarter wave antenna. Which is very well within the physical sizes of most animals. – slebetman Feb 29 at 9:24
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A single "antenna" (of some kind) will only, at best, tell you that RF of approximately its resonant frequency (or any integer odd multiplier thereof) is around: not very useful. To be able to tell where it's coming from, you need something much larger, because you need to get at least reasonable directionality. By then, you also start limiting the useful frequency range further. Compare for example How to find the front-to-back ratio given an antenna radiation pattern diagram?. – Michael Kjörling Feb 29 at 10:32
    
@MichaelKjörling: Not really that big. We've been using dual and triple antenna trackers in the RC community to point the antennas of video receivers for FPV flying for some time now. The setups are not too bulky. Also, if you can move (especially if you can move really fast) you can paint a reasonable picture of your environment from passive radio signals by taking periodic samples at different points in your path. A few people have built prototypes but you need quite a lot of processing power. Processing power isn't something nature can't solve. – slebetman Feb 29 at 10:46
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The correct name for 8) is - Proprioception – SeanR Feb 29 at 12:55

TL;DR

Everything that can be measured can also be a sense.

Short explanation

  • Take a data source of your choosing.
  • Feed the data to a neural network (brain).
  • Let the network make sense from the data it receives.
  • You have created a new sense.

Long explanation

Neural networks are incredibly well suited for taking in complex (historical) data and allowing you to make statements about a new data point based on previous observations. This holds true both for artificial neural networks used in machine learning as well as for the neural network in humans we call brain.

If you are interested in learning more about potential new senses in humans – or generally senses an organism could have – you should check out David Eagleman's 2015 TED talk "Can we create new senses for humans?".

He shows how you can use technology for what he calls sensory substitution – e.g. giving deaf people a sense of hearing – and sensory addition – i.e. tapping into data humans cannot naturally perceive and creating artificial senses.

He developed a vest fitted with several vibrating motors on it's back. Using a microphone to get auditory data which was translated into a complex pattern of vibrations of the different motors – too complex to consciously grasp – he enabled a deaf person to recognize how certain patterns correspond to certain words spoken. This was achieved after just a few days of training.

He also managed to "extend" the senses of pilots to a remote-controlled quadcopter by streaming flight data to the vest.

Two more applications mentioned in his talk:

  • Stock market data from the internet
  • real-time results of text analysis of twitter feeds (positive/negative) during his talk

This all just goes to show you there is basically unlimited potential for creating senses.

Some more ideas for senses and applications:

  • sensing density of materials – side note: human echolocation already allows you to do this.

  • sensing structural integrity, e.g. know when a building is about to collapse

  • sensing chemical composition – think spectroscopy or super taste sensing objective rareness – although humans can recognize something subjectively as being rare from their personal experience, if you get fed data measured globally you could sense things as being rare independently of you having encountered it individually. Note: The description of the "rareness sense" is intentional vague to convey how abstract and intangible a sense could be.

However, if the fictional organisms you are designing should have a naturally occurring form of sensory perception, you have to think of a plausible low level mechanism that generates the data, i.e. some receptor is excited in some way due to some phenomenon.

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Ability to "see" heat. We have machines that can do that, and certain animals have similar abilities.

Depending on what environment your aliens come from you could have creatures that can sense the presence of radiation. This could be particularly useful for creature living in a very radioactive planet. Maybe through some form of sight or smell. This ability would call them to sense radiation from far away and avoided it.

Read a book once where an alien had the ability to sense "Mass" the details weren't exactly explain though.

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Several have said that humans have more than five senses, but based on your statement that you consider echolocation just very good hearing, you could say that really we have only 3 senses: electromagnetic radiation (sight, temperature), chemical reaction (taste and smell, acidity), and kinetic energy (touch, hearing).

One could imagine extending any of those, such as:

Sensing radio waves or other parts of the EM spectrum.

Sensing heat in a way that allows you to "see" a picture of the heat sources around you, like night-vision goggles.

Perceiving other sorts of chemicals, like being able to "see" or "smell" chemicals produced by other living creatures, and so literally "smell fear", etc. Or being able to look at the ground and see where there are metal ores or oil.

Feeling other forms of motion or vibration, like sensing subtle air movements, e.g. know what weather is coming, subtle ground movements, e.g. know an earthquake is coming. Or know when things are moving near you by changes in air pressure.

Directly sense magnetism.

What senses could one have that go in a totally different direction?

Someone mentioned sensing gravity. (Whether there is such a thing as gravity waves or not, one could still discuss sensing a gravitational field.) This could tell you your altitude if fine enough, which might be useful. Not sure what else it would do for a creature living on a planet. If the creature can travel in space, either naturally or in a spaceship, this becomes more useful.

Directly sense nuclear strong and weak forces? I'm not sure how that would work or be useful to a macroscopic creature.

You mentioned you're not looking for telepathy and such. That reminds me of a story I read years ago by Murray Leinster, I forget the title, where humans meet aliens, and they learn that the aliens communicate by broadcasting microwave signals between their brains. And one person says, "They have telepathy?" And another replies, "Sort of. But from their point of view, we have telepathy, because they've never thought of sound as a means of communicating." Which I thought was an excellent point. To aliens who do not have ears, the idea of communicating by generating and receiving sound waves might seem like a mysterious psychic phenomenon.

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Beyond the basics:

  • Extending visual into ultraviolet/infrared
  • EM fields, sense hidden creatures/active electrical devices.
  • Magnetic fields, never get lost.

You could have more complex options:

  • Ability to distinguish between acceleration and gravity: I can't see a use for this, but why not given that the theory of gravity says it's impossible.
  • Sense tensions in structures and materials: Allows you to see where something will break, or even predict earthquakes.

You could even give them different ways of interacting with the same information. Seeing infrared is an easily understood example, we can feel heat, but if you can see into infrared then you can "see" heat. As my father used to say:

Don't talk to me in that tone of voice, it smells a funny colour.

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Note that heat and infrared aren't the same thing. All objects are "hot" to some degree, and they all emit EM radiation as a result. Hotter objects emit more energetic, shorter wavelength light. Objects at normal Earth temperatures happen to primarily emit light in the mid IR band. Objects at the Sun's temperature primarily emit visible light. If your eye could see infrared light, the brightest thing around would be itself, without some kind of intricate cooling system. – MichaelS Feb 29 at 11:38
    
What you say is true. I shall tweak accordingly to make it clearer that the one is not entirely the other. – Separatrix Feb 29 at 11:59

There are some things I could imagine:

  • See Radiation
  • Night vision or similar

or my favourite:

See in four dimensions! It is very unlikely that this would be possible, but we once thought the earth was a plate :)
No human could ever get or imagine how this would work or even worse how it would look from their point of view. But this would really make them to some super aliens, so if you're going the let your protagonists fight those aliens you'd better chose one of the other additional senses :)

PS: English isn't my native language (as you can easily tell) so feel free to correct my typography/grammar

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Night vision is just vision. We have plenty of species on Earth that have very good low-light vision without having any extraordinary sensory abilities otherwise. – Michael Kjörling Feb 29 at 8:27

Perhaps there is an alien race that has an extremely sensitive organ that can sense gravity waves. Consider that we have recently detected them with LIGO:

https://www.ligo.caltech.edu/news/ligo20160211

Gravity waves are an entirely new way for astronomers to "see" things in space. So maybe these alien can sense gravity waves the same way we feel the wind on our skin? And perhaps the more fierce the gravitational event, the greater the sensation?

For example, the gravity waves we detected from LIGO were from the most intense moment of when the two black holes were colliding, called "ring down." Consider that to detect this "crest" of the waves coming out of this event, we needed an event as violent as two black holes colliding, each of which are many, many solar masses swinging around each other at 1,000 revolutions a second before they collided. The rest of the waves from the event were too weak to be detected by LIGO. So these aliens' senses would have to be attuned in such a way that the noise from all the gravitational perturbations in spacetime wouldn't overwhelm them.

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The problem with gravitational waves is that we use circular reasoning to prove they are indeed gravitational waves. We say Einstein's theory says X, and if it says X then Y is true, and if Ynis true then X is true, so it is all true. Although this is a nice idea. – XandarTheZenon Feb 29 at 5:34
    
Hmm if you apply the semantics of what you just wrote to any physical theory, it becomes "circular reasoning." Certainly observation counts as evidence? Do you have a different definition of science? – alkah3st Feb 29 at 5:57
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I'm really hard-pressed to think of any way this would be useful. I'm coming up with pictures of an alien world orbiting a pair of neutron stars with some kind of periodic destructive pulse, and predicting the pulse by counting the star orbits via gravity waves would be good. But if the world were hospitable enough to survive long enough to evolve gravity wave sensors, the creatures would just evolve something that worked a million times better for a thousand times less energy budget. – MichaelS Feb 29 at 7:38
    
This is not going to happen, unless you are talking about creatures the size of planets. See "Could a species evolve a biological gravitational wave detector?" for details. – Philipp Feb 29 at 13:06
    
I'm just saying it may not be a gravity wave, we supposedly detected a wave from two celestial objects crashing, and we think it made the earth a millimeter bigger. It may not actually be a gravity wave, it could be something else. But by Einstein's theory, that's what it is, so that is what we assume the wave is. – XandarTheZenon Feb 29 at 14:38

What about a chemistry sense? This would work in a manner similar to taste and smell, but to a far more accurate degree, so it could tell you the proportions of different elements and chemical structures in your surroundings. Basically a creature that evolved to understand and use elementary chemistry on an instinctive level, and would know immediately upon sniffing two different chemicals what would happen if you combined them, even if it had never encountered them before. Since chemistry is basically applied mathematics, it is not impossible for an organism to have such an ability, and would certainly lead to a very alien way of seeing the world. Bonus points if there are non-sapient organisms on the planet that have this ability as well - you don't need to be sapient to 'understand' the rules of Newtonian physics.

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Like others have pointed out, humans have more than five senses. But this knowledge isn't really useful for making an alien species with new senses. Instead, take a look at some other animals. Some animals have senses humans don't have, and others have the same senses that humans have, only more sensitive and with lateral application that would make you think a comic book author came up with them. Echolocation is a great example. Another good example is roaches having Spider-Man's "spider sense".

Another good idea is to look at the problem the other way around. Think about the environment and what information about it we can't directly observe. For example, imagine if we could sense germs. Well, that would suck on Earth but maybe not wherever your species is from.

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this has been said before, but after a certain point you start to run out of different ways to input data about an organism surroundings in ways that are meaningfully different. maybe try to change what the aliens do with the information that they receive? you could have a race that only processes data on a subconscious level, and literally cant recognize the physical world. maybe the aliens think at a wildly different timescale than humans. or maybe they perceive the world in some even weirder way, something so far removed from our human thought processes that they can barely be said to live in the same universe? who knows! (apparently not me)

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I'm surprised nobody has mentioned sensing the passage of time, although that's hardly alien. One odd manifestation here on earth are the various N-year cicada broods. If they do not count (which seems unlikely) they have either a number sense or a remarkably accurate longterm clock!

The other thing is that a cetacean's sonar sense is almost certainly very much more than "enhanced hearing". It is a form of seeing, but very different in what can be perceived. At its simplest, most objects (food, people) are opaque to visible light. Ultrasound goes through them, reflecting in complex ways at boundaries. Interpretation will give a 3D map similar to a CT scan.

So a dolphin can almost certainly see other dolphins' internals. Stomach and bowel contents. Pregnancy. Tumours. Heartrate and muscle tension. Also very probably their own internals. I wonder whether it is possible for a dolphin to lie? On top of that it may be possible to directly create sound signals having properties something like a low resolution hologram in another dolphins sonar view. This might be as close to telepathy as is physically possible. Far beyond speech as we know it.

I say dolphin but we still do not know how smart our dolphins are. Too alien to understand? Or not quite as smart as we think or hope? If alien "cetaceans" have achieved technology despite the handicap imposed by an aqueous environment it is a fair bet they are considerably smarter than we are.

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