Not a duplicate of "Overcoming language barrier; no speech" which confines answers to nothing that is clearly a form of communication; it focuses on translation, not physiology or evolution

Not a duplicate of "Where Speech is Impossible" which confines the scenario to sign language and asks for justification as to why that would be

Is it feasible for alien life forms to evolve intelligent communication other than"speaking" using sound waves and sensing "speech" by "hearing" those sound waves?

If so, what else is feasible?

To avoid broadness
I am asking for science as close to hard as you can get without needing math or citations; stick to realism, and explain ideas thoroughly. Consider basing answers on Earth species' communication systems as well.

  • $\begingroup$ While I recognize that there is some broadness to this question, the likes of "Would aliens be humanoid" are on par with this - and there are reasonable, narrow approaches to both of these questions. $\endgroup$ – Zxyrra Dec 1 '16 at 2:23
  • $\begingroup$ What level of communication are you looking for? Vague feelings? Detailed conversation? How fast would this communication need to be? $\endgroup$ – Pork Dec 1 '16 at 2:31
  • $\begingroup$ @Pork Edited to say "Intelligent" conversation - not necessarily detailed, but it should be possible to convey complex ideas. $\endgroup$ – Zxyrra Dec 1 '16 at 2:33
  • $\begingroup$ Hellen Keller communicated via touch through her hands, even though she was deaf and blind, and there are people at Gallaudet University today who do the same thing. Steven Hawkings handles outward communication through eye movement directed at a machine that makes a noise, although he receives inbound communication via sound. I am communicating with you through a machine using my fingers on a board and my eyes to read what you say through a machine. I could do the same by writing on paper in your view and seeing what you write back on paper. $\endgroup$ – ohwilleke Dec 1 '16 at 7:10

Radio is possible at least hypothetically, the simplest types of radio, crystal radio are structurally simple and don't need power to receive and there are animals that incorporate crystals into their tissue. it's a stretch but not an impossible one. Would really mess with a human observer too it would look a lot like telepathy. MIT cas produced radio reactive biological molecules so you know it is at least possible.

pulses of light are another option, basically think morse code with bioluminosity, there are plenty of deep sea organisms that can emit light in patterns. a side benefit is light can be focused much easier than sound so they might not have problems with people overhearing their conversation.

Smell is possible but unlikely, it's just too slow and limited for complex conversation.

Journeyman mentioned squid aka cuttlefish can use color and pattern, and can even say one thing with the left and another with the right side. I couls easily see this evolving in to full blown conversation. http://dlkr7699fk9jt.cloudfront.net/content/roybiolett/8/5/729/F1.large.jpg

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    $\begingroup$ Thisis nice, "there are animals that incorporate crystals into their tissue." Can you show an example? $\endgroup$ – Hariz Rizki Dec 1 '16 at 6:28
  • $\begingroup$ Smell is used for communication by many mammals (trees are the Internet for dogs) and chemical exchange and visual movement patterns are both used to communicate by bees and ants. $\endgroup$ – ohwilleke Dec 1 '16 at 7:06
  • $\begingroup$ Radio communication is unlikely to evolve naturally, as there are no reliable sources of radio in nature. I also recall reading that for an organism to absorb enough radio to carry a meaningful signal it would have to be tens of metres in length and breadth. $\endgroup$ – rek Dec 1 '16 at 16:51
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    $\begingroup$ @rek only if it tried to see in radio, just picking up pulses is not that hard the necessary crystal is miniscule. It would have to be coincidental at first, but a lot of biology starts that way. I could see a organism producing a crystal for some other purpose that turns out to be a radio receiver. Stars do emit radio, some more than others. It might even evolve at first as protection against ionizing radiation be detecting spikes. $\endgroup$ – John Dec 1 '16 at 21:00
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    $\begingroup$ there you have a choice you can go with a crystal oscillator or you can use a coil, bacteria can generate radio using DNA coils. arxiv.org/abs/1104.3113. basically any process that can generate visible light can at least hypothetically also generate radio if scaled up. $\endgroup$ – John Dec 2 '16 at 22:40

To some extent, cephelapods communicate by colour. In theory, deaf people communicate through the manipulation of EM waves - aka sign language. While Probably completely alien to us these are the 'simplest' modes of communication and pretty much have reasonable 'bandwidth', specially with more adapted limbs or other body parts. For example you could get far more combinations of 'words' or 'letters' from a limb with a reasonable amount of prehensile sub-components, colour and even texture than from a human hand.

While communication by pheromones, or smell is another possibility, the need to wait for the chemicals to dissipate makes complex communication hard.

  • $\begingroup$ Humboldt squid can get pretty complex it helps that they can control color and pattern on their skin. some octopi take even further and can change texture as well. What's even more impressive is the squid can say one thing with the left side and the exact opposite with the right, so possibility for two simultaneous conversations. $\endgroup$ – John Dec 1 '16 at 4:26
  • $\begingroup$ Cuttlefish in particular have very intricate systems for changing their skin color and even making complex patterns. If they were as intelligent as humans, I think this would absolutely be a feasible means of communication. $\endgroup$ – Charles Burge Dec 1 '16 at 21:22

There are three communication channels which are able to carry reasonable bandwidth: mechanical vibrations in the surrounding fluid (or transmitted by direct contact), electromagnetic waves, and optical changes (shape, color, albedo). Humans commonly use mechanical vibrations (speech) or shape changes (sign languages). We don't use electromagnetc waves because we cannot control their generation (we do generate electromagnetic waves but they are not under volitional control) and we cannot sense the electromagnetic waves generated by other persons.

There is nothing stopping an alien species communicating through electromagnetic waves, either in their visible spectrum (using bioluminescence to generate them and their visual system to sense them) or in a separate spectrum (using dedicated organs to generate and sense them). Or they can communicate through color changes, maybe localized to some dedicated organ.

If you allow the aliens to require direct contact in order to carry out a conversation then you can imagine some sort of direct communication between their nervous systems, using for example dedicated patches on their tegument; this is much more tricky because as far as we know the operation of synapses requires a very strict alignment between the relevant parts of the neurons -- Wikipedia says that the gap between connected neurons is 20 to 40 nm wide for chemical synapses and 3.5 nm wide for electrical synapses. (For comparison, the wavelength of green light is 555 nm.)

  • $\begingroup$ An example of bioluminescence communication is fireflies. They make signals with their biolights that communicate things to other fireflies (clever humans can even spoof this system). $\endgroup$ – ohwilleke Dec 1 '16 at 7:04

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