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I want to have an alien species have trouble communicating with the hero(s), I've decided that this will be done in part because they don't even understand the concept of hearing, as in none of the animals of their world has the ability to hear.

While some animals on earth can't hear I would find it hard to believe an evolution of an entire planet will be able to skip such benefits unless there's something making hearing be useless or a hindrance, so I came up with the idea that something on that planet is so noisy that an animal wouldn't be able to hear anything else anyway, making hearing on that planet be a waste of resources and thus never resulting in an evolutionary benefit.

Now the only problem is that I'm stuck with the question what will be able to cause so much noise on a planet to render hearing useless yet keep the planet livable (to the aliens) for an evolutionary time scale?

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    $\begingroup$ There isn't a good answer to this, because noise, if it's consistent, is no impediment to hearing. The ocean is always noisy, but creatures use echolocation in the ocean because they're so good at separating noise from signal. Having constant noise would just create evolutionary pressure to evolve better ears. $\endgroup$
    – jdunlop
    Commented Oct 2, 2022 at 21:47
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    $\begingroup$ Perhaps instead of perpetually noisy, a better "hearing-defeating" environment would be one which is extremely loud at unpredictable intervals. Good luck maintaining a delicate sense organ which will be blown out in the next few hours, or even weeks. Except that amount of explosive disruption would cause damage to other tissues... $\endgroup$
    – Jedediah
    Commented Oct 2, 2022 at 22:03
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    $\begingroup$ @jdunlop First of all, the ocean isn't that loud all the time. The noise level needed to rationalize the OP's goals would be more like a thunderous downpour or a howling wind. But more importantly, Real Life cannot be an overriding limitation on any question unless specifically requested and the OP hasn't tagged this science-based. All we're trying to do is help the OP justify a rule of his/her world. Unless directed otherwise, it needn't be a science-perfect solution. $\endgroup$
    – JBH
    Commented Oct 2, 2022 at 22:31
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    $\begingroup$ If you read E. E. "Doc" Smith's "First Lensman", the title character visits a planet that has this issue. The natives used telepathy and "perception" instead of speech&hearing and sight. As a result, they didn't use anything like a "muffler" on any mechanical device. There is a nice description of what is essentially a taxi ride. Fortunately, the title character was not the first human to visit, so proper defenses (armor) had been developed. $\endgroup$
    – David G.
    Commented Oct 4, 2022 at 2:03
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    $\begingroup$ rickandmorty.fandom.com/wiki/Screaming_Sun_Earth $\endgroup$ Commented Oct 4, 2022 at 13:40

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It all began billions of years ago, when the ancestor of all surviving modern plants first developed. In those times dust clouds covered the sky and little sunlight reached the ground. But there was an intense and constant wind whipping all over the planet. These plants evolved leaves and structures that somewhat resemble windsocks. The tapered end extracts energy from the wind (I don't know how, ask the aliens). Wind-powered plants quickly out-competed the variants using only the dim sun-light. And this spelled doom for the sense of hearing on the planet; as the plants extract wind energy, they also produce a sound not unlike a kazoo, quite loudly, and not well played either. Since billions of years, countless "blades" of grass and "leaves" of trees were trumpeting about.

Animals never had a chance to evolve hearing. With ambient noises ranging from deafening to bone-crunching, there is no useful information in hearing. And even if hearing would be possible - listening to the cacophony of thousands, millions even, off-tune kazoos would quickly induce insanity in anything able to perceive it. A horrible fate awaits any unprotected human...

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    $\begingroup$ Love it, anti hearing evolutionary of grass! $\endgroup$
    – cypher
    Commented Oct 3, 2022 at 15:44
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    $\begingroup$ @cypher Actually, this answer would work well in combination with my cicada answer, because the increased background noise levels would help explain the evolution of audiotroph organisms. The cicadas would bring noise to the places where the wind wasn't blowing. ooak +1 $\endgroup$
    – DWKraus
    Commented Oct 4, 2022 at 2:13
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    $\begingroup$ Marking this as the answer as this will be the solution I'm going to use, "In a world where the grass speaks the loudest..." $\endgroup$
    – cypher
    Commented Oct 6, 2022 at 21:20
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Possible alternative: the planet has no (or a very thin) atmosphere.

Lots of celestial bodies have no atmosphere at all. Sound does not exist in these places, since sound requires a medium. A life form which evolved in this environment would never evolve vibration-based communication.

A noise-less world seems more plausible than a continuously noisy world, as the former is actually extremely common in real life. Of course, this opens up other questions, like how such a species survives on land without air to breathe - but in my opinion, these are easier to explain away. Perhaps this species respires by drinking liquid methane every so often.

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  • $\begingroup$ This could result in an interesting effect: They developed very sensative hearing. Our world is just so damn loud to them. Soft breathing is like a close by explosion. $\endgroup$
    – Martijn
    Commented Oct 6, 2022 at 11:11
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Ultra-Cicadas:

There is ONE species that could hear - a cicada-like insect that once communicated through sound. But a curious symbiotic relationship developed that amped these insects up to absurd levels and has rendered hearing worthless. Any hearing ability has degenerated away long ago.

A Fungus-like autotroph on this planet forms a perfect sheltering environment for these insects to nest in. It insulates in cold climates and cools in hot ones. defends against predation, etc. But it gets energy from absorbing soundwaves. The insects made louder and louder noises in a more sustained way until the environment was incoherently loud. The noise eventually got so loud as to actively select against any species with the ability to hear.

The variety and range of these insects and audiotrophs (?) has spread around the world after a mass-extinction event. All sea life comes from re-colonized land organisms. While there is the possibility of hearing evolving, no current species have done it yet.

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    $\begingroup$ Preys and predators of these cicadas could benefit from hearing to locate them $\endgroup$
    – Headax
    Commented Oct 4, 2022 at 13:32
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In your solar system, something has caused a constant stream of debris to enter the atmosphere of your world. The result is a constant loud rumble or thunder, constantly changing in pitch and volume depending on the debris that enters the atmosphere.

Sound is nothing more than vibrations in the atmosphere. Or, more generally, vibrations in any medium. We humans call it "hearing" when the atmosphere vibrates and "feeling" when something else, like the floor, vibrates.

So the question simplifies to, "what can cause the atmosphere to vibrate enough to lead to limited or no evolution of the ability to hear?"

I'm voting for something entering the atmosphere constantly. As it enters, it causes explosions, rumbles, and thunder-sounding-stuff. If the mass varies from dense streams of dust or pebbles to larger Buick-sized objects, then you get variation in frequencies and volume.

An alternative (and it might even be easier to rationalize than dust/debris) is for energy such as the Solar Wind to cause constant lightning to form on the planet, leading to constant sound.

So, the next question is, what can cause debris to constantly enter the atmosphere over the time scales necessary for evolution?

The lightening might be easier to justify because you could do something like a binary star where one star is stealing from the companion star and the resulting spiral of stellar debris is something the planet must regularly (if not constantly) pass through. This is a fast and kinda tag:Science-Fiction type of answer, but frankly, we're deep in tag:Science-Fiction territory anyway.

So, let's focus on the debris. Planets have a habit of sweeping their orbits clear of debris fairly quickly when we're talking about evolutionary time scales. So this must be something that's constantly adding new material to the orbit of the planet. Conveniently, I shouldn't think that (compared to the mass of your planet) a large quantity of material would be needed to achieve the necessary sound.

Which is good, otherwise we'd have to deal with your planet's diameter increasing by a meter or two a year, which would have massive consequences on evolutionary time scales.

My suggestion is an asteroid field caused by the break-up of two super-Earths early in your world's evolutionary period. The assumption is that together they represent a LOT of material to draw from. The goal is to have a very wide asteroid field, one so wide that it places the edge of the field at the orbit of your world. As mass within the asteroid field bounces around, it's constantly (but not debilitatingly) bouncing into the orbit of your world.

Is this believable?

I'm comfortable with its ability to meet suspension-of-disbelief. From a scientific perspective, what I've described is impossible. Such an asteroid field would remain tightly bound due to the nature of gravity. It wouldn't spread out as I've suggested. And if it did, there's enough mass involved that it would, I believe, have a pretty good chance of slowly drawing your world into the asteroid field to eventually become the core of a new massive planet (maybe even a dwarf star, given the mass needed for the two original colliding worlds).

But, then again, if that were really happening, that would be a convenient way to rationalize the debris causing the noise. It just means your planet has a life span that's quite a bit shorter than Earth's.

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    $\begingroup$ Won't non stop asteroids impacts destroy any chance of alien life evolving? I agree with it creating a lot of noise but how can the alien species survive rocks falling from the sky non stop for thousands of years? $\endgroup$
    – cypher
    Commented Oct 3, 2022 at 9:08
  • $\begingroup$ @cypher That depends on how many hit the ground. What you're looking to do is turn the upper atmosphere into a drum head by burning them all up. Not looking for a dinosaur-killer here, just gravel. $\endgroup$
    – JBH
    Commented Oct 3, 2022 at 9:43
  • $\begingroup$ I am having hard time believing this as an option for one reason : we are speaking about a phenomenom long enough to justify it having an impact (no bad jokes here) on the evolutionary scale... But as you say in your last part, if well presented the suspension of disbelief can be properly set. $\endgroup$
    – ohpif
    Commented Oct 3, 2022 at 11:28
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Super-rotating dense atmosphere

A super-rotating atmosphere is a planetary atmosphere that rotates faster than its host planet. On Venus, for instance, the atmosphere above the clouds moves at anywhere from 300-400 km/h. That’s approximately the speed of an F5 tornado, which are nightmarishly loud.

Combine that with a thicker atmosphere that conducts sound better, and you will get a continuous roaring sound in excess of 100db at ground level at all times. That will seriously disincentivize the development of hearing as a meaningful way to navigate or identify threats.

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  • $\begingroup$ Of course, it would be pretty hard for advanced life (i.e. something beyond fungus) to evolve on such a harsh planet. And by "pretty hard", I mean stunningly difficult, since "super-rotating atmosphere" implies all sorts of other problems. $\endgroup$
    – RonJohn
    Commented Oct 4, 2022 at 22:12
  • $\begingroup$ @RonJohn wind at surface level on Venus is measured in single digits MPH, so surface winds might be fine. As for implying other problems, we don’t even 100% know why Venus has a super rotating atmosphere. Seems a little premature to assume a habitable plane couldn’t. $\endgroup$
    – Daniel B
    Commented Oct 4, 2022 at 22:42
  • $\begingroup$ How high are the Venusian clouds? Would high winds above the clouds be heard on the surface? $\endgroup$
    – RonJohn
    Commented Oct 4, 2022 at 22:50
  • $\begingroup$ As for "Seems a little premature to assume a habitable plane couldn’t" have a super-speed winds low enough to be loud on the surface... no part of a system works in isolation. The cause of such low altitude high speed winds would certainly have knock-on effects which would make advanced (especially terrestrial) life difficult. $\endgroup$
    – RonJohn
    Commented Oct 4, 2022 at 22:53
  • $\begingroup$ @RonJohn the atmosphere of titan super rotates, despite having vastly different environmental characteristics than Venus. I find it entirely plausible that one could construct a planetary atmosphere and solar distance to be reasonably habitable and continuously as loud as a jet engine. $\endgroup$
    – Daniel B
    Commented Oct 4, 2022 at 23:14
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They can hear, they just can't hear us.

Humans hear at certain frequencies, between 2000-5000 hertz. Due to some atmospheric influences on the alien world, perhaps some constant noises that make it hard or impossible to hear at normal human frequencies, the aliens have adapted to hearing and speaking at much higher frequencies than humans. Therefore, the humans and aliens won't be able to communicate, due to their vastly different ranges of hearing. In addition, they use organs specialized for the production of high frequencies, not just using the mouth to create sound, so human and alien speech would be completely different, so they can't even understand that the other is attempting to speak.

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  • $\begingroup$ Note that this is the premise of "Little Fuzzy" $\endgroup$ Commented Oct 5, 2022 at 15:49
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    $\begingroup$ One possible problem with this is that human audition is not just for communication; it's also for parsing the environment, where many things resonate in our 20-20k hearing range. Maybe this could be handwaved with an atmosphere that somehow dampens these frequencies and amplifies higher, and/or a commonly bioincorporated mineral that makes everything stiff (and so the rustling of your prey is in higher freqs). $\endgroup$
    – tsbertalan
    Commented Oct 6, 2022 at 12:37

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