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A planet much like Earth orbits a star much like the Sun, but with one difference: the energy from the star is magically transformed into sound within the planet's atmosphere. There is no longer starlight, only starsound. Every point on the planet is still bathed with an equivalent amount of energy, but now it's in the form of sound, not light. The spectrum is mapped such that visible light roughly corresponds to audible sound on a logarithmic scale (so green light roughly corresponds to middle C), with frequencies and intensities scaled as necessary. No other sources of light or sound are affected.

Clearly, life on this planet would be subject to different evolutionary pressures. In another question, someone asked about the equivalent of photosynthesis in this ecosystem. What adaptations would animal-like life need to evolve in order to take advantage of this sound?

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    $\begingroup$ Do you mean that the sun is basically constantly humming/screaming? Or would normal soundsources be transformed to light in turn? $\endgroup$ – dot_Sp0T Sep 18 at 15:33
  • $\begingroup$ Also would lightsources like fire emit sound as well? $\endgroup$ – dot_Sp0T Sep 18 at 15:34
  • $\begingroup$ Wouldn't the planet be a frozen wasteland near absolute zero (0K) as no light reaches its surface? $\endgroup$ – TheDyingOfLight Sep 18 at 15:35
  • $\begingroup$ @dot_Sp0T Only the star's light is affected. All other sources of light and sound are unchanged. $\endgroup$ – user53026 Sep 18 at 15:35
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    $\begingroup$ @Mnemonic That's vague. could you please be very specific. $\endgroup$ – We are Monica. Sep 18 at 15:59
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Wikipedia quotes the average radiance we get from the sun to be around 1.05 kW to 1.367 kW per square meter. Converted to sound, that's like being next to a jet plane during takeoff.

It's okay to have that radiance around us because light will impart you with very little momentum, and you will reflect most of it. Sound, though... it will shake you in harmful ways. For us humans, 150 decibels is enough to rupture our eardrums. Your creatures will have to adapt to such levels of ambient noise.

Another problem is, if you are hit by a standing wave of sound, it will affect your phisiology. In us humans, even a few seconds of exposure to the sound of a fan can cause us to hear and see things that are not there. With ubiquitous sound like that, any closed space is potentially a resonance chamber, and being in such a place can negatively affect one organ or another.

Your land fauna will adapt by either having large whiskers, antennae, feelers or other organs in order to assert that they are out in the open, and will avoid confined spaces; Or by staying underground, digging tunnels in shapes that make sure as little resonance as possible is present. Underwater, creatures will tend to avoid the SOFAR channels, under penalty of going deaf.

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    $\begingroup$ "Converted to sound, that's like being in a restaurant.": This isn't correct-- based on your links, I think you're mixing up the dBm scale used in electronics with the SPI scale used in acoustics. The difference is that dBm uses $1mW$ as the reference (ie 0 dBm), while the SPI scale uses $1pW/m^2$ as a reference-- a difference of 9 orders of magnitude (also, different units altogether). The given solar flux in SPL/SPI units would be a whopping 150 dB-- about as loud as a jet engine at a distance of 1 meter. $\endgroup$ – el duderino Sep 19 at 3:47
  • $\begingroup$ @elduderino thank you - I will edit my answer. $\endgroup$ – Renan Sep 19 at 10:01
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If it receives the same radiant energy, the planet will be significantly hotter than Earth. Quite a lot of sunlight reflects directly off the Earth and back into space without contributing to heating. Sound, however, will be entirely trapped within the atmosphere until it is converted into heat.

Impedance mismatch will keep most of the sunnoise out of bodies of water and solid ground. That makes the oceans effectively "dark" (as well as actually dark), so ocean life will probably rely entirely on active sonar in place of passive visual mechanisms, and won't care about the difference between day and night. You might be able to maintain the ocean food chain with plants floating on the surface; otherwise, global oxygen production will be severely reduced and ocean ecosystems will be limited to geothermal vents and scavengers of material washing out from the coasts. The same goes for freshwater plants--they won't be able to survive without growing on or up to the surface for decent access to sonic energy.

Out of the water, there's no point to active sonar during the day, since the environment is naturally illuminated with sound, but having adapted to sonic vision already, I expect you'd see.a lot more echolocating nocturnal animals like bats. Sonic eyes need to be significantly larger than light-eyes, so you'd likely only get one of them, rather than two, in lineages that actually manage to evolve an image-resolving eye, as opposed to simply relying on ears for much lower resolution environmental information. If a sonuc eye evolves in the head, it'll take up most of the head; there are significant advantages to locating it in the body cavity (like Hal Clement's Hot Abyormenites) instead, although it's less aimable that way. Even with a large and well-developed sonic eye, visual acuity will be severely limited by the large wavelengths of sound compared to light. Thus, you won't get anything like Earth's raptors, which rely on highly acute eyesight to find tiny prey animals from enormous distances and close at high speed. In fact, nocturnal animals that can rely on active sonar in a less sonically cluttered environment, and thus get by with much simpler sensory apparatus, will be at a significant advantage for hunting by "sight".

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So the sun and the stars are just like in our own universe, it is the atmosphere of the planet that converts the light into sound. Or is it some sort of layer above the atmosphere that convert the ligth? Or is it fantasy and therefore a magic spell that wraps the whole world like a blanket? You're not mentioning the mechanism here.

Whatever it is, the process needs to reflect some of the energy to prevent the world from becoming too hot, judging by some of the other replies here. What about hot objects? They radiate infrared light. If it is the whole atmosphere that is responsible for the conversion, light on the planet is not possible. But if it is only happening high up in the stratosphere or ionosphere, then it should be possible for animals and other organisms to produce their own light. Once organic light and primitive eyes have evolved, there would be an arms race, and there would probably be creatures with huge eyes communicating with light and even use light to see their environment. If not, all you have is echolocation and sensitive hairs that gives you an impression of the surroundings. Or if this is fantasy, some sort of sixth sense.

The biggest challenge would be for organisms to convert the sound energy into an energy form they can use. Would it be enough to sustain an ecosystem of advanced and complex organisms? Hard to say. Scientists are experimenting with ways to convert sound into electricity.

Sound is as everybody knows vibrations travelling through matter. How can you harvest these vibrations? You could have organs that convert the vibrations directly into piezoelectricity, which the organism use as an energy source. Dolphins and other toothed whales have a fatty organ called the melon that is used as a lens to focus sound. Perhaps that would work here as well. Other organisms could make use acoustic resonance, where the sound is amplified and turned into mechanical movements, setting large membranes into movement that convert the motion into electricity. Huge gas filled structures or "blankets" stretched over an area. This could be a living organism, or it could be created by small animals that excrete the material they use to build them (if termites can build complex mounds and spiders intricate webs, why can't other small social creatures with limited intelligence build something that can harvest sound in a world defined by it?).

Then natural selection would take care of rest. The most efficient textures, sizes and adjustments would extract more energy from sound than others. Today the trees in a forest are competing for the light, which is why they are as tall and wide as possible. Others are epiphytes. In water with floating plants height is no longer the issue. In this world, "plants" or similar organisms harvesting energy from sound would compete for the best places which can provide them with the right amount of sound they need to survive and thrive. Different organisms could be adapted to different sounds on the logarithmic scale to avoid competition.

But what is biological possible, and what is evolutionary possible, is not always the same thing.

If the sound convertion is an anaerobic process, there would be little to no oxygen in the atmosphere, and animals would be anaerobic too. According to this article, complex life without oxygen doesn't sound impossible:

https://www.sciencedirect.com/science/article/pii/S0891584918324006?via%3Dihub

"It is often stated or assumed that O2 improves the energetics of the cell and that O2 thus might have impacted the origin of mitochondria, but life in O2 is thermodynamically thirteen times more expensive than life without O2, because O2 tends to oxidize things, including the chemical substance of cells."

Mitochondria enable cells to produce 15 times more ATP than they could otherwise, but if aerobic metabolism is 13 times higher than metabolism without oxygen, the difference shouldn't be that huge.

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Sonic Problems With Sonic Solutions

I would liken this Earth to our own but exponentially rich of possibility given some imagining. Think of the implications in a place in parallel to a String Theory; taken at face value. Reality as oscillating strings experienced at the macro level.

As an animal that doesn't know "light" or similar stimuli within said environment. My sonic experience would have to balance with sonic ability utilizing both input and output. Ideally, I would evolve basic and intuitive sorting of sonic information; I also need to navigate, analyze, and process matter. With these tools, our chance to perform the work that leads next as trial and error are critically improved to aid in survival. I need the ability to evolve as more than merely a sonic observer. Surely I would also need to interact with this environment to begin to shape life as animals do.

The Synthesis Animal

I would look for the answer for both input and output of sonic stimuli as a sound wave being processed through appendages that evolve in comparison to modules of a synthesizer. Imagine in this case you could seemingly perform magical feats through actually shaping matter via cut off freq or a variable oscillator in the form of a sonic brain evolved. Interact with "sonic matter" that represents as Saw Wave with X Hertz at X beat frequency by outputting this wave of data as Pulse Wave that's cut off @ X hertz and then sequenced in some order for x time. Given a reality shaped sonically such an animal would literally be a shapeshifting mage. Of course, the evolution of the exact bodily appendages is all open to imagine. The possibilities are endless if your a Bob Moog...;)

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Without Sunlight No sunlight means no natural light source. Eyes wouldn't provide any evolutionary advantage if your world is perpetually dark. Maybe eyes evolved to detect the infrared spectrum to aid in finding food or mates by the heat they give off? Maybe eyes evolved alongside organs that glow?

Our world encodes a lot of information in sight. But with no eyes, there would be no use for: facial expressions, mating dances, zebra stripes, windows, flower pedals, written language, peacock tails, traffic lights, street signs, hair dye.

Communication and navigation would be sound based. Ears might be bigger, more plentiful, more sensitive. Echolocation is the only way to probe the geometry of your surroundings but that broadcasts your position. Stealth replaces camouflage.

Would people just invent the lightbulb? No, because they don't have eyes.

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  • $\begingroup$ Active echolocation is the only way to probe the geometry of your surrounding at night. During the daytime, there is plenty of ambient sonic energy splashing around and making itself useful for passive detection, just like light would. $\endgroup$ – Logan R. Kearsley Sep 19 at 3:26

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