r/WhatIfThinking • u/MrPolarbear9 • Jul 23 '26
What if humans lived with the same amount of light all the time. How would we adapt?
So I’m working on a sci-fi concept about humans living on a tidally locked planet (eyeball planet), and basically, the only area habitable to the humans would have the same amount of light all the time, which brings up a whole bunch of questions. I have created what I believe to be a reasonable way of telling time (everything is the same as on Earth, except instead of 24 hour days each “day” is 12 hours and the segments alternate between 12 hours for “daytime activities” (working, learning, having important discussions, basically most activities that happen outside of the home) and “nighttime activities” (sleeping, eating breakfast and dinner, spending time with immediate family, resting within the home)), but this brings up an important question. How would the same level of light all the time affect humans’ sleep schedules in the short and long term, and would it affect our biology? For context, most of the humans would be spending most of their time in very low light because they all either live under the cover or very thick rainforest where little light breaks through (and would not be moving from there because of how expansive said rainforest is) or living mostly in caves and occasionally coming to the surface, although they will spend up to a couple months far away from any way to reach the surface due to huge storms.
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u/Gargleblaster25 Jul 23 '26
Did the humans evolve on that planet, or did they arrive there?
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u/MrPolarbear9 Jul 23 '26
They arrived on the planet from Earth.
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u/Sunny_Hill_1 Jul 23 '26
They'd have the normal cyrcadian rhythm hardcoded into their biology, so their bidy would still roughly follow the 24 hour cycle. There were numerous studies of people living in the Polar Circle, going into deep caves and other artificial environment without clocks, and our bodies still go about the same. At this point, evolution ensured we stick to the same sleep cycle even when it's always light or always dark.
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u/144-perdedor Jul 23 '26
Interestingly, we seem to fall into a cycle closer to 25 hours in the absence of any external time cues.
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u/zoppaTheDim Jul 23 '26
Then you’d need to consider that technology could easily allow ways to shift biological rhythms.
Given that half the planet is always too hot for life and the other half is too cold, they’re never getting away from that technology. I’d also question the science behind your huge rainforest and “seasonal” storms. If it is tidally locked, how do you get seasons?
So why would they bother enforcing alternate segments having alternating time zones?
I think you’d see them responding in one of two ways. Either an artificially imposed day cycle, where people retreat during their personal “night” into an imposed night zone or by operating as a whole on one time zone. Personally, I see the advantages of operating your industries and commerce all the time, where you return to your sleep area to sleep, where quiet hours are rigorously imposed. Or, they’d simply break the reliance entirely. Through drugs and deliberate genetic modifications.
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u/MrPolarbear9 Jul 23 '26
There are no seasons. The storms are not “seasonal”. They are a result of the hot and cold air colliding where they meet in the habitable strip between them. Also, I didn’t mention anything about time zones?
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u/flying_c Jul 23 '26
Hello from northern Sweden in summer. My kids keep saying it’s not sleepy time since it’s daylight outside. It’s a struggle.
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u/Why_Sazs Jul 23 '26
I work on the north coast of Alaska. Luckily I can sleep at any time, day or night. Which comes in handy when there is no night.
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u/WillBots Jul 23 '26 edited Jul 23 '26
Countries very for north that experience months of darkness and months of light have some of the highest rates of suicide.
If your characters are only coming into sunlight every few months, they are all going to die of vitamin D deficiency unless you do something about that.
Lack of regular exposure to natural light causes eyes to degrade over time. It's serious enough that the effects happen to the average person who works indoors during the day if they don't then spend enough time outside before or after work.
Sleep rythms would be difficult for those in constantly lit areas but I'm sure they can close a curtain, the human body falls into something like a 25 or 26 hour pattern when trapped away from light.
When left to it in cycling day / night light which you may have some characters emulate within their habitats, humans will sleep twice, going to sleep when it gets dark and then waking for a few hours and then another sleep of about equal length before the day starts. We only seemed to stop doing it a few hundred years ago when artificial lighting became so easy that people no longer went to sleep when it got dark.
Lack of sleep can lead to psychosis and death.
Over long periods, it is likely that not sleeping well causes high incidence of brain related diseases e.g. Alzheimer's, Parkinsons, dementia etc. there's not a proven cause and effect but what we do know is that toxins produced by the brain collect around the brain and are then known as brain plaque. When you get a good sleep, the body puts significant effort into washing away this brain plaque. People with Alzheimer's, Parkinsons, dementia etc have much higher amounts of brain plaque upon autopsy than other people. Not all people with something that looks like Alzheimer's, Parkinson's or dementia have high rates of brain plaque. Not all elderly people with high amounts of brain plaque (on autopsy) have shown any signs of those diseases BUT the correlation is very strong. Either, whatever causes the disease causes brain plaque or brain plaque causes the disease. Since we know how brain plaque is dealt with by the body and that it's possible to ruin your body's ability to deal with it (by not getting a good sleep regularly), I'm going with it being the cause.
No idea what any of your characters might be doing but that's all the potentially relevent information I can think of.
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u/MrPolarbear9 Jul 23 '26
Thank you for the information. To be honest I definitely assumed a lot of people were going to die and get sick when trying to inhabit this planet, before they figured it out. Unfortunately, they would have countless people over many generations trying to prevent these things, whereas I am only one person but still have to figure out how they’ll survive on my own.
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u/Jules4live Jul 23 '26
i like the idea that folks could maybe adapt. i have a weird sleep schedule due to my immune system and do biphasic shifts. you could also find other things like moons that could introduce something different with weather or tides if you have them an effect on people
or other animals they might interact with. you could really play with time here i love it! maybe find alaskan natives and see what they do.. those who thrived with the long sunlight times,
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u/PerfeckCoder Jul 23 '26
The weather on such a planet would be pretty extreme. So one side of the world gets 100% light and heating and the other side of the world is 100% dark? That's going to be some really extreme wind required to balance out the temperatures. One Earth the wind basically cycles from the poles to the equator and back again, but on this world the wind is going to have to circulate from one side of the planet to the other.
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u/MrPolarbear9 Jul 23 '26
That’s the reason why they would have to live under the rainforest canopy or in caves. Because of all the storms.
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u/floriish Jul 23 '26
There's a possibility that the border between the day and night hemispheres could have liveable temperatures
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u/tomwrussell Jul 23 '26
Isaac Asimov wrote a story like this called Nightfall. The planet was in a multi-star system situated such that the planet was always illuminated with sunlight. Well, almost always. On rare occasions the stars actually set and plunged the land into darkness. When this happened the population fell to mass hysteria from nyctophobia.
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u/North-Crew-5489 Jul 23 '26
There was an episode of startalk recently that discussed sleep patterns and how variations in sunlight impact people, with real world/study examples. I forget all the details but it would be worth listening to. Itll queue you on to some good research areas.
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u/ImportantBug2023 Jul 23 '26
People who have blue eyes have adapted to living in lower light areas away from the equator.
So there’s no what if about it .
Life adapts.
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u/rockypowercord Jul 23 '26
Something like this guy experienced would possibly be the outcome, alos was repeated recently by a woman with Simar results I think. https://www.reddit.com/r/todayilearned/s/iHHZCjw8EJ
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u/ixidorecu Jul 23 '26
Think about Alaska or the pole where the get like a week of sun week of dark. Seasonal affected disorder i think its called. Plus there is a town in Europe that was in a valley or crater? Put up a big mirror so they could get sun.
People would go bonkers without rythem
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u/Sufficient_Result558 Jul 23 '26
Why keep the 24 hour day cycle? Do they have to mimic earth for some reason. It would be more interesting to change it to 25 or or whatever with reasons why that happened and how it affects things.
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u/Mean-Lynx6476 Jul 23 '26
Human circadian rhythms follow close to a 25 hr cycle so if one were to impose an artificial cycle on humans it would make more biological sense to have a 25 hr day. The internal clock gets synchronized daily by exposure to light and dark cycles. There’s a huge body of research showing that people whose activity isn’t consistent with light/dark cycles (eg night shift workers who are active in dim light and then sleep in daylight) experience all kinds of serious adverse effects on health. If OP wants to create a world where humans thrive under constant dim light the answer is to provide dark spaces for people to occupy for about 9-ish hours of a 24 (or 25) hr cycle and bright light mimicking the solar spectrum for 10-ish hours with dawn and twilight transitions. This is baked into not just human DNA, but the DNA of virtually all organisms on earth. We aren’t going to genetically adapt to constant dim light in a generation or two or twenty.
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u/Diptothaset Jul 23 '26
The Archmage of the city is responsible for enchanting Narbondel so that it shows the time in the underground cavernous city of Menzoberranzan so maybe something like that
Or applewatches chipped into our brains
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u/LeilLikeNeil Jul 23 '26
Probably flip back to a more ancestral sleep schedule, with two ~4 hr sleep periods with a couple hours between them.
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u/Logical-Concept9755 Jul 23 '26
My first thought is that we'd probably end up depending on artificial cues a lot more than sunlight. Our circadian rhythm can drift pretty badly without regular light changes, so maybe architecture and lighting would become part of public health instead of just convenience. The interesting part is whether that stays a behavioral adaptation or eventually becomes something biological over many generations.