We're diurnal, and have eyes optimised to see maximum colour and detail instead of well in dim light (at least by mammal standards). It makes sense we'd gravitate to fairly dark conditions to sleep, because while nature at night is not perfectly unlit, it's still pretty dark. Darker than a developed-world urban area will ever get, for example.
That being said, many people are completely capable of sleeping in a bright area, myself included.
As for the bonus question, yes, the hormones at least work backwards in nocturnal animals. Melatonin wakes something like a shrew up.
We’re diurnal, and have eyes optimised to see maximum colour and detail instead of well in dim light (at least by mammal standards)
Human variation.
There's two main structures in our eyes.
Rods: take large amounts of any wave length of light
Cones: take in a very small amount of a specific wavelength and only that wavelength
Most of the area (like 95%) are rods. And there's a couple (usually three) types of cones.
Some people have more different types of cones, and can see more differences in color. Some have less types meaning less cones overall even.
But the eye won't just have more blank spots. So it fills in with more rods.
This is actually related to why the further away from the equator people got, the lighter their eyes got.
With longer variation in day/night cycle, it was advantages to let as much light in as possible. That outweighed the downside of too much light during the day, as that could be solved with hat brims, or that age old move where you make a visor with your palm.
By limiting the amount of light going to your rods, your cones get less "washed out" and that's how we get more detail/colors.
But even in a single population, there's going to be a lot of human variation. Rod/cone distribution has a high amount of variability even when genetics are steady. Genetics has a large effect, but it's not like the body always follows directions closely.
I could nitpick some of the details there, but instead maybe I'll just ask what point you're trying to make? A healthy human can still pick out something small way better than a goat.
Optimised just means designed for something at the expense of other parameters. We lost our tepetum lucidum at some point in evolution, probably for the 3x-ish resolution gain, while becoming much more shit in lowlight in the process. That's a tradeoff, but a good one for a tree-based diurnal frugivore.
Cats (for example) still have theirs, which means light as two chances to hit their retina, but means there's an upper limit on how clear an image can be, exactly because there's light bouncing around. It sounds like 20/100 is typical for them, from a quick search. Cats are traditionally thought to be dichromats, as well.
We actually have less genetic variation than most animals. There was a lot of bottlenecking in the paleolithic. And what little we do have is still mostly confined to Africa, because the rest or the world shared common ancestry as we left our original continent.
Like, 1 in 200 people is colourblind, or something? I don't think that's a reasonable argument that we're not trichromats.
Like, 1 in 200 people is colourblind, or something?
....
Again, you're talking genetics, where it is clearly broken down in 2,3,4.
However like pretty much everything else, it's not that clear cut just because the plans were.
Two people with the same amount of different types of cones are not guaranteed to have the same rod/cone ratio. Even when they have similar genetics for the ratio, things rarely go according to plan as a human develops.
Like, you know that's why facial symmetry is attractive right? It shows that things on both halves went according to plan. Which especially for women is a huge bonus for reproductive health.
Especially for something made up of a whole bunch of small things like rods/cones, it's not even perfect for identical twins.
"Full darkness" isn't even a real thing in nature. It's hard to tell with light pollution, but even in the absolute middle of nowhere with no artificial lights, you're going to be able to see fairly well. Even with no moon, starlight isn't just an expression. And on a full moon it can be surprisingly "bright" if you're just out there for a while.
It's not like climbing into a cupboard, shutting the door, and sealing all the cracks with duct tape.
You may be used to needi g full darkness to sleep, but that's a learned habit. I guarantee if there was nothing you could do, it wouldn't take you long to adapt your "requirement" of total darkness.
but even in the absolute middle of nowhere with no artificial lights, you’re going to be able to see fairly well.
I'm not sure I'd say fairly well. Maybe always well enough to not walk directly into a tree in otherwise open terrain. A full moon will be comfortable to walk around in, but new moons happen just as often, and sometimes the moon is below the horizon.
Source: Have walked around in the country at night.
I mean, my night vision was always better than most...
But growing up as kids we'd be sprinting thru the woods playing tag at like 10pm summer nights, not a single electric light in sight
You're not going to recognize someone 100 yards away, but you're not walking around with your hands in front of your face to make sure you don't run into anything.
If you're under an open sky, or even a primitive shelter, you're not in complete darkness.
Hmm. Are we talking a high canopy, and fairly level ground? I feel like I'd definitely break an ankle if I tried sprinting otherwise.
I never had too much trouble, but sometimes things hiding in tall grass would surprise me, and in heavily treed patches I'd occasionally hit a low branch I didn't notice.
I also have to account for the fact that there was some light pollution, and I could always see skyglow from towns in the distance. I doubt land ever gets close, prehistoric or not, but in the darkest conditions that happen at sea apparently you can't see your own hands.
I feel like I’d definitely break an ankle if I tried sprinting otherwise
Yeah, we played paintball even, but stopped because one guy ran straight off like a 6 foot mini cliff. A couple of us were chasing him and he just disappeared. Was freaky as shit like that scene from LotRs.
I also have to account for the fact that there was some light pollution
Yeah, I'm talking really hillbilly stuff, zero light pollution.
but in the darkest conditions that happen at sea apparently you can’t see your own hands.
A ship gives off a lot of light pollution, but even without that, between the water reflecting and nothing blocking light, it's brighter out there unless there's heavy clouds cover. And even then it's gotta be a lot of clouds and rough waves or else the light would still be refracting some.
Now a watertight compartment on a ship with the light switch on the outside?
Yeah, that's complete darkness. It's not just "can't see your hand in front of your face". It's the absolute and complete absence of light. That's total darkness.
Yeah, we played paintball even, but stopped because one guy ran straight off like a 6 foot mini cliff. A couple of us were chasing him and he just disappeared. Was freaky as shit like that scene from LotRs.
Lol, yup, that sounds right. I did that once, although it was only like 3 or 4 feet, and I didn't like it one bit. Is was a sinkhole or something too, because it was cliff all around, and I had to find a spot to climb out. I didn't visit that area again.
I forget where I heard about the sailing thing now. That would be a 1 on the Bortle dark sky scale, though.
i found i did indeed need to have hands out because i can’t see much at all in deep country at night on a new moon. maybe i just don’t have great night vision.
That's why there's "blue light filters" on electronics these days. That wavelength isnt included with moonlight/starlight.. maybe on a big full moon there's be some.
And why people prefer soft yellowish lights when relaxing and not the bright ass LEDs.
Full darkness is most certainly a thing and is more of a thing then light..light is artificial. Remove the sun...what do you get, full darkness. Light is added, darkness isn't.
Same with heat..everything is cold unless heat is added.
Cold and full dark are forever, heat and light are techcially temporary.
“Full darkness” isn’t even a real thing in nature.
And
It’s not like climbing into a cupboard, shutting the door, and sealing all the cracks with duct tape.
So I thought it was pretty clear I meant that to get "full darkness" where you really can't see, requires extra steps to intentionally make it happen. Just that for the vast majority of human evolution, we weren't really capable of it, and would have no reason to even try.
The experience of people working the night shift, who use blackout curtains to sleep during the day, would disagree.
But that's for a relatively highly regimented sleep cycle. If you slept and worked completely at your leisure, you might end up with one shorter sleep period at night, and one even shorter nap during the day. And without any day-night cycle at all, some people naturally adopt cycles of varying lengths.
The experience of people working the night shift, who use blackout curtains to sleep during the day, would disagree.
Wow, I didn't know my own experience disagreed with me...
Or that during my childhood when my dad was swing shift, he was apparently a freak of nature too...
But that’s for a relatively highly regimented sleep cycle. If you slept and worked completely at your leisure, you might end up with one shorter sleep period at night, and one even shorter nap during the day. And without any day-night cycle at all, some people naturally adopt cycles of varying lengths.
Again, human variation is a big thing.
But an individual will change their sleep schedule as they age, which is another supporting point for what I'm saying.
Evolutionary biologists hypothesis that it was so out of an entire tribe of early hominds, at least some members were likely to be awake. It wasn't an inate guard duty rotation. But kids and middle age went to bed early, teens went to bed super late, and by then the elderly were waking up.
If something happened, someone screamed and everyone woke up. And the fires stayed lit all night.
This is untrue - we have explicitly evolved to sleep in the dark. Sleeping in the light is a learned behavior that's more or less an exploitation of a loophole in the circadian clock
The intensity and the wavelength of light influence entrainment.[2] Dim light can affect entrainment relative to darkness.[15] Brighter light is more effective than dim light.[12] In humans, a lower intensity short wavelength (blue/violet) light appears to be equally effective as a higher intensity of white light.[11]
Yes, but your wikipedia link doesn't prove that animals are only sensitive to blue light, only that they are more sensitive to blue light. That is a very well-documented phenomenon. But there is plenty of evidence that red light can entrain circadian rhythms as well, dating well back to the 80's. There has even been a study that identified different mechanisms of entrainment to low-wavelength and high-wavelength light in bacteria, which you can find below. My point is that it is very scientifically irresponsible, and in fact, blatantly wrong, to claim that humans are sensitive only to particular wavelengths of light, when in fact humans and other animals are sensitive to all wavelengths of visible light.
Beyond that, I don't necessarily know why you seem to be claiming that the intensity of the ambient light does not matter for photic entrainment, when this is a highly documented and, in fact, highly studied phenomenon in the circadian field. Yes, the moon reflects light, but this is dim enough that mammalian SCN's can interpret the difference between that and the full daylight. See below for some papers that look into light intensity and their effects on entrainment.
If we're going that far, then no radio or person either. Black holes have disappeared from Hawking radiation, protons have all decayed, and the distribution of energy is so even and so rarified no exchange can happen, so literally nothing can happen.
If we allow a magic radio, we can allow a magic air bubble.
In the unimaginably vast and vacant void, a single plain white half-dome radio drifts, aimlessly.
The eons stretch onward, silence fills the universe.
When the last vestiges of everything have finally ceased, and the universe at last becomes one with nothing, a single, dim, red light inexplicably flickers to life.
A speaker crackles to life, a soft but angry voice emanating from within and stretching across the abyss.
I'm by no means an authority on this subject. At best I'm an enthusiastic amateur, so take my answer with a bucket of salt.
The static on the radio comes from the redshifted heat of the universe expanding. Even if all energy in the universe has evened out, the expansion is still going on, creating the redshifted heat.
However, so much time will have passed that the distances involved will cause this redshift to be even greater. At some point this static will be on a spectrum too low for a radio to pick up.
Also, even if you were able to tune your radio low enough, as the static is now created outside of the observable universe, there's no new noise that can reach you.
And the universe's expansion is accelerating, so even if you have the most sensitive receiver that can pick up very low frequencies, at some point the waves will be stretched so thin that they'll be essentially nothing. Of course they won't be zero, but where you draw the line for "essentially zero" is up to you.
Not all radio noise is from the CMB. There's also thermal noise, though this would be minimized too if our hypothetical radio at the end of time is near absolute zero.
To narrow the scope and for ease, I take that information as "measurement" from quantum field.
If the many-world interpretation is real, we have multiverses branching off by different measurements as wave function collapse from the same universe (with all of its information). It seems to me that symmetry of information is broken continuously, as wave functions collapse continuously. This lead me to believe that it is beyond our comprehension to theorize and observe said symmetry.
One clarification: electric charge, angular momentum, and color charge are conserved quantities, not symmetries. Time is a continuous symmetry though, and its associated conserved quantity is energy.
Similarly, information isn't a symmetry, but it is a conserved quantity. So I assume you're asking if there's an associated symmetry for it from Noether's theorem. This is an interesting question: while Noether's theorem ensures that any continuous symmetry will have a corresponding conserved quantity, the reverse isn't necessarily true as far as I know. In the case of information conservation, this normally follows naturally from the fact that the laws of physics are deterministic and reversible (Newton's laws or the Schrodinger equation).
If you insist on trying to find such a symmetry, then you can do so by equating conservation of information with the conservation of probability current in quantum mechanics. This then becomes a math problem: is there a transformation of the quantum mechanical wavefunction (psi) that leaves its action invariant? It turns there is: the transformation psi -> exp(i*theta)*psi. So it seems the symmetry of the wavefunction with respect to complex phase necessitates the conservation of probability current (i.e. information).
Edit: Looking into it a bit more, Noether's theorem does work both ways. Also, the Wikipedia page outlines this invariance of the wavefunction with complex phase. In that article, they use it to show conservation of electric current density by multiplying the wavefunction by the particle's charge, but it seems to me the first thing it shows is conservation of probability current density. If you're interested in other conserved quantities and their associated symmetries, there's a nice table on Wikipedia that summarizes them.
This falls a bit outside my wheelhouse but I believe the answer is no. The established symmetries in particle physics are all associated with the quantum mechanical state of a particle (charge, parity, etc) and to my knowledge there isn’t an “information” quantum number.
The closest you might get to this is quantum information theory, where information is encoded in other physical characteristics (spin, parity, energy, etc). In this sense information is more of an emergent phenomenon than a fundamental property.
But isn't entropy an emergent phenomenon, manifesting only at larger, relativistic (by which I mean non-quantum) levels?
Entropy doesn't affect the fundamental symmetries I mentioned in the title. So information may not be fundamental, then?
Man... information is such a weird concept when one stops to look at it, I wonder if a true definition of it is as difficult to pin down as time.
If your lifespan was an hour, every generation that witnessed a sunrise or sunset would freak the fuck out and think the world was ending.
I've always thought of entropy like that, it seems one direction, but only because we're on a comparativly tiny timescale.
Used to subscribe to the "big crunch" theory that it'll just all start over. But the more Penrose and Hawking I read, the more I think the Big Bang just isn't that unique.
There's a lot of signs that the vast majority of existence is dark matter, and with how it interacts with regular matter, I don't think we have sequential big bangs like a single light slowly flashing. I think it's more like fireworks in the sky.
There's probably not anyway to travel through the dark matter to get to another "bubble", and even if we did, that bubbles laws of physics could be drastically incompatible with us.
Like, if you remember the Narnia books it's like that "main world" where it was just an infinite number of ponds and jumping into one shoots you out to some world world everything works better. I think The Magicians kind of ripped off the idea, and by now more people may be familiar with that then one of the least popular (but underrated) books in a children's series from ww2.
Entropy is functionally persistent, but only because everything we can see and interact isnt all there is. There could be multiple other bubbles of matter happening right now, it's just about what frame of reference we have.
[In] the Narnia books it's like that "main world" where it was just an infinite number of ponds and jumping into one shoots you out to some world ... I think The Magicians kind of ripped off the idea.
Completely off-topic from symmetries and entropies, but I can't pass up the opportunity to mention that the specific Narnia installment where we see this "main world" and branches is The Magician's Nephew, the sixth out of seven books.
As with Isaac Asimov, I much prefer order of publication.
Woe the poor soul trying to get into Foundation and instead of getting the original trilogy, they start with Prelude To Foundation. I met a guy who did that, in college; he didn't know where to start, at the bookstore thought "Hey... Prelude... sounds like a good place to start!"
For example, if one starts with Prelude To Foundation as the entry point, the reveal of Eto Demerzel being R. Daneel Olivaw in disguise all loses its' punch, while if one reads the original Robot books first, it becomes an astounding reveal, a true "holy shit!" moment, on several levels, the delightful surprise of clearly seeing Asimov kneading together two separate series so intimately and right before your eyes, the narrative doubles in size and scope in the snap of a finger.
The power of that moment, that opportunity that Asimov seized, makes it worthwhile to follow Isaac's mind instead of the plot in chronological order.
It doesn't lose its punch, because he's described all through Prelude To Foundation, it's still a big reveal. And then you read the later books in that context.
Fully-aquatic mammals that I can think of, like whales or dolphins, aren't furry, so I'd say that while fur may be a net positive for animals that spend some time out of the water, it's probably not because of their time in the water.
It'll increase drag, which means that they have to expend more energy to move through the water.
It might have some insulation benefit, but I'm not sure how significant that is in water, and I'd guess that fat is probably preferable in that case.
My guess is that the main benefit is for outside water.
First, thermal insulation, where the fur limits convection of air, so you get air pockets, which doesn't conduct well.
Second, as a disposable, dead layer, it also provides protection against UV light and such. We don't think of living out of water under the direct radiation from the sun as being particularly difficult or the environment harsh, because we casually do it every day, but it was a very hard problem for life to solve.
Ourasphaira giraldae is an extinct process-bearing multicellular eukaryotic microorganism. Corentin Loron argues that it was an early fungus. It existed approximately a billion years ago during the time of the transition from the Mesoproterozoic to Neoproterozoic periods, and was unearthed in the Amundsen Basin in the Canadian Arctic. This fungus may have existed on land well before plants.
I know that when people are moving dolphins and whales around, they keep them covered, partly to keep them wet, but also because they will suffer badly from sunburn if not done. This dolphin had a lot of its skin get destroyed and fall off its body after being exposed to the sun for some hours:
Second, as a disposable, dead layer, it also provides protection against UV light and such. We don’t think of living out of water under the direct radiation from the sun as being particularly difficult or the environment harsh, because we casually do it every day, but it was a very hard problem for life to solve.
Oh yeah, that's a good point! I'd typically be more concerned with the drying out part for a lot of aquatic life, forgetting about the UV exposure issues.
Their fur is very dense, otter fur has more hairs per square inch than any other mammal, a million per square inch, like a hundred times what humans have. The oils excreted into their fur creates a hydrophobic layer that keeps the water on the outside. It's in nowhere near shark skin (which exhibits incredibe hydrodynamics, like we're studying it in labs to better improve aerodynamics of cars and planes, a single bite of food is enough to get a great white shark from California to Japan their skin is so efficient at moving through water), but it's very good at keeping the water out and their movement efficient, their hair does not cause Resistance like human hair does. Our hair hangs out and gets water in it and creates drag, otter hair seals itself around the meat and creates a cylinder, keeping happy warm dry otter inside.
I got the treat of touching/petting a wild otter while it was sedated, it's on of my top 10 experiences. It was not a happy camper when it woke up. It had to be in an ice bath while sedated otherwise it's hair/fur coat would've caused it to overheat while being knocked out because it is incapable of homeostatic regulation while sedated. When it woke up it was a wild otter in an ice bath, lil (haha, huge actually) dude was pissed.
Huh, thanks for the detailed reply! I suspected some of them must have something extra going on to help their time in the water, but wouldn't have thought this!
Were you able to feel how dry the otter was through the sealed fur, or was it sealed enough that you couldn't really tell?
I've never felt one under water, nor did I try to go skin deep when I had my opportunity, but I would guess they're pretty dry under there, I couldn't say for sure though.
I know otters blow bubbles into their fur to isolate themselves, but this also makes them extra buoyant. For the babies this is quite handy (less drowning etc) but for adults idk if it really helps.
It really depends on the fur texture probably, seals are also coated in fur but streamlined to perfection.
The required temperature depends on the mass of the particles you're considering. You could say photons are always relativistic, so even the photon gas that is the cosmic microwave background is relativistic at 2.7 K. But you're presumably more interested in massive particles.
If you apply the kinetic theory of gases to hydrogen, you'll find that the average kinetic energy will reach relativistic levels (taken to be when it becomes comparable to the rest mass energy) around 10^12^ K. For the free electrons (since we'll be dealing with plasmas at any sort of relativistic temperatures), this temperature is around 10^9^ K due to the smaller mass of the electron. These temperatures are reached at the cores of newly-formed neutron stars (~10^12^ K) [1] and the accretion disks of stellar-mass black holes (~10^9^ K) [2], but not at the cores of typical stars. Regarding time dilation, an individual particle's clock would tick slower from the perspective of an observer in the center-of-mass frame of the relativistic gas, but I don't think this would have any noticeable effect on any of the bulk properties of the gas (except for the decay of any unstable particles). Length contraction would probably affect collision cross-sections, though I haven't done any calculations for this to say anything specific. One important effect would be the fact that the distribution of speeds would follow a Maxwell–Jüttner distribution instead of a Maxwell-Boltzmann distribution, and that collisions between particles could be energetic enough to create particle-antiparticle pairs. This would affect things like the number of particles in the gas, the relationship between temperature and pressure, the specific heat of the gas, etc.
You mention the early history of the Universe in your other comment. You can look through this table on Wikipedia to see the temperature range during each of the epochs of the early Universe, as well as a description of what happened. The temperatures become non-relativistic for electrons at some point during the photon epoch.
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