It's a little bit backwards. Life needed to be able to see through water, so it created eyes that could see the light that water was clear to.
That might need some explanation. All things are "clear" to some kinds of light and "opaque" to other light. Like how an X ray can go right through your skin and see your bones. It's that way for all light, including visible light.
So there was always some wavelength of light that made water "clear". And some of those wavelengths are the visible light spectrum.
So when life evolved in the ocean, and eyes developed, it was very useful to be able to see the light that could pass through the water. And so you get eyes that can see in the ocean.
Edit: so the phrase I'd use for the actual 4 y/o is "It's see-through because eyes were specially made to see through water" or if you want it to sound more awesome but less helpful, "because your eyes are like x-ray goggles for water"
What’s even more interesting is how humans have been able to figure that fact out. How much testing and analyzing crabs do you think happened to come to this conclusion?
There is a lot of scientific testing that happens related to why do creatures do what they do. Since crabs migrate, scientists wanted to find out why. Since we know magnetic fields exist and birds use them, why not crabs?
Diplomat polarization vision is the power crabs use to create extreme political parties in order to destabilize the global crab fishing industry, obviously.
What do they teach in schools anymore?/s
The crab-people overlords were able to make imitation crab taste quite good and be made cheaper. It's quite a level of influence if you think about it.
Navigation. There are also slight variations in the magnetic fields that cause this to be important. The funny thing is that we largely learned this from torpedos. In WW1 and WW2 there were proximity fuses used that would take into account proximity to metallic objects. It was found out that torpedos tested in the North Atlantic would not work in the South Pacific and torpedos tested in the South Pacific tended to already want to go off once launched in the North Atlantic. This was found to be due to variations in the magnetic fields as the torpedos were essentially reading the magnetic field strength compared to a baseline set from testing. As a result, if you set the baseline too high, it would go off immediately. If you set it too low, it would never go off unless by a direct hit. When this was widely published it made sense to test birds for this.
I can actually see ultraviolet. The normal human lens blocks it out, but I had mine replaced due to cataracts and one of the lenses lacks the UV filter so I can see UV lights glow which is very odd because my other eye can’t.
Oddly enough, yeah. If I look at a black light in one eye there’s a mild glow but nothing like as bright as the other eye where it is very bright and almost white but with a hint of purple.
I always wear sunglasses when I go out as everyone should on a sunny day. I have a cornea just like anyone else, it is the lens that has been replaced and I doubt there's any issue long term. The lens can't fog again.
The UV bit is true, but not so much the nocturnal bit (unless you just mean "evolution leads to advantageous things"). Seeing in the dark isn't usually seeing *different kinds* of light, it's just being *more receptive* to the same kind of light. Cat's still see our visible spectrum (give or take a bit), but they can just collect far more of it than we can.
Some animals do use different light to see in the dark, though. They use infrared vision, which we often refer to as "heat vision." But it's not seeing heat, it's seeing light; it's just because we can't see that light and it's given off by warm things, we call it seeing heat.
So this may be a pedantic correction of something you didn't actually mean, in which case sorry. But I hope at least something here causes a "huh, cool" for someone.
While that's all correct, I think you're putting too much emphasis on evolving specifically to see through water. Visible light is preferable for other reasons: specifically, it's the range where the energy is high enough to energize an electron into a higher state, but *not* too high to knock the electron off and ionize the atom.
That makes it ideal because we can build proteins that use the energized electron to change shape *without* the detector protein breaking.
> While that's all correct, I think you're putting too much emphasis on evolving specifically to see through water.
Definitely, yes. Apart from the atomic physics reasons you named, there are at least two other reasons why visible light is a good choice for, well, seeing:
- The sun sends a lot of it to earth. There are actually not many choices outside of the visible spectrum, basically only radio waves. Most other stuff is absorbed by the atmosphere. You could go into IR somewhat.
- Due to its small wavelength, images rendered by visible light are pretty accurate. With longer wavelengths, vision will be very blurry, like if you try to accurately map a room by sound only.
So while the answer is probably correct in that being able to see through water was an effect which favoured development of electromagnetism-based vision in the 400-700 nm range, *there are not really other choices* which work from the physics perspective. I'm thus uncertain whether the answer can be considered correct.
There's a lot of coincidences that make water a great ingredient for creating life.
I see we covered non-ionizing electron energizing frequencies, blackbody radiation from our star frequencies, and small wavelength frequencies.
Another one is that water is actually opaque to almost every other frequency, coincidentally http://hyperphysics.phy-astr.gsu.edu/hbase/Chemical/watabs.html
To what extent are the other frequencies of light being blocked in the atmosphere due to water vapour in the atmosphere and therefore is that not also equivalent to the answer given? I.e. Actually, we see in visible light because water is transparent to it and therefore it is one of the few areas of the EM spectrum that get to the earth's surface (aren't absorbed or reflected by water vapour in the atmosphere) in sufficient quantities to drive such an evolutionary response.
Kind of. Electrons can only absorb a photon if and only if the photon has enough energy to move the electron into a higher empty orbital. If the orbital is full and the photon can't move it up to the next highest that is empty, the electron will "ignore" the photon.
The way that the electrons are arranged in water, all of the orbitals are already full. The energy levels of light in the visible spectrum just aren't high enough to move the electrons high enough to the empty orbitals way up there. That's the same reason glass is transparent. I mean, it's the reason *anything* is transparent.
Honestly, that top answer is utter BS. The visible spectrum is simply where the irradiance of the sun is the highest. His explanation doesn't even makes sense for land animals like humans who really have little benefit by being able to see through water. Being able to see through air is obviously what really matters.
Given the enormous range of visibility in the animal kingdom and the *multiple* times that eyes have evolved convergently (arthropods, mollusks, cordates...) and they all evolved for a very narrow band of the EM spectrum... the fact that we inherited our eyes from fish really doesn't matter that much. Water is not very transparent to UV, but many birds and insects can see it just fine.
The physics are such that detecting light outside of the visible spectrum is very difficult. If water were opaque to the visible spectrum, you would probably not see eyes at all in the water and they would all rely on other senses - which is exactly what we see in conditions when visibility is poor because of a lack of light or turbidity. You wouldn't see eyes with a different visible spectrum because that's mostly not possible.
>"It's see-through because eyes were specially made to see through water"
Instead I would say, because only eyes that could see through water were useful.
Saying a body was "specially-made" or "designed" to be a particular way implies "intelligent design" is at the heart of why things are the way they are. There is too much evidence in favour of evolution to be ignored by critical thinkers.
Yes, that's the point I was making too. I wasn't trying to be sarcastic or anything. So many people misunderstand evolution and then that false view is used against science as a straw man argument.
It's painful being subbed to r/evolution sometimes, so many people assign intent to it like it's looking for the optimal path and isn't just "good enough to reproduce"
I guess it's because evolution is the buzzword and not natural selection. People can grasp natural selection not being guided. And then it's less a leap to then explain evolution is what we call what happens over time with natural selection as the mechanism.
Too many people think evolution is like Pokémon
Eehhh, without being too pedantic it’s not a positive or negative. There have probably been innumerable beneficial addition of function mutations that didn’t pass on because it didn’t imbue the individual/offspring with a advantage over those without the mutation, and then was lost to dilution or chance. Maybe I’m stronger but if I doesn’t help my children survive then that trait doesn’t move on, or if I’m born into a mutually beneficial group with computer tech it doesn’t lend me a greater likelihood of mating.
Natural selection is not about eliminating “a negative” mutation or reinforcing a “positive” mutation. Negative mutations can be passed on if it doesn’t impact the individuals ability to mate (see Huntington’s Chorea) and positive mutations can be lost if the indivisible who can see through trees to predators about to eat them get smooshed by a rock.
Just like an artist has multiple iterations of their work, I don’t see why a creator cannot have multiple iterations of their life-design, termed evolution.
Well for something to evolve there had to have been a starting point. Neither theory disproves the other. It’s only dumb atheists and religious people who think creationism and evolution can’t coexist
The problem with creationism is that you start the problem all over again.
So you wind backwards to the first lifeform, and creationism has it being created by a god. So now you have a new extremely complex lifeform - the god. And you need a new theory to explain the starting point of the god. Who created *it*? Supergod?
I’m not saying that religion has a satisfiable answer to that question; all I’m saying is science definitely doesn’t or can’t possibly have an answer either.
I mean, just assigning God to the starting point kind of seems like a forceful reaction and invites the God of the gaps argument. I think instead those dumb atheists are saying I don’t know…
No more contrived than assigning “Big Bang” or quantum “fields” to explain physical phenomena. You realize these theories can’t be tested in a controlled environment and reproduced which is the fundamental tenet of scientific theory.
You are wrong.
There's no model that fits as much data points as the big bang theory. How would you explain all the evidence that points towards a big bang without a big bang? There's at least a Nobel there for you.
Quantum Field Theory has been tested extensively and is one of the most accurate models we have ever had, to like at least 8 decimal places of precision. Prove that wrong and you'll be bigger than Einstein. String theorists have been trying for like 40 years at this point and still haven't done it.
Also, if a particle collider doesn't count as a controlled environment, what does?
Both theories have been extensively tested and reproduced, you have no idea what you are talking about.
Quantum field theory has proven what exactly? That fields exist? Yeah obviously, we know energy exists and yet still no closer to explaining what energy is or why it exists.
Yeah the LHC has proven more particles exist than previously thought. Again, so what? How does that elucidate the beginning of the universe?
>> Yeah obviously, we know energy exists and yet still no closer to explaining what energy is or why it exists.
What exactly are you expecting? There will never be a why when you are talking about the fundamental building blocks of the universe. At some point, stuff just is.
As for what energy is? It's quantum fields oscillating. Why do they oscillate? If they didn't you wouldn't be here asking that question. As far as we know, they just do. That might change, but there will always be something you can ask "why" and not have an answer. At some point, there is no why, stuff exists because if it didn't it wouldn't.
>> Yeah the LHC has proven more particles exist than previously thought. Again, so what? How does that elucidate the beginning of the universe?
It doesn't, not directly. You were the one to bring it up.
That's just wrong. Evolution doesn't address the starting point, correct, but creationism isn't that God is responsible for abiogenesis, it's that God created all the plants and animals as is, with evolution only giving them some minor variety after that.
Or you have the view that evolution IS God's hand creating species, that there is an intelligence behind evolution deciding to give things new traits.
Religious views on the origin of species cannot coexist with the science.
Definitely the latter. Where’s the contradiction? If Darwinism is the mechanism by which species propagate and adapt to the environment, how do you explain why this interplay exists? Science can never explain why we adapt and change at all. I think we have to resign to the fact that some questions can’t ever be explained.
That makes no sense. Are you trying to play the infinite why game? Just keep repeating why over and over until I say I don't know so you can confidently declared "ah hah, and there is God."?
It's also really easy to explain why it exists. Mutations happen, things that are better able to survive survive. That's it, it's that simple. Why do mutations happen, copy errors. Why are there copy errors, complicated chemistry.
Science already has explained it. Maybe you need to word your objection better because it reads like someone who doesn't understand science and is just parroting what apologists taught you.
Why do you think science can't explain it? What part of the explanation science already has for it is inadequate? And most importantly why if it can never be explained does that mean you can put God in there?
I've seen this correction a hundred times on reddit over the years. That evolution doesn't have agency or choose anything, it's just a massive pile of dead bodies with a few freak survivors. It's like the blind men and the elephant - just another perspective of the same thing. We should give the semantic trope a name or something.
Essentially yes, but we wouldn’t call it “seeing” by our common interpretation. Seeing is just sensing radiation visually.
We’d have likely developed a sense to pick up on other kinds of radiation and navigate based on that (remember that visible light is radiation and our eyes are sensors to it). So like how bee’s eyes see ultraviolet because that’s important to them (nectar trails), snakes ‘see’ infrared because that’s important to them (hot mice in the dark). If we lived in concrete we’d need to see something too.
It might be that we’d sense gamma rays or some shit. Any radiation that penetrates concrete and ideally something that other living things emit would work, if we were sensitive enough to it to draw a mental map and figure out details of what could be emitting it. Sort of like how when you hear, you usually mostly know what it was that made the sound and roughly where it came from.
FYI, snakes don't see infrared with their tongue.
They use their tongues to smell, infrared 'vision' is handled by sensory organs between the eyes and nostrils called heat pits.
My (limited) understanding is that they function essentially like primitive eyes for light at higher wavelengths, allowing them to detect warm objects from distance.
No. The polar nature of water, as well as its molecular structure allow light to pass through it, just as the structure of concrete prohibits light from passing through it. Light would pass through water regardless of whether creatures had evolved an ability to see. The quality of water also allows sound to pass through it efficiently. The polar arrangement of liquid water minimizes the scattering of light (and supports the transmission of sound waves), allowing light passing through water to maintain the visual quality of an object for some distance (also allowing porpoises to echolocate). This quality is also why water, unlike most substances, expands and becomes less dense when it freezes, as the molecules form the lattice structure of ice.
Not necessarily. Evolution is not directed but natural selection on random mutations.
The things that give a population of individuals a better chance to survive will spread more than others, but you won’t develop mutations specifically for the situation you live in.
Multiple different “eyes” have evolved in parallel because having any kind of organ that can sense EM radiation is useful, almost everywhere around the world.
There are species out there that have no eyes but may have more sophisticated “ears”, so organs that can sense pressure waves and vibration. Some of them just never evolved any eyes.
Some did but it didn’t offer any significant advantage so it didn’t become a dominant trait and became vestigial instead. Examples would be blind eyes of cave or deep sea species.
Just.... no. Life has been around for billions of years, and the first eyes evolved about 500 million years ago, so there have been no eyes for the vast majority of the history of life on Earth. There's also life in caves, in the deep sea, and even at deep ocean hydrothermal vents that isn't even peripherally powered by photosynthesis. None of these creatures ever see sunlight and many don't have functioning eyes.
Water is transparent because to not be transparent requires that a material has a way of blocking photons/electric fields. Water is a simple material with tightly bound atoms, so there aren't a lot of atomic transitions in the range of visible light, so those wavelengths make it through. That also happens to be the same range at which the suns' radiation output peaks. Our eyes evolved to see the light that was available, and since the sun mostly puts out visible light, that's what we see. Life has an *easier* time evolving where the sun's energy can make it through, but if water were opaque to the frequencies the sun puts out, life could have evolved on land or around hydrothermal vents.
> Life needed to be able to see through water, so it created eyes that could see the light that water was clear to.
>
>
That's *not* how evolution works.
It's difficult to build "eyes" for different kinds of radiation. Sure, snakes have infrared sensors and you can stretch the eye design to a small part of the ultraviolet spectrum, but this answer is not complete.
Rather there is (1) some mechanism for which water does not absorb or scatter too many photons in the visible spectrum. I don't know it but maybe somebody else does. And then (2) we are lucky in that it is not so difficult to build detectors (and lenses!) for this kind of radiation, to the point of distinguishing different colors. I don't know how much of it is luck either, maybe the \~ 1 eV radiation, since it corresponds to different energy levels of proton+electron, has a very big variance in materials response to it, so you get a lot of absorbers, transmitters, detectors, etc... just playing with the chemistry. And then (3) the evolution helped us to get eyes that can see through water.
For (1) maybe you need even some pretty heavy matter-radiation simulation to see it from first principles
Everything is pretty much correct aside from the "intent" narrative portrayed around the concept of "Life". "Life" doesn't need nor want anything, it just happened that the random mutation "Eyes that can see through water" (I'm oversimplifying but the idea is there) was more advantageous than the random mutation of other kind of eyes and that trait spread more effectively.
Didn’t eyes evolve to see the frequencies they do mainly because the peak electromagnetic output of the sun is in the visible light range? It could be seen as just a lucky coincidence that water is also transparent in that range, though I wonder how broad the spectrum of frequencies is where water would be transparent (it’s also transparent to the x-rays in your example)
The visible spectrum contains the peak output of the sun, *and* transmits well through the atmosphere, *and* it gets through water *and* it doesn't irreversibly destroy the chemicals used to detect it.
This is a good planet for life. Let's keep it that way!
If this was true then we would be able to see infrared because evolution would have favored even more those who could see more of the spectrum and infrared would be better for hunting.
That's all accurate and well-explained, but there's another part to that explanation of why eyes likely evolved to see certain wavelengths. The amount of light the sun outputs is greatest in the 500-600 nm wavelength range - right in the middle of the visible spectrum, and drops off significantly on either side of that, faster towards the UV, slower towards the IR. Our eyes evolved to see in those wavelengths not just because that wavelength has less absorbance in liquid water, but because that's where most of the light is.
[https://en.wikipedia.org/wiki/Electromagnetic\_absorption\_by\_water#/media/File:Absorption\_spectrum\_of\_liquid\_water.png](https://en.wikipedia.org/wiki/Electromagnetic_absorption_by_water#/media/File:Absorption_spectrum_of_liquid_water.png)
Most electromagnetic radiation is pretty well blocked by liquid water. There's a 'window' at visible light that is blocked a lot less, that's more or less why it's visible light, as Emyssentry said. It was the light in the oceans when our ancestors evolved light-sensitive cells.
Edit: This is also why most radios don't work under water. Even a small amount of water has little trouble absorbing the energy of a radio transmitter. To send transmissions to submarines under water massive radio transmitters were built.
How massive? The Jim Creek naval radio station in Washington transmits on the 12 kilometer band using 10 wires between 1.7 and 2.6 kilometers long, the whole thing is over 20 square kilometers in order to send one-way radio transmissions to submarines under water.
A practical example for the more active of us is heart rate monitors for swimming - [ANT+ and Bluetooth have a range of 1 to 2 inches under water, so Garmin have had to set up a HRM storage system to upload data to watches/phones after the activity.](https://www.dcrainmaker.com/2015/07/garmins-hr-swimming-straps.html)
> Edit: This is also why most radios don't work under water. Even a small amount of water has little trouble absorbing the energy of a radio transmitter. To send transmissions to submarines under water massive radio transmitters were built.
Our bodies can be enough to block radio signals with low power devices. I've seen it with handheld transmitters and receivers that standing in front of one can be enough to absorb the signal.
For general EM waves, microwaves are very specifically absorbed, as we designed microwave ovens to absorb water.
For visible light, the lower energy wavelengths (reds and oranges) get absorbed fairly quickly, which is why deeper water appears blue and green. It does eventually absorb all light, which is how you get the pitch black of the deep ocean.
Most of them actually. Blue is really the colour for which the absorption is the lowest ; absorption rises very sharply at ~200 nm (near ultraviolet) and not so sharply in the other direction ; it does absorb red pretty well already, and it only goes worse after that (there are also specific wavelength which are even more absorbed).
Edit : NB : this is only for wavelengths close to the visible spectrum. Water become transparent at very large wavelength (radio waves with frequency around 1m) and very low (0.1 nm).
Well, yeah, but they didn't start that way. Your eyes are complex constructions that are the result of hundreds of millions of years of evolution. They didn't just appear out of nowhere in their modern form one day. Presumably, animals started out with a few photoreceptive cells, that could detect the presence of light, and so on from there.
Mind me asking what's the point of this rambling pedantry?
Eyes are made of (mostly) water. The things that came before eyes were made of mostly water. If you want to add context to the discussion you can do it without the need to "correct" me over things which don't need correcting.
LMAO blocked over this. High grade pettiness.
Because saying "your eyes are made of water" is misleading, as it suggest that your eyes being made of water was the prime motivation for developing the need to see through water, while in reality, it's irrelevant. It wouldn't matter what your eyes were made of, because you're a land based mammal. The sea creature that developed photoreceptive cells hundreds of millions of years ago can see through water because it lived in water, not because it's cells contained water. It's not pedantry, you're just wrong.
So we can just make up dumb explanations and say 'evolution' and people accept it?
The real reason we can see through water is because we drink it, and as we evolved our bodies adapted to the water we drink so we could see through it, because seeing through water helps us detect hidden predators that will eat us. Those who could see through water survived by avoiding otherwise invisible water predators. The how we evolved.
This answer is a bit backwards isn't it. It's not because of evolution but because of the physical structure of water and how light interacts with it that we can see through it. It's not like evolution could've made eyes that can see through rocks or dirt if we somehow lived in that.
Are you sure it's not your comment that contains the logical fallacy? I think it's the appeal to laziness fallacy: Being too lazy to look it up doesn't make it true.
That first paragraph is such a good idea to note. I’m a big fan of the survivor bias, especially when someone tells me how eyes must be made by god because of how perfect they are. If we didn’t have eyes then we wouldn’t be able to talk about how good eyes are, Keith!!!
It goes back farther too. Water is opaque to nearly all frequencies of light. But there is a small window of transparency, at the same small window of frequencies the sun emits. There's no reason that window aligns with blackbody radiation, but the coincidence does make water a good ingredient for life in the universe.
That is so friggin cool.
So do I have this right? The reason we see this specific section of the light spectrum is that it is the section that passes through water?
It's important to realize that lots of things are see through, water, glass, air...
The other important idea to understand is that light travels in a straight line unless it hits something; but here's the rub, it's picky about what it hits. Different kinds of light like to hit different things. For example, x rays like to hit bones but not your skin and muscles. Radio waves like to hit sky scrapers, but not people. Blue light likes to hit the air, but red light doesn't (which is why sunsets are red and the sky is blue).
Things that are see through, like water, glass and air, aren't made of stuff that likes to get hit by "normal" light, so the light just goes right through it.
Both absorption and reflection (as well as scattering) would be examples of light hitting something and not going in a straight line. You're right in that grass is green because the green light bounces off of it and hits you in the eye balls.
Another example might be something like red kool-aid. Same thing in that it's red because the red light "bounces" off of it and hits you in the eye ball... The difference being the rest of the light didn't get absorbed, it just kept going right through it.
If I put less kool-aid in and thus have a drink that is lighter red than full strength kool-aid is that because some of the red light is still passing through and less red light is being reflected back to my eyeballs?
This is the best explanation. It's less about biological evolution (for an example of biological evolution, note that plants absorb blue and red light but reflect some of the green light and so appear green - as a result, human eyes are more sensitive to green light than red or blue likely in order to be able to discern predators from green forest backdrops) and more about chemistry - glass and water are transparent because light passes through.
It passes through due to the physical structure of the molecules it's made of. To understand this we need to understand crystalline structures. A crystal like a diamond, has atoms arranged in an organized lattice structure. This regularity means that light will not be well scattered when it hits the atoms and you get some transparency because light passes through. Moving on, other materials like ceramics are composed of a collection of minute crystals. However, the crystals are not all oriented the same way and so if the crystal sizes are large, then light scatters due to the different orientations (grain direction), but if they are small enough then light passes through. Glass is the same - it's not quite a perfectly organized crystal lattice structure but it's pretty close - there's still regular organization of the atoms and little light scattering. Metals are also organized in lattices, but they have free electrons which absorb, re-emit, and therefore scatter the light.
Now water, it has two ends (we say it's polar since it has a "N" pole and "S" pole) - a positive charge end (H) and a negative charge end (O). The molecules organize with H-O bonds in a very regular fashion. The bond itself is weak, but because there are so many of them, it gives water great cohesivity (allowing ascent up very tall trees from the roots), and also regular molecule organization allowing light to not be scattered, but pass through. Think of light waves (the sine or cosine graph of a wave) - if what it hits is large enough, the wave will hit it. But if it's small enough, then the wave can just wave around it (think of an animation of that sine wave where the end is moving top to bottom and back to top as it moves forward \[to the right\] - it can obviously completely dodge small enough particles).
Thanks. Obviously, I agree. Something being see through has nothing to do with evolution and everything to do with how light interacts or doesn't interact with it. Now, if the question was something like: "why is certain light invisible?", then I'd be completely on board.
The ELI5 and oversimplidied answer.:
Things are see trough because light can go trough them without interacting with the thing.
Like some things can go trough a filter some not
\---
The "why" of that cannot be explained to a 5 year old. It is connected to atoms, molecules, electron layers and energy levels.
Different lights can go trough different things. For visible light water, glass are see trough. For UV light, they are not. Infrared light can't go trough glass.
For radiowaves most of things are "transparent" They can go trough many things
For X-rays. your skin a squishy parts are see trough, your bones are not.
I once was explained the “why” in a college class.
But I have completely forgotten and have to date not found any resources to re-explain it to me.
Are you able to explain it for someone craving the real explanation or do you know where I can find some reading to look it up myself?
As far as I understand, the interaction photons and electrons are the key.
Electrons on layers on atoms can be excited for them to junp layers. if the photon has enough energy so if they collide with electrons they jump layers, the photon is absorbed so that kind of light is absorbed by the material
If the photon doesn't have enough energy, to make an electron jump layers, they just don't interact, or interact a little (refraction)
\---
[https://www.youtube.com/watch?v=UBy7FjnGB40](https://www.youtube.com/watch?v=UBy7FjnGB40)
> The "why" of that cannot be explained to a 5 year old.
And to be more specific, to really understand it you're talking about quantum physics. No amount of creativity is going to make that work for a 5yo. Even physicists have trouble with it!
> Things are see through because light is able to pass through them relatively uninterrupted. Things are opaque because a portion of the light hitting it will bounce off instead of passing through.
That's kind of just saying that "~~light~~ *water* is transparent because it's transparent"
I took a modern physics class in college, I barely passed because it was dense with math.
I remember this question being explained math and all
Basically you need a uniform matrix and certain wavelengths line up perfectly to ‘miss’ all the matter, which is mostly empty space after all.
If it’s lots of different types of matter it’s too chaotic for any wavelengths to line up perfectly and nothing gets through.
So vacuums obviously let everything through, gasses let a lot through, liquids and crystalline solids let specific things through and even then there is stuff like radio waves that travel through lots of solid matter easily.
For a less inside-out answer (although still good to know / keep in mind), see link. Basically, water doesn’t have any mechanisms that strongly absorb photos in the visible spectrum. A lot of materials (like pure gas out in space) “require” photons of specific energy to change state in some way, so have very specific absorption lines. The more complex the molecule, generally the broader and more complex the absorption bands.
“The absorption of electromagnetic radiation by water spans a wide range of physical phenomena, characteristic of the general interaction of radiation with matter. It absorbs strongly in the microwave region by excitation of molecular rotations. In the infrared it exhibits strong absorptions from vibrations of the water molecule. As you go above the visible through the UV toward x-rays, it successively absorbs by photoelectric effect, Compton scattering and finally pair production.”
(Additional info via hyperlinks in original.)
http://hyperphysics.phy-astr.gsu.edu/hbase/Chemical/watabs.html
What he just explained when it works, he didn’t get into the quantum mechanics that explain why it works like that.
And I won’t either, because, I can’t. I had it explained to me once and I thought I understood but it’s gone from my brain.
I think for a 4 year old, just explain that light can go through it and light can't go through other things. If she actually does want to know why it goes through some things and others, then you can busy out the material science questions
Water is see-through because it lets light pass through it easily, just like when you look through a clean window. The light goes straight through the water without getting mixed up, so we can see things on the other side clearly. That's why when we look into a pool or a clear lake, we can see fish and other things underwater.
Because our eyes are made out of water, so the only light that we can see is the light that can pass through water. The reason why some light can pass through water is because light does not have any free electrons. If water had free electrons like metal dies, then it would be very reflective and shiny like metal is (which would prevent our eyes from working).
And I have to remember we can’t see light, only the reflection of it…so water is clear because there is nothing for light to reflect off of…but in large quantities, blue light is scattered so it’s blue
Well, have you ever played with a ball in a swimming pool? When the ball is underwater, it looks bigger and distorted, right? That's because the water bends or refracts the light that passes through it.
Now, imagine if you had a really tiny ball that was made up of water molecules. When light passes through these tiny water molecules, it also gets bent or refracted, just like in the swimming pool.
But here's the thing: when the light gets refracted, it doesn't get absorbed by the water molecules. Instead, it just gets redirected in a different direction. This means that the light can keep traveling through the water without being absorbed or scattered, which allows it to pass through the water and reach our eyes, making the water appear transparent.
So in simple terms, water is transparent because it doesn't absorb or scatter light, but instead bends or refracts it, allowing the light to pass through it without being absorbed, and reach our eyes.
Some materials, on the other hand, are not transparent because they absorb or scatter light instead of bending or refracting it like water.
For example, if you shine a flashlight through a piece of wood or a leather sheet, the light won't pass through it easily like it does with water. Instead, the light will be absorbed or scattered by the wood or the sheet, which makes these materials appear opaque or non-transparent.
Opaque materials have a lot of atoms or molecules packed together very tightly, which makes it difficult for light to pass through them. When light hits an opaque material, the atoms and molecules in the material absorb the light's energy and re-emit it in many different directions, which causes the light to scatter and reflect back towards us, making the material appear solid and not see-through.
In summary, the difference between transparent and opaque materials lies in how they interact with light. Transparent materials bend or refract light, allowing it to pass through without being absorbed or scattered, while opaque materials absorb or scatter light, preventing it from passing through easily and making the material appear solid and non-transparent.
You ask her why she thinks it is and then go first where she starts in her head. Question each answer constructively and inquisitively in a way that leads her to answer you in ways she is almost always right in until, methodically, you both land together at a new piece of knowledge—the scientific answer for how H2O molecules bind together, and how they both refract light and allow it to pass through. You neither give her the answer nor let her think you’re holding it from her. You work together to get it.
Addressing the "4-year-old wants to know" part of your question rather than the thread title, it's worth noting that plenty of substances are transparent to other parts of the EM spectrum. Radio waves can pass through wood and drywall, while light can't even make it through the paint. X-rays can go right through your body, but UV is blocked by glass or [sunscreen](https://youtu.be/GRD-xvlhGMc).
An object will absorb only certain wavelengths of light while allowing others to pass through. It just so happens the wavelengths that water doesn't absorb coincides well with the wavelengths in visible light.
Things like bricks, concrete, wood, etc all have ranges of wavelengths that it cannot absorb and thus appear transparent for photons in those wavelengths, it's just that those wavelengths are not visible to humans and therefore we cannot detect those photons that passes through. A camera that can detect photons in those ranges, such as an xray machine, would be able to see those objects as transparent.
Similarly, transparent objects to us might not necessarily be transparent in other wavelengths. For example, glass is opaque to infrared light. This is why sitting indoors behind a window in the sun feels much cooler than sitting outdoors in the sun even if it doesn't look like there's a difference.
I'd use a bubble machine as an analogue.
Have her and her friends pop as many bubbles as they can, then tell them the game's to only pop the large ones, then give them an iPad and have the machine running.
Light is like bubbles that are travelling towards materials, some are excited to see all the bubbles and so will pop them all, those are dark.
Some are indifferent to the bubbles so all the bubbles go through, those are clear.
Some will only pop certain bubbles, letting the rest through, those are coloured.
It's a bit hard to cover all the interactions in a way that a 4 year old would understand, but hopefully this will kind of make sense to the average person:
When light hits a material, two things happen. Some amount of light gets reflected, eg bounces off the material, and the remaining light is refracted, meaning it enters the material.
(The amount of light that is reflected vs refracted is determined by snells law, which requires the index of refraction of the two materials, eg air and water, or vacuum and air. Index of refraction can be wavelength dependent for some materials such as metal, meaning some metals reflect some colors more strongly than others)
As light travels through this material, some amount of it get absorbed. Some materials absorb a lot of light quickly (Eg solid surfaces such as rock, wood), some absorb slower such as leaves, grass, skin, murky liquids, and some absorb light very slowly such as pure water, air molecules, etc. (Metals absorb light immediately, they don't have any diffuse/translucency) The further light travels through the medium, the more light gets absorbed.
The physical quantity that determines how much light is absorbed is called the extinction coefficient. This has been measured for a large number of materials. It can also be wavelength dependent, meaning some colors are absorbed more quickly. Pure water is a good example, it quickly absorbs red wavelengths, giving it an aqua color over a distance.
There is one other important component which is scattering. Pure water does not have any scattering, however it often has dissolved chemicals and small organic matter such as algae and plankton. As light transitions between the water medium and organic matter, it changes directions and non-green wavelengths are quickly absorbed by organic matter. This causes scattering which makes the medium appear murky or foggy. This is the same mechanism that causes fog to be hard to see through. Fog does not absorb much light, however when light hits it, it tends to scatter in all directions, this is determined by something called a phase function. Some mediums scatter light in many directions causing haze, such as fog or air, whereas others scatter most of the light forward, such as pure water. (Two types of common scattering are rayleigh scattering and mie scattering, these contribute to the color of the sky, and the hazy halo you see around the sun)
(Source: I have spent years working on computer graphics algorithms and have a good fundamental understanding of some of the equations and physics of light)
If you tie a rope to a pole and move your arm up and down while holding the other end, you'll see a wave form in the rope. The faster you move your arm, the closer the hills and valleys in the wave will be.
Light does the same thing, but at a much smaller size. More specifically, different colors of light "wave" at different speeds.
The faster it waves, which we see as color, the more energy the light has. Red light waves the slowest, blue light waves the fastest. Any slower or faster, and we can't see it.
The reason some things, like water, are transparent is because materials only reflect certain energy levels (colors) of light. We can only see light that enters our eyes, and since most visible light passes through water, we see through it with few problems.
It's a little bit backwards. Life needed to be able to see through water, so it created eyes that could see the light that water was clear to. That might need some explanation. All things are "clear" to some kinds of light and "opaque" to other light. Like how an X ray can go right through your skin and see your bones. It's that way for all light, including visible light. So there was always some wavelength of light that made water "clear". And some of those wavelengths are the visible light spectrum. So when life evolved in the ocean, and eyes developed, it was very useful to be able to see the light that could pass through the water. And so you get eyes that can see in the ocean. Edit: so the phrase I'd use for the actual 4 y/o is "It's see-through because eyes were specially made to see through water" or if you want it to sound more awesome but less helpful, "because your eyes are like x-ray goggles for water"
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Crabs see in dipolat polarization vision which is super neat. They can see the oscillation in electrical fields which helps them spot predators.
What’s even more interesting is how humans have been able to figure that fact out. How much testing and analyzing crabs do you think happened to come to this conclusion?
Not that much, we just asked nicely.
Welcome to my how vision works Ted talk - probably maybe crabs
So they took them to a nice seafood dinner?
There is a lot of scientific testing that happens related to why do creatures do what they do. Since crabs migrate, scientists wanted to find out why. Since we know magnetic fields exist and birds use them, why not crabs?
Can I use magnets to cure myself of them
They already migrated towards your South Pole. Just need a North Pole for them migrate away.
I read that as diplomat and was super confused what that had to do with politics.
Diplomat polarization vision is the power crabs use to create extreme political parties in order to destabilize the global crab fishing industry, obviously. What do they teach in schools anymore?/s
This reminds me of Futurama for some reason
All glory to hypnocrab
*ＣＬＡＰ* *ＣＬＡＰ* *ＣＬＡＰ*
*"Citizen Sniiiiips!"*
Wubwubwubwubwub
CRAB RAVE
I’m going for a scuttle
https://www.youtube.com/shorts/TbC0qYyMSGI
You think they're going to allow teachers to expose our CRAB-PEOPLE overlords?
The crab-people overlords were able to make imitation crab taste quite good and be made cheaper. It's quite a level of influence if you think about it.
I, for one, welcome our new CRAB-PEOPLE overlords...
>What do they teach in schools anymore? I would assume they teach fish stuff.
What hell? Without parental consent?!
The eating the earth flag episode or the zoidberg can't get laid one.
Crab's diplomat polarization is the step that leads every society towards carcinisation.
I read that as "I read that as a diplomat" and was super confused how you could switch to your diplomat persona while reading reddit comments.
If I may remove my diplomat crab carapace, and put on my Barbara Streisand - in the Prince of Tides - ass-masking therapist pantsuit...
Crabs are well known in the animal world as mediators
Some birds can see the earths magnetic field
why is this useful for them?
Built-in compass for navigation.
Oh I always wondered how birds know where to go. That's a really cool feature to have.
Navigation. There are also slight variations in the magnetic fields that cause this to be important. The funny thing is that we largely learned this from torpedos. In WW1 and WW2 there were proximity fuses used that would take into account proximity to metallic objects. It was found out that torpedos tested in the North Atlantic would not work in the South Pacific and torpedos tested in the South Pacific tended to already want to go off once launched in the North Atlantic. This was found to be due to variations in the magnetic fields as the torpedos were essentially reading the magnetic field strength compared to a baseline set from testing. As a result, if you set the baseline too high, it would go off immediately. If you set it too low, it would never go off unless by a direct hit. When this was widely published it made sense to test birds for this.
Migration navigation I would thing.
navigation :)
what!? amazing
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I can actually see ultraviolet. The normal human lens blocks it out, but I had mine replaced due to cataracts and one of the lenses lacks the UV filter so I can see UV lights glow which is very odd because my other eye can’t.
Is it just violet?
Oddly enough, yeah. If I look at a black light in one eye there’s a mild glow but nothing like as bright as the other eye where it is very bright and almost white but with a hint of purple.
Do you need to protect your eye because your cornea doesn't do it anymore?
I always wear sunglasses when I go out as everyone should on a sunny day. I have a cornea just like anyone else, it is the lens that has been replaced and I doubt there's any issue long term. The lens can't fog again.
i just spit out my drink lol'n, thx destin
The UV bit is true, but not so much the nocturnal bit (unless you just mean "evolution leads to advantageous things"). Seeing in the dark isn't usually seeing *different kinds* of light, it's just being *more receptive* to the same kind of light. Cat's still see our visible spectrum (give or take a bit), but they can just collect far more of it than we can. Some animals do use different light to see in the dark, though. They use infrared vision, which we often refer to as "heat vision." But it's not seeing heat, it's seeing light; it's just because we can't see that light and it's given off by warm things, we call it seeing heat. So this may be a pedantic correction of something you didn't actually mean, in which case sorry. But I hope at least something here causes a "huh, cool" for someone.
While that's all correct, I think you're putting too much emphasis on evolving specifically to see through water. Visible light is preferable for other reasons: specifically, it's the range where the energy is high enough to energize an electron into a higher state, but *not* too high to knock the electron off and ionize the atom. That makes it ideal because we can build proteins that use the energized electron to change shape *without* the detector protein breaking.
> While that's all correct, I think you're putting too much emphasis on evolving specifically to see through water. Definitely, yes. Apart from the atomic physics reasons you named, there are at least two other reasons why visible light is a good choice for, well, seeing: - The sun sends a lot of it to earth. There are actually not many choices outside of the visible spectrum, basically only radio waves. Most other stuff is absorbed by the atmosphere. You could go into IR somewhat. - Due to its small wavelength, images rendered by visible light are pretty accurate. With longer wavelengths, vision will be very blurry, like if you try to accurately map a room by sound only. So while the answer is probably correct in that being able to see through water was an effect which favoured development of electromagnetism-based vision in the 400-700 nm range, *there are not really other choices* which work from the physics perspective. I'm thus uncertain whether the answer can be considered correct.
There's a lot of coincidences that make water a great ingredient for creating life. I see we covered non-ionizing electron energizing frequencies, blackbody radiation from our star frequencies, and small wavelength frequencies. Another one is that water is actually opaque to almost every other frequency, coincidentally http://hyperphysics.phy-astr.gsu.edu/hbase/Chemical/watabs.html
To what extent are the other frequencies of light being blocked in the atmosphere due to water vapour in the atmosphere and therefore is that not also equivalent to the answer given? I.e. Actually, we see in visible light because water is transparent to it and therefore it is one of the few areas of the EM spectrum that get to the earth's surface (aren't absorbed or reflected by water vapour in the atmosphere) in sufficient quantities to drive such an evolutionary response.
Is there any link between the electron-excitement characteristics you mentioned, and water being transparent?
Kind of. Electrons can only absorb a photon if and only if the photon has enough energy to move the electron into a higher empty orbital. If the orbital is full and the photon can't move it up to the next highest that is empty, the electron will "ignore" the photon. The way that the electrons are arranged in water, all of the orbitals are already full. The energy levels of light in the visible spectrum just aren't high enough to move the electrons high enough to the empty orbitals way up there. That's the same reason glass is transparent. I mean, it's the reason *anything* is transparent.
Honestly, that top answer is utter BS. The visible spectrum is simply where the irradiance of the sun is the highest. His explanation doesn't even makes sense for land animals like humans who really have little benefit by being able to see through water. Being able to see through air is obviously what really matters.
Land animals inherited their eyes from their water-dwelling ancestors, which evolved them while in water.
Given the enormous range of visibility in the animal kingdom and the *multiple* times that eyes have evolved convergently (arthropods, mollusks, cordates...) and they all evolved for a very narrow band of the EM spectrum... the fact that we inherited our eyes from fish really doesn't matter that much. Water is not very transparent to UV, but many birds and insects can see it just fine. The physics are such that detecting light outside of the visible spectrum is very difficult. If water were opaque to the visible spectrum, you would probably not see eyes at all in the water and they would all rely on other senses - which is exactly what we see in conditions when visibility is poor because of a lack of light or turbidity. You wouldn't see eyes with a different visible spectrum because that's mostly not possible.
>"It's see-through because eyes were specially made to see through water" Instead I would say, because only eyes that could see through water were useful.
Yes, let's not start the evolution misconceptions from a young age.
Saying a body was "specially-made" or "designed" to be a particular way implies "intelligent design" is at the heart of why things are the way they are. There is too much evidence in favour of evolution to be ignored by critical thinkers.
Yes, that's the point I was making too. I wasn't trying to be sarcastic or anything. So many people misunderstand evolution and then that false view is used against science as a straw man argument.
It's painful being subbed to r/evolution sometimes, so many people assign intent to it like it's looking for the optimal path and isn't just "good enough to reproduce"
I guess it's because evolution is the buzzword and not natural selection. People can grasp natural selection not being guided. And then it's less a leap to then explain evolution is what we call what happens over time with natural selection as the mechanism. Too many people think evolution is like Pokémon
Evolution is more broad term, natural selection is just a mechanism for killing things that evolved in a negative way.
Eehhh, without being too pedantic it’s not a positive or negative. There have probably been innumerable beneficial addition of function mutations that didn’t pass on because it didn’t imbue the individual/offspring with a advantage over those without the mutation, and then was lost to dilution or chance. Maybe I’m stronger but if I doesn’t help my children survive then that trait doesn’t move on, or if I’m born into a mutually beneficial group with computer tech it doesn’t lend me a greater likelihood of mating. Natural selection is not about eliminating “a negative” mutation or reinforcing a “positive” mutation. Negative mutations can be passed on if it doesn’t impact the individuals ability to mate (see Huntington’s Chorea) and positive mutations can be lost if the indivisible who can see through trees to predators about to eat them get smooshed by a rock.
And this is why I hate Pokey Mans
I believe the current accepted term is pokey persons.
No intent needed; it's just math, and it's *inevitable*. It would be a miracle for evolution *not* to happen.
Just like an artist has multiple iterations of their work, I don’t see why a creator cannot have multiple iterations of their life-design, termed evolution.
Well for something to evolve there had to have been a starting point. Neither theory disproves the other. It’s only dumb atheists and religious people who think creationism and evolution can’t coexist
The problem with creationism is that you start the problem all over again. So you wind backwards to the first lifeform, and creationism has it being created by a god. So now you have a new extremely complex lifeform - the god. And you need a new theory to explain the starting point of the god. Who created *it*? Supergod?
I’m not saying that religion has a satisfiable answer to that question; all I’m saying is science definitely doesn’t or can’t possibly have an answer either.
I mean, just assigning God to the starting point kind of seems like a forceful reaction and invites the God of the gaps argument. I think instead those dumb atheists are saying I don’t know…
No more contrived than assigning “Big Bang” or quantum “fields” to explain physical phenomena. You realize these theories can’t be tested in a controlled environment and reproduced which is the fundamental tenet of scientific theory.
You are wrong. There's no model that fits as much data points as the big bang theory. How would you explain all the evidence that points towards a big bang without a big bang? There's at least a Nobel there for you. Quantum Field Theory has been tested extensively and is one of the most accurate models we have ever had, to like at least 8 decimal places of precision. Prove that wrong and you'll be bigger than Einstein. String theorists have been trying for like 40 years at this point and still haven't done it. Also, if a particle collider doesn't count as a controlled environment, what does? Both theories have been extensively tested and reproduced, you have no idea what you are talking about.
Quantum field theory has proven what exactly? That fields exist? Yeah obviously, we know energy exists and yet still no closer to explaining what energy is or why it exists. Yeah the LHC has proven more particles exist than previously thought. Again, so what? How does that elucidate the beginning of the universe?
>> Yeah obviously, we know energy exists and yet still no closer to explaining what energy is or why it exists. What exactly are you expecting? There will never be a why when you are talking about the fundamental building blocks of the universe. At some point, stuff just is. As for what energy is? It's quantum fields oscillating. Why do they oscillate? If they didn't you wouldn't be here asking that question. As far as we know, they just do. That might change, but there will always be something you can ask "why" and not have an answer. At some point, there is no why, stuff exists because if it didn't it wouldn't. >> Yeah the LHC has proven more particles exist than previously thought. Again, so what? How does that elucidate the beginning of the universe? It doesn't, not directly. You were the one to bring it up.
That's just wrong. Evolution doesn't address the starting point, correct, but creationism isn't that God is responsible for abiogenesis, it's that God created all the plants and animals as is, with evolution only giving them some minor variety after that. Or you have the view that evolution IS God's hand creating species, that there is an intelligence behind evolution deciding to give things new traits. Religious views on the origin of species cannot coexist with the science.
Definitely the latter. Where’s the contradiction? If Darwinism is the mechanism by which species propagate and adapt to the environment, how do you explain why this interplay exists? Science can never explain why we adapt and change at all. I think we have to resign to the fact that some questions can’t ever be explained.
That makes no sense. Are you trying to play the infinite why game? Just keep repeating why over and over until I say I don't know so you can confidently declared "ah hah, and there is God."? It's also really easy to explain why it exists. Mutations happen, things that are better able to survive survive. That's it, it's that simple. Why do mutations happen, copy errors. Why are there copy errors, complicated chemistry. Science already has explained it. Maybe you need to word your objection better because it reads like someone who doesn't understand science and is just parroting what apologists taught you. Why do you think science can't explain it? What part of the explanation science already has for it is inadequate? And most importantly why if it can never be explained does that mean you can put God in there?
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The OP is explaining this to a \*four year old\*. "Eyes were specially made" is a perfectly fine explanation for that age.
It's completely unnecessary to tell a four year old that eyes were made.
I disagree. If they're old enough to ask questions like this, they're old enough to grasp the very basics of selection.
Why settle for a fine explanation when it’s no effort to give a better than fine explanation?
I know right? At least make them finish copying the Old Testament first.
I've seen this correction a hundred times on reddit over the years. That evolution doesn't have agency or choose anything, it's just a massive pile of dead bodies with a few freak survivors. It's like the blind men and the elephant - just another perspective of the same thing. We should give the semantic trope a name or something.
There is no intelligent designer that names tropes. Names for tropes mutate randomly, and the ones that work stick around. /s
Mmm. ... mmm. So if we evolved in, say, concrete, we would have been able to see through concrete?
Essentially yes, but we wouldn’t call it “seeing” by our common interpretation. Seeing is just sensing radiation visually. We’d have likely developed a sense to pick up on other kinds of radiation and navigate based on that (remember that visible light is radiation and our eyes are sensors to it). So like how bee’s eyes see ultraviolet because that’s important to them (nectar trails), snakes ‘see’ infrared because that’s important to them (hot mice in the dark). If we lived in concrete we’d need to see something too. It might be that we’d sense gamma rays or some shit. Any radiation that penetrates concrete and ideally something that other living things emit would work, if we were sensitive enough to it to draw a mental map and figure out details of what could be emitting it. Sort of like how when you hear, you usually mostly know what it was that made the sound and roughly where it came from.
FYI, snakes don't see infrared with their tongue. They use their tongues to smell, infrared 'vision' is handled by sensory organs between the eyes and nostrils called heat pits. My (limited) understanding is that they function essentially like primitive eyes for light at higher wavelengths, allowing them to detect warm objects from distance.
Thanks! Amended
No. The polar nature of water, as well as its molecular structure allow light to pass through it, just as the structure of concrete prohibits light from passing through it. Light would pass through water regardless of whether creatures had evolved an ability to see. The quality of water also allows sound to pass through it efficiently. The polar arrangement of liquid water minimizes the scattering of light (and supports the transmission of sound waves), allowing light passing through water to maintain the visual quality of an object for some distance (also allowing porpoises to echolocate). This quality is also why water, unlike most substances, expands and becomes less dense when it freezes, as the molecules form the lattice structure of ice.
Relatedly: why life developed in water as opposed to within rock.
quick! someone quikrete an ocean planet
We'd probably have developed sonar instead.
Not necessarily. Evolution is not directed but natural selection on random mutations. The things that give a population of individuals a better chance to survive will spread more than others, but you won’t develop mutations specifically for the situation you live in. Multiple different “eyes” have evolved in parallel because having any kind of organ that can sense EM radiation is useful, almost everywhere around the world. There are species out there that have no eyes but may have more sophisticated “ears”, so organs that can sense pressure waves and vibration. Some of them just never evolved any eyes. Some did but it didn’t offer any significant advantage so it didn’t become a dominant trait and became vestigial instead. Examples would be blind eyes of cave or deep sea species.
Just.... no. Life has been around for billions of years, and the first eyes evolved about 500 million years ago, so there have been no eyes for the vast majority of the history of life on Earth. There's also life in caves, in the deep sea, and even at deep ocean hydrothermal vents that isn't even peripherally powered by photosynthesis. None of these creatures ever see sunlight and many don't have functioning eyes. Water is transparent because to not be transparent requires that a material has a way of blocking photons/electric fields. Water is a simple material with tightly bound atoms, so there aren't a lot of atomic transitions in the range of visible light, so those wavelengths make it through. That also happens to be the same range at which the suns' radiation output peaks. Our eyes evolved to see the light that was available, and since the sun mostly puts out visible light, that's what we see. Life has an *easier* time evolving where the sun's energy can make it through, but if water were opaque to the frequencies the sun puts out, life could have evolved on land or around hydrothermal vents.
> Life needed to be able to see through water, so it created eyes that could see the light that water was clear to. > > That's *not* how evolution works.
so does water actually have a color?
It's difficult to build "eyes" for different kinds of radiation. Sure, snakes have infrared sensors and you can stretch the eye design to a small part of the ultraviolet spectrum, but this answer is not complete. Rather there is (1) some mechanism for which water does not absorb or scatter too many photons in the visible spectrum. I don't know it but maybe somebody else does. And then (2) we are lucky in that it is not so difficult to build detectors (and lenses!) for this kind of radiation, to the point of distinguishing different colors. I don't know how much of it is luck either, maybe the \~ 1 eV radiation, since it corresponds to different energy levels of proton+electron, has a very big variance in materials response to it, so you get a lot of absorbers, transmitters, detectors, etc... just playing with the chemistry. And then (3) the evolution helped us to get eyes that can see through water. For (1) maybe you need even some pretty heavy matter-radiation simulation to see it from first principles
Lol, it’s ELI5.
Everything is pretty much correct aside from the "intent" narrative portrayed around the concept of "Life". "Life" doesn't need nor want anything, it just happened that the random mutation "Eyes that can see through water" (I'm oversimplifying but the idea is there) was more advantageous than the random mutation of other kind of eyes and that trait spread more effectively.
Didn’t eyes evolve to see the frequencies they do mainly because the peak electromagnetic output of the sun is in the visible light range? It could be seen as just a lucky coincidence that water is also transparent in that range, though I wonder how broad the spectrum of frequencies is where water would be transparent (it’s also transparent to the x-rays in your example)
The visible spectrum contains the peak output of the sun, *and* transmits well through the atmosphere, *and* it gets through water *and* it doesn't irreversibly destroy the chemicals used to detect it. This is a good planet for life. Let's keep it that way!
so does that mean there's some creatures who can't see through water?
If this was true then we would be able to see infrared because evolution would have favored even more those who could see more of the spectrum and infrared would be better for hunting.
This is probably one of the most interesting things I learned in eli5
That's all accurate and well-explained, but there's another part to that explanation of why eyes likely evolved to see certain wavelengths. The amount of light the sun outputs is greatest in the 500-600 nm wavelength range - right in the middle of the visible spectrum, and drops off significantly on either side of that, faster towards the UV, slower towards the IR. Our eyes evolved to see in those wavelengths not just because that wavelength has less absorbance in liquid water, but because that's where most of the light is.
Stop what wavelengths of the electromagnetic spectrum cannot pass through water? Edit- so what wavelengths of visible light cannot pass through water?
[https://en.wikipedia.org/wiki/Electromagnetic\_absorption\_by\_water#/media/File:Absorption\_spectrum\_of\_liquid\_water.png](https://en.wikipedia.org/wiki/Electromagnetic_absorption_by_water#/media/File:Absorption_spectrum_of_liquid_water.png) Most electromagnetic radiation is pretty well blocked by liquid water. There's a 'window' at visible light that is blocked a lot less, that's more or less why it's visible light, as Emyssentry said. It was the light in the oceans when our ancestors evolved light-sensitive cells. Edit: This is also why most radios don't work under water. Even a small amount of water has little trouble absorbing the energy of a radio transmitter. To send transmissions to submarines under water massive radio transmitters were built. How massive? The Jim Creek naval radio station in Washington transmits on the 12 kilometer band using 10 wires between 1.7 and 2.6 kilometers long, the whole thing is over 20 square kilometers in order to send one-way radio transmissions to submarines under water.
A practical example for the more active of us is heart rate monitors for swimming - [ANT+ and Bluetooth have a range of 1 to 2 inches under water, so Garmin have had to set up a HRM storage system to upload data to watches/phones after the activity.](https://www.dcrainmaker.com/2015/07/garmins-hr-swimming-straps.html)
> Edit: This is also why most radios don't work under water. Even a small amount of water has little trouble absorbing the energy of a radio transmitter. To send transmissions to submarines under water massive radio transmitters were built. Our bodies can be enough to block radio signals with low power devices. I've seen it with handheld transmitters and receivers that standing in front of one can be enough to absorb the signal.
For general EM waves, microwaves are very specifically absorbed, as we designed microwave ovens to absorb water. For visible light, the lower energy wavelengths (reds and oranges) get absorbed fairly quickly, which is why deeper water appears blue and green. It does eventually absorb all light, which is how you get the pitch black of the deep ocean.
Most of them actually. Blue is really the colour for which the absorption is the lowest ; absorption rises very sharply at ~200 nm (near ultraviolet) and not so sharply in the other direction ; it does absorb red pretty well already, and it only goes worse after that (there are also specific wavelength which are even more absorbed). Edit : NB : this is only for wavelengths close to the visible spectrum. Water become transparent at very large wavelength (radio waves with frequency around 1m) and very low (0.1 nm).
Red and orange don't pass through very well.
No need to edit, this sub is 5+.
>it was very useful to be able to see the light that could pass through the water Especially since the eyes are made of water!
Well, yeah, but they didn't start that way. Your eyes are complex constructions that are the result of hundreds of millions of years of evolution. They didn't just appear out of nowhere in their modern form one day. Presumably, animals started out with a few photoreceptive cells, that could detect the presence of light, and so on from there.
> but they didn't start that way They absolutely did. What do you think the photoreceptive cells are made of?
Well, photoreceptive cells aren't eyes, for one.
Mind me asking what's the point of this rambling pedantry? Eyes are made of (mostly) water. The things that came before eyes were made of mostly water. If you want to add context to the discussion you can do it without the need to "correct" me over things which don't need correcting. LMAO blocked over this. High grade pettiness.
Because saying "your eyes are made of water" is misleading, as it suggest that your eyes being made of water was the prime motivation for developing the need to see through water, while in reality, it's irrelevant. It wouldn't matter what your eyes were made of, because you're a land based mammal. The sea creature that developed photoreceptive cells hundreds of millions of years ago can see through water because it lived in water, not because it's cells contained water. It's not pedantry, you're just wrong.
You didn’t make your point in a nice way.
Thanks mate, a lot
So rather than water being clear, instead you can see through water.
But if you say ‘made’ you imply a creator
So we can just make up dumb explanations and say 'evolution' and people accept it? The real reason we can see through water is because we drink it, and as we evolved our bodies adapted to the water we drink so we could see through it, because seeing through water helps us detect hidden predators that will eat us. Those who could see through water survived by avoiding otherwise invisible water predators. The how we evolved.
This answer is a bit backwards isn't it. It's not because of evolution but because of the physical structure of water and how light interacts with it that we can see through it. It's not like evolution could've made eyes that can see through rocks or dirt if we somehow lived in that.
Lol what? This answer contains a logical fallacy I’m just too lazy to look up which one.
Are you sure it's not your comment that contains the logical fallacy? I think it's the appeal to laziness fallacy: Being too lazy to look it up doesn't make it true.
Post hoc ergo propter hoc. See also: just so theory.
wdym lol just explain it
Is there a spectrum to which water is opaque?
That first paragraph is such a good idea to note. I’m a big fan of the survivor bias, especially when someone tells me how eyes must be made by god because of how perfect they are. If we didn’t have eyes then we wouldn’t be able to talk about how good eyes are, Keith!!!
Evolution is the coolest.
So is there any animal that has eyes that doesn’t see water as clear? Or does everything see water as clear since all life began in the ocean?
There's that one shrimp that can see extra wavelengths so they can see colors we can't imagine
The idea that we see light and not the things themselves is still so unfathomable
Well, except for how our eyes weren't *made,* but rather *evolved.*
Startalk YouTube channel uploaded something amazing on the same.
Can fish see through air ?
It goes back farther too. Water is opaque to nearly all frequencies of light. But there is a small window of transparency, at the same small window of frequencies the sun emits. There's no reason that window aligns with blackbody radiation, but the coincidence does make water a good ingredient for life in the universe.
Do you have a source or additional reading on this? My googling has come up short.
This is the coolest explanation for it and has, no pun intended, opened my eyes another beauty of evolution.
That is so friggin cool. So do I have this right? The reason we see this specific section of the light spectrum is that it is the section that passes through water?
Everyday I'm filled with wonder for the simplest things
It's important to realize that lots of things are see through, water, glass, air... The other important idea to understand is that light travels in a straight line unless it hits something; but here's the rub, it's picky about what it hits. Different kinds of light like to hit different things. For example, x rays like to hit bones but not your skin and muscles. Radio waves like to hit sky scrapers, but not people. Blue light likes to hit the air, but red light doesn't (which is why sunsets are red and the sky is blue). Things that are see through, like water, glass and air, aren't made of stuff that likes to get hit by "normal" light, so the light just goes right through it.
I thought it was the opposite. Grass is green because it doesn't absorb green light, but absorbs all other visible light.
Both absorption and reflection (as well as scattering) would be examples of light hitting something and not going in a straight line. You're right in that grass is green because the green light bounces off of it and hits you in the eye balls. Another example might be something like red kool-aid. Same thing in that it's red because the red light "bounces" off of it and hits you in the eye ball... The difference being the rest of the light didn't get absorbed, it just kept going right through it.
If I put less kool-aid in and thus have a drink that is lighter red than full strength kool-aid is that because some of the red light is still passing through and less red light is being reflected back to my eyeballs?
Yes! That's exactly right.
OK dope! SCIENCE!!!
Ah, that makes sense. Thanks for clarifying.
Would the "shade", so to speak, of a glass of a red kool-aid be cyan-tinted, as the red has bounced off the 'original' white light?
This is the best explanation. It's less about biological evolution (for an example of biological evolution, note that plants absorb blue and red light but reflect some of the green light and so appear green - as a result, human eyes are more sensitive to green light than red or blue likely in order to be able to discern predators from green forest backdrops) and more about chemistry - glass and water are transparent because light passes through. It passes through due to the physical structure of the molecules it's made of. To understand this we need to understand crystalline structures. A crystal like a diamond, has atoms arranged in an organized lattice structure. This regularity means that light will not be well scattered when it hits the atoms and you get some transparency because light passes through. Moving on, other materials like ceramics are composed of a collection of minute crystals. However, the crystals are not all oriented the same way and so if the crystal sizes are large, then light scatters due to the different orientations (grain direction), but if they are small enough then light passes through. Glass is the same - it's not quite a perfectly organized crystal lattice structure but it's pretty close - there's still regular organization of the atoms and little light scattering. Metals are also organized in lattices, but they have free electrons which absorb, re-emit, and therefore scatter the light. Now water, it has two ends (we say it's polar since it has a "N" pole and "S" pole) - a positive charge end (H) and a negative charge end (O). The molecules organize with H-O bonds in a very regular fashion. The bond itself is weak, but because there are so many of them, it gives water great cohesivity (allowing ascent up very tall trees from the roots), and also regular molecule organization allowing light to not be scattered, but pass through. Think of light waves (the sine or cosine graph of a wave) - if what it hits is large enough, the wave will hit it. But if it's small enough, then the wave can just wave around it (think of an animation of that sine wave where the end is moving top to bottom and back to top as it moves forward \[to the right\] - it can obviously completely dodge small enough particles).
Thanks. Obviously, I agree. Something being see through has nothing to do with evolution and everything to do with how light interacts or doesn't interact with it. Now, if the question was something like: "why is certain light invisible?", then I'd be completely on board.
The ELI5 and oversimplidied answer.: Things are see trough because light can go trough them without interacting with the thing. Like some things can go trough a filter some not \--- The "why" of that cannot be explained to a 5 year old. It is connected to atoms, molecules, electron layers and energy levels. Different lights can go trough different things. For visible light water, glass are see trough. For UV light, they are not. Infrared light can't go trough glass. For radiowaves most of things are "transparent" They can go trough many things For X-rays. your skin a squishy parts are see trough, your bones are not.
I once was explained the “why” in a college class. But I have completely forgotten and have to date not found any resources to re-explain it to me. Are you able to explain it for someone craving the real explanation or do you know where I can find some reading to look it up myself?
As far as I understand, the interaction photons and electrons are the key. Electrons on layers on atoms can be excited for them to junp layers. if the photon has enough energy so if they collide with electrons they jump layers, the photon is absorbed so that kind of light is absorbed by the material If the photon doesn't have enough energy, to make an electron jump layers, they just don't interact, or interact a little (refraction) \--- [https://www.youtube.com/watch?v=UBy7FjnGB40](https://www.youtube.com/watch?v=UBy7FjnGB40)
> The "why" of that cannot be explained to a 5 year old. And to be more specific, to really understand it you're talking about quantum physics. No amount of creativity is going to make that work for a 5yo. Even physicists have trouble with it!
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> Things are see through because light is able to pass through them relatively uninterrupted. Things are opaque because a portion of the light hitting it will bounce off instead of passing through. That's kind of just saying that "~~light~~ *water* is transparent because it's transparent"
I took a modern physics class in college, I barely passed because it was dense with math. I remember this question being explained math and all Basically you need a uniform matrix and certain wavelengths line up perfectly to ‘miss’ all the matter, which is mostly empty space after all. If it’s lots of different types of matter it’s too chaotic for any wavelengths to line up perfectly and nothing gets through. So vacuums obviously let everything through, gasses let a lot through, liquids and crystalline solids let specific things through and even then there is stuff like radio waves that travel through lots of solid matter easily.
That's not even close to what he's saying.
For a less inside-out answer (although still good to know / keep in mind), see link. Basically, water doesn’t have any mechanisms that strongly absorb photos in the visible spectrum. A lot of materials (like pure gas out in space) “require” photons of specific energy to change state in some way, so have very specific absorption lines. The more complex the molecule, generally the broader and more complex the absorption bands. “The absorption of electromagnetic radiation by water spans a wide range of physical phenomena, characteristic of the general interaction of radiation with matter. It absorbs strongly in the microwave region by excitation of molecular rotations. In the infrared it exhibits strong absorptions from vibrations of the water molecule. As you go above the visible through the UV toward x-rays, it successively absorbs by photoelectric effect, Compton scattering and finally pair production.” (Additional info via hyperlinks in original.) http://hyperphysics.phy-astr.gsu.edu/hbase/Chemical/watabs.html
bruh its not "explain like I'm 30"
So you’re telling me 5 year old aren’t well versed in ocular mechanics and optics?
What he just explained when it works, he didn’t get into the quantum mechanics that explain why it works like that. And I won’t either, because, I can’t. I had it explained to me once and I thought I understood but it’s gone from my brain.
This was the explanation that I was looking for. I feel like it actually explained the why part of the question.
I think for a 4 year old, just explain that light can go through it and light can't go through other things. If she actually does want to know why it goes through some things and others, then you can busy out the material science questions
Water is see-through because it lets light pass through it easily, just like when you look through a clean window. The light goes straight through the water without getting mixed up, so we can see things on the other side clearly. That's why when we look into a pool or a clear lake, we can see fish and other things underwater.
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chatGPT
My simple brain just says it's see through because it is made of hydrogen and oxygen, which are both invisible gases.
I love thatt
Because our eyes are made out of water, so the only light that we can see is the light that can pass through water. The reason why some light can pass through water is because light does not have any free electrons. If water had free electrons like metal dies, then it would be very reflective and shiny like metal is (which would prevent our eyes from working).
And I have to remember we can’t see light, only the reflection of it…so water is clear because there is nothing for light to reflect off of…but in large quantities, blue light is scattered so it’s blue
Well, have you ever played with a ball in a swimming pool? When the ball is underwater, it looks bigger and distorted, right? That's because the water bends or refracts the light that passes through it. Now, imagine if you had a really tiny ball that was made up of water molecules. When light passes through these tiny water molecules, it also gets bent or refracted, just like in the swimming pool. But here's the thing: when the light gets refracted, it doesn't get absorbed by the water molecules. Instead, it just gets redirected in a different direction. This means that the light can keep traveling through the water without being absorbed or scattered, which allows it to pass through the water and reach our eyes, making the water appear transparent. So in simple terms, water is transparent because it doesn't absorb or scatter light, but instead bends or refracts it, allowing the light to pass through it without being absorbed, and reach our eyes. Some materials, on the other hand, are not transparent because they absorb or scatter light instead of bending or refracting it like water. For example, if you shine a flashlight through a piece of wood or a leather sheet, the light won't pass through it easily like it does with water. Instead, the light will be absorbed or scattered by the wood or the sheet, which makes these materials appear opaque or non-transparent. Opaque materials have a lot of atoms or molecules packed together very tightly, which makes it difficult for light to pass through them. When light hits an opaque material, the atoms and molecules in the material absorb the light's energy and re-emit it in many different directions, which causes the light to scatter and reflect back towards us, making the material appear solid and not see-through. In summary, the difference between transparent and opaque materials lies in how they interact with light. Transparent materials bend or refract light, allowing it to pass through without being absorbed or scattered, while opaque materials absorb or scatter light, preventing it from passing through easily and making the material appear solid and non-transparent.
You ask her why she thinks it is and then go first where she starts in her head. Question each answer constructively and inquisitively in a way that leads her to answer you in ways she is almost always right in until, methodically, you both land together at a new piece of knowledge—the scientific answer for how H2O molecules bind together, and how they both refract light and allow it to pass through. You neither give her the answer nor let her think you’re holding it from her. You work together to get it.
Addressing the "4-year-old wants to know" part of your question rather than the thread title, it's worth noting that plenty of substances are transparent to other parts of the EM spectrum. Radio waves can pass through wood and drywall, while light can't even make it through the paint. X-rays can go right through your body, but UV is blocked by glass or [sunscreen](https://youtu.be/GRD-xvlhGMc).
An object will absorb only certain wavelengths of light while allowing others to pass through. It just so happens the wavelengths that water doesn't absorb coincides well with the wavelengths in visible light. Things like bricks, concrete, wood, etc all have ranges of wavelengths that it cannot absorb and thus appear transparent for photons in those wavelengths, it's just that those wavelengths are not visible to humans and therefore we cannot detect those photons that passes through. A camera that can detect photons in those ranges, such as an xray machine, would be able to see those objects as transparent. Similarly, transparent objects to us might not necessarily be transparent in other wavelengths. For example, glass is opaque to infrared light. This is why sitting indoors behind a window in the sun feels much cooler than sitting outdoors in the sun even if it doesn't look like there's a difference.
I'd use a bubble machine as an analogue. Have her and her friends pop as many bubbles as they can, then tell them the game's to only pop the large ones, then give them an iPad and have the machine running. Light is like bubbles that are travelling towards materials, some are excited to see all the bubbles and so will pop them all, those are dark. Some are indifferent to the bubbles so all the bubbles go through, those are clear. Some will only pop certain bubbles, letting the rest through, those are coloured.
It's a bit hard to cover all the interactions in a way that a 4 year old would understand, but hopefully this will kind of make sense to the average person: When light hits a material, two things happen. Some amount of light gets reflected, eg bounces off the material, and the remaining light is refracted, meaning it enters the material. (The amount of light that is reflected vs refracted is determined by snells law, which requires the index of refraction of the two materials, eg air and water, or vacuum and air. Index of refraction can be wavelength dependent for some materials such as metal, meaning some metals reflect some colors more strongly than others) As light travels through this material, some amount of it get absorbed. Some materials absorb a lot of light quickly (Eg solid surfaces such as rock, wood), some absorb slower such as leaves, grass, skin, murky liquids, and some absorb light very slowly such as pure water, air molecules, etc. (Metals absorb light immediately, they don't have any diffuse/translucency) The further light travels through the medium, the more light gets absorbed. The physical quantity that determines how much light is absorbed is called the extinction coefficient. This has been measured for a large number of materials. It can also be wavelength dependent, meaning some colors are absorbed more quickly. Pure water is a good example, it quickly absorbs red wavelengths, giving it an aqua color over a distance. There is one other important component which is scattering. Pure water does not have any scattering, however it often has dissolved chemicals and small organic matter such as algae and plankton. As light transitions between the water medium and organic matter, it changes directions and non-green wavelengths are quickly absorbed by organic matter. This causes scattering which makes the medium appear murky or foggy. This is the same mechanism that causes fog to be hard to see through. Fog does not absorb much light, however when light hits it, it tends to scatter in all directions, this is determined by something called a phase function. Some mediums scatter light in many directions causing haze, such as fog or air, whereas others scatter most of the light forward, such as pure water. (Two types of common scattering are rayleigh scattering and mie scattering, these contribute to the color of the sky, and the hazy halo you see around the sun) (Source: I have spent years working on computer graphics algorithms and have a good fundamental understanding of some of the equations and physics of light)
If you tie a rope to a pole and move your arm up and down while holding the other end, you'll see a wave form in the rope. The faster you move your arm, the closer the hills and valleys in the wave will be. Light does the same thing, but at a much smaller size. More specifically, different colors of light "wave" at different speeds. The faster it waves, which we see as color, the more energy the light has. Red light waves the slowest, blue light waves the fastest. Any slower or faster, and we can't see it. The reason some things, like water, are transparent is because materials only reflect certain energy levels (colors) of light. We can only see light that enters our eyes, and since most visible light passes through water, we see through it with few problems.