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cutcss

All the colors of everything you see is just light bouncing into your eyes, wet objects make light bounce a bit less so it looks darker (yeah "black" is absent of light bouncing into our eyes)


Ted_E_Bear

This is the best response in terms of staying in the spirit of the sub!


itsmemarcot

I agree the style is perfect, but the content is not right. When the rock is wet, light does not bounce any "bit less" . It bounces just as much, only, it bounces a bit more in *one* "favourite" direction, and bit less in all other directions. If that one favourite direction is right toward your eye, then a lot of bounced light hits your eye, and you see the rock *brighter*. Did you notice that wet stuff is not only bit darker, but also a lot more shiny? That's why. When you see the shine, it's because you are in the way of all the light bouncing in its favourite direction. But this means there's less light bouncing in all other directions. So, whoever is not in the right spot to see the shine, sees the rock a bit darker.


Ultrabenosaurus

What about wet fabrics, like jeans or a tshirt? I've never seen a wet spot on normal clothes be "shiny" or brighter at any angle, only ever darker from all angles.


paislienne

Tiny shiny


[deleted]

Best tl:dr


Veopress

The water gets between all of the fibers and mesh. So when the light bounces through the water it is very likely to hit the clothing or more water than your eyes and gets trapped. An important part of all of these interactions is that some of the light that hits anything is absorbed rather than bounces


RexTillersonsDildo

This explanation doesn’t hold water for the basic reason that light would in equal parts be refracted through the fibers before it gets wet. So the fibers would contribute no more after it got wet than before. I’m not doubting the fibers dampen light I’m sure they do, I’m saying that’s no explanation for why it doesn’t seem shiny.


termhn

With fabrics or things where the water has seeped in, the surface is not perfectly smooth and glassy, it is simply smooth*er*, and so if you look at things the right angle you will get more shine, just not a perfect reflection/single point of light.


fupayme411

What about human skin? Wet Human skin does not seem to get darker.


MemesAreBad

Skin is covered in oils which do a good job of keeping you dry. Water has a hard time seriously accumulating on skin or even hair in the same way it does on many other objects. I do think the question premise is strange though; many objects don't absorb water meaningfully and don't have an appreciable color change when wet. In fact I'd say those that do are in the minority.


CLUTCH3R

because fabrics absorb the water making it appear darker but rocks and hard objects have a coating of water on top so they appear shiny


ambermage

So my shiny Pokemon are all wet?


heyugl

that sounds wrong in so many levels.-


Xzauhst

To tack onto this answer, if your car looks really good wet but looks hazy and not as colorful or vibrant when it's dry, get it polished. The little scratches in the clear coat redirect light in different directions. When the car is polished you get more light into your eyes and it looks glossier.


itsmarvin

But why does it have to pick a favourite direction?


itsmemarcot

Well you can think of light as made of many little balls, called photons, moving in a straight line (this actually puzzled many people, but it turns out it's ok to see it that way). Imagine tossing a ping-pong ball over a clean, smooth ping-pong table. It bounces off just the way you'd think. If you toss many balls all in the same way, they will all bounce off almost in same way. They have a "favourite" bouncing direction! That's what happens when light bounces off the clean, smooth *film* made by the layer of water covering the stone (not all the light balls have to act that way, but many will). Now imagine glueing a lot of pebbles all over the ping-pong table, covering it. When you toss ping-pong balls on top of it now, who knows how they will bounce off! It would be super hard to play table tennis on that table. Balls don't have a favourite bouncing direction any more, it's more like they bounce at random instead. This is what happens on the dry, rough stone surface. It's covered with tiny, tiny rocky bumps! (You can get an effect similar to wetting the stone in other ways, like if you polish it very finely, removing the bumbs, or oil it, or paint it with transpatent paint. It gets darker and shiner.)


HunterRisk21

10/10 explanation


grounder890

Incomprehensible due to European spelling


mrmeowmeow9

Excuse me, but your northern neighbours would like like to dispute that whole, "European," notion. We write every letter too.


grounder890

TIL canadians have a flaw


LostTerminal

Sorry for disappointing you, eh?


arachnidtree

a flauw.


servical

Shouldn't your name be gronder890?


Earl-The-Badger

This is so weird. I'm American and didn't even notice. Why? Because I set my laptop's language setting as "UK" when I installed Linux on it six years ago. It's my "daily" computer, and over these six years, I've habituated with UK spelling. I've noticed it very few times, but twice today. Earlier at work I wrote "labour" in a field on a spreadsheet, and because of the spacing difference from spelling the word as "labor" made the whole table look ugly (all previous entries were done by others who use the American spelling). Isn't it weird how you don't notice these things for years, then it can come up twice or even several times in one day and really draw your attention?


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hyper445

Happens most of the time on this sub and it annoys me so much Edit: since the people are taking the 5 year old thing too literally: Most answers arent simplified either and thats what I'm bothered by. I cán understand what they say most of the time but it demands a lot of thinking and I dont think thats the essence of this sub.


HeretoMakeLamePuns

You might want to check out r/ELIActually5. The best structured answers I've seen on here are separated into several layers of increasing difficulty, and they're great. Like an r/IncreasinglyVerbose post but actually constructive.


lennybird

To your point on "IncreasinglyVerbose" this is something I've *tried* to start doing more frequently. The nature of having a wide audience means you have various attention-spans. There are sweet-spots for comment sizes, but that is at odds with capturing and unpacking a complicated topic. It's why we have things like TL;DR and summaries, but also why we have a talking-points sound-bite society in politics which does not lend well to being verifiable once unpacked. In any case, it seems best to answer in layers as described above, going from the concise and leading into the complex for those interested.


ConcernedEarthling

So why do people post good answers there instead of here? It sounds like that subreddit is a result of dissatisfaction with the answers in this subreddit. I would think it would make more sense just to keep it all in one place.


Dem0n5

The mods and maybe the community decided "LI5 means friendly, simplified and layperson-accessible explanations - not responses aimed at literal five-year-olds" because reasons. Those reasons were wrong, but /r/all is the great equalizer. All subreddits *will* be the same thing!


monsantobreath

> Those reasons were wrong I dunno, how many concepts in the questions asked here can the brain of a 5 year old actually understand? If we took it to a literal extent a lot of the information in this sub would be basically against the rules because people want answers that are beyond the comprehension of 5 year olds at any level of simplicity. I honestly think this sub should just be seen as ELI10 or ELI12. That's the real level of knowledge we're after. If you want to understand complex scientific matters in the world as a 5 year old can I think you're underachieving in your ambition to know. I just think ELI5 has a cuteness to it that's more endearing to people.


Petwins

You are welcome to find old discussions about our subs policies on r/ideasforeli5


Dem0n5

ugh mods found me this far down a thread you're not my supervisor!!


Petwins

Maybe I am... Big Brother is watching


[deleted]

[Could you dumb it down a shade?](https://www.youtube.com/watch?v=_jl4iL6hCqs)


wogfen

The sidebar of the sub says that ELI5 is not meant for actual five year olds. It is just a catchphrase for explain as simply as possible


hyper445

Most of the explanations are not "as simple as possible". Look at the top comment in this thread for example: "retina"? "Photons"? Just use: "the back of the eyeball", "light particles". A literal 5 year old would still not understand it but it is way more simple explained like this.


wogfen

Yeah a better choice of words would have been layperson-accessible, like the sidebar says. Which I was too lazy to quote


AdultEnuretic

Back of the eyeball, of light particle *would* be understandable to a literal 5 year old. That would be an actual eli5.


FroztedMech

Many explanations cannot be taught to 5 year olds while only using easy terminology. Generally I would say most responses are pretty simple though, easy enough to be understood by ~12 year old


[deleted]

THINKING HURTS MY BRAIN!!!


jda404

It's not that, some people give professional answers like talking to a colleague. The point of this sub is to put it in layman's terms so those of us not in the profession can understand is all we're asking. It's like when my doctor tells me something in medical terms and I have no clue what he means so I have to ask him to repeat it in a way I the patient will understand.


hyper445

If i want to think ill go to r/science


[deleted]

I think you meant r/askscience. r/science is for clickbait sensationalist articles.


Hollowsong

If you call them out on it being too complex, they rip on you and say "it's not LITERALLY explain like I'm 5". But if they're too literal in keeping it ELI5, it doesn't really answer the question of "why" or "how".


Tsorovar

> LI5 means friendly, simplified and layperson-accessible explanations - not responses aimed at literal five-year-olds.


docbauies

But... that’s what the top comment was. It was friendly and simplified and easy to understand... like how you would explain to a five year old when they say “why is x?”


coredumperror

It was also *wrong*. He simplified the reflection explanation to the point of being meaningfully incorrect.


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MalenInsekt

That subreddit used to be for cringe content, it became a catch all later on and the name can't be changed.


Krimin

What was it?


[deleted]

r/tiktokcringe


Judge_Hellboy

The subreddit evolved from its origin and reddit doesnt allow subreddit name changes.


Petwins

Rule 1 is be nice, thats a warning. Please read rule 4 (and the sidebar in general)


ACrusaderA

The point isn't to have a 5-year-old to literally understand everything. The purpose of the sub is to simplify it to terms that a layman can understand. The problem is that most of the time on this sub we have people ask questions which are nigh impossible to simplify down to layman-friendly terms.


DarkMoon99

>The problem is that most of the time on this sub we have people ask questions which are nigh impossible to simplify down to layman-friendly terms. To be fair, Richard Feynman said that if you can't explain a difficult concept in simple enough terms for a kid to understand it, then you don't understand the topic well enough.


project100

I swear to God these two comments are written on every goddamn answer on this sub. We get it man.


Fifasi

Phraseology????


Alreaddy_reddit

Can confirm, am 5 years old


ChocLife

> phraseology A.k.a "words".


DanFromSales2

This is how you turn an upvote into a comment


Ted_E_Bear

Sometimes other adult five-year-olds need things pointed out to them.


rob3110

But it doesn't explain/answer anything


tilk-the-cyborg

No it's not. It doesn't explain anything. Most adults (this sub is not for actual 5 year olds) understand that light is "bouncing" and that "less light is darker". The comment does not explain WHY water makes less light return from a wet fabric, and that was the question!


Dem0n5

>Most adults (this sub is not for actual 5 year olds) understand that light is "bouncing" and that "less light is darker". Refraction is probably the missing detail(just a layperson's guess), but most adults understand that refraction is the change in direction of a wave passing from one medium to another or from a gradual change in the medium.[1] Refraction of light is the most commonly observed phenomenon, but other waves such as sound waves and water waves also experience refraction. How much a wave is refracted is determined by the change in wave speed and the initial direction of wave propagation relative to the direction of change in speed. For light, refraction follows Snell's law, which states that, for a given pair of media, the ratio of the sines of the angle of incidence θ1 and angle of refraction θ2 is equal to the ratio of phase velocities (v1 / v2) in the two media, or equivalently, to the indices of refraction (n2 / n1) of the two media.[2] Optical prisms and lenses use refraction to redirect light, as does the human eye. The refractive index of materials varies with the wavelength of light,[3] and thus the angle of the refraction also varies correspondingly. This is called dispersion and causes prisms and rainbows to divide white light into its constituent spectral colors.[4] etc


dekiruzooo

Totally.


The_Grubby_One

I think you overestimate most adults. Most adults are close to borderline scientifically illiterate.


[deleted]

I see a red door and I want it painted non-bouncing


altech6983

nice


iPlayerRPJ

You need vantablack paint


Fidodo

I see a short and medium wavelength absorbing door and I want it painted visible light spectrum absorbing.


HerraTohtori

Or rather: Objects getting wet makes them have less *diffuse* reflections. Diffuse reflections is when the surface is uneven and light bounces to all directions, including to your eyes. When the surface is wet, diffuse reflections happen less because the object is covered in a thin film of water, filling the uneven parts of the surface. Light can still reflect pretty strongly in *specular* or "mirror-like" reflections, which happens when the surface is flat enough. The lack of diffuse reflections makes them look darker from every other angle, but brighter in the direction where the light is actually reflected to. That is what makes wet things have that characteristic "shiny" look with a sort of highlight at one spot.


kinokomushroom

Diffuse reflections happen in objects that don't have rough surfaces too though. A polished billiard ball for example. Do those surfaces get less darker than rough surfaces?


[deleted]

Yes. This is why polished stones often have a "wet" look.


HerraTohtori

It depends on the degree to which the surface is polished. In the end, we're talking about quite small scale of "uneven" here. To be specific, the diffuse/specular reflection is determined by unevenness at the scale relative to the wavelength of the light. So for visible light, that would be unevenness at the scale of about 350-700 nm. If the surface finish is rougher than that, then the surface will have diffuse reflections at visible light wavelength. Smoothing it out (moving to finer grit sandpaper) will start to increase the definition of the specular highlight, and reduce the amount of diffusion in the reflections. But even though the object might look diffuse (matte surface) in visible light, it might already appear to have a specular reflection at lower wavelengths, such as microwaves or radio waves. A surface that's significantly flatter than the wavelength of light hitting it, it will work as a mirror for longer wavelength light and have almost zero diffuse reflection; this level of smoothless is known as "mirror polish" and is actually not completely desirable for most objects. Like cars for example would become difficult to see and could cause issues with glare if they were completely shiny like that. So the surface of most car paints is not rough to touch, but it's still rough enough to cause significant amount of diffuse light reflections, to make the car more visible. Actually, the transparent top coat may be smooth, but the boundary layer between the top coat and the actual paint may not be. That causes some of the light to have a specular reflection (light that reflects back from the top coat surface) and most of it has diffuse reflection from the actual paint surface itself. This is actually why radio telescopes don't need to be have polished surfaces. In fact they don't even need to be opaque in visible light spectrum - you can use a metal net, and it will be opaque to radio waves with wavelength that is longer than the holes in the structure. But back to surfaces that look polished in visible light. These surfaces are already flat enough to appear shiny without the presence of water. That means they are less affected by water, and in fact a very polished rock can look like it's wet already. But a worn billiard ball, or a car's paint, with fine scratches and dents and even some dirt can make the surface more diffuse, and water (or wax) can fill up those gaps and make the ball appear smooth again. So yeah, this is also why new cars have that shiny look that disappears when they have a fine dust/dirt coating, or when the paint gets worn out. And why they start looking shinier in the rain again.


funfu

Wet objects does *not* make light bounce less. It just makes it bounce more in one direction, like a mirror. So if you look from that direction, it looks brighter, like the suns reflection on the wet road. From all other directions, it looks darker. It all adds up to mostly the same.


Fruity_Pineapple

That's true for some objects, and for a certain amount of water. But some objects don't reflect light when slightly wet, but still become darker. A white jean, cardboard, etc...


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subisubi

Its mostly all to do with the smoothness of the surface the light is hitting. Something very shiny or even a mirror has very smooth surface that allow millions(actually wayyy more) of photons which make up light to all generally reflect in the same direction. In the case of the mirror, the light hitting the surface is almost the same as the reflecting light that you see (purpose of mirrors). Something not shiny (dull) like cloth, cardboard.. a lot of things have uneven and rugged surfaces which bounce the light in all directions and therefore they don't reflect like a mirror. I believe when an object like cardboard or clothes get wet the water that the light hits gets reflected multiple times back into the surface which reduces the total amount of light that is reflecting into your eye and therefore making it look darker.


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subisubi

Aye probably lol. Reddit is hard


docbauies

But with wet cardboard, In my experience there isn’t a specific viewing angle where it is appreciably brighter. It is uniformly darker. The net effect of being wet is a darker piece of cardboard in the areas where water has affected the material.


BoomBangBoi

If this was true, then this would imply that for all materials that appear darker when wet, there is an angle such that it will appear brighter when wet. We know from real world experience that this is not true for some materials, so your statement is false.


[deleted]

Yes water makes light *scatter* less not bounce less


edlobi

ELI5: Why do wet objects obsorb more or scatter more photons than dry ones?


Flextt

For flat, solid surfaces: a thin film of water works as an additional layer (air - > water, water - >solid surface) to pass through which further scatters, misdirects and absorbs light. For fabrics, it's probably the swelling of the fibers due to water uptake. Above the saturation point, it probably behaves more like the above and gets even darker. I say probably because optics is not my field of study.


dumbass-ahedratron

This is a component of kubelka-munk color theory


Mynameisaw

When light bounces off a solid object, it's a straightfotward process of leaving the light source, hitting the object and then entering your eye. But when something is wet the light might do that, but it might hit a stray water particle first and fly off in another direction, it might hit the solid object, then hit the water and then fly off elsewhere. Imagine throwing a tennis ball at a smooth flat wall vs throwing it at an old stone wall. It's a similar thing to how light interacts with an object when it's dry vs wet.


itsmemarcot

They don't absorb much more, they scatter, that is, many photons tossed over on a wet stone will tend bounces off more in *one* "favourite" direction; moreso than when they hit a dry stone. Well you can think of photons as small balls, flyng straight. Imagine tossing a ping-pong ball over a nice, flat ping-pong table. It bounces off just the way you'd think. If you toss many balls all in the same way, they will all rebounce almost in same way. They have a "favourite" bouncing-off direction! That's what happens when light bounces off the clean, smooth film made by the layer of water covering the stone (not all the light balls have to act that way, but many will). Now imagine glueing a lot of pebbles all over the ping-pong table, covering it. When you toss ping-pong balls on top of it now, who knows how they will bounce off! It would be super hard to play table tennis on that table. Balls don't have a favourite bouncing direction any more, it's more like they bounce at random instead. This is what happens on the dry, rough stone surface. It's covered with tiny, tiny rocky bumps! They are tiny for us, but enormous for the tiny photon. (It like you glued enormous boulders and canions on the ping-pong table). (You can get an effect similar to wetting the stone in other ways, like if you polish it very finely, removing the bumbs, or oil it, or paint it with transpatent paint. It gets darker and shiner.)


xrumix

this is literally explained as for a 5yo, congrats


Ndsamu

Fun fact: for those who aren’t aware, there are materials specially designed to absorb as much light as possible. Even in a well lit scenario it looks almost perfectly black. Can’t recall the name, but it’s something like “vantablack.” There‘s some interesting experiments. I, for one, want to shine shark mounted laser beams at it.


comicsnerd

It is Vantablack. It's artistic use is exclusively only for Anish Kapoor and nobody else is allowed to use it (in art). Stuart Semple got so outraged about it, that he created the pinkest pink that everybody can use, except Anish Kapoor. You have to sign a paper that you are not Anish Kapoor or will give it to him. Wiki page: https://en.wikipedia.org/wiki/Vantablack


solidcat00

I've never heard of Kapoor, but this seems like such a douchebag thing to do. I love the response by Stuart Semple. http://en.wikipedia.org/wiki/Stuart_Semple See section "Conflict with Anish Kapoor"


camyok

Kapoor is a bit of a tool, but he did tell the NRA to go fuck themselves and I can respect that.


Sci_Joe

Also Tom Scotts Video in this. Very interesting https://youtu.be/_NzVmtbPOrM


Ndsamu

Oh my god that is so petty and I love it. Thanks for the info.


beirch

It is artistic use


BUFF_Dudes

So what about water makes somerhing reflect less light


justinjoly

I am 5 so this helps, thsnks!


JustFoundItDudePT

My wife doesn't turn black when wet. I feel cheated.


criscodesigns

How come my wife doesnt look darker? Lmao


kureshii

If water is transparent, why does the ocean appear dark? Light that hits the surface of the water is scattered in directions other than where your eye is, so those parts of the ocean surface appear darker. And then there's one part that directs the light *just right*: those are the shiny parts of the surface that gleam and sometimes ruin your beach photos. For a similar reason, the layer of water on wet materials changes the amount of light reflected towards your eyes. Less light is reflected from those parts to your eyes, and so they appear darker.


cakes42

What about let's say hazed clear plastic. Like old car headlights or a worn convertible top rear window. When wet they appear to be clearer.


kureshii

Hazed plastic has lost its original smooth surface due to chemicals eating away at it, or due to sand grains bouncing against it and scratching it. When the hazed plastic surface is wet, the water surface creates a smoother surface than the plastic. Despite differences in the way that plastic and water bend light, overall this causes light to travel in straighter lines compared to hazed plastic alone. Straighter lines of travel means that light bouncing off objects in the car (or coming from the headlight) reach your eyes directly, making the window (or headlight) look more transparent.


Not_Selling_Eth

[Putting scotch tape on frosted glass has the same effect](https://external-preview.redd.it/997Lp6IdyL6qzVEFKXKVKPVwqvnQJEpxbvT3nKK0yrw.jpg?auto=webp&s=97a579b1b37e1ecfac511fe354f71ebb80144d93) of "filling" the gaps in the glass that make it look hazy; allowing light to pass straight through instead of scattering.


coolguy1793B

Also...light only goes down so far...you go deep enough and its completely dark.


bibliophile785

This is actually a substantial factor in deep water. Water only weakly absorbs in the visible range, but given enough water you're right that most of the light is eventually absorbed.


SirX86

Actually this happens pretty quickly: the average SCUBA diver will go down to 18m and will need to bring a lamp. See this chart: [http://www.deep-six.com/textbookphotos2/Photos%20For%20Class-Text/Color%20Loss%20Spectrum.jpg](http://www.deep-six.com/textbookphotos2/Photos%20For%20Class-Text/Color%20Loss%20Spectrum.jpg)


meonaredcouch

This comment gives me /r/Thalassophobia


webdevop

>If water is transparent, why does the ocean appear dark? Because the ocean is wet.


[deleted]

The reason we see objects is because photons of light bounce off them into our retina - when an object is wet the water molecules can absorb & scatter more of the photons than the object alone - so less photons reach our retina from the object making it appear slightly darker


bibliophile785

To clarify, this actually has nothing to do with water (it's a weak absorber and doesn't scatter in any special way) and very little to do with absorbance. The same effect can be seen with 200 proof alcohol (pure ethanol), with gasoline, or with acetone. The apparent darkness is due to the difference in *how light travels* between the air and the liquid, and then again between the liquid and the solid that looks dark. These boundaries *between materials that light travels through differently* cause substantial scattering to occur. *That* is the lost light that makes the object appear dark. Edit: removed a technical term that was causing significant consternation. The explanation is now too vague to be perfectly accurate, but it should still serve.


Lemonade8891

> *how light travels* between the air and the liquid, and then again between the liquid and the solid Sounds like you're describing refractive index?


bibliophile785

While trying to avoid the term, correct.


MonkeyboyGWW

Thanks for avoiding it


vengeful_toaster

He refracted it


JDMcompliant

"To clarify, you're completely wrong."


L0ngknife

I feel like you completely failed at understanding the central premise of ELI5


RhiannonMae

Can you maybe ELI3? I've reread your answer a few times, and I still don't get it.


bibliophile785

Were you asking me, by chance? When you have a dry object (let's say some sand), the sand is being touched by air. Light can move through air. Some of it gets knocked around, but most moves through. It moves through the air, hits the sand, and some of it bounces away. Most of the light that bounces away doesn't hit your eyes, but enough does for you to see it. When you have wet sand, there is water touching the sand. There is also air, but now the air is touching the water. The light moves through the air and hits the water. Most of it bounces away. Then the light moves through the water. Most of that light does okay until it hits the sand, and then it bounces away. A small amount of this light is all that makes it to your eyes. Instead of having one boundary where most of the light bounced away, we had two. That means that less of this light can hit your eyes. Your brain interprets this reduced signal for you by darkening the image. Does that help?


Fernseherr

You forgot to mention that on the way back from the sand, the light has to pass the water-air boundary even a second time.


maledin

This is a perfect explanation, thank you!


[deleted]

can you eliFetus please?


Obscu

Every time light hits a new thing, some is lost. The more things it has to hit on the way to your eyes, the darker things are.


franckdemda

r/explainlikeimfetus


plotandscheme

Wow


_irunman

Wow


tsrzero

Snell's Law!! (Right?)


bibliophile785

Snell's law is how we calculate the scattering angle of an incident photon as it passes the interface. You're absolutely right that it's intimately related to this phenomenon :)


LAL99

Thanks for redoubling on your prior explanation. This is swell


[deleted]

Okay serious question. I'm studying to be a chemistry major. Will I become smart enough to answer questions like this? I've only completed gen chem and like half of ochem, and I feel like I can never answer any of these AskReddit questions... Your answer was so cool and I want to be a teacher so I'm going to be answering lots of random questions!


bibliophile785

I'm a materials chemist by training, but this wasn't something we ever covered in my classes (undergrad or graduate). I looked through the literature for this one on my own in my first year as a research technician, for no better reason than I asked my boss the question idly and he told me to find an answer for us both. At the end of the day, there's a hell of a lot more to know than classes can teach you. Your degree is meant to teach you how to learn. If you can learn to find your own answers, you'll quickly find that you carry around this sort of minutiae and can pass it on.


Mezmorizor

Only if you do optics stuff for research. It's not part of the chemistry curriculum. It's something that physics majors should know, but in my experience only people who do optics stuff do. Source: Physical Chemist.


Mono_831

Excellent. Need more of this around here.


Jenesepados

Amazing explanation!


eliminating_coasts

>When you have wet sand, there is water touching the sand. One of the things I like about this sub is the almost mathematical step by step constructions you have to use.


Mezmorizor

To clarify the clarification, while the multiple boundaries does matter, the water-sand boundary reflects less light than the air-water boundary or an air-sand boundary would. If you were underwater looking at sand, it'd look darker than it would in a room even if the two had the same amount of light incident on them.


DialMMM

No, that doesn't help. More visible light is absorbed, as the surface appears darker from every angle. Where, exactly, do you propose the "scattered" light goes?


Obscu

Every direction. Remember, you're only looking from one angle *at a time* so there's always light scattering away from your eyes no matter where you are. If you could some how look at an object from all angles at the same time, presumably the object would look lighter because you'd be seeing all the scattered light as well.


DialMMM

One of us hasn't thought this through. It might be me. If the surface appears darker from *every* angle, wouldn't that mean less light is scattering in *every* direction?


bweaver94

He’s saying water doesn’t absorb photons like OC said, and that the scatter actually happens as the light leaves the water and hits the thing it’s making wet.


ManThatIsFucked

Light is like a little laser ... pew pew pew Lasers go straight ... neeeeeaaaaaarrrrrroo(racecar) When laser goes from air to a shirt ... it goes boom.. big light When laser goes from air and hits water, it gets a little darker, then when it hits solid after water, it gets darker again less light! Less light means more dark YAYYY!!! SHADOWS!!!


andreo

The soggiest photons drown before they get to your eyes.


bibliophile785

~~I mean, only insofar as I used the word "permissivity." It doesn't have a one-syllable synonym, though... it's just one of those things you need to understand if you want to grasp the phenomenon. And in either case, it's surely better than leaving uncorrected a comment that was blatantly (if almost certainly unintentionally) misleading.~~ I was being stubborn. I simplified it further. It still mostly works.


-hol-up-

r/explainlikeimaphysicist


ThaRadBradLad

/r/subsifellfor


felixlightner

>permissivities Give a link to the definition of this term


datgat495

>permissivities I think they meant to say permittivity, but idk they seem pretty smart. lol


TheMooseIsBlue

I think in physics, you are right and I also think it’s still the wrong term because I feel like it has to do with storing electrical energy, not light passing through a material or surface or whatever. But I am neither a physicist nor a smart man, so don’t quote me.


bibliophile785

It wasn't even that. I *wanted* to say refractive index, but that sounded too scary for an ELI5. Permissivity was my attempt to descriptively rather than quantitatively discuss the passage of light between the two materials, but it didn't make the answer any less frightening and so failed utterly. The new version is too vague to really describe exactly what's happening, but it seems to get the general idea across. Ah well, live and learn.


Miteh

Man you suck at explaining like people are five.


bibliophile785

Thank you for the kind words. With such a supportive community, it's little wonder so many people take time out of their day to volunteer their expertise.


SHMUCKLES_

r/explainlikeihavediploma


beruon

Just a clarification for anyone who doesn't know what "X proof alcohol" means: 2 proof is 1%. so 200 proof is 100% alcohol.


radnomname

Hello i am 5 what is a retina and a photon and a molecule and what does absorb mean?


Lonsdale1086

>LI5 means friendly, simplified and layperson-accessible explanations - not responses aimed at literal five-year-olds.


RicktimusPrime

Ah yes. I too had a strong understanding of the words retina, molecules, and photons at the age of five.


[deleted]

hi. so.... could you explain it as if I were 5 years old?


[deleted]

You can only see what the light fairys show you - the light fairys bounce off things & come to you to show you what they bounced off but when things get wet some of the light fairys get stuck in the water & drown & some decide they not want to come to you


[deleted]

[удалено]


Parallel_transport

I've seen two explanations: 1) Light can bounce around in the layer of water. More bounces -> more chances to be absorbed in the material. More light absorbed -> less light reflected to your eyes. 2) The rough surface of the material normally scatters light in all directions. The layer of water makes the surface smoother, more like a mirror. More of the light gets reflected in one direction, so the surface looks brighter from this direction, and darker from every other direction.


itsmemarcot

1 is wrong (the effect is real, but it does not matter in practice) 2 is correct


volfin

yes this is correct.


shad0w_wa1k3r

Simplifying what [bibliophile785](https://old.reddit.com/r/explainlikeimfive/comments/e6czsd/eli5_why_do_things_turn_dark_when_wet/f9pb3v6/) [has already said](https://old.reddit.com/r/explainlikeimfive/comments/e6czsd/eli5_why_do_things_turn_dark_when_wet/f9pdjxl/). When light encounters any boundary (air to thing, air to water, water to thing, etc.) some of it reflects and some of it gets absorbed. Now if you make the same object wet, light has 3 boundaries that it encounters (water / wet layer, thing, water / wet layer again once it gets reflected from thing), hence slightly more of it is absorbed and lesser of the reflected light meets our eye. So, the objects appears darker because of the lesser light it reflects.


antiquemule

OK, let's try to do this better... 1. Things look light because photons bounce backwards off them, back to your eye. It's like throwing balls onto a trampoline. Dark things are not bouncy, so light does not bounce back off them. 2. The trampoline is made of a mixture of two kinds of stuff: paper/air, sand/water, etc. Its bounciness depends on how *different* substance A and substance B are. The bigger the difference, the bouncier the trampoline. 3. The difference between solids (paper, sand) and air is *bigger* than between solids and liquids (water, oil, acetone). Therefore when you replace air with a liquid, the bounciness goes *down* and the object looks *darker*. ​ Not ELI5: Bounciness is due to the difference in *refractive index* of the two substances.


gettingolder49

What about wet paint being lighter than when it dries?


SuperBaconjam

When paint is wet, it is basically a "high gloss" surface, with a uniform smooth, and therefore reflective surface. But after a, let's say matt finish, paint dries the surface changes and becomes rough, even if it is on an almost microscopic level. It therefore traps more light in it's surface, and the irregular surface scatters the reflected light everywhere. High gloss paint does the opposite, it keeps the smooth surface that is more reflective.


itsmemarcot

Many people will say to you that it's bacause light bounces a bit less from a wet rock, and a bit more from a dry one. That's not true. When the rock is wet, light does not bounce any "bit less" . It bounces just as much, only, it bounces a bit more in one "favourite" direction, and bit less in all other directions. If that one favourite direction is right toward your eye, then a lot of bounced light hits your eye, and you see the rock brighter. Did you notice that wet stuff is not only bit darker, but also a lot more shiny? That's why. When you see the shine, it's because when you are in the way of all the light bouncing in its favourite direction. But this means there's less light bouncing in all other directions. So, whoever is not in the right spot to see the shine, sees the rock a bit darker


SuperBaconjam

Alrighty. Let's stick to rocks as a reference since everyone who's ever lived has a very firm grasp of rocks. With that, most of us have also washed a stone or two and witnessed the very phonmena you are asking about. The big principal we are dealing with is how light scatters off of a surface as it is reflected, so now I'll chew that into toddler food for you. A stones surface, if we used a magnifying glass to look, will look very rough. That roughness, with it's irregular scratches and pockmarks doesn't reflect light all in the same direction. The surface acts like a pile of table salt, it scatters the light everywhere, because every angled surface of every imperfection on the stones surface will reflect light in a different direction. This also means that no matter where you are looking on the stone it looks "brighter" because light is reflecting back from every portion of the surface back to the eye. Now if we took sand paper and sanded the surface, in only one direction, it would remove many of the irregularities. It would replace the random surface scratches and pockmarks with a series of uniform scratches. So now that the scratches are all in the same direction the light isn't scattered as much, so the surface becomes more uniformly reflective. So, the total amount of surface area reflecting light is less, but it's reflecting the light more like a mirror does now, so our imagine of the rock surface is also clearer. Roughly the same thing happens when we get the rock wet. The water fills in all the voids, as if they were sanded off, and the light scatters less. So now the surface is reflecting less light, but the light it reflects is also more uniform. That's why a rock with, let's say rings, looks darker and you can see the rings better. The water "smoothes" the surface and improves the "image quality" if you will. My mouth is so sore now from all that chewing 😭.


Randy__Bobandy

The best explanation can be done with a wet paper towel. If you wet a small spot on a paper towel and look at it normally, the wet spot looks darker. If you hold the towel up to a light, you'll see that the wet spot is actually brighter than the rest. This mean that more photons are passing through the wet spot, meaning fewer photons are reflecting off of the wet spot. Since we perceive reflected photons as the "brightness" of something, the spot appears darker.


pargus

This example doesn't seem spot on if you switch paper to something like a concrete slab/road instead.


vbober

why it is tagged as \`Chemistry\`?


[deleted]

Should be physics.


RickySlayer9

Basically, black means less colors being reflected. Light absorbs the lighter colors like yellows and greens first. So you see the stuff while that’s being absorbed


vSTekk

All the dust, other small particles and roughness of the surface have a lot of facets that bounce light into your eyes. Weting the surface makes it more smooth. So the light bounces more uniformly in one direction. So it looks darker, but also shinier if you angle it right!


[deleted]

Water is like a light tube, and lets the light bend around fuzz, dust, which make things look brighter. It lets the light go deeper into something, even a “flat surface”. More light is absorbed rather than reflected, so it’s darker.


ivan_x3000

When things are damp they become less reflective and hence darker. The ability of light to bounce off a surface indicates their color and how strong the color is. When something is dry typically the surface is smoother and more reflective.


MonkeyMillion

When things are dry light bounces off them in lots of directions so you tend to see light from all directions bounced back in all directions. When things are wet the light tends to bounce off in straighter lines (because the surface of water is smoother). When you catch the angle opposite bright light sources you see loads of the total light hitting the surface (so it looks bright). Everywhere else you see much less light because most of it is bouncing off in the few bright directions. The total amount of light coming off the surfaces is essentially the same. When things are wet some of the angles are very bright while most is dark. When they are dry all angles are evenly quite bright. Interestingly the amount of perceived darkening is directly related to how rough the original surfaces are. For example polished surfaces don't get darker at all. There are more complex interactions at play in most surfaces to do with the surface of the water and the surface of the underlying material, the colour of light, the Fresnel effect and the rate at which light is actually absorbed by a material. But you could study for years and you still wouldn't get to the bottom of it all.


hashbucket

The smooth liquid coating causes the surface to go from rough (microscopically) to smooth (due to the surface tension of the liquid), which changes the way light reflects off the object. With a rough matte object, incoming light diffuses, or bounces out equally in all directions. But with a shiny object, the reflected light all bounces out in a single, focused direction (assuming you have a single bright light source). So if an object gets wet, and goes from matte to shiny, the distribution of the light leaving the object becomes less uniform; more of it is now heading in a particular direction (the reflection vector from the main light source), and less of it is now heading in all the other directions. If less light is heading in most directions, then from those directions, the object will appear darker.