Transparenting: Fill & Download for Free

I think water is transparent because eyes first evolved in water. The range of the EM spectrum we detect corresponds to the spectrum for which water is transparent (absorbs the least). Had we evolved in mercury, we would think mercury is transparent and detect EM waves that pass through mercury.Now why is it so?Because being able to detect EM waves that pass through water can greatly help us survive through detecting the source of energy (sun) and avoiding predators (or finding prey/food). Why can't we detect higher energy wavelengths that pass through more dense material? Well first of all, some creatures do (e.g. Mantis shrimp). Second, not much of the higher spectrum radiation makes its way all the way to the earth surface. Third, high energy beams are difficult to handle by the receptor; they destroy you if you interact with them, and therefore the receptors (eyes) that detect them are expensive to make.For more see User-9281586733273582199's great (more detailed and complementary) answer. [I decided to update this answer as many more people read it than I expected, there was some hand-waving in my original answer that I tried to get rid of, while not changing too much.]

Why are air, water, and glass transparent, when practically no other materials are?Many non-conductive materials can be transparent. Conductive materials like metals absorb light because their free electrons interact with photons. Non-conductive materials don’t absorb photons in the same way. So, most transparent materials tend to be non-conductive.That includes numerous polymers like Plexiglas:And countless crystals can be transparent. Even table salt is transparent if you grow it in large crystals. I work with some really weird crystals for infrared optics, stuff I’d never consider to be transparent but are. (Sodium chloride is, in fact, one of the options for optics. It just doesn’t handle humidity too well.)(Table salt)Solid carbon can be transparent, too.A key factor is preparation. Table salt generally doesn’t look transparent because it is a pile of shattered crystals filled with voids, defects, and contaminants.Likewise, this pile of glass used to be transparent. Now light has to pass through a maze of surfaces.Grow table salt as a large crystal and then polish it and it’ll be transparent:Aluminum oxynitride is generally made by sintering many small particles of the ceramic, resulting in opaque and translucent materials like this:But with a sintering aide to close the pores in the ceramic, you can get panels like this and launch a thousand bad news articles about “transparent aluminum.” (AlON is not “transparent aluminum.”)Likewise, a pile of alumina (aluminum oxide) dust is not transparent:And when you sinter it into useful parts, alumina’s often opaque:But when you grow the alumina as large crystals and polish it, you can get some very hard, transparent crystals like the panels on the nose of this Sniper targeting pod. (Apple also tried and failed to make alumina screens for its iPhones.)And when nature grows a large alumina crystal, it often botches the job and lets it get contaminated with metals. For some reason, people pay a lot for these dirty, transparent crystals (called sapphire):And ruby…Then there are liquids that are transparent, like (almost) pure alcohol:Liquid nitrogen:And even hydrocarbons like gasoline (quite a stew of hydrocarbons) are transparent:The first step to finding a transparent material is usually to identify a non-conductive material. Often no one bothers making them transparent, but they can. Even something like wood:

This is a question that is easy to answer empirically. Try an experiment. Spend six months being open and transparent and observe the results.I’ve done this. As many people (including many folks right here on Quora) can attest, I am as a matter of policy open and transparent when I interact with people. Looking at the results, I have to say that overall, the effects of openness and transparency are quite positive.There is one confounding factor you need to account for in your experimental design, and that is being open and transparent is not the same as being an asshole. Don’t confuse the two. A lot of people do.Honesty should not be brutal. People who say they practice brutal honesty are basically just brutes. You can be open and transparent and also be compassionate at the same time; those two things are not contradictory.