Why is glass transparent? 

"it's 4 am what on earth are you doing?" "learning why glass is transparent"

I like how he held up a piece of glass to show it's transparency when he's wearing a pair of glasses.

I could listen to that guy all day. It's awesome how excited he gets when he explains things.

I wish u gave him 10 mins, great explanation

I'm glad to see all those photons getting true..

I'm an electrical engineer with a rough understanding of quantum mechanics. But I have always wondered about this question. Thanks for a "crystal clear" answer.

As a keen photographer, knowing why glass is transparent has promoted me from a ground state to an excited level!

I really like seeing someone this animated about science.

Maybe a little more detail about how important the arrangements of the atoms is. That way you could explain why graphite is opaque, yet diamonds are transparent, yet both are almost pure carbon.

I could watch this guy explaining stuff for days, he is the best

Well that was an unexpected treat. Thanx for explaining exactly how the color filters on my camera lenses work. Have used them for going on 45 years, only knowing the effects the different color filters will give to different kinds of photo situations. Now I know how they work. PS, if you take pictures in anything more than a casual way, LEARN how color filters can help your artistic efforts. Too much done with digital processing these days. Purists that use digital but grew up with chemical get 5 times the fun out of tweaking their pictorial efforts, by knowing what types of effects can ONLY be applied at the time the picture is taken, and ONLY before the light actually hits the CCD parts of the camera. LEARN what you can DO with the LIGHT before it GETS to the computer, and then on to the printer. You'll gain a new appreciation for your talents.

Wow. His name is Moriarty, guys. Moriarty. PROFESSOR MORIARTY.

So, for instance, a substance like glass that might be transparent to visible light might be opaque, or partially so, to an energy source like X-rays, if the quanta had enough energy to excite the electron to a higher energy state? TNX for the video!

So the trick to becoming invisible is not to get exited....hmmm!!...but that would defeat the purpose of becoming invisible...darn!!!

Another amazing video, I love how the professors are always so excited about their material.

The fact that Si-O and Si-Si bonds don't absorb in the visible is NOT the explanation why glass is transparent. It's true that glass doesn’t *absorb* visible light. But why is sand (which is chemically exactly the same as glass) opaque, then? Why is it that other materials that do not absorb in the visible spectrum are opaque? For instance, syndiotactic polypropylene is opaque, yet it is only composed of C-H and C-C bonds that do not absorb in the visible spectrum. Moreover, if Si-O and Si-Si bonds did absorb in the visible light, it would absorb specific wavelengths, say 450-475nm, and the material would be (in this example) red, but it wouldn’t be opaque. Absorption is only one part of the story. Most of the opaque materials around us is opaque because they are (at least partially) crystalline and the size of the repeating cells in the crystalline structure is such that it *refracts* visible light (think Braggs diffraction). That's the reason why most of the transparent materials are transparent: because the repeating cells in the crystalline structure isn't in the same spacial order of magnitude as the wavelength of visible light or there is no crystalline structure, and therefore doesn’t refract visible light and is transparent. As for sand, the minuscule particles that compose a pile of sand are in the size domain that refract light and that’s why light doesn’t go through sand - most of it is refracted. The same explanation is valid for polypropylene; you would expect PP to be transparent because C-C and C-H bonds don’t absorb in the visible spectrum. But it’s opaque because the crystalline structure refracts visible light. Glass is transparent because Si-O bonds don’t absorb light AND because glass isn’t crystalline and doesn’t refract light. The latter is a lot more relevant. Again, if Si-O bond did absorb visible light, glass would be colored, not opaque. Glass is transparent because it’s amorphous.

Why is paper opaque, but when it gets greasy it becomes transparent? Does it change atomic energy levels?

Now this is what I call a professor!! In 5 minutes I understood what I've never been able to in class

He gives the example of Diamonds when comparing the properties to glass, which brought up a new question. Why can the photons not excite the electrons in the carbon atoms of Diamonds, but they can excite the electrons of elemental Carbon? If you've seen Carbon before, you'd notice that it is the complete opposite of Diamond in the fact that it is completely opaque and black, whereas diamonds are clear or translucent. Why is this so?

Great video. First thing I was thinking at the start was changing the photons energy and it's effect then boom. Thanks for giving him more than 10minutes and editing down

That light's going "stroo."

So basically glass doesn't absorb photons with its electrons and thats why it is transparent! You're my favourite professor Phil, so nicely explained and always passionate! :D

Some videos on RU-vid are absolutely fantastic. This is one of those.

When i was 5 or 6 i used to bug my parents by repeatedly asking them how and why glass is transparent. They ordered me an information pack from pilkington glass but it didn't give any answers. 25 years later this video randomly pops up on my youtube feed and now i know the answer. Your videos are awesome, thank you.

Does that mean that glass is opaque to higher energy (frequency) EM radiation, such as xrays?

Very very well explained! Nice job. This is the proof that when well explained, science is for everybody.

Thanks for clear and concise explanation. Best Wishes for your future projects.

It was an awesome explanation. Thanks for this amazing channel and Professor Moriarty

Question: So what happens after the photon is absorbed ? The electron must come down at some point releasing that energy. In fluorescent substances that bit of energy is regenerated as another photon of a slightly higher wavelength. But not everything is fluorescent. What happens then ? Is it emitted as infrared, a.k.a. thermal radiative energy ?

idea for new channel: prof. Moriarty reviews science articles

One of the clearest and precise explanations I have seen about this subject.

The best teacher makes every student the best student. We would all have been served well to have Moriarty as our professor.

Why do many glasses stop being transparent when they are, say, scratched or pulverized into a powder? As far as I know, the chemical structure of the compounds in the glass hasn't changed, so why does it suddenly absorb light better?

Great video as always! After several views, I finally had the "I get it!" moment from it, and it was by comparing the visible light to a higher energy light like Ultra-Violet light. I think that viewers will understand better this concept of higher electron states and photons if they're shown a comparison between visible light passing through glass and UV light not passing through it at all. This explanation / experiment will help explain two concepts: first, that glass only "absorbs" higher energy photons, and that UV light is of higher energy (and wavelength) than visible light. Just a thought, maybe for a future vid :)

I'd like to let you know you helped me at my final thesis. Thank you.

Love the video/explanation, you explain a prism, including input to output of a spectrum?

I have a doubt. Gamma rays are electromagnetic waves and they can pass through walls which means that the wall is essentially transparent to gamma rays? Does that mean that they don't have enough energy to excite the electrons to a higher energy state? I don't know if this is a silly question but i would appreciate it if anyone can explain.

Right! What I am going to do know is pretend to be a photon.

ah man moriarty is just the best, nobody explains concepts with such vigor yet beautiful simplicity like he can

Thanks -- Loved the experiment in particular

For some strange reason, I love this video.

Why isn't the photon absorbed anyway, just in the trying to knock the electron up a level. Another way to explain my befuddlement is: if a photon bashes an electron, how does it know the future? The future of whether or not it succeeds in pushing the electron up a level, and therefore whether or not it is absorbed?

I love this guy, he is always so enthusiastic and good at explaining

That's such a beautifully simple experiment!

But what if the transparent material was blue-tinted instead of red-tinted? Then the lower-energy levels would be absorbed, but the higher levels wouldn't? And why do x-rays pass through objects? They're energy levels are a lot higher, aren't they? So why aren't the all absorbed?

So if an electron can only exist in a ground or exited state and a photon has more than enough energy what happens to the extra energy? Does the electron absorb it and stay in the exited state longer, does it get reflected, or can an electron just go to a higher exited state? Sixty Symbols

From something that I didn't know to something that I now understand in 5 mins.Wonderful; thank you.

Awesome!! You not only have great knowledge but you can explain effortlessly awesome.

I need a 2 hr video on this

Man, I'm glad I made it 'trew' that video, that was amazing!

That is a brilliant explanation. Despite of the wrong justifications for glass, most people just blow up a lot of quantum physics concepts, which are not accessible or elucidative at all. What you did was a marvelous visual representation of energy levels, which made possible understand the general idea of it. Thank you so much for that.

Professor Moriarty is probably my favorite!

Can we make things like transparent wood or transparent steel depending on how we arrange the atoms in a certain matter without changing the chemical properties which makes those materials?

So this explains why radio waves can go through walls and buildings. They're just very low energy

Interesting, great examples and wonderful explanation.

Thanks! I had been wondering if the photons that came through glass were the same that went in. I'd had a picture of something more like electron conduction.

How does absorption work? I already get reflection and transparency. Where does the energy from the absorbed photons go? It doesn't just disappear.

i really like this guy. he gets so excited about science! i love it! can he be my professor?

Question regarding the amber semiconductor. I get that the red would go through due to the lower energy level not bumping the electrons up to the next level and how the violet, given its higher energy, is absorbed due having enough energy to bump the electrons to the next level. But if we continue that reasoning, wouldn't x-ray and gamma rays also be blocked given the energy-to-electron bump-up rule?

Excellent explanation !!! Absolutely useful. ! Thank you!

How can water let higher energy photons through(visible light), but interact with lower energy photons like microwaves?

thanks for this! when the photons hit the wall, then I assume the same happens, i.e. elektrons get pushed to higher energy levels. Why then does the wall never get saturated? Is it so that the electrons fall back to lower energy levels more or less quickly and then radiate heat? And if so, why is the higher energy state instable? Thanks!

So many things I never learned yet. Thanks for this!

4:22 Xen crystal! Resonance cascade imminent!

_"Why is glass transparent?"_ Isn't it clear? ;-)

omg this video answers all my questions thanks a lot! btw that machine in your lab is amazing what is it called?

Awesome. I never knew this. Such a simple explanation. bravo!

What happens if you just shine absolutely huge amounts of light onto an opaque surface? If all the electrons are raised in their energies, then surely (and eventually) one photon could pass through. If this is the case, then surely enough photons could make a material transparent?

Isn't the electron going back to it's ground state, therefor releasing a photon again? What happens to that? Are those the reflected photons, making the color we see from objects?

I'd love to see an explanation of diffraction, tied in to this. I'm confused as to how the light changes direction if it doesn't interact with the electrons in the material

Fantastic video. I'm a complete layman and now have a bit of a clue about the subject. Really well explained!

Is this the same reason that high frequency, high energy signals like 5 GHz WIFI are easily blocked by a wall, while low frequency, low energy radio signals can be transmitted across the entire world and all throughout space?

See this is the stuff of science I like, the reasoning behind things. The math part is what absolutely kills me. At least in my AP Physics High school class it did back when I took it. I can watch these videos all day and understand what they are conveying. Just not the math unfortunately.

That was awesome ! Just wondering if there is a similar explanation for how mirrors work.

followup question 1: most glass is opaque at around 250nm wavelength, suddenly becomes transparent at longer wavelengths, but transmittance diminishes again at around 2700nm. When transparency is due to photon not having enough energy to excite electron, how is the material not transparent to lower energy photons? followup question 2: It's transparent because photons don't have enough energy to excite the electrons, yet, if you powder the glass, it becomes opaque once again even though they're the same atoms as before. What role does the structure of the material play in determining opacity?

Would someone please explain to me why electrons have specific energy levels they can have around a nucleus, rather than simply occupying a fractionally higher level if it receives a fractionally higher amount of energy from a photon?

Just because a material doesn't absorbed photons doesn't make it transparent. Some materials scatter light and are therefore translucent. The question is then why do photons continue on straight lines after bumping into atoms in transparent materials but not in translucent ones?

great explanation on electron energy levels and why glass is transparent, thank you...

Great! But what causes the speed of light to fall as it passes through the glass (i.e. in refraction)? The band gaps explanation seems to suggest the the light is transmitted because it is not of high enough energy level to excite the electrons - so what slows the light down?

So why don't gamma rays get blocked by glass?

Why not

Amazing explanation, but creates a whole lot of new questions for me. How do refraction and reflection play into this? What happens with these energy levels? Does the material ever get saturated where all electrons have achieved maximum energy level and it becomes opaque or does it lose energy levels by emitting photons out (is that refraction)? What if a photon has twice the energy needed to excite an electron, does it raise the energy level of two electrons before it disappears?

Brilliant explanation! Thank you!

Wow I learned something

Vsause lean back anyone??

Brilliant explanation; however, it has triggered a series of questions about macro phenomena related to propagation of light in a transparent medium. Namely: - refraction and Snell's law - reflection of light through glass I am also pretty interested in reconciling the above and the explanation in video with the interpretation of a photon's energy as (proportional to the square root of) the probability density of a photon's or electron's position? Any help with these questions would be greatly appreciated.

Thank you. That was a great explanation and demonstration. Think I get it.

theres too many books on the shelf :O gravity

Glass is opaque for IR radiation, that is called the greenhouse effect. But according to your video if visible photons can't bridge the energy gap, then IR photons even less so. Help, please!

thank you! this answers a question i didnt even know i had for a long time

I've been wondering for a while now, so the colors we see when we look at certain materials are caused by electrons being moved to higher energy levels ( it's actually the opposite wavelength which is absorbed right?). I've also read once that if these electrons return to their ground state, the material emits light (I'm not sure if this is true). So if we keep on shining light on a certain material, after a while there won't be any electrons left in their ground state sooo what happens then? Because when no more electrons are being moved to higher energy levels, the material is actually transparant then? Maybe I'm just wrong and these electrons do return to grond state after a while. And is it possible that the material starts getting another color when for example the fotons move these excited electrons to a higher energy level? Or does that not happen?

I have a begginer question... So photons only can be absorved by electrons? Glass is a mass made of atons, with protons and electrons... so I thought that the most of the photons would be "absorved" or be blocked by the protons that is much larger than an electron. If the glass is solid and made of atoms, how can be possible to light gets through!? I still don't get it! Help me!

so that is why transparent metals are rare !!!!

I wish i have such friend like Phil. He is so great!

this video really helps me study and understand Concepts from my instrumental analysis class

The English accents and speed of babble make these videos irritating and tiresome.

You sound so rude! when you said ur not getting 10 minutes!

Hey Brady and prof Moriarty - this might be a naive question, I have watched this video couple of times now and I have one question. You told for opaque objects the photons excite the electrons to higher energy state, does this mean the excited electrons remain there? That I guess is not possible as this would be a high energy state for he system and the system would want to come to lower state. If the electrons remain there, we can hit the opaque object with a lot of photons and this would excite all electrons in the object and after some time the gap between the two energy state will be so high that that object will not absorb photons anymore? Or if the electrons gets de-excited again and bounce back to lower state do they do so in non-visible range? In this case they should be emitting IR or UV range? Which is the correct explanation?

okay, but i still have questions. so if i have red/orange glass it lets through the lower (energy/frequency) part of visible light only because they dont have enough energy to make electron go higher state as i understood. but if i have blue glass. is it like the opposite that it lets through only blue and those above it (with more energy) because they have too much energy and there is no state for 1 electron to go to with that amount of energy and red, yellow, green etc fit the range that exites electrons? or is it still that the detector would show 0 at red, yellow and green light and some value at purple colours, and how would that make sense (like that i would see red objects still red watching through it right?). but then again if my first version is true then how is green glass supposed to work, because its in between and this way it should also let through red OR blue light. also i was wondering if this is similar how non-transparent (dunno how to write opeig or sth) objects have their colour? for other comment writers -> give answer if you know its true, otherwise write that you speculate, also additional questions never do harm.

incredible explanation....loved it a lot