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Why Can We See Through Glass? | Earth Science
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- Опубліковано 23 січ 2013
- Why can we see through glass, but not other solid objects. James May explains.
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There are a lot of errors in this one:
- Glass is not liquid but amorphous solid. It does not flow. Thicker bottom in old windows is a result of imperfect methods of creating glass panes at that time and the usual way of putting things (thicker goes at the bottom) but there are windows where the thicker end is at a side or up. (Lead is much less viscous than glass so if glass in stained glass windows flowed, the lead would be a puddle on the floor.)
- Supercooled liquids flow like normal liquids. (Reuseable hand warmers use supercooled sodium acetate solution and you can see that it flows just fine.) The proper term for slowly flowing liquids is high-viscosity liquids.
- Photons of visible light can be transmitted through crystalline solids as well, e.g. through diamonds.
- Regular glass blocks some UV light but not all, and about 90 % of UVA gets through. It is still easy to get a tan or even burns behind a window. (UV is the reason why white plastics turn yellow over time and you can clearly see this even indoors.) Glass for greenhouses is usually tampered to block UV light to prevent overheating of plants.
1:28 is the correct explanation why glass is transparent (although it's electrons, not atoms that have this energy level). It's the only reason, nothing else mentioned in this video causes it.
I completely agree with you. This channel needs to take down misleading videos like this. Thank you so much for correcting the errors. I was about to write the same thing and luckily I saw your comment. Your comment has more accuracy than what I would written. Hats off to you. Thank you on behalf of all the guys who are interested in this topic
+Jan Sten Adámek Thanks for posting. Saved me the trouble.
Came searching for this comment when I realised the first error
this is so full of shit. 1) glass is not a liquid, it's an amorphous solid 2) visible light goes through glass because indeed it's not absorb, but the main reason is because glass is amorphous - not crystalline - and light is not SCATTERED. If glass were transparent because its atoms don't *absorb* the photons, then why is sand opaque? Sand is opaque because it's microscopic stucture is such that all the tiny facets of the tiny particles scatter light in all direction so very little gets to your eyes and you see it opaque. glass is amorphous, doesn't have crystals and light is not scattered. it's not absorbed either, but that doesn't explain why sand is not transparent - if it was an absorption issue, then sand would be transparent. it's not. just like the polypropylene plastic: it doesn't absorb light (it's only C-H and C-C bonds that don't absorb in the visible), but it's a crystalline polymer and its crystals scatter light away and it looks opaque.
+GOBELDYGOOK yes
+GOBELDYGOOK yes
why diamonds are transperant? Its a crystal, and one of the best
it's a single crystal. 1 diamond is one giant crystal. the crystalline structure and the arrangement of carbon atoms is such that the repetition pattern is very very small compared to visible light and therefore visible light is not diffracted - visible wavelengths just don't "see" the crystalline structure of diamond (it's like when you walk on the street - the distance between each of your steps is very large compared to grains of sand on the street and you don't trip on them. however, if you have huge rocks that are similar in size to the distance of your steps, you'll notice them and it'll affect your walk - it's the same for light: if the "steps" i.e. the wavelength is very large compared to what's in the way then it doesn't interact). for example, in contrast to visible light, xrays are diffracted by the diamond lattice because the wavelengths of xrays are much shorter than visible light and comparable to the distance between each carbon atoms. glass is transparent because it is amorphous and there are no microscopic structures such as tiny crystals to diffract light. of course, it doesn't absorb light either, but the special thing about glass is that it is totally amorphous - and this is a rare characteristics in nature and that's why glass is so special. there are *lots* of material that do not absorb visible light - totally amorphous materials are much much rarer.
Carl Coppens thank you
I'd have thought somebody like James May would watch QI and realise that this is actually a common misconception...
Glass is in no way a liquid, that is a myth. The non-crystalline structure thing is true but that's not the same thing. There are super viscous liquids which look solid, like pitch, but glass is not one of them.
Glass is not a liquid this is an old misconception because the glass in some old windows was thinker at the bottom because of old glass manufacturing techniques.
hmm... There seems to be alot of mistakes in this one...
Both Mercury and Gallium are metals that a liquid near room temperature, yet they are not transparent, conversely there are crystals (e.g. diamonds) that are transparent. It's not the phase of matter, but the electron energy levels that determine transparency to visible light. You almost got it right at the end, but overall this video is wrong and you should probably take it down to avoid misinforming your viewers.
Dear Head Squeeze people:
Forehand Anhyzer is right ... amorphous solid, not super-cooled liquid.
The sinking glass is a misunderstanding of archaeological evidence. Before glass was made in panes, it was made in huge discs, with this huge boss in the middle. The thinner glass was out towards the edge and this was practically the same thickness for smallish panes or pieces of glass; but the closer to the central boss that it came from, the glass's thickness would vary more greatly. And this glass was always placed thick side down. For this reason, it would appear as if the glass were slowly flowing down, like a super-cooled liquid.
My understanding is that an amorphous solid is a super cooled liquid. This is because a transition from a liquid to an amorphous solid is not actually a transition as no change in structure occurs. Am I not right?
Also a bit of anecdotal evidence, panes of modern glass can often be observed to be warped. Is that bad production processes again?
slapnthface Not quite so. Super-cooled liquids have no crystal formations happening, whereas there is a randomly-arranged crystal formation happening in an amorphous solid.
David Andrews I went on a definition hunt and amorphous solids are non-crystalline. Supercooling is the process of bringing a material below its melting point without it forming a solid or crystalline structure. It would seem to me that an amorphous solid could be called a supercooled liquid. My point is I don't think we can fault them for using this term (one which is actually a lot more easy to understand)
slapnthface Indeed it is a difficult one to get. I had to rethink it when I found the stuff out.
David Andrews Yep, I read about this. It was misuderstood, bullshit spreads fast dun 'it?
love these videos!
Very interesting!
i Love that i subbed. James May's with Tecnikal and Geeky info about different things funn to learn from too :D
Imagining an electron wave in a box, fixed at both ends, the length of the box must be equal to an integer number of half wavelengths for the wave to be a standing wave (Draw it or just imagine it in your head, it is easy to see by sight that this must be the case) Therefore L=nλ/2 [1] where L is length of box and n is an integer.
From λ=h/p, p=h/λ. Squaring this you'll get p²=h²/λ² [2]
People who know why glass is transparent is crystallographers (James Watson & Francis Crick use this field of knowledge to discoverer the Double Helix). Because light is a waves (which goes up-&-down at regular interval); it scatter best by matter which had atoms placed at similar intervals (eg: crystal, and not random like amorphous glass). Light reflection & blocking is mostly due to atomic arrangement and less to do with electron-configurations (of atoms), except for metal crystal; which reflect light thru free electrons cloud at surface.
Thanks :)
We love you James!
So disappointed this time ... go watch sixty symbols video about why is glass transparent and remove-correct this video here, please.
"Light, simply doesn't have enough OOMPH..."
-Classic :)
Ignoring relativistic effects (Though if you want just say and I'll derive it with relativistic effects, it's not more difficult though it makes the equation at the end less easy for you to understand how different factors will affect the energy) Kinetic energy=mv²/2, or as p=mv when ignoring relativistic effects, kinetic energy=p²/2m [3]
Just substittue [2] into [3] to get kinetic energy=h²/2mλ², then using [1] L=nλ/2, just rearrange for λ, λ=2L/n, square it, λ²=4L²/n² then substitute back.
That video only disagrees with the liquid bit, but agrees with the bit about energy levels, but explains it in more detail.
I'm not trying to sell you on any idea, I'm telling you to look it up for yourself. This video is correct, albeit largely simplified. The reason the energy gap is so large in glass is very much due to the fact that the molecules do not arrange in a crystalline structure.
True
well they showed an experiment on that video with the material where the point at which light was too low energy to get absorbed was in the visible light spectrum. that was fairly convincing
"It is trivially because the structure is not the part that matters" You might want to go rewatch the video you're recommending, specifically 1:20. "The important thing is how the atoms arrange" which yes goes on to dictate how the electron waves arrange.
But in that video, Phil says that visible photons do not have enough energy to move an electron in glass to the next energy level, and therefore the photon cannot get absorbed; it passes through. In this video, James also says that "light doesn't have enough umph" to make the electrons jump to a higher energy level. Correct me if I'm wrong here
The thumbnail for this video gave me a good giggle.
I've heard both, but more recently I've heard that glass is a solid. [but i forget the source] do you have a source for this consensus?
yes James, I have subscribed long ago
Getting rid of all constants, Energy is proportional to n²/L² and therefore it is easy to see the energy gap is proportional to just the length it is bound in. Which as you can tell is defined by the structure of the substance as where the electron can travel is determined by the structure and whether it is crystalline or not. The boundaries of the electron wave is determined largely by whether or not a substance is crystalline.
They are substances of the same state - noncrystalline solids, or amorphous substances, which is like the middle thing between solid and liquid. The principle is the same. See Wikipedia article "Glass Transition" if curious.
There are however proper crystalline solids which are see-through - think diamond as an example.
light has to bounce around more in denser materials, it just takes longer to get out of the material because it hits all of the particles, but it remains the speed throughout it
While it might take millions of years for glass to "form a puddle on the windowsill," in fact it IS possible to see the flow of glass over centuries. If you look at windows even a hundred years old you'll see that they are thicker at the bottom and thinner at the top. The effect is actually pronounced in stained glass windows from churches that are many centuries old, but we usually don't notice it because we focus on the colors.
I´m glad you said that; going by what James says here I would have to start trying to persuade myself that clear polycarbonate is also a liquid...
Just thought that you might want to see this,
Why is glass transparent?
I was hoping somebody would link to that video.
Glass is defined as an amorphous solid, meaning it's not made up of crystals or fibres. That's what makes it "flow" plastically very slowly. It's not close to metals or alloys at all because they are usually crystalline and don't exhibit plastic flow.
a better explanation is that it is effectively travelling further or less depending on the density of the material it is passing through
It would be interesting to measure the top and the bottom of one of the pieces of glass put in one of the first sky scrapers. The width I mean with that...
I think the fact that glass is a liquid is considered a misconception at this point. I also think that the ability to see through glass also doesn't depend on the state of glass as a material but rather just it's molecular structure.
true
Glass isn't actually a liquid, but an amorphous solid. Molten glass solidifies so quickly that molecules don't have time to settle into a regular crystal lattice because it contains small amounts of sodium carbonate (soda) and calcium oxide (lime) that interfere with the structure of the silica atoms as they cool. This is what makes it not a chemically neat solid. If there was no soda or lime glass would instead form into chemically neat quartz.
Also, to be fair, air is also transparent. Many gases can stop light (think of any colored gas). You cannot describe an object's state (solid, liquid, gas) based on how light passes through it. If you want see light traveling un-altered you need a vacuum, and in the case of the sun: space.
Most car "glass" isn't actually glass, it's a mix of several materials, layered for resistance (and to make sure it shatters in a controlled way and won't cut the passengers). Any "car glass" made in the last 30 years will block UV light even better than greenhouse glass, though.
glass is an amorphous solid, not a liquid. the whole "sinking glass" thing is a wives tale. what gives, james?!
Yes. Absolutely.
So, dear Head Squeeze people:
The sinking glass is a misunderstanding of archaeological evidence. Before glass was made in panes, it was made in huge discs, with this huge boss in the middle. The thinner glass was out towards the edge and this was practically the same thickness for smallish panes or pieces of glass; but the closer to the central boss that it came from, the glass's thickness would vary more greatly. And this glass was always placed thick side down. For this reason, it would appear as if the glass were slowly flowing down, like a super-cooled liquid.
Doing this you get kinetic energy=h²n²/8L²m. But as you recall from before, n MUST be an integer as the electrons are bounded as they are in a substance and must therefore be standing waves. The energy gap is the difference between two integer n's.
By consensus perhaps, but not by active cutting edge research via electron microscopes. Glass has properties of both solids and liquids however are closer to metals/alloys except the arrangement of nuclei and crystallization is less organized than most alloys.
the reason why people thought glass was a liquid was because they saw that glass was thicker at the bottom part of old cathedral glass. In reality, the glassmakers spun the melted glass into a disk, and the disk is thicker on the outside. They generally orient the pieces of the plane so that the outside of the disk, the thicker part, is at the bottom.
so diamonds are liquid?
Sure. Because diamonds are made from glass, as we all know.
Bernhard Baron I believe his point is that we can see through diamonds in the same way as glass so if they're not liquid then the fact that glass is a liquid is irrelevant to the question posed in the videos title.
Bernhard Baron LMAOOOOOOOO
Glass is not a liquid, and diamonds have very intricate crystalline structures.
Not true. Where are you getting your information from???
I heard that glass is not a liquid, many believed it was because the glass was thicker at the bottom, but only because of the way it was made a long time ago.
So the super-cooled liquid (amorphus solid) phase part are totally incidental, all that matters is the atoms electrons high energy gap, as that allows both Diamond and Glass to transmit visible light.
Glass is not a liquid!
While some antique windowpanes are thicker at the bottom, there are no statistical studies to show that all or most antique windowpanes are thicker at the bottom than at the top. The variations in thickness of antique windowpanes has nothing to do with whether glass is a solid or a liquid; its cause lies in the glass manufacturing process employed at the time, which made the production of glass panes of constant thickness quite difficult.
yes... But it would be something you wouldn't be able to see anyway. Something like an ultraviolet laser dot on a wall, assuming the wall would reflect that in the first place.
Most solid objects would reflect or emit many wavelengths of light, some of which could probably be seen through glass.
You must remember that as long as any visible light is present, at least a tiny bit would be reflected off an object.and could be seen.
Which part? Glass is a liquid (actually "amorphous solid" is the correct term) but moves very, very slowly. The myth is that older panes of glass are thicker at the bottom because of this. That is incorrect as no pane of glass made by humans has existed long enough to visibly deform due to "flowing."
He does kind of describe the quantum properties of protons, which is the reason why glass is see through, so they mainly agree, apart from glass being a liquid or a solid, I tend to think glass is a solid cause when I touch it my hand doesn't get wet and I have seen liquid glass, which is definitely NOT something I would want to touch with my bare hands.
Electrons in a substance are bounded and not travelling I'm sure you'll agree. Due to this they must be standing waves as any other type of wave would transfer energy and hence travel.
If Glass naturally blocks out UV rays, then how come it has been said that ceasium is added to make it UV blocking? does it lower the energy needed to raise the electron's energy level?
He failed to mention the other way light can react, refraction. This is what happens in a diamond, as light passes through the diamond the sold bonds change the direction of the light (usually not very noticeable), not enough to split or reverse the direction of the light (what happens when we see an object with color).
I love all the people here that have doctorates in chemistry. *eye roll*
Why can we see trough glass in a nutshell:Because it's transparent. :D
Ok i may have been a little hasty but the fact it has liquid structure may not fully explain it because there are many liquids that aren't see through. Diamond for example is a solid that is see through, and mercury is a liquid that's not see through. So it kind of doesn't add up. the state they are in is only relevant to earth's environmental temperature. eg. in outer space water is a rock. So to simply say 'it's liquid isn't enough.
Glass was hard to make in years past. You have an uneven glass pane, so where are you gonna put the thickest edge? On the bottom, where it has the most support. It's why the myth of liquid glass exists now.
You can still see some panes of old glass with the thickest side on the sides, or even on top, from window makers who didn't put the thickest side down where it provides the most support.
Maybe I am missing somehing else, but I am pretty sure he covered what sixty symbols also covered, referring to energy absorption levels of the glass atoms.
So... why will some materials transmit a substantial amount of a small section of the electromagnetic spectrum?
I didn't think the state would matter, H2O is transparent whether as liquid water or solid Ice.
Yea i've heard from other sources i believe one was minutephysics or somebody who is also big here on youtube say glass isn't actually a liquid.
I was about to post a link to exactly that same video xD
Now, it's all to do whether the material has weak enough electronic energy level structure for the light to make the electrons in the material to jump (quantum leap) from a lower energy level to a higher one if the light hasn't got enough energy to excite the electrons in the material then it won't pass through, and will simply get reflected, or completely absorbed by a black body (like our own sun) black bodies, do not reflect light. if light manages to excite the electron it will go through :)
Light passes through glass because the crystal lattice is sufficiently spaced that photons of a certain bnd of wavelengths can pass through. Glass is a solid. It has weak interaction between the silicon dioxide molecules which is why it creeps. Now take a Diamond or a Ruby or a Saphire for example. Transparent to certain frequencies of light (wavelengths) but not others. This is the principle on how wavelengths are selected for lasers.
Eh, glass is really both it's sort of both depending on what definition you use whether you looks at viscosity, melting point. Generally the best description is Supercooled Liquid. But the distinction between the two is largely set at a macroscopic level rather than microscopic level so really it's tough to actually set a set of rules for it. It is however still wrong to say someone's wrong when they're not...strictly speaking. Second it was the animator that implied the latter issue.
how does a two way window or mirror work
The energy levels of electrons is affected a hell of a lot by structure which in turn is affected a hell of a lot by if the substance is crystalline or not. At no point whatsoever have I said that the structure is the only thing that determines energy levels, however it contributes largely to it.
And no I have not been misled by this video, it has changed my view in no way at all.
Let me help :) well, first of all light to be emitted, you need to excite an electron from a lower energy level to a higher on by shining light at a particular frequency at it, or simply heating it up. As the electron then "cools" down to a lower state of energy after being advanced a level, it emits what we call a photon, a discrete packet of light that we see as normal light, thats the first step...
Why and how do things break?
Infact I have just watched the video on sixtysymbols that you're recommending and it says exactly what I'm saying. You in fact have been misled by that video in where he says "glass is like a liquid and therefore the molecules don't pack as tightly and therefore there are gaps. That is wrong badly wrong on so many different levels."
I was just about to add that the part about glass being a liquid is incorrect, it is an amorphous solid. Now that I've seen the comments I decided to comment anyway, just to help the disagreement along. I would love to see a video were he admits to being wrong and correcting that part with some real facts.
if iron was added to the glass mix it would block out almoast all UV but if it wasn't then it will only block out a tiny mount
What about transparent plastic? Is that also a liquid?
Well air is very small molecules very far apart. Most of the "things in the air" that I obscuring are actually suspended particulates, not gas, like suspended water droplets in fog, or carbon fragments in smoke.
At high temperatures, elements and compounds are liquids, and as the temperature is lowered the crystalline solid becomes stable. We think of solids as rigid and elastic, whilst liquids are unable to support a shear stress, and so flow. The problem is that as a liquid is cooled below its melting point, although it should transform to a solid, it can find it hard to nucleate a region of crystalline solid, primarily because it will create a region of interface between the liquid and new crystalline solid, which is neither one thing nor the other, and so is effectively an energy barrier to the appearance of the new solid. So liquids will invariably undercool below their nominal melting point before forming a crystalline solid. In many cases the undercooling is only a degree or two, but in some systems, such as window glass, the energy barrier to forming a new crystalline region are just too large, and the liquid carries on undercooling. As its temperature continues to fall, it gets more and more viscous as the atoms have less and less energy (that is what falling temperature means) and so find it harder and harder to move around. This is often called the super-cooled liquid state. In this state, the atoms are still moving around (as they would in a liquid, but not in a crystalline solid), albeit slowly. But eventually as the temperature continues to fall, the atoms become so sluggish they get effectively locked in place in a random arrangement, and we call that a glass. The difference between a glass and a crystal is simply that the atoms in the glass are randomly arranged, whereas in a crystal they are all lined up on a regular repeating lattice structure.
This of course has nothing to do with why we can see through glass. You can make liquid silica crystallise: we call that solid quartz. And last time I looked. quartz is transparent just like glass. Whether or not a solid (or liquid) is transparent depends on whether the energy associated with a light particle (photon) is able to be absorbed e.g. by the atomic bonds in the material. If it van be absorbed, the material is opaque (and gets hotter when illuminated), otherwise the light passes through, although it may slow down whilst in the material.
Why does that happen with diamond's regular molecular bonds and not with other covalent solids like Silicon Carbide?
Sorry to be fussy, but I'm not really seeing a coherent explanation of why some things are translucent. I mean water also refracts, yet has no covalent bonds between molecules, only dipoles.
So, glass is a liquid? Now I understand why we say: -''please, give me a glass of water!'' LOL
Don't you dare question the teachings of the Great James May.
So there have been statistical studies that prove glass makers and fitters always made sure the glass was thickest at the bottom? Interesting...
Glass is a solid, it's thicker at the bottom of old buildings as the glass poured wasn't even so it made sense to put the thicker end at the bottom.
its also was taught to be the most viscus materiel however after it was found false the most viscus materiel is pitch
You saying the structure is trivial not only goes against the video that you're saying is completely correct it is also just like saying the structure of an engine doesn't matter it's how the engine works, which is entirely determined by the structure.
He did say it is TECHNICALLY a liquid (because of the molecular structure), he never affirmed that it IS a liquid.
I'll derive how the energy gaps of an electron are determined in 1D. Unfortunately 3D solutions of the Schrodinger equation would be too complicated to be shown in UA-cam's comments. I'm going to assume you have a knowledge of physics of an average 16 year old and as such you understand why λ=h/p and do not contest it, and understand the meaning of it. (If you do not please say and I'll try to explain more simply.)
At least he mentioned energy levels. But for a better explanation, go check out Professor Moriarty on Sixty Symbols et al.
Light does not travel at the same speed all the time. It slows depending on the material it is passing through.
he's entirely correct that this is wrong, it has nothing to do with there being gaps. However you have gone on to assume this means that how the atoms arrange in a non-crystalline way does not matter. But as he goes on to say "the important think is how the atoms are arranged". Even according to the video you're referencing you are wrong. The way the atoms are arranged is incredibly affected by whether or not it is crystalline, not "only trivally"
I have gotten a sunburn in a car with the window up. At the very least some UV light does pass through glass.
Having said that, for the majority of it you are entirely correct. As far as I know.
I would think that Mercury disproves this since it is a liquid and quite opaque. Not to mention pure quartz, which is a solid yet can be seen though.
If you had watched the sixty symbols video explaining this, than you would of known that both videos say the same thing. James just mentions something extra about glass being a liquid.
Water ( liquid state of H2O ) is used for cutting metal and many other things, so indeed a liquid can cut you, and Iron.
But I allways get my arm tanned in my car trough the glass
old glass windows are wavy and thicker at the bottom, due to poor production techniques no longer used. NOT due to it being a semi-liquid, which it isn't.
this also has left me a little puzzled unfortunately i only have another question. Rooster Teeth podcast?
I teach this stuff and have been battling this misconception for 10 years, glass is a solid, this idea of super cooled liquid is bogus. there are no special properties that glass has that other non-crystalline solids don't have, including clear plastics, Glass can occupy a solid, or liquid state, the same as any other material that is heated or cooled, the idea of "super cooled" is only relative to room temperature and using the same logic, water or even mercury are "super heated solids"
Okay... then why can we-see-through/light-travel-through diamond that has a very regular structure of molecular bonds?
I bet jezza is having a field day :D