I'm a chem major in college. He just gave an organic chemistry lecture to lay people and it made sense. Steve Mould is amazing Edit: a year later and I'm almost done! My last final is in 6 hours then I'll have completed my bachelors! :D
I am a chemist. I learned about optical rotation in school and I test optical rotation on a fairly regular basis. This is by far the best explanation I have ever heard and I understand it better now than I did 20 minutes ago. Thank you.
This explanation was leagues above any explanation I learnt at school about optical rotation. Thinking of linearly polarized lights in terms of two circularly polarized components was basically what I needed to get this concept through to my brain. That was amazing!
I eventually just accepted that chiral molecules twist linearly polarised light and never questioned why exactly that is. In all the chemistry and physics lectures (even in optics where we talked about many polarisation effects, so it would have been perfect to give an in-depth explanation of this phenomenon) we were never explained why that is. I'm so amazed of how comprehensible your explanation was. Thank you so much for blowing my mind.
It's weird how much of traditional teaching (or maybe just how some school curriculums were set up) was just learn the facts / models instead of explaining why, visualizing it, or even just explaining why it's useful. Now that I'm older I"m more willing to take up dry reading like wikipedia while also checking out youtube videos for that extra insight, and when I find them I"m stupefied why this wasn't in school because it seems like such a small investment in extra explanation for the huge help in understanding. So I've learned enough that way so that once he said helical polarization is possible, I immediately figured out a helix is chiral, the sugar molecules must be, there we go. Still kept the video playing for the watch time lol
I have a physics degree and this is literally the best answer I've ever gotten to this question. My professors at university always resorted to a lot of math to explain this, but your explanation is so simple, yet so complete.
Your professors wanted to ensure that you wouldn't get a physical understanding. They wanted you to have only a mathematical understanding. In general, they want you to have no physical understanding.
@@christophergame7977 where did you get that impression from? During my degree only a couple of professors were fantastic at explaining intuitive explanations that go along with the heavy mathematics. Being able to do so is an incredibly difficult skill, it is why Richard Feynman was so revered through his lectures and red books. When you have spent decades studying a specific highly complex field, it becomes difficult to put your self in the position of a first year student, particularly when they come from all over the world with different educational backgrounds. However mathematics is a universal language and despite the complexity of harnessing the Schrödinger equation, it is still easier than relating the underlying concepts in an intuitive, but vitally still accurate, manner. > In general, they want you to have no physical understanding. Why on earth would this ever be their aim?
@beardedchimp Thank you for your response. I didn't say 'intuitive'. I said "physical". Perhaps I malign them? You say that only a couple were good at intuitive explanation. Why only a few?
@@christophergame7977 explanations are intuitive when we can understand them in the context of our physical reality. This is why he used physical pasta to help our intuition. > Why only a few? I thought I had explained that? It is an incredibly difficult skill, hence the revere for Feynman's public speaking. I can give a funny example, my quantum mechanics lecturer was Jeff Forshaw. He was great at giving physical, intuitive examples of systems that are fundamentally non-intuitive, but it still helps. He had to unexpectedly move to CERN for a couple of months and was replaced by his former student. The contrast was stark, he went between using far too advanced mathematics and concepts to patronising us explaining simple concepts we knew at 13. I remember coming out of a lecture and telling some friends that I felt bad for the guy, he clearly lacked experience in public speaking and conveying complex information, Forshaw had put him in a difficult position half way through the year. That man was Brian Cox. When I first saw him doing work with the BBC several years later I was shocked, I thought to myself "Wow! He clearly worked hard and learnt a lot from his early lecture disasters". It is a skill, it is easier for some than others but more importantly it takes hard work and effort which is difficult when you are under pressure to publish papers.
@beardedchimp Thank you again. Yes, now I get your point. It's hard for them to present a physical understanding, so they just give up trying. I'm not so sure. I think perhaps they gave up trying to get a physical understanding themselves, so they didn't even try to present one to their students: maths without physical understanding has become their nature?
Can I ask you a dumb question? When he says polarized light is a superposition of two circularly polarized light waves pointing in opposition directions, does he mean literally just two? Or, like, dozens or thousands that cancel each other out that way? Why would they travel in pairs?
@@TristanCleveland i think we're starting with linearly polarised light, so we have that as a firm statement. From there that could be split up in all sorts of ways actually. It's just for this experiment, because of the handedness of the molecules, rotationally polarised light is the relevant way that the light is affected. The counterclockwise and clockwise aspects of the linearly polarised light are affected differently. Seemingly you could make up any number of different pairs (or other symmetrical sets) of subdivisions of the light wave, but they wouldn't be useful for understanding what's happening here.
@@TristanCleveland in the end the thing is the field and the substance it overlaps with, not the wave. The wave is merely a description of the movement of that field, and you can describe that movement in all sorts of ways as are useful to you and accurate.
@@JohnGottschalk I hope I got that right. The wave is just a description of a field, as to my understanding to make a field "visible" to the human mind it has to have a "material" property like a point moving through space - wave. Am I right? And out of this construct one can build the explanatory construct of different waves "creating" the sum-wave of the "visible" light, correct?
Alternative title for this video: how to finally understand why in God's name optical isomers are different, how are they different and what the hell does "they bend the light right or leftwards" mean. It's amazing how you get a topic as hellishly complicated as optical polarization applied to chemistry and make it sound like it makes sense. Also, I think a good follow up for this would be why the direction the molecules twists the light matter. The case for thalidomide is famous: when it twists the right to the right it's a sedative but when it twists to the left it causes birth defects. How so?
The above explanation is correct, differently oriented molecules fit into different molecular receptors in the body. Hence the weird 'double personality' of otherwise identical molecules.
A large part of the reason is that many/most molecules in biology, are chiral. And therefore can react differently to the different enantiomers of a molecule.
@@franchufranchu119 I vaguely remember reading somewhere that certain molecules when encountered in the human body (perhaps 'biologically' would be better) have a consistent handedness, but those created in the lab (perhaps 'chemically' would be better) do not, and at the time the author wrote that, the cause was unknown. Have we figured this out yet? have we figured out how to 'artificially' recreate the handedness of molecules yet?
if you had a solution of levose (dextrose stereo-isomer) it would , of course polarize light in the opposite direction. If you mix dextrose and levose together, you could determine the ratio of each substance by how much and in what direction the light is polarized.
Or he could have added an equal amount of L-Glucose and had no rotation of light. He seems to ignore that D-Glucose has a levorotatory form in L-Glucose.
l-Glucose was once proposed as a low-calorie sweetener and it is suitable for patients with diabetes mellitus, but it was never marketed due to excessive manufacturing costs. The acetate derivative of l-glucose, l-glucose pentaacetate, was found to stimulate insulin release, and might therefore be of therapeutic value for type 2 diabetes.[3] l-Glucose was also found to be a laxative, and has been proposed as a colon-cleansing agent which would not produce the disruption of fluid and electrolyte levels associated with the significant liquid quantities of bad-tasting osmotic laxatives conventionally used in preparation for colonoscopy. I thought, honestly that was a fatal mistake to eat much of that.
I found this explanation to be fascinating but kept waiting for the corroborating demonstration of the L-glucose case which sadly never came. But wait. Wasn’t he using sucrose there?
I worked for a decade and a half in sugar mills as a "Sugar Chemist"/Lab Technician. We did indeed us polarimetry to determine the amount of 'sugar' in the crushed cane juice at the start of the milling process and the processed raw sugar at the end. We also had a process to determine levels of fructose and other "reducing sugars" by measuring the angle of light bent to the left (levo-rotary).
l-Fusilli is indistinguishable in taste from d-fusilli, but cannot be used by living organisms as a source of energy because it cannot be phosphorylated by hexokinase, the first enzyme in the glycolysis pathway.
0:00 - Introduction 0:44 - Polarized Light: short explanation 2:31 - Polarization of Sugar 3:49 - Superposition of Polarized States 3:55 - Superposition of in-phase waves (linearly polarized light) 5:17 - Superposition of 0.25λ out-of-phase waves (circularly polarized light) 6:33 - Superposition of circularly polarized states (linearly polarized light 😮) 8:01 - Pasta 9:53 - Index of refraction of pasta 10:52 - Superposition of pasta shifted states (wave-plate retarder) 11:20 - And to Reiterate... 12:17 - PASTA SYMMETRY 13:40 - Handedness (fundamental common attribute between pasta & sugar molecules) 14:36 - Mirror symmetry in molecules 16:12 - Answer: "Why Sugar Always Twists Light To The Right" 16:25 - BTW: Dextrose
Absolutely brilliant. You covered circularly polarized light, chiral sugar, and superposition all without reference to one equation. Very, very well done.
@@simonvetter2420 haha no you need The polarization to be oriented vertically/horizontally and the microwave doesn't have a polarization filter so overall net-value is zero, the comment above was purely for the sake of good humor
A microwave oven works by passing microwave radiation, usually at a frequency of 2450 MHz (a wavelength of 12.24 cm) That's probably to big a wavelength for the pasta to have a strong effect 😞
Hey Steve! You could extend this to explaining how liquid crystal displays work really easily! Basically just using a voltage to orient chiral molecules either along the direction of the light, or perpendicular to it, which then either make it through the polarizer (bright pixel) or don't (dark pixel). Thanks for some great animation, this will definitely help me teach polarization a bit better!
I remember vividly in 2005 when starting my degree, my optical physics lecturer was explaining polarisation along with some mathematics. As the lecture went on he would stop for a second and place a strip of sellotape (scotch tape) onto the overhead projector. Each strip was at a slight angle so that they only overlapped at the centre. Finally he placed another polariser on top and it projected a beautiful ring of colours, while in the centre white light shone through. It was a beautiful example of polarisation and he used it to teach us how liquid crystal displays worked. Funny enough this was in Manchester where another physicist got the noble prize for isolating and characterising graphene using sellotape. Amazing what you can learn and teach with a bit of ingenuity and some sticky stuff.
Thank you, Steve Mould, for bringing to light (pun intended is in a superimposed state with pun not intended) this very thorough and comprehensive explanation of circular polarisation. I've always heard the term being thrown around, but the actual physical meaning of circular polarisation had always eluded me before now.
That’s really neat. I wanted to see an example where the amount of sugar was not linearly spread out in the glass. For example, set the screen up normally, vertical, and then have a vase or something. The vase changes diameter as it goes up, so different spots would be different colors, and the middle would be a different color than near the edges because light had to pass through more sugar water.
You'd be shining through a prism in the center while the outside would have light diffracting in all sorts of directions. You would need a stepped vase if you will.
I think I get what you're going for and I was wondering the same thing but I think its not the volume of sugar water that matters but its concentration. If so, changing the shape of the vessel doesn't matter. Instead of using water which is the universal solvent, it would almost need to be an optical gel or something that more capable of stratification. *I haven't actually experimented myself so I'm speaking purely about expectations and willing to be surprised.
@@MrCwildeman the concentration does matter, but so does the distance through which the light has to travel. Look up 'specific rotation' on Wikipedia if you wanna read more about this
@@samj6837 Thank you. That actually unravels my understanding of Steve's explanation though. For refraction, the speed of the light changes at the interface not continually through the medium. For volume to have an effect on the angle of twist, one component of the superposition is continually being slowed down within a homogeneous mixture. That sort of goes against the light slowing logic of refraction right? I'll do more research on my own, but discussion yields better quality results!
I’ve been trying to understand this for years, and this is the first time anybody actually explained it to me. I think part of the secret to his success is that he is genuinely curious and is answering questions that he had himself. It helps put him in the audience’s shoes. Taking your audience through your journey of you came to understand something yourself is very effective.
Tsgphysics.mit.edu/pics/T%20Polarization/T8_2.jpg shows an image of a polarized tube of fluid which gives a spiral appearance. Odd since the wavelengths of visible light are much shorter.
7:20 At the time when both helix waves are at the same position, their superposition should actually be twice as far from the axis, since adding their position vectors would give you a location two times further from the axis. The general wave form will still be a sinusoid, just the amplitude should be two times bigger.
09:00 "It's constantly bumping into those flaps of pasta" - I don't think anyone has ever used that combination of words in the history of time before.
Here's a cool follow-up experiment you could show: Take two equal concentrations of optically active solutions of the enantiomers of a given molecule, show the colors as you rotate the polarizing filter, then mix them together and watch the color disappear as the solution no longer becomes optically active. It would look like a chemical reaction, when really it's just mixing two solutions with no reaction occuring. This would be really interesting to see! I was going to suggest using L-dextrose to do this, but it's a bit too expensive. I'm sure there are cheaper chiral alternatives available to demonstrate this.
@@clockworkkirlia7475 Sinstrose; when the devil wants sugar. Fun fact (which you probably already know, given your "sinistrous" suggestion): dexter is Latin for right and sinister is Latin for left. Since left-handed people were considered "of the devil", sinister became a word roughly meaning "evil". And the word ambidextrous simply means "two right hands". Since right hands were "not of the devil", I guees they just thought it sounded better to call you right-handed but twice as much.
I've seen this video of yours multiple times. Each time, it makes sense, and yet I'm pretty much 100% certain that I wouldn't be able to recount it properly.. Fascinating, intuitive, and basically un-paraphrasable 🙂 Keep it up!
I remember reading about how modern 3d movies use two different rotational polarizations, one for the image going to your left eye, and another for your right eye. I loved the explanation and sort of shuffled through the idea of rotational polarization as quickly as I could, so as not to trip over my own ignorance. Your visual makes so much sense and your overall explanation is priceless Steve. This might be my favorite video you have ever made! Thanks! (I just burnt my pizza because I had to write this comment. I blame you for that.)
Have you ever used polarised sunglasses? I think that are popular with skiers, because light reflected from the snow is partially polarised and they are great bloacking those reflections, but they may have weird effects when looking to the screen of your phone, depending if your phone has a LCD screen or an OLED/AMOLED one.
I’ve been using a refractometer to measure sugar when making beer and wine for years. Never really understood how it works, but I now have a better idea.
Refractometry has little to do with polarization of light, but I think you understood that. The idea of light traveling more slowly through some mediums over others and how that bends light is briefly explained here.
Wow that's exactly how polarimeters work! Ever since I learnt in high school that optically active isomers rotated polarised light, I always wondered how exactly.Now with this superposition of superpositions concept I can finally see how!Thanks Steve for providing such high quality content!You are truly awesome! 👍
I have a PhD in physics and I want to see this video is wonderful: accessible and informative, and conveys the information in a way that makes it intuitive. This is very well done and I will suggest it to others!
1:30 Correction: unpolarized light is a _classical_ ensemble of differently oriented polarized photons. It's not superposition. Individual photons are always polarized. This is confusing because quantum mechanics has two kinds of "superposition": the actual superposition that follows the Born rule; and the mixed state, which follows the laws of probability that we learn in school. Detailed explanation: en.wikipedia.org/wiki/Density_matrix#Example%3A_light_polarization
I am afraid you are wrong here. I am not an expert, correct me please, but one thing is having stream of differently polarized photons (what you refer to as unpolarized - classical ensemble) and another thing is to have superposition of polarization (even with single photon). The difference is in how you create them - you either bounce them from known surface (but with mixed edges/planes thus the ensemble) or you produce or bounce them from unknown source which itself is in superposition producing unknown/superposed polarization... is that possible? I am not a physicist, but do not cut corners in those things, quantum things especially, unless I see good reason for it. Proove me wrong, please :) EDIT: ...and I got corrected - continue reading the responses ;)
@@firdacz Physicist here. He isn't wrong. If you had a completely unpolarized photon - a superposition of ALL polarizations - the net photon would not exist, since all the polarizations would cancel each other out. Isn't any fancier than that. Unpolarized light is always an ensemble.
@@MSpangeO I am struggling a bit with your explanation - why would they cancel out? Electron can be in spin-superposition, does that cancel the spin? ...but I think I got a bit of understanding reading the wiki, that polarized light already is superposition (which is also stated in the video I think), therefore α | R ⟩ + β | L ⟩ and unpolarized would need that α and β be "in superposition" which is not possible, these are constants (complex numbers, right?), so single photon cannot be unpolarized, because it always is some superposition of left and right which itself defines polarization.
@@firdacz You definitely have the right idea! Polarization is an intrinsic quality of light, just like spin is an intrinsic quality of electrons. The left/right circular polarization or x/y linear polarization are normalized axes from which you can completely define the polarization of a photon. For example, if I wanted to describe a photon polarized at 20 degrees to the x-axis, I would only need to describe the state | ψ > as a superposition of the | x > and | y > states, using some complex amplitudes α and β. I'm not sure exactly if a photon that is a superposition of ALL polarizations would not exist, per se, but really what it is is that a photon in a superposition of "ALL polarizations" is not a valid way to describe a photon's polarization, and I believe this is what ElderberryEnt was getting at. To quote Harry Nilsson, "A point in every direction is the same as no point at all". I suppose, in some sense, all photons are in a superposition of all polarizations, since you can arbitrarily define your x and y axes (provided that they remain perpendicular) to align with any linear polarization you want (and often we do in order to simplify calculations). If you're still a bit confused, try to describe a photon which is in a superposition of "all polarizations" using that bracket notation. | ψ > = a1 | α1 > + a2 | α2 > + a3 | α3 > + ... + an | αn > where (a1...an) are complex coefficients and (| α1 > ... | αn >) are polarizations along some line. Assuming we're in 3 dimensions, light can only be polarized in a plane. To describe linear polarization using bracket notation, we only need two orthogonal axes. Therefore, all we need to do is pick 2 orthogonal lines, call them x and y, and we can describe every polarization a1 | α1 >...an | αn > as a superposition of those two states, | x > and | y >. If you do some algebra to combine all the coefficients, you'll end up with a photon in a superposition of x polarization and y polarization. So, a photon in a superposition of all polarizations is really just a photon in a superposition of two orthogonal polarizations, as expected. And seeing as right and left polarized photon are just superpositions of linear polarizations (and vice-versa), you can describe circularly polarized photons in terms of linear polarizations and apply the exact same logic.
Really great stuff! I have been taught before that chiral (handed) molecules rotate circularly polarized light in a characteristic way, and have done circular dichroism experiments in a lab before, but it was mostly covered as a fundamental attribute of anything chiral. This is a great visualization of why that property arises from the chirality. Also, as a biochemist I’d like to mention that the reason that sugar as we know it is virtually all one-handed and not the other is that the enzymes that make sugars are ALSO chiral and make “left-handed” molecules preferentially over “right-handed.” Which is true of virtually all biological molecules, at least to my knowledge, which is absolutely bonkers!! The building blocks of our bodies and of, like, all living things preferentially have a certain chirality 🤯
How does sugar rotate in terms of its electron cloud arrangement. Is it linear in solution. I can understand DNA has a clear spiral structure and coupled oscillators could rotate the polarization. Is it because glucose has particular position of OH in the ring.
This is far and away the best explanation of this phenomenon I've seen. Your animation of the summation of 2 circularly polarised waves was an epiphany. Also - your science books for kids are awesome and my niece absolutely loved and devoured them last Christmas.
This was the experiment that first piqued my interest in chemistry - remember seeing it in class when I was about 13 and it fascinated me. And fun fact - spearmint and caraway seeds both contain the same compound that gives them their scent, but they're optical isomers so smell completely different.
I believe that the same applies to compounds in the oil in lemon and orange skin. Can't find he reference though............my organic chemistry is 50 years old!!! Stavros
Seriously it’s the first time I’ve understood optical activity so clearly ....brilliant explanation I believe optical isomerism will be much easier now that I’ve seen it in action..... : )
Steve, you are hands-down the best teacher I've had. My professor didn't seem to have the same insight as yours. Heck, even the textbooks confuse me. I'm GLAD I stumbled upon your fantastic channel!
Wonderfully made, thank you! Also, sucrose turns polarized light +65 degrees. If you split a sucrose solution into one of glucose (+52 degrees) and fructose (-92 degrees), we have a net change of optical rotation to -40 degrees. The direction has been inverted, and hence it's called inverted sugar syrup.
Why can we assume that all molecules are oriented either upwards or downwards? Surely the light hits molecules in all kinds of orientations at all kinds of angles. But if some light was always blocked the solution shouldn't be as transparent 🤔
@@koloblicin4599 Basically, the molecule slows down the light that travels through it, but doesn't absorb it (screws and pasta are opaque but a molecule of glucose is transparent). When a molecule is oriented perpendicularly or something, it just slows down both components equally, so has no effect on polarization. Under an other angle, it might have a reduced effect: for example the clockwise portion crosses the "helix" 21 times while the counterclockwise crosses it 19 times, and therefore travels a tiny bit faster.
The technical term in chemistry for this "handedness" is called "Chirality" - So you would say, sugar is a chiral molecule and the left-handed and right-handed versions of the molecules are known as enantiomers. Also, fun fact, there are certain chiral molecules where one of the enantiomers is toxic to humans, while the other is not. Sugar is fine though, don't worry.
@@laurendoe168 I think this is the case for glucose. It needs to be produced synthetically though, as all known lifeforms that produce glucose produce it in the same handedness. Then in order to make it unusable for our bodies, you need to feed the synthetic creation (which will typically be an even distribution) to an organism that can process it, and once that's been done you're left with the other version. That can then be sold off as low calorie sugar. As I understand it, the chirality does not affect the taste receptors, so it's a perfect substitute for taste, feel and looks, but due to the extra steps in creation it's going to be quite expensive.
@@MrMartinSchou yep. The first thing I thought about when he said the molecule handed and the you can't move it to make the mirror was but why can't the mirror just form? There is not way we can separate molecules based on that can we... Oh right sugar is organically made!
EDIT: @kehrnal shared this amazing online tool emanim.szialab.org/index.html. You can use it to play with adding waves together! Set the two waves to left and right circular, tick the box to show the addition, tick the box to add a material then change the refractive index of the material! So cool. And here's a link where that's already set up for you: emanim.szialab.org/index.html?7VWwGgABgA The sponsor is Blinkist: The first 100 people to go to blinkist.com/stevemould will get unlimited access for 1 week to try it out. You'll also get 25% off if you want full membership
I would love for you to show people magnets can be used as gears. It is possible to create an entire transmission system with all moving parts suspended in a magnet field. Again no gears should touch but still push or pull depending on the set up. If you really cant make a design please ask me for one.
Thanks for making this. I teach polarimetry and will point students here. I had a hard time explaining the random orientation being a no issue at first (maybe because im very visual so I had no problem working thorough the orientations in my head ... I was just confused why anyone would think that). So thanks for givibg me tools to better communicate all this. You did a great job!
3:24 "always clockwise" until you cook the sugar, which is almost 100% sucrose. Heat and sometimes a little bit of acid (a catalyst) hydrolyses the sucrose into its base monosaccharides fructose and glucose and both spin polarized light counterclockwise, which is why a mix of fructose and glucose (either added separately or from the result of sucrose hydrolysis) is called *inverted* sugar. Out of that, it is nearly the exact same thing! This is something that is quite interesting, too. The total chemical net was simply adding water (sucrose + H2O = glucose + fructose) and it inverts the polarization!
After some digging, it looks like invert syrup is actually D-Fructose and D-Glucose: en.wikipedia.org/wiki/Inverted_sugar_syrup But, D-Sucrose rotates counterclockwise much more than D-Glucose rotates clockwise so the effect is a counterclockwise rotation: pubchem.ncbi.nlm.nih.gov/compound/fructose#section=Decomposition Apparently you can’t tell the difference between D and L Glucose by taste, but because only the D form is found in nature we can’t digest the L form. Apparently it’s marketed as an artificial sweetener as “Tagatose”: spinoff.nasa.gov/Spinoff2004/ch_4.html
@@MrIanrocks Oh I thought I didn't need to point out it was specifically the D isomer since, as you said, it is the only one in nature. It is implied (much like the isomer for all aminoacids). We tend to leave information out when it is implied.
You elegantly explained something to me that multiple teachers and professors couldn't get across. I love how youtube is basically gifting the world a ton of new feynmans, all for free. This video also made me realize that "dexterity" is a word because most people are more dexterous with their right hand
Ah, chirality. My friend and enemy in the lab. As a chemist I often record the optical rotation of my compounds (and working with DNA recording its circular dichorism tells me a lot about its solution state as well), but predicting which way it polarises it from the structure is a whole different thing...
I used to love organic chemistry but never really got a satisfaction kinda thing from studying and pretty much forgot about it. Looking at the start of the video, it instantly reminded me of all the stereoisomers, racemic mixture, chiral carbon, etc stuff that I had studied, and it actually makes things more interesting. In reality, this concept is so difficult when studied with all the technical jargon that students face difficulty to garb on to the concepts, but the way you explained it makes it so easy to relate and a lot of things that I don't know how to put into words here. XD Super amazing video.
Fun fact: Louis Pasteur was actually the one to discover the relationship between chirality and plane-polarized light (with the help of some of his days' leading physicists)
Not true. Fresnel published a paper about it in 1825 when Pasteur was still 3 years old. Fresnel, A. J. (1825). Sur La Loi Des Modifications Imprimees A La Lumiere Polarise Par Sa Reflexion Totale Dans L'interieur Descorps Transparents. Ann. Chim, 29, 175-87.
@@SirPhysics Wikipedia says "This was the first time anyone had demonstrated molecular chirality, and also the first explanation of isomerism." en.wikipedia.org/wiki/Louis_Pasteur#Molecular_asymmetry Does Fresnel's paper supersede Pasteur's work?
@@JimC Yes, and the work of others does as well. Also from wikipedia [1]: "The rotation of plane polarized light by chiral substances was first observed by Jean-Baptiste Biot in 1815" Pasteur was the first person to suspect that 'chirality' (it wasn't known by that name until Lord Kelvin coined it almost a century later) was a result of molecular structure, not the first person to observe the effects of chiral materials on circularly polarized light. In fact, in Pasteur's time chiral molecules were known as optical isomers specifically because the effect they had on light was already known. [1] en.wikipedia.org/wiki/Chirality_(chemistry)#History
@Richard Lockwood Yeah, the shit scientists had to deal with back then was insane. If you ever want to a story of scientific tedium, look up how Henry Cavendish did his experiment to test Newton's Law of Universal Gravitation. It's hard to imagine that someone managed to directly measure the gravitational force that two metal spheres exert on one another before 1800. It's such a shame that the history of science often isn't taught alongside the science. Knowing where these ideas came from and how we figured shit out is really cool.
@@SirPhysics just started reading "The Structure of Scientific Revolutions", on science history. And holy shit, yeah we should learn this before being let out into the world.
This is a difficult topic, this was my high school physics graduation experiment. I didn't understand the superimposed circular polarization aspect until now, 15 years later. Thanks for another great video!
This explains everything! Polarization is now explained! I was long confused by the "insertion of 45* polarization pane between 0* and 90* causing light to partially pass"
This is genuinely one of my favourite videos on UA-cam, amazing work! I wish this video was shown in optics and organic chemistry classes, it is the definition of fantastic educational content.
Ever since I was 12, my favorite experiment you can do at home was the double slit experiment. I always found it fascinating that it's an easy way to see quantum mechanics in action. 11 years later, I've found a new favorite physics experiment because this is the first video in several years that has actually blown my mind. Oh my God. WOW.
Thanks Steve for making this very complicated phenomenon understandable (Well, very nearly. I got lost right at the end. I feel a rewatch coming). I think this is one of the most important videos about light on UA-cam and it's definitely going in my favourites folder.
dude im always impressed by how knowlegeable you are and by how smart you are in explaining you REALLY understand the thing others speak well but have limitation themselves.. THANK YOU A LOT ♥
I really liked the way you explained this. When you said "convimce yourself" i thought you sounded like every boring maths lecturer i have ever had but actually it was fairly simple to convince yourself yourself using the reasoning you used earlier. This just cuts down on long unecessary explanation and boosts confidence because you have just applied that reasoning all by yourself. Neat trick!
Just one small remark: at the beginning you say that unpolarized light is a superposition of different polarization states. That's not true: unpolarized light is actually a statistical mixture (also called mixed state). In fact in the rest of the video you point out (rightly) that a superposition of two polarized state is still a polarized state, just in another direction :)
@@dielaughing73 nope, if you had a true superposition of all possible polarization then everything just cancels out. Unpolarized light is a bunch of photons, each polarized in a different way, so that on average the net polarization of the beam is 0. Thats what op means by statistical mixture. The way you treat them in quantum mechanics is also different than a superposition: roughly speaking a superposition can be seen as a vector whereas a mixed state can be seen as a square matrix
I have tried to understand what is circular polarised light is from wiki and it is totally incomprehensible to me. The phase shift of electric and magnetic components are most clear and simple explanation with your visualisation. It just makes me understand immediately what it is about! Thx a lot.
My curiosity insists that I ask... what about "left handed sugar"?? Does it twist light to the left? Wikipedia doesn't say, that I can see... en.wikipedia.org/wiki/L-Glucose Good video! Thanks!
The wiki page of normal glucose says: "The earlier notation according to the rotation of the plane of linearly polarized light (d and l-nomenclature) [...]" So I guess it does indeed!
Glucose turns left by some amount and fructose turns right by some higher amount (or it is the orther way around but it does not matter) so that when in sucrose (kitchen sugar, in which they are 1:1 ratio) they turn the light to the right, but if you have pure glucose and fructose you can play with concentrations and make it turn whichever way you want by the amount you want, its pretty neat
I like how you talked about quantum mechanics but then afterwards spent 2 minutes talking about how when you invert spirals they still twist the same way
Oh my God .!!!! I have been searching this kinda video for 3 days to clear my concepts about how glucose and fructose rotates polarized light ...and yes!!!! I found this video ...thank u soooooooo much !!!!! The experiment is so satisfying .!!!❤
What I find more amazing is the effect of two polarising filters in a line, set to cross polarise light, so no light passes through, can have the effect undone by a third polarising filter placed AFTER the first two. That appears to be no light being turned back into light. In other words the order of the filters does not matter, only the combined effect. I am surprised you did not mention this quantum effect in the video. I suppose that the above would just have added a level of complication to a very good explanation of the way sugar solution rotates the polarisation of light.
2:32 "If I put this cylinder full of sugar water between the monitor and the filter..." *monitor > sugar water > filter > camera* I initially thought (I think you do, too) that he was placing the filter underneath the cylinder, like so: monitor > filter > sugar water > camera I struggled with this for about 45 minutes before going back and listening more carefully.
@@88fibonaccisequence I also thought that but then saw how easily he was rotating the filter. However, Nigel here is talking about the quantum weirdness effects of a *third* filter! The first filter polarises the light. The second filter blocks the light due to being perpendicular to the first. But then the third filter... shows light again?? So, did the second one really block it? What's going on here?! I'm aware about this phenomenon but don't have any idea how it happens.
The best explanation ever! Thank you! I am a teacher and I have a master's degree in physics and this is so precious! If only we had such explanations 10-15 years ago to make it easier to understand!
Where was this when I was studying chemistry :( I had to draw them out to convince myself of all the chirality and optical effects. Amazing video. Thank you! The downvoters must be dem teachers losing jobs...
I developed my own tricks to study stereochemistry easier, and they are never wrong, it always works😃😃. By the way, i had to study it in my 11th class but i am still learning more of it, it's interesting right?
@@daphenomenalz4100 Yeah as I kept learning, I realized some tricks and had them noted down. I must say though, organic chemistry is a pleasure to learn when there's a lot of discipline, as there's a lot of linked topics at play. Glad to say these were inculcated into me nicely by a really good teacher :)
The best explanation I've ever seen of optical rotation with chiral molecules. Also, the best explanation of circularly-polarized light. This video is real progress in science education.
I love your explanations! You put them in a very real world way and their importance for how they make many technologies we take for granted... work. You’re videos are amazing and I can’t begin to express my appreciation! Keep doing what you do, and I look forward to all of your videos! Thank you for adding knowledge to us all from an extremely knowledgeable person!
Grammatical error meant your and when I meant extremely knowledgeable person I mean you are an extremely knowledgeable person! I’m just an avid learner lol and I can’t wait to keep learning from all of your videos!
Great video! This led me down a chemistry rabbit hole. Upon visiting Wikipedia you will notice that several types of glucose exist. The natural and most common one is D-glucose, which has two anomers: alpha and beta. These two variants have very different specific rotations, but if you dissolve both or either they will interconvert and eventually reach an equilibrium ratio, and so the specific rotation is a function of this ratio and the value for each variant. There is also L-glucose which seems to have the exact opposite specific rotation, so if you had a racemic mixture, I suppose you would indeed get zero rotation. An interesting experiment that Steve could do is to get a hold of a pure alpha or beta anomer (alpha would be best since it's the least abundant at equilibrium), dissolve it in water, and then do a timelapse of the change in colour. According to Wikipedia, they interconvert over a time scale of hours. Alternatively, you could try it with a chemical that interconverts over a shorter time scale.
This is the first time I understand the theroy of mirror image, handedness and all the things you taught . Really Hatts off !! GReat!! I like the teacher like you.
Humans: Ray Tracing is so hard! Reality: How about I throw some virtual spirals into it? Oh, and make them interact with a shifted version of itself! Humans: ...... um.....
The newest set of hardware has got to a point where the ray tracing light can be refracted through a virtual prism at seemingly infinite number of times without an FPS drop, in real time, it separates the white light into all of the possible colors in the light spectrum. As well when light passes through colored glass it passes through filtering only that color in the lighting source; it's able to both bend and refracts the light, likely able to reflect the light as well.
@@なかった事に無言フォロー I'm not sure what you are talking about (I am interested), but computation will always have cost. The way RTX works is they are using a machine learning (artificial intelligence) to _guess_ the results based on tracing only a 'few' rays. The results are just an approximation that happens to look good enough most of the time. - I don't know of anything real-time that surpasses that.
I went to one of the world's best science and engineering colleges, and they didn't do nearly as good a job of explaining optical activity as you did. I could have saved a fortune on tuition and just stayed home watching UA-cam videos.
Yep, it's simply like a _distributive property_ for interference of waves. (a+b)+(a-b)=2a where: [a] vertical polarized wave [b] horizontal polarized wave with -pi/2 phase in respect to [a] [-b]: horizontal polarized wave with +pi/2 phase to [a], which is the same as inverse of [b], that why the minus sign
Imagine a circle of radius 1. Any point on the circle is a superposition of an x-coordinate and a y-coordinate; the superposition is chosen such that the amplitude is always 1. So, for the point on the circle at 45°, you have 1/√2 in the x and 1/√2 in the y. The same applies here, but for visual purposes it's better to display all the waves as having the same amplitude because mathematical rigor isn't the goal here, just general understanding.
Chirality. This is how the "handyness" of molecules is called, just in case anyone wants to search for it. Glucose molecules are always right-handed because they are created in a biological process and all forms of life have the same chirality.
@@MetatronicModsLLC glucose that's inverted still works as glucose, the problem is, that the enzymes we have to to process glucose are built for a specific type of glucose. as I understand it, proper glucose intollerance, is where your glucose enzymes are built to process glucose of the wrong type. for the "inverted life" they'd be fine, but it's likely their glucose intollerant peoples could digest our glucose, if it wasn't for all the other things that'd be just as nasty for them in our food(all the things that have chirality that they can't process)
The technical term for that handiness of molecules is chirality. I knew the short answer from the school days but never did any thought experiment for the mechanics of polarized light through chiral molecules. This was brilliant explanation.
I just tried this and it turned the light both ways!
Turns out my solution was Ambidextrose.
hah!
Angry upvote
This is good. This is really good. Have a like.
/facepalm
My one didn’t do anything, it’s dyslexic !
I'm a chem major in college. He just gave an organic chemistry lecture to lay people and it made sense. Steve Mould is amazing
Edit: a year later and I'm almost done! My last final is in 6 hours then I'll have completed my bachelors! :D
No. He just gave a physics lecture that chemistry students could understand. That's even more impressive :)
@@khaitomretro ...shots fired
look at this flextrosexual
He lost me halfway through, then blew my mind when he put it together.
@@khaitomretro this is the principles of optical quantum computing I think
I am a chemist. I learned about optical rotation in school and I test optical rotation on a fairly regular basis. This is by far the best explanation I have ever heard and I understand it better now than I did 20 minutes ago. Thank you.
This explanation was leagues above any explanation I learnt at school about optical rotation. Thinking of linearly polarized lights in terms of two circularly polarized components was basically what I needed to get this concept through to my brain. That was amazing!
I agree, first time it clicked. visual learner here
I mean it kinda makes sense since there are similar concepts in maths as well
Was your stash in shot?
Yep, several pennies finally dropped for me too!
Which school did you go I didn't even knew about this up till now.
I eventually just accepted that chiral molecules twist linearly polarised light and never questioned why exactly that is. In all the chemistry and physics lectures (even in optics where we talked about many polarisation effects, so it would have been perfect to give an in-depth explanation of this phenomenon) we were never explained why that is. I'm so amazed of how comprehensible your explanation was. Thank you so much for blowing my mind.
Profs usually can't explain it in a comprehensive way because they don't fully understand it themselves.
I always had this lack of clarity when it came to chirality. Well, now it's sloved.
@@MagicMarv Not always the case. Good institutions usually have excellent professors. What matters is whether the students are curious or not.
It was explained to use during the first semester for the first time and repeated/applied several times so far...
I'm studying bioinformatics.
It's weird how much of traditional teaching (or maybe just how some school curriculums were set up) was just learn the facts / models instead of explaining why, visualizing it, or even just explaining why it's useful. Now that I'm older I"m more willing to take up dry reading like wikipedia while also checking out youtube videos for that extra insight, and when I find them I"m stupefied why this wasn't in school because it seems like such a small investment in extra explanation for the huge help in understanding. So I've learned enough that way so that once he said helical polarization is possible, I immediately figured out a helix is chiral, the sugar molecules must be, there we go. Still kept the video playing for the watch time lol
I have a physics degree and this is literally the best answer I've ever gotten to this question. My professors at university always resorted to a lot of math to explain this, but your explanation is so simple, yet so complete.
Your professors wanted to ensure that you wouldn't get a physical understanding. They wanted you to have only a mathematical understanding. In general, they want you to have no physical understanding.
@@christophergame7977 where did you get that impression from? During my degree only a couple of professors were fantastic at explaining intuitive explanations that go along with the heavy mathematics. Being able to do so is an incredibly difficult skill, it is why Richard Feynman was so revered through his lectures and red books.
When you have spent decades studying a specific highly complex field, it becomes difficult to put your self in the position of a first year student, particularly when they come from all over the world with different educational backgrounds. However mathematics is a universal language and despite the complexity of harnessing the Schrödinger equation, it is still easier than relating the underlying concepts in an intuitive, but vitally still accurate, manner.
> In general, they want you to have no physical understanding.
Why on earth would this ever be their aim?
@beardedchimp Thank you for your response. I didn't say 'intuitive'. I said "physical". Perhaps I malign them? You say that only a couple were good at intuitive explanation. Why only a few?
@@christophergame7977 explanations are intuitive when we can understand them in the context of our physical reality. This is why he used physical pasta to help our intuition.
> Why only a few?
I thought I had explained that? It is an incredibly difficult skill, hence the revere for Feynman's public speaking.
I can give a funny example, my quantum mechanics lecturer was Jeff Forshaw. He was great at giving physical, intuitive examples of systems that are fundamentally non-intuitive, but it still helps.
He had to unexpectedly move to CERN for a couple of months and was replaced by his former student. The contrast was stark, he went between using far too advanced mathematics and concepts to patronising us explaining simple concepts we knew at 13.
I remember coming out of a lecture and telling some friends that I felt bad for the guy, he clearly lacked experience in public speaking and conveying complex information, Forshaw had put him in a difficult position half way through the year.
That man was Brian Cox. When I first saw him doing work with the BBC several years later I was shocked, I thought to myself "Wow! He clearly worked hard and learnt a lot from his early lecture disasters".
It is a skill, it is easier for some than others but more importantly it takes hard work and effort which is difficult when you are under pressure to publish papers.
@beardedchimp Thank you again. Yes, now I get your point. It's hard for them to present a physical understanding, so they just give up trying. I'm not so sure. I think perhaps they gave up trying to get a physical understanding themselves, so they didn't even try to present one to their students: maths without physical understanding has become their nature?
I've got my degree in physics and this was the best description of circularly polarized light I've ever heard. Thanks Steve.
Can I ask you a dumb question? When he says polarized light is a superposition of two circularly polarized light waves pointing in opposition directions, does he mean literally just two? Or, like, dozens or thousands that cancel each other out that way? Why would they travel in pairs?
@@TristanCleveland i think we're starting with linearly polarised light, so we have that as a firm statement.
From there that could be split up in all sorts of ways actually. It's just for this experiment, because of the handedness of the molecules, rotationally polarised light is the relevant way that the light is affected. The counterclockwise and clockwise aspects of the linearly polarised light are affected differently.
Seemingly you could make up any number of different pairs (or other symmetrical sets) of subdivisions of the light wave, but they wouldn't be useful for understanding what's happening here.
@@TristanCleveland in the end the thing is the field and the substance it overlaps with, not the wave. The wave is merely a description of the movement of that field, and you can describe that movement in all sorts of ways as are useful to you and accurate.
Yup a tea genius in physics, and gifted teacher. It's rare.
@@JohnGottschalk I hope I got that right.
The wave is just a description of a field, as to my understanding to make a field "visible" to the human mind it has to have a "material" property like a point moving through space - wave. Am I right?
And out of this construct one can build the explanatory construct of different waves "creating" the sum-wave of the "visible" light, correct?
Alternative title for this video: how to finally understand why in God's name optical isomers are different, how are they different and what the hell does "they bend the light right or leftwards" mean. It's amazing how you get a topic as hellishly complicated as optical polarization applied to chemistry and make it sound like it makes sense.
Also, I think a good follow up for this would be why the direction the molecules twists the light matter. The case for thalidomide is famous: when it twists the right to the right it's a sedative but when it twists to the left it causes birth defects. How so?
Because right-handed molecules don't fit on left-handed "slots", and as far as nature is concerned, they are completely different molecules
The above explanation is correct, differently oriented molecules fit into different molecular receptors in the body. Hence the weird 'double personality' of otherwise identical molecules.
A large part of the reason is that many/most molecules in biology, are chiral. And therefore can react differently to the different enantiomers of a molecule.
@@franchufranchu119 I vaguely remember reading somewhere that certain molecules when encountered in the human body (perhaps 'biologically' would be better) have a consistent handedness, but those created in the lab (perhaps 'chemically' would be better) do not, and at the time the author wrote that, the cause was unknown.
Have we figured this out yet? have we figured out how to 'artificially' recreate the handedness of molecules yet?
@@temseti0 They usually create both and filter out the undesired ones
if you had a solution of levose (dextrose stereo-isomer) it would , of course polarize light in the opposite direction. If you mix dextrose and levose together, you could determine the ratio of each substance by how much and in what direction the light is polarized.
Or he could have added an equal amount of L-Glucose and had no rotation of light. He seems to ignore that D-Glucose has a levorotatory form in L-Glucose.
l-Glucose was once proposed as a low-calorie sweetener and it is suitable for patients with diabetes mellitus, but it was never marketed due to excessive manufacturing costs.
The acetate derivative of l-glucose, l-glucose pentaacetate, was found to stimulate insulin release, and might therefore be of therapeutic value for type 2 diabetes.[3] l-Glucose was also found to be a laxative, and has been proposed as a colon-cleansing agent which would not produce the disruption of fluid and electrolyte levels associated with the significant liquid quantities of bad-tasting osmotic laxatives conventionally used in preparation for colonoscopy.
I thought, honestly that was a fatal mistake to eat much of that.
I found this explanation to be fascinating but kept waiting for the corroborating demonstration of the L-glucose case which sadly never came. But wait. Wasn’t he using sucrose there?
I worked for a decade and a half in sugar mills as a "Sugar Chemist"/Lab Technician. We did indeed us polarimetry to determine the amount of 'sugar' in the crushed cane juice at the start of the milling process and the processed raw sugar at the end. We also had a process to determine levels of fructose and other "reducing sugars" by measuring the angle of light bent to the left (levo-rotary).
But where did the levose go? Why isn't it 50/50 spit in the sugar he bought from the store?
Does left-handed fusilli taste different to right-handed ? Do Italians care about the handedness of their fusilli - maybe a regional thing ?
l-Fusilli is indistinguishable in taste from d-fusilli, but cannot be used by living organisms as a source of energy because it cannot be phosphorylated by hexokinase, the first enzyme in the glycolysis pathway.
Hrm, so is the superposition of l-fusilli and d-fusilli just tagliatelle? 🤔
These are the trully interesting questions that we need answered! Not this bogus about right-handed light. Everyone knows light doesn't have hands!
s-fusilli* and d-fusilli :P or l-fusilli and r-fusilli... can't mix them or the pot will explode...
@@Taricus Handedness of molecules in chemistry is actually notated by D-L or R-S, not D-S or R-L
“Watch what happens if I turn this pasta upside down” - Steve Mould, 2020.
"It's genuinely unremarkable."
It was genius. He's making it seem really simple, but I'm sure I'm not the only one who made the reasoning mistake he explained in the beginning.
We need a Steve Mould but out of context
Watch what happens if I turn this _pastor_ upside down.
He made a video about that already
0:00 - Introduction
0:44 - Polarized Light: short explanation
2:31 - Polarization of Sugar
3:49 - Superposition of Polarized States
3:55 - Superposition of in-phase waves (linearly polarized light)
5:17 - Superposition of 0.25λ out-of-phase waves (circularly polarized light)
6:33 - Superposition of circularly polarized states (linearly polarized light 😮)
8:01 - Pasta
9:53 - Index of refraction of pasta
10:52 - Superposition of pasta shifted states (wave-plate retarder)
11:20 - And to Reiterate...
12:17 - PASTA SYMMETRY
13:40 - Handedness (fundamental common attribute between pasta & sugar molecules)
14:36 - Mirror symmetry in molecules
16:12 - Answer: "Why Sugar Always Twists Light To The Right"
16:25 - BTW: Dextrose
Thanks!
Absolutely brilliant.
You covered circularly polarized light, chiral sugar, and superposition all without reference to one equation. Very, very well done.
I wonder if you can twists the polarization of microwaves with cooked pasta.
You, sir, are a genius!
Oh my god that's brilliant. The wavelength is a match, so... probably?
FBI wants to know your location
@@simonvetter2420 haha no you need The polarization to be oriented vertically/horizontally and the microwave doesn't have a polarization filter so overall net-value is zero, the comment above was purely for the sake of good humor
A microwave oven works by passing microwave radiation, usually at a frequency of 2450 MHz (a wavelength of 12.24 cm)
That's probably to big a wavelength for the pasta to have a strong effect 😞
Hey Steve! You could extend this to explaining how liquid crystal displays work really easily! Basically just using a voltage to orient chiral molecules either along the direction of the light, or perpendicular to it, which then either make it through the polarizer (bright pixel) or don't (dark pixel). Thanks for some great animation, this will definitely help me teach polarization a bit better!
Don't need a video for that you just explained it perfectly here. wow.
I remember vividly in 2005 when starting my degree, my optical physics lecturer was explaining polarisation along with some mathematics. As the lecture went on he would stop for a second and place a strip of sellotape (scotch tape) onto the overhead projector. Each strip was at a slight angle so that they only overlapped at the centre.
Finally he placed another polariser on top and it projected a beautiful ring of colours, while in the centre white light shone through. It was a beautiful example of polarisation and he used it to teach us how liquid crystal displays worked.
Funny enough this was in Manchester where another physicist got the noble prize for isolating and characterising graphene using sellotape. Amazing what you can learn and teach with a bit of ingenuity and some sticky stuff.
Glad you gave us the correct _solution_ without _sugar coating_ it.
You made _light_ work of a difficult subject!
Fine, have your thumbs up!
@@SteveMouldua-cam.com/play/PLElOK3eZ5OO9uhBTi2aK1ifjDBhTVe2bu.html&si=HST3uOSmUOwQoN2H
@@SteveMouldua-cam.com/play/PLFre9LVBTdQpdfWRktdufJu3mb0OQHko1.html&si=STmEWhVDpIPNgOaX
holy crap
Dang the depth and quality is insane!
Thank you, Steve Mould, for bringing to light (pun intended is in a superimposed state with pun not intended) this very thorough and comprehensive explanation of circular polarisation. I've always heard the term being thrown around, but the actual physical meaning of circular polarisation had always eluded me before now.
This is the best visualised and most satisfying explanation of chirality and its relationship with light polarisation I've encountered.
True! But I was disappointed that the word "chirality" was absent.
That’s really neat. I wanted to see an example where the amount of sugar was not linearly spread out in the glass. For example, set the screen up normally, vertical, and then have a vase or something. The vase changes diameter as it goes up, so different spots would be different colors, and the middle would be a different color than near the edges because light had to pass through more sugar water.
You'd be shining through a prism in the center while the outside would have light diffracting in all sorts of directions. You would need a stepped vase if you will.
I'm pretty sure you can see that with a piece of plastic (like a plastic ruler)
I think I get what you're going for and I was wondering the same thing but I think its not the volume of sugar water that matters but its concentration. If so, changing the shape of the vessel doesn't matter. Instead of using water which is the universal solvent, it would almost need to be an optical gel or something that more capable of stratification.
*I haven't actually experimented myself so I'm speaking purely about expectations and willing to be surprised.
@@MrCwildeman the concentration does matter, but so does the distance through which the light has to travel. Look up 'specific rotation' on Wikipedia if you wanna read more about this
@@samj6837 Thank you. That actually unravels my understanding of Steve's explanation though. For refraction, the speed of the light changes at the interface not continually through the medium. For volume to have an effect on the angle of twist, one component of the superposition is continually being slowed down within a homogeneous mixture. That sort of goes against the light slowing logic of refraction right?
I'll do more research on my own, but discussion yields better quality results!
I’ve been trying to understand this for years, and this is the first time anybody actually explained it to me. I think part of the secret to his success is that he is genuinely curious and is answering questions that he had himself. It helps put him in the audience’s shoes. Taking your audience through your journey of you came to understand something yourself is very effective.
"I've chosen a wavelength of light that matches the spacing of the pasta spirals" - a sentence not spoken often
A brand new sentence in the universe
Looks like something in the sub-radar range i2.wp.com/yatebts.com/wp-content/uploads/2018/11/Frequency.png
@@gregbernstein9126 Lol!
@@gregbernstein9126 Thank you! I was about to look it up :-D
Tsgphysics.mit.edu/pics/T%20Polarization/T8_2.jpg shows an image of a polarized tube of fluid which gives a spiral appearance. Odd since the wavelengths of visible light are much shorter.
This video shows a great example of how to explain a scientific concept in a way that's easy to understand but still with no compromise in accuracy
7:20 At the time when both helix waves are at the same position, their superposition should actually be twice as far from the axis, since adding their position vectors would give you a location two times further from the axis. The general wave form will still be a sinusoid, just the amplitude should be two times bigger.
09:00 "It's constantly bumping into those flaps of pasta" - I don't think anyone has ever used that combination of words in the history of time before.
Oh, I can see that we don't know the same people..lol
You obviously never had "feelings" for lasagna
Here's a cool follow-up experiment you could show:
Take two equal concentrations of optically active solutions of the enantiomers of a given molecule, show the colors as you rotate the polarizing filter, then mix them together and watch the color disappear as the solution no longer becomes optically active. It would look like a chemical reaction, when really it's just mixing two solutions with no reaction occuring. This would be really interesting to see!
I was going to suggest using L-dextrose to do this, but it's a bit too expensive. I'm sure there are cheaper chiral alternatives available to demonstrate this.
That's fascinating and I'd love to see that!
That said, slightly unfortunate that it's just called L-dextrose. Sinistrose sounds so much cooler.
@@clockworkkirlia7475 Sinstrose; when the devil wants sugar.
Fun fact (which you probably already know, given your "sinistrous" suggestion): dexter is Latin for right and sinister is Latin for left. Since left-handed people were considered "of the devil", sinister became a word roughly meaning "evil". And the word ambidextrous simply means "two right hands". Since right hands were "not of the devil", I guees they just thought it sounded better to call you right-handed but twice as much.
@@trickytreyperfected1482 Furthermore, people who are bad at writing with both their left and right hands, are called ambisinister!
@@LittlePharma always wondered where the "two left feet" thing came from
I think it should be called Levose.
I've seen this video of yours multiple times. Each time, it makes sense, and yet I'm pretty much 100% certain that I wouldn't be able to recount it properly.. Fascinating, intuitive, and basically un-paraphrasable 🙂 Keep it up!
I remember reading about how modern 3d movies use two different rotational polarizations, one for the image going to your left eye, and another for your right eye. I loved the explanation and sort of shuffled through the idea of rotational polarization as quickly as I could, so as not to trip over my own ignorance. Your visual makes so much sense and your overall explanation is priceless Steve. This might be my favorite video you have ever made! Thanks! (I just burnt my pizza because I had to write this comment. I blame you for that.)
Have you ever used polarised sunglasses? I think that are popular with skiers, because light reflected from the snow is partially polarised and they are great bloacking those reflections, but they may have weird effects when looking to the screen of your phone, depending if your phone has a LCD screen or an OLED/AMOLED one.
I’ve been using a refractometer to measure sugar when making beer and wine for years. Never really understood how it works, but I now have a better idea.
Refractometry has little to do with polarization of light, but I think you understood that. The idea of light traveling more slowly through some mediums over others and how that bends light is briefly explained here.
Wow that's exactly how polarimeters work! Ever since I learnt in high school that optically active isomers rotated polarised light, I always wondered how exactly.Now with this superposition of superpositions concept I can finally see how!Thanks Steve for providing such high quality content!You are truly awesome! 👍
I have a PhD in physics and I want to see this video is wonderful: accessible and informative, and conveys the information in a way that makes it intuitive. This is very well done and I will suggest it to others!
why ?
*say instead see, for anyone confused.
I dunno why interests and degrees have any connections at all
@Mr. H looks like some rote memoriser got butt hurt
@Mr. H must be nice
1:30 Correction: unpolarized light is a _classical_ ensemble of differently oriented polarized photons. It's not superposition. Individual photons are always polarized. This is confusing because quantum mechanics has two kinds of "superposition": the actual superposition that follows the Born rule; and the mixed state, which follows the laws of probability that we learn in school.
Detailed explanation: en.wikipedia.org/wiki/Density_matrix#Example%3A_light_polarization
I am afraid you are wrong here. I am not an expert, correct me please, but one thing is having stream of differently polarized photons (what you refer to as unpolarized - classical ensemble) and another thing is to have superposition of polarization (even with single photon). The difference is in how you create them - you either bounce them from known surface (but with mixed edges/planes thus the ensemble) or you produce or bounce them from unknown source which itself is in superposition producing unknown/superposed polarization... is that possible?
I am not a physicist, but do not cut corners in those things, quantum things especially, unless I see good reason for it. Proove me wrong, please :)
EDIT: ...and I got corrected - continue reading the responses ;)
@@firdacz Physicist here. He isn't wrong. If you had a completely unpolarized photon - a superposition of ALL polarizations - the net photon would not exist, since all the polarizations would cancel each other out. Isn't any fancier than that.
Unpolarized light is always an ensemble.
@@MSpangeO I was confused, but after reading this, it actually makes perfect sense!
@@MSpangeO I am struggling a bit with your explanation - why would they cancel out? Electron can be in spin-superposition, does that cancel the spin?
...but I think I got a bit of understanding reading the wiki, that polarized light already is superposition (which is also stated in the video I think), therefore α | R ⟩ + β | L ⟩ and unpolarized would need that α and β be "in superposition" which is not possible, these are constants (complex numbers, right?), so single photon cannot be unpolarized, because it always is some superposition of left and right which itself defines polarization.
@@firdacz You definitely have the right idea! Polarization is an intrinsic quality of light, just like spin is an intrinsic quality of electrons. The left/right circular polarization or x/y linear polarization are normalized axes from which you can completely define the polarization of a photon. For example, if I wanted to describe a photon polarized at 20 degrees to the x-axis, I would only need to describe the state | ψ > as a superposition of the | x > and | y > states, using some complex amplitudes α and β. I'm not sure exactly if a photon that is a superposition of ALL polarizations would not exist, per se, but really what it is is that a photon in a superposition of "ALL polarizations" is not a valid way to describe a photon's polarization, and I believe this is what ElderberryEnt was getting at. To quote Harry Nilsson, "A point in every direction is the same as no point at all".
I suppose, in some sense, all photons are in a superposition of all polarizations, since you can arbitrarily define your x and y axes (provided that they remain perpendicular) to align with any linear polarization you want (and often we do in order to simplify calculations). If you're still a bit confused, try to describe a photon which is in a superposition of "all polarizations" using that bracket notation.
| ψ > = a1 | α1 > + a2 | α2 > + a3 | α3 > + ... + an | αn > where (a1...an) are complex coefficients and (| α1 > ... | αn >) are polarizations along some line. Assuming we're in 3 dimensions, light can only be polarized in a plane. To describe linear polarization using bracket notation, we only need two orthogonal axes. Therefore, all we need to do is pick 2 orthogonal lines, call them x and y, and we can describe every polarization a1 | α1 >...an | αn > as a superposition of those two states, | x > and | y >. If you do some algebra to combine all the coefficients, you'll end up with a photon in a superposition of x polarization and y polarization. So, a photon in a superposition of all polarizations is really just a photon in a superposition of two orthogonal polarizations, as expected. And seeing as right and left polarized photon are just superpositions of linear polarizations (and vice-versa), you can describe circularly polarized photons in terms of linear polarizations and apply the exact same logic.
Really great stuff! I have been taught before that chiral (handed) molecules rotate circularly polarized light in a characteristic way, and have done circular dichroism experiments in a lab before, but it was mostly covered as a fundamental attribute of anything chiral. This is a great visualization of why that property arises from the chirality.
Also, as a biochemist I’d like to mention that the reason that sugar as we know it is virtually all one-handed and not the other is that the enzymes that make sugars are ALSO chiral and make “left-handed” molecules preferentially over “right-handed.” Which is true of virtually all biological molecules, at least to my knowledge, which is absolutely bonkers!! The building blocks of our bodies and of, like, all living things preferentially have a certain chirality 🤯
Actually, all natural sugars are right-handed.
How does sugar rotate in terms of its electron cloud arrangement. Is it linear in solution.
I can understand DNA has a clear spiral structure and coupled oscillators could rotate the polarization. Is it because glucose has particular position of OH in the ring.
This is far and away the best explanation of this phenomenon I've seen. Your animation of the summation of 2 circularly polarised waves was an epiphany.
Also - your science books for kids are awesome and my niece absolutely loved and devoured them last Christmas.
This was the experiment that first piqued my interest in chemistry - remember seeing it in class when I was about 13 and it fascinated me.
And fun fact - spearmint and caraway seeds both contain the same compound that gives them their scent, but they're optical isomers so smell completely different.
That is quite interesting. 🤓
Yes! Carvone in anyone's curious
I believe that the same applies to compounds in the oil in lemon and orange skin. Can't find he reference though............my organic chemistry is 50 years old!!!
Stavros
I just came back to this one for a re-watch. This is truly excellent coverage of the material. You are master of your craft, Steve.
Seriously it’s the first time I’ve understood optical activity so clearly ....brilliant explanation
I believe optical isomerism will be much easier now that I’ve seen it in action.....
: )
Steve, you are hands-down the best teacher I've had. My professor didn't seem to have the same insight as yours. Heck, even the textbooks confuse me.
I'm GLAD I stumbled upon your fantastic channel!
Wonderfully made, thank you!
Also, sucrose turns polarized light +65 degrees. If you split a sucrose solution into one of glucose (+52 degrees) and fructose (-92 degrees), we have a net change of optical rotation to -40 degrees. The direction has been inverted, and hence it's called inverted sugar syrup.
Why can we assume that all molecules are oriented either upwards or downwards? Surely the light hits molecules in all kinds of orientations at all kinds of angles. But if some light was always blocked the solution shouldn't be as transparent 🤔
@@koloblicin4599 Basically, the molecule slows down the light that travels through it, but doesn't absorb it (screws and pasta are opaque but a molecule of glucose is transparent). When a molecule is oriented perpendicularly or something, it just slows down both components equally, so has no effect on polarization. Under an other angle, it might have a reduced effect: for example the clockwise portion crosses the "helix" 21 times while the counterclockwise crosses it 19 times, and therefore travels a tiny bit faster.
The technical term in chemistry for this "handedness" is called "Chirality" - So you would say, sugar is a chiral molecule and the left-handed and right-handed versions of the molecules are known as enantiomers. Also, fun fact, there are certain chiral molecules where one of the enantiomers is toxic to humans, while the other is not. Sugar is fine though, don't worry.
If I remember right, there is a sugar that is normal calorie count when it's one hand, and almost no calories when it's the other hand.
It's even a literal translation. Chir (hand) al (ed) ity (ness), the first part Greek and the next two parts (Anglified) Latin.
@@laurendoe168 I think this is the case for glucose. It needs to be produced synthetically though, as all known lifeforms that produce glucose produce it in the same handedness. Then in order to make it unusable for our bodies, you need to feed the synthetic creation (which will typically be an even distribution) to an organism that can process it, and once that's been done you're left with the other version.
That can then be sold off as low calorie sugar.
As I understand it, the chirality does not affect the taste receptors, so it's a perfect substitute for taste, feel and looks, but due to the extra steps in creation it's going to be quite expensive.
@@MrMartinSchou Thank you for both confirming what I seemed to recall, and offering more information about it.
@@MrMartinSchou yep. The first thing I thought about when he said the molecule handed and the you can't move it to make the mirror was but why can't the mirror just form? There is not way we can separate molecules based on that can we... Oh right sugar is organically made!
EDIT: @kehrnal shared this amazing online tool emanim.szialab.org/index.html. You can use it to play with adding waves together! Set the two waves to left and right circular, tick the box to show the addition, tick the box to add a material then change the refractive index of the material! So cool. And here's a link where that's already set up for you: emanim.szialab.org/index.html?7VWwGgABgA
The sponsor is Blinkist: The first 100 people to go to blinkist.com/stevemould will get unlimited access for 1 week to try it out. You'll also get 25% off if you want full membership
How was this commented before the video went live? 😂😂
SUGAAAH!
I would love for you to show people magnets can be used as gears. It is possible to create an entire transmission system with all moving parts suspended in a magnet field. Again no gears should touch but still push or pull depending on the set up. If you really cant make a design please ask me for one.
10:16 this is the smartest sentence I've heard this month
Are you trying to say that the light polarization is a phase angle between electric and magnetic component?
Never thought that is possible.
Thanks for making this. I teach polarimetry and will point students here. I had a hard time explaining the random orientation being a no issue at first (maybe because im very visual so I had no problem working thorough the orientations in my head ... I was just confused why anyone would think that). So thanks for givibg me tools to better communicate all this. You did a great job!
3:24 "always clockwise" until you cook the sugar, which is almost 100% sucrose. Heat and sometimes a little bit of acid (a catalyst) hydrolyses the sucrose into its base monosaccharides fructose and glucose and both spin polarized light counterclockwise, which is why a mix of fructose and glucose (either added separately or from the result of sucrose hydrolysis) is called *inverted* sugar. Out of that, it is nearly the exact same thing!
This is something that is quite interesting, too. The total chemical net was simply adding water (sucrose + H2O = glucose + fructose) and it inverts the polarization!
Nice, I had wondered why it was called inverted, but never bothered to look it up.
After some digging, it looks like invert syrup is actually D-Fructose and D-Glucose: en.wikipedia.org/wiki/Inverted_sugar_syrup But, D-Sucrose rotates counterclockwise much more than D-Glucose rotates clockwise so the effect is a counterclockwise rotation: pubchem.ncbi.nlm.nih.gov/compound/fructose#section=Decomposition Apparently you can’t tell the difference between D and L Glucose by taste, but because only the D form is found in nature we can’t digest the L form. Apparently it’s marketed as an artificial sweetener as “Tagatose”: spinoff.nasa.gov/Spinoff2004/ch_4.html
Wow...good information
@@MrIanrocks
Oh I thought I didn't need to point out it was specifically the D isomer since, as you said, it is the only one in nature. It is implied (much like the isomer for all aminoacids).
We tend to leave information out when it is implied.
You elegantly explained something to me that multiple teachers and professors couldn't get across. I love how youtube is basically gifting the world a ton of new feynmans, all for free. This video also made me realize that "dexterity" is a word because most people are more dexterous with their right hand
Wait till you hear the one about sinister people!
By far the best science channel on UA-cam.
You explained something quite complex in a very comprehensive way! Congratulations. No one was able to explain it to me in physics classes...
Photon A: how was your day?
Photon B: Terrible, I kept bumping into flaps of pasta.
Photon C: What the hell is a "day"?
Technicaly they are not photons they are oscilations in the magnetic and electric field. Together they make a photon(superposition of those 2)
@@Bishox Technically, it's spelled technically.
Also, the comment you replied to was technically a joke.
@@imveryangryitsnotbutter Proton D: Ahh! Talking protons!
Wave-particle: what are these old timers still doing here
Very cool intuitive explanation. Don’t know how I missed this video when it came out
6:02 I now healize how perfectly this illustrates how two phase shifted sine waves make circular motion or oscillations in filter/signal theory happen
Like how cosine is just a 90 degree phase-shifted sine and used together provide the coordinates of a circle.
Ah, chirality. My friend and enemy in the lab. As a chemist I often record the optical rotation of my compounds (and working with DNA recording its circular dichorism tells me a lot about its solution state as well), but predicting which way it polarises it from the structure is a whole different thing...
I used to love organic chemistry but never really got a satisfaction kinda thing from studying and pretty much forgot about it. Looking at the start of the video, it instantly reminded me of all the stereoisomers, racemic mixture, chiral carbon, etc stuff that I had studied, and it actually makes things more interesting. In reality, this concept is so difficult when studied with all the technical jargon that students face difficulty to garb on to the concepts, but the way you explained it makes it so easy to relate and a lot of things that I don't know how to put into words here. XD
Super amazing video.
Fun fact: Louis Pasteur was actually the one to discover the relationship between chirality and plane-polarized light (with the help of some of his days' leading physicists)
Not true. Fresnel published a paper about it in 1825 when Pasteur was still 3 years old.
Fresnel, A. J. (1825). Sur La Loi Des Modifications Imprimees A La Lumiere Polarise Par Sa Reflexion Totale Dans L'interieur Descorps Transparents. Ann. Chim, 29, 175-87.
@@SirPhysics Wikipedia says "This was the first time anyone had demonstrated molecular chirality, and also the first explanation of isomerism." en.wikipedia.org/wiki/Louis_Pasteur#Molecular_asymmetry
Does Fresnel's paper supersede Pasteur's work?
@@JimC Yes, and the work of others does as well. Also from wikipedia [1]: "The rotation of plane polarized light by chiral substances was first observed by Jean-Baptiste Biot in 1815" Pasteur was the first person to suspect that 'chirality' (it wasn't known by that name until Lord Kelvin coined it almost a century later) was a result of molecular structure, not the first person to observe the effects of chiral materials on circularly polarized light. In fact, in Pasteur's time chiral molecules were known as optical isomers specifically because the effect they had on light was already known.
[1] en.wikipedia.org/wiki/Chirality_(chemistry)#History
@Richard Lockwood Yeah, the shit scientists had to deal with back then was insane. If you ever want to a story of scientific tedium, look up how Henry Cavendish did his experiment to test Newton's Law of Universal Gravitation. It's hard to imagine that someone managed to directly measure the gravitational force that two metal spheres exert on one another before 1800.
It's such a shame that the history of science often isn't taught alongside the science. Knowing where these ideas came from and how we figured shit out is really cool.
@@SirPhysics just started reading "The Structure of Scientific Revolutions", on science history. And holy shit, yeah we should learn this before being let out into the world.
This is a difficult topic, this was my high school physics graduation experiment. I didn't understand the superimposed circular polarization aspect until now, 15 years later. Thanks for another great video!
this is the most convincing way of explaining chirality and the reason why molecules turn light the way that they do. Hands Down. Amazing.
this is too much effort.. you're spoiling us with the quality. love the video, mate
Thanks!
I've watched a lot of educational videos on UA-cam and that has to be one of the best I've seen. An absolute pleasure to watch.
This explains everything! Polarization is now explained! I was long confused by the "insertion of 45* polarization pane between 0* and 90* causing light to partially pass"
This is genuinely one of my favourite videos on UA-cam, amazing work! I wish this video was shown in optics and organic chemistry classes, it is the definition of fantastic educational content.
Ever since I was 12, my favorite experiment you can do at home was the double slit experiment. I always found it fascinating that it's an easy way to see quantum mechanics in action. 11 years later, I've found a new favorite physics experiment because this is the first video in several years that has actually blown my mind. Oh my God. WOW.
Explained much better than my university Physics lecturer did over a 3 week period. Fantastic work!
Thanks Steve for making this very complicated phenomenon understandable (Well, very nearly. I got lost right at the end. I feel a rewatch coming).
I think this is one of the most important videos about light on UA-cam and it's definitely going in my favourites folder.
damn this made chirality so clear , its absolutely brilliant after watching this things just clicked and i realised that my understanding was lacking
the animations were GOD SENT aaa they were so helpful to understand
THIS, this is so good. All the demos added to the intuition, thanks for explaining a phenomenon I didn't even know occurred
You, sir, are unbelievably good at explaining things. Thank you.
dude
im always impressed by how knowlegeable you are
and by how smart you are in explaining
you REALLY understand the thing
others speak well but have limitation themselves..
THANK YOU A LOT
♥
I really liked the way you explained this. When you said "convimce yourself" i thought you sounded like every boring maths lecturer i have ever had but actually it was fairly simple to convince yourself yourself using the reasoning you used earlier. This just cuts down on long unecessary explanation and boosts confidence because you have just applied that reasoning all by yourself. Neat trick!
Just one small remark: at the beginning you say that unpolarized light is a superposition of different polarization states. That's not true: unpolarized light is actually a statistical mixture (also called mixed state). In fact in the rest of the video you point out (rightly) that a superposition of two polarized state is still a polarized state, just in another direction :)
Doesn't he mean a superposition of all states of polarisation?
@@dielaughing73 nope, if you had a true superposition of all possible polarization then everything just cancels out. Unpolarized light is a bunch of photons, each polarized in a different way, so that on average the net polarization of the beam is 0. Thats what op means by statistical mixture. The way you treat them in quantum mechanics is also different than a superposition: roughly speaking a superposition can be seen as a vector whereas a mixed state can be seen as a square matrix
I have tried to understand what is circular polarised light is from wiki and it is totally incomprehensible to me. The phase shift of electric and magnetic components are most clear and simple explanation with your visualisation. It just makes me understand immediately what it is about! Thx a lot.
My curiosity insists that I ask... what about "left handed sugar"?? Does it twist light to the left? Wikipedia doesn't say, that I can see... en.wikipedia.org/wiki/L-Glucose Good video! Thanks!
It does, and if you get racemic mixture it should not really affect the light much... would be cool to test it.
Please test this, Steve
The wiki page of normal glucose says: "The earlier notation according to the rotation of the plane of linearly polarized light (d and l-nomenclature) [...]" So I guess it does indeed!
If you have the mirror image of right-handed glucose, you would have the exact same amount of light rotation but in the opposite direction.
Glucose turns left by some amount and fructose turns right by some higher amount (or it is the orther way around but it does not matter) so that when in sucrose (kitchen sugar, in which they are 1:1 ratio) they turn the light to the right, but if you have pure glucose and fructose you can play with concentrations and make it turn whichever way you want by the amount you want, its pretty neat
I like how you talked about quantum mechanics but then afterwards spent 2 minutes talking about how when you invert spirals they still twist the same way
Oh my God .!!!! I have been searching this kinda video for 3 days to clear my concepts about how glucose and fructose rotates polarized light ...and yes!!!! I found this video ...thank u soooooooo much !!!!! The experiment is so satisfying .!!!❤
Steve: Watch what happens when I turn this pasta upsidedown
*turns pasta
Steve: It's genuinly unremarkable
*can't stop himself from laughing
this also made me giggle to.
Steve discovers chirality of pasta . Nice
Everyone hail the giant spaghetti monster !
*Pastah
Beautiful. This is the peak. Nothing can top this explanation for this concept. Just beautiful. I think I'm gonna cry.
There is always something new to know about sugar
What I find more amazing is the effect of two polarising filters in a line, set to cross polarise light, so no light passes through, can have the effect undone by a third polarising filter placed AFTER the first two. That appears to be no light being turned back into light.
In other words the order of the filters does not matter, only the combined effect. I am surprised you did not mention this quantum effect in the video.
I suppose that the above would just have added a level of complication to a very good explanation of the way sugar solution rotates the polarisation of light.
Whoah that is pretty strange!
2:32 "If I put this cylinder full of sugar water between the monitor and the filter..."
*monitor > sugar water > filter > camera*
I initially thought (I think you do, too) that he was placing the filter underneath the cylinder, like so:
monitor > filter > sugar water > camera
I struggled with this for about 45 minutes before going back and listening more carefully.
@@88fibonaccisequence I also thought that but then saw how easily he was rotating the filter. However, Nigel here is talking about the quantum weirdness effects of a *third* filter! The first filter polarises the light. The second filter blocks the light due to being perpendicular to the first. But then the third filter... shows light again?? So, did the second one really block it? What's going on here?! I'm aware about this phenomenon but don't have any idea how it happens.
The best explanation ever! Thank you! I am a teacher and I have a master's degree in physics and this is so precious! If only we had such explanations 10-15 years ago to make it easier to understand!
"its genuinely unremarkable" lmao. great explanation.
In the middle of a big complicated explanation he just goes "now look what happens when I turn this pasta upside down"
after a long time of searching, i finally got this life-saver
So there's value of 'Tau' on the display at 2:58. Not sure how Matt feels about it 🤣
This is next-level trolling
how were you able to read that ?
I just couldnt distinguish what those numbers were !
Nice spot!
I was able to read it by putting the video in the highest quality available and looking at the screen at a weird angle
Beat me to it.
Where was this when I was studying chemistry :(
I had to draw them out to convince myself of all the chirality and optical effects.
Amazing video. Thank you!
The downvoters must be dem teachers losing jobs...
Did u study it in school?
I developed my own tricks to study stereochemistry easier, and they are never wrong, it always works😃😃. By the way, i had to study it in my 11th class but i am still learning more of it, it's interesting right?
@@daphenomenalz4100 Yeah around my 10th grade; was part of advanced coaching, so got introduced to these sooner.
@@daphenomenalz4100 Yeah as I kept learning, I realized some tricks and had them noted down. I must say though, organic chemistry is a pleasure to learn when there's a lot of discipline, as there's a lot of linked topics at play. Glad to say these were inculcated into me nicely by a really good teacher :)
It would be nice if you could actually share your tricks 😉
The best explanation I've ever seen of optical rotation with chiral molecules.
Also, the best explanation of circularly-polarized light.
This video is real progress in science education.
I love your explanations! You put them in a very real world way and their importance for how they make many technologies we take for granted... work. You’re videos are amazing and I can’t begin to express my appreciation! Keep doing what you do, and I look forward to all of your videos! Thank you for adding knowledge to us all from an extremely knowledgeable person!
Grammatical error meant your and when I meant extremely knowledgeable person I mean you are an extremely knowledgeable person! I’m just an avid learner lol and I can’t wait to keep learning from all of your videos!
Great video! This led me down a chemistry rabbit hole. Upon visiting Wikipedia you will notice that several types of glucose exist. The natural and most common one is D-glucose, which has two anomers: alpha and beta. These two variants have very different specific rotations, but if you dissolve both or either they will interconvert and eventually reach an equilibrium ratio, and so the specific rotation is a function of this ratio and the value for each variant.
There is also L-glucose which seems to have the exact opposite specific rotation, so if you had a racemic mixture, I suppose you would indeed get zero rotation.
An interesting experiment that Steve could do is to get a hold of a pure alpha or beta anomer (alpha would be best since it's the least abundant at equilibrium), dissolve it in water, and then do a timelapse of the change in colour. According to Wikipedia, they interconvert over a time scale of hours. Alternatively, you could try it with a chemical that interconverts over a shorter time scale.
Just the explanation of circular superposition to linear alone makes this video golden.
This was awesome! FYI: The term for "offset by a quarter of a wavelength" is "in quadrature".
0:39
Tau in the background, detected!
This is the first time I understand the theroy of mirror image, handedness and all the things you taught . Really Hatts off !! GReat!!
I like the teacher like you.
Humans: Ray Tracing is so hard!
Reality: How about I throw some virtual spirals into it? Oh, and make them interact with a shifted version of itself!
Humans: ...... um.....
nvidia RTX: hold my FPS
Reality: I have held them for a month now, when are you finally done?
The newest set of hardware has got to a point where the ray tracing light can be refracted through a virtual prism at seemingly infinite number of times without an FPS drop, in real time, it separates the white light into all of the possible colors in the light spectrum. As well when light passes through colored glass it passes through filtering only that color in the lighting source; it's able to both bend and refracts the light, likely able to reflect the light as well.
@@なかった事に無言フォロー I'm not sure what you are talking about (I am interested), but computation will always have cost. The way RTX works is they are using a machine learning (artificial intelligence) to _guess_ the results based on tracing only a 'few' rays. The results are just an approximation that happens to look good enough most of the time.
- I don't know of anything real-time that surpasses that.
I went to one of the world's best science and engineering colleges, and they didn't do nearly as good a job of explaining optical activity as you did.
I could have saved a fortune on tuition and just stayed home watching UA-cam videos.
Eggsactly
This was amazing. I've been trying to understand polarized light all day, and you finally made it make sense. Thank you.
"The clockwise circularly polarized light is nestled into the grooves of the pasta."
Welcome to educational UA-cam, everyone.
7:18 wait... Wouldn't the superposition be twice the individual amplitude?
Yep, it's simply like a _distributive property_ for interference of waves.
(a+b)+(a-b)=2a
where:
[a] vertical polarized wave
[b] horizontal polarized wave with -pi/2 phase in respect to [a]
[-b]: horizontal polarized wave with +pi/2 phase to [a], which is the same as inverse of [b], that why the minus sign
Almost - amplitude would be √2 of the original amplitudes
Imagine a circle of radius 1. Any point on the circle is a superposition of an x-coordinate and a y-coordinate; the superposition is chosen such that the amplitude is always 1. So, for the point on the circle at 45°, you have 1/√2 in the x and 1/√2 in the y.
The same applies here, but for visual purposes it's better to display all the waves as having the same amplitude because mathematical rigor isn't the goal here, just general understanding.
Steve. You just won my Feynman explanations award. It might be worthless. But it is the highest rank I can award to a teacher. 👍🏼
Steve: How did you do that?
Nature: A magician never reveals his secrets.
Years later ...
Steve: How did you do that?
Nature: Stop pastaring me.
pestering*
@@TS-jm7jm I think he was referring to the pasta used in the example...
Tristan smith wooosh
@@martin-__- degenerate
@@andycrask3531 ah, i see what you mean, i hate puns.
Chirality.
This is how the "handyness" of molecules is called, just in case anyone wants to search for it.
Glucose molecules are always right-handed because they are created in a biological process and all forms of life have the same chirality.
Would mirror-image life still work?
@@9072997 Providing everything was a mirror image yes
What about when you invert glucose molecules?
@@MetatronicModsLLC glucose that's inverted still works as glucose, the problem is, that the enzymes we have to to process glucose are built for a specific type of glucose.
as I understand it, proper glucose intollerance, is where your glucose enzymes are built to process glucose of the wrong type.
for the "inverted life" they'd be fine, but it's likely their glucose intollerant peoples could digest our glucose, if it wasn't for all the other things that'd be just as nasty for them in our food(all the things that have chirality that they can't process)
The technical term for that handiness of molecules is chirality.
I knew the short answer from the school days but never did any thought experiment for the mechanics of polarized light through chiral molecules. This was brilliant explanation.
Where that bread crumb in your 5'o'clock shadow appeared from is the biggest mystery
And he had a scratch.
Biscuits (crumpets maybe) and tea in between takes obviously.
Could be a skin flake
@@mattm7535 pppfffttt we all know he nails it in one take. Stop playin'