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.
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?
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'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
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).
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.
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
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?
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
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.
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.
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.
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?
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!
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.
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! 👍
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.
Absolutely brilliant. You covered circularly polarized light, chiral sugar, and superposition all without reference to one equation. Very, very well done.
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.
the way youve explained these topics in such a fluid manner is amazing. loved it, would surely help my understanding get better in school :D especially the diagram and the animation that was shown, so so important in understanding superposition
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!
@@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 😞
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.
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 ♥
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 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.
I love your videos Steve and wanted to thank you for them! I have been researching patterns across disciplines (my primary discipline being music) and it has been fun to discover and notice more connections with the help of your videos. You rock!
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.
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.
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..... : )
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
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 .!!!❤
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.
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.
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!
Oh wow. This is amazing! Thank you for the explaination. I haven't even known about this weird behaviour of sugar. I'd love to show it and try to explain it to my friends and family.
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.
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!
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!
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!
Thanks Steve, these types of visual diagrams really allow people like me who aren't super familiar with this kind of thing to totally understand it, and it was fun. Love these!
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
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.
That was a remarkable performance, explaining all of that. I had to concentrate to keep up but it was worth it. You did well keeping it all straight., I must say. Thanks.
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.
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...
Hey, I actually just read about this circular-to-linear polarization superposition while studying for my MRI thesis. I didn't quite get what it meant (and it wasn't hugely important in my case) until now! Thanks, Steve!
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!
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.
Steveeee you are awesome! I studied organic chemistry and one of the examples when teaching the chirality of organic molecules is this experiment! Very very interesting!
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.
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.
Amazing! I think this explains something I've always wondered about using a 'circular polarising filter' on a camera lens - turning the filter alters the brightness of light from the sky/water etc. I never could understand why turning something 'circular' could have that effect - now I know! Thank you for bringing it down to a level that more of us can understand ;-)
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
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.
I've been searching for ages for an explanation on both the web and youtube, this video is the only one that explained it to me, I was felt that it's counter intuitive because molecules are usually not all oriented the same in a solution.
“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
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 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.
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?
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'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
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?
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.
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'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?
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!
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
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
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.
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.
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
"I've chosen a wavelength of light that matches the spacing of the pasta spirals" - a sentence not spoken often
The Italian chef scientist
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
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 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.
Dang the depth and quality is insane!
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
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! 👍
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.
Absolutely brilliant.
You covered circularly polarized light, chiral sugar, and superposition all without reference to one equation. Very, very well done.
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
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 video for me is up there among your best ones, Steve. Never learned about polarization with such clarity. Kudos man.
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.
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
the way youve explained these topics in such a fluid manner is amazing. loved it, would surely help my understanding get better in school :D especially the diagram and the animation that was shown, so so important in understanding superposition
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!
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 😞
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.
This was amazing. I've been trying to understand polarized light all day, and you finally made it make sense. 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
♥
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 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.
Very cool intuitive explanation. Don’t know how I missed this video when it came out
I love your videos Steve and wanted to thank you for them! I have been researching patterns across disciplines (my primary discipline being music) and it has been fun to discover and notice more connections with the help of your videos. You rock!
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.
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.
Thank you for the explanation and the 3D animations were suberb! The visuals made it so much easier to imagine the whole thing
Amazing work Steve, this is the best one of your videos I have seen so far! 👍
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.....
: )
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
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 .!!!❤
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.
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.
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
Oh wow. This is amazing! Thank you for the explaination. I haven't even known about this weird behaviour of sugar. I'd love to show it and try to explain it to my friends and family.
Beautiful. This is the peak. Nothing can top this explanation for this concept. Just beautiful. I think I'm gonna cry.
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.
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!
Steve, I must say honestly I find your channel to be the most interesting content on the web. No joke. Kudos.
Fantastic Steve…thanks so much for sharing your intuition. Enjoyable and easy to follow!😊
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!
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.
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!
Thanks Steve, these types of visual diagrams really allow people like me who aren't super familiar with this kind of thing to totally understand it, and it was fun. Love these!
You explained something quite complex in a very comprehensive way! Congratulations. No one was able to explain it to me in physics classes...
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!
One of your best videos, which I had the answer to for once since I read an article related to quantum mechanics and spin symmetry.
This is the first time I've truly grokked this subject. Thanks Steve!!
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.
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.
That was a remarkable performance, explaining all of that. I had to concentrate to keep up but it was worth it. You did well keeping it all straight., I must say. Thanks.
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.
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...
this is too much effort.. you're spoiling us with the quality. love the video, mate
Thanks!
This really helped me understand Optical Activity. Thank you!
Hey, I actually just read about this circular-to-linear polarization superposition while studying for my MRI thesis.
I didn't quite get what it meant (and it wasn't hugely important in my case) until now! Thanks, Steve!
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!
A very long and good explanation for a very complex riddle. Thank you for all the thought that went into it 👍🏻♥️🙂
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'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.
Steve discovers chirality of pasta . Nice
Everyone hail the giant spaghetti monster !
*Pastah
Steveeee you are awesome!
I studied organic chemistry and one of the examples when teaching the chirality of organic molecules is this experiment! Very very interesting!
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.
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.
Went through this in my chemistry class the other day, really helped me get my head around this topic even more
Amazing! I think this explains something I've always wondered about using a 'circular polarising filter' on a camera lens - turning the filter alters the brightness of light from the sky/water etc. I never could understand why turning something 'circular' could have that effect - now I know!
Thank you for bringing it down to a level that more of us can understand ;-)
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
"its genuinely unremarkable" lmao. great explanation.
the animations were GOD SENT aaa they were so helpful to understand
Thank you for finally explaining this cool effect to me, wondering 2 decades ago in school already 😁💪
damn this made chirality so clear , its absolutely brilliant after watching this things just clicked and i realised that my understanding was lacking
THIS, this is so good. All the demos added to the intuition, thanks for explaining a phenomenon I didn't even know occurred
you are one of the greatest teachers, I have ever seen. Thank you so much...
This is a great Segway into your video on natural mirror imagery!
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.
You, sir, are unbelievably good at explaining things. Thank you.
very very amazing visualizations, thanks so much for it!!
that was just excellent. Thank you very much. Never explained better.
There is always something new to know about sugar
My mechanical engineering uni needs more people like Steve. Imagine having a Steve for every subject, that would be awesome
Fascinating video, so glad I found this channel.
I've been searching for ages for an explanation on both the web and youtube, this video is the only one that explained it to me, I was felt that it's counter intuitive because molecules are usually not all oriented the same in a solution.