Euler's formula with introductory group theory
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- Опубліковано 24 тра 2024
- Intuition for e^(πi) = -1, using the main ideas from group theory
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There's a slight mistake at 13:33, where the angle should be arctan(1/2) = 26.565 degrees, not 30 degrees. Arg! If anyone asks, I was just...er...rounding to the nearest 10's.
For those looking to read more into group theory, I'm a fan of Keith Conrad's expository papers: www.math.uconn.edu/~kconrad/bl...
Thanks to these viewers for their contributions to translations
Hebrew: Omer Tuchfeld
Italian: Filippo
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For those who want to learn more about where the number e comes from, and why that constant 0.6931... showed up for 2^s, there's a video out it in the "Essence of calculus" series: ua-cam.com/video/m2MIpDrF7Es/v-deo.html
3Blue1Brown could you do simplectic geometry in classical mechanics ? Maybe a topic from Arnold's or mardsens book on classical mechanics. Those are graduate text to mathematics, but they cover physics
3Blue1Brown If i^2 = -1, does i^4 (4x90° rotation) equal 1?
EV4 Gaming yes. Multiply i by itself 4 times.
Max Yurievich Okay, thank you
This is no proof, i really can't answer a teacher this way can I?
You need to get mathematical with intuition.
07:06 Sliiiide to the left!
06:57 Sliiiide to the right!
12:57 Criss cross!
10:47 Take it back now y'all!
13:37 Cha-cha real smooth!
02:30 Freeze!
24:28 Everybody clap your hands!
you are a genius.
Brilliant!
@19:07 - now it's time to get funky
that comment is under rated AHAHAHAHAHAHAHA
Lmao can someone explain
This is just so, so great. Approachable but rigorous, and in its way, kind of thrilling. -John
Thanks so much John!
John! You watch this channel?! I didn't know there were other nerdfighters around here!
But he didn't really prove anything whatsoever!
aa That's not the point of the channel. Anyone who has done a maths degree has seen the proofs. This channel is to show maths to people who haven't done a maths degree
Hey nerdfighter!!!
As a 70 year old man, I thank you for at last you made me comprehend more the beauty of mathematics...
still alive?
@@slinkywhite9255bruh
@@ryan-tabar I mean he's legitimate 70
@@slinkywhite9255💀
Whenever I get demotivated with my studies, I watch your videos to remind myself the beauty of mathematics to motivate me to learn more of it. I know a lot of people say thank you, but through all my struggles, you make me want to continue to learn! So, Mr. Brown, thank you!!!!!
same
Final year math undergad.
NOBODY (not even any top level book) has explained isomorphism/homomorphism to me the way you did.
Much,much love and respect from India.
which uni?
Same!!!
Of course it's india...
@@aurelia8028 no, he just got a shitty teacher. There are good and bad teachers everywhere. I'm in high school and my teacher introduced me to this channel. He has taught so many things that are out of my syllabus because he has real passion of teaching.
@@notsoclearsky you are lucky man , we got teachers who just want marks
We will never say this enough : your animation is gorgeous
Archibald Belanus it is.
Fascinating video, I really appreciate the visualization of the group theory. but I can't help but point out a minor ISSUE at 13:27 The rotation of 2+i is not 30 degrees, but approximately 26.565 degrees (arctan(1/2))
Yeah this hurt me too
@@MatthewWroten What hurts me is that my comment didn't get a heart. I want to assume that Grant didn't have a chance to read it! :)
thanks for point out error❤
So all e^(i*pi) = -1 is saying is that "rotation by 180 degrees is the same as a reflection". Neat!
not the same as a reflection, only the same as reflecting the point at 1+0i using the imaginary axis as a mirror line, note that such an action does however reflect the real axis across the "mirror point" of 0 because the real line is 1 dimensional and therefore has no orientation to help distinguish reflection and rotation
It is the same as the central reflection centered on 0, but not as the axial reflection along the imaginary axis
The one thing I didn't understand is what is the rule according to which the points on the vertical axis get mapped to the points on the circle at the end
@@randomname7918 you take the imginary Number shown on the left and that's your x, then you raise the esponent (2, then 5 then e) to the x and that Is your result shown on the right
Very cool way to interpret it geometrically.
I've seen both Essence of series multiple times, watched space filling curves and towers of hanoi, but this video, this one right here, is the most beautiful thing on this channel. Maybe I care too much about math, but the transition near the end from 2^x to 5^x to e^x, building up to that e^i*pi chokes me up every time. Pretty sure I had tears the first time I watched it. This video transitions from "why would this ever make sense" into "what else could it be" over the course of 20 minutes. Truly a masterpiece...
+Tim H. Wow, thanks so much! That's kind of you on so many levels, I'm glad you enjoyed.
His videos have the same effect on me!
Ohh i thought i was the only weird guy who cried over mathematics videos 😂
Wow, could have said it better myself. I never thought I'd cry over math---with happy tears.
if there was a bit of sad music i probably would've cried too
Please make more videos on group theory! Group theory in general is such a good topic to give intuition about because no one know what it is unless you study math. Also, I really need a good way to picture quotient groups!
I intend to, I agree that it's a really nice topic. For quotient groups, it helps a lot to contemplate of tightening up on the structure you care about for the thing being acted on, so to speak. For example, think of the map from D_8 -> Z_2, where for each square symmetry, you consider how it shuffles the two diagonal lines. That each, a symmetry maps to 1 if those diagonal lines are exchanged, and 0 otherwise. The Kernel of this map (which is a quotient D_8/Z_2) can be seen in all actions of D_8 that don't exchange those two diagonal lines, which consists of four actions, isomorphic to K_4. That would be better with some animations, but hopefully it helps a bit.
3Blue1Brown Algebraic Geometry is a really interesting and visual discipline for Group Theory, Rings, Ideals, as well as concepts in Topology and Linear Algebra.
the quotient group G/H is a generalisation of "congruence modulo n". take 2 elements, a,b in G. in G/H, these elements represent the cosets aH and bH, which are equal if and only if ab^-1 is in H (or a+H = b+H iff a-b in H if you use additive notation). notice that this is basically the definition of congruence mod n: integers a,b are congruent mod n iff a-b is a multiple of n.
example: suppose G = Z, H = 5Z. if a,b are elements in G, then the elements a+H, b+H are equal in G/H iff a-b is in H, i.e. if a-b is divisible by 5, i.e. if a=b mod 5. so G/H is the group of integers mod 5.
another way to think about it is that to find the group G/H, you take G and replace all elements of H by the identity. so in the example Z/5Z, take the integers and replace all multiples of 5 with zero. consequently you have to replace all numbers of the form 5n+1 with 1, etc. so you are just left with 0,1,2,3,4 in the group.
this idea is the same for quotients of rings by ideals. an example i like is R[x]/(x^2+1) where R[x] is the ring of real polynomials and (x^2+1) is the ideal generated by x^2+1, i.e. all real polynomials that have x^2+1 as a factor. the quotient ring R[x]/(x^2+1) is what you get when you take R[x] and replace all instances of x^2+1 by 0, so this ring is isomorphic to C. if f(x) in R[x] is a polynomial, you can write f(x) = (x^2+1)q(x)+r(x) where r has degree 0 or 1 by euclidean division, then x^2+1 becomes zero so f(x) is the same as r(x) in the quotient.
example: take f(x) = 9x^3 + 2x^2 - x - 7. then f(x) = (9x+2)(x^2+1) + (-9-10x). replacing x^2+1 with 0, you see that f(x) is the same as -9-10x in the quotient, and indeed, f(i) = -9-10i
Yes please! That's probably the closest he will ever get to number theory.
I absolutely love this
I'm a chemist, and I love how this video in particular gets me thinking about how group theory works
Some day I want to teach group theory for chemists too chemists so this mathematical understanding is really awesome
Who is this? The perfect math teacher? Indeed.
I really wish I'd had a video of my class (a collection of 11th and 12th graders finishing up a multivariable calculus elective) watching this video just now. They broke out clapping and hooting when the big reveal happened at 20:50. You're doing something really special and greatly appreciated with these videos. Thank you for sharing this with all of us.
A year ago, I wasn't able to find a single math student watching your videos. Nowadays this is a different story.
And we even start to infect the new students with your amazing work.
Your way to look at the topic is most of the time just ... amazing. And gives a perfect base to jump into even complex topics head on. Your videos led me to many really interesting discussions and that's why I always appreciate to see a new video of yours.
If I had a wish, I would love to see your take on absolute continuous or smoothness (probably because I love the cantor function...) some day in the future.
Have a great day!
I would definitely like to do an "Essence of real analysis" one day, and the topics you mention would be right on there.
This would be amazing.....I have thought the hardest part of math is analysis and you're just the guy to do it.
Evi1M4chine
I study math and most of the people I know don't like to memorize something.
We try to understand. And this counts for every single one of my lecturers and their assistances.
Sometimes this goes so far down the rabbit hole, that we nearly commit an entire lecture, just to understand that one thing.
Sure there are theorems you might only need to know exist in the first place, like stuff from Frobenius, fudge this dude and his proofs. Also there was a time in mathematics, where it wasn't accepted to use graphical assistance to help the understanding of a topic. Just look at most of Euler's and Gauß's proofs. Those feel like they had a completely different understanding for the topic, but every evidence of sketches or graphical explanation got deleted, since it was a 'no go' in the era.
But this isn't the case anymore. Not to say that everything get's easier with graphical understanding of a simplified problem, but either way you have to put effort and a lot of work in understanding simple theorems to explain them in the way 3Blue1Brown does. And if it takes 10 hours just to get one idea, that's okay.
And most of the fellow students I share my time with, love mathematics. Like two friends of mine stood in front of a chalkboard, trying to understand why you need certain properties in a theorem, if it would be enough to use more global statements. They spent 2 hours (after a complete day of lectures) just to understand this one bit.
This is what studying mathematics is for. Understanding and expanding your knowledge on the topic of your choosing.
BUT Wikipedia is a page of knowledge, not understanding. If you want to understand, you are welcomed to study mathematics. Get books about a topic or just search it up on Math Stackexchange.
Wikipedia is to fast look up a certain theorem and it's not built for mathematicians, it's for everyone.
To much information will sometimes lead to struggle, if certain people are unwilling to put in the said effort and time. They don't need an explanation how it works or why it works, but only that it will work and achieve the output needed. Nothing else.
They simply don't have the time and energy to do so.
Don't try to force them to understand those things.
Wikipedia decided long ago to be an _encyclopedia,_ that is, to collect knowledge supported by reputable sources. It's not the place to add your own explanations for complicated concepts.
A blog would be a better place; or an homepage provided by your institution or company; or a UA-cam channel like this one; or you could write a book if you have enough material.
Either way, if and when your material gains acceptance and recognition, in a way that can be measured by that "cabal" of editors you despise, then it will be gladly accepted into Wikipedia.
Zaknafein Do'Urden
A Zin-Carla in the comment section? Didn't thought you could type...
I am the most grateful human being after discovering this. Thank you so much. I was almost about to quit my master's thesis in maths (just because we never visualize anything, just learning stuff with the speed of light but no-one ever explains us how to imagine things and that really makes me nervous), but you're a part of the people/things that helped me get my thrill back. This is pure gold, thank you so much Sir, from the bottom of my heart.
I am in the same situation, feeling the same gratitude.
Jovana Krstevska Hi
Jovana Krstevska I can relate. That is very true. Lesser and lesser imagination and visualization as we try to learn more. Kinda kills the fun. Fortunately, you have been saved. I am happy for you.
Prvpat gledam makedonec da komentira na vakvo video lol
No offense but I find it really surpising a master's student would say this. Don't get me wrong, I'm up late watching this for the hell of it because I like the teaching elements, but I'm just shocked someone in a graduate program needs to be taught to imagine things.
I can say with utter confidence that this is the best UA-cam channel I've ever come across. So incredible how much of my education clicks every time I watch one of your videos.
If you were to start from square one and do a complete course covering math from calculus I, it would become the new standard reference of the modern world, replacing all those crappy books.
I'm currently in grad school studying robotics. One of the cruxes of engineering is taking maths on faith. We don't necessarily have the time to make sense of these things. Your videos have helped me understand Linear Algebra and Diff Eq so much better beyond it's applications. I really appreciate what you do. e makes more and more sense every day.
The crazy thing is even in math programs (at least at my undergraduate institution), a lot of what we had to do was take math on faith. We were basically given the definition of a group as though they were handed to us on stone tablets like Mosses on Mount Sinai. Never asking "why the hell are we using this as our definition of a group?" or "what even IS a group and what is the broader concept it's supposed to represent?" It would be like teaching a six year old: multiplication is the process of repeating the addition property an indicated number of times. Sure it's correct, but you aren't really learning multiplication at a deeper level and it becomes harder to later generalize to multiplying by zero, fractions, or God forbid, negative numbers. Visuals of rotating a 4x5 grid to show that 4x5 = 5x4 are a much better way of understanding the fact that multiplication is commutative than simply being told it's an axiom and just something you have to accept.
These 3Blue 1 Brown videos are a great example of the rotating the grid type of visuals that give one a much deeper understanding of what these concepts actually represent as opposed to some vague abstract construct with which to work.
So the tales were true: there really are friendly, constructive and informative comment sections on youtube.
This is such a nice crowd of subscribers.
Ur mom gay
@@mohsinuddin7049 no u
@@mohsinuddin7049 Lol!
12:50 GOOD LORD IT ACTUALLY MAKES SENSE NOW
After a bit of abstract algebra I finally understand the reason why you move zero in the additive group and one in the multiplicative group. They're the identities of that group! I'm still realizing things from these videos even after watching them in the past.
Oh shit, that intuition leading to the conclusion i*i=-1 is just beautiful!
Well, i is DEFINED by being the square root of one. it would be the same thing as saying: "Wow! way to prove that the ratio between a circles perimiter and its diameter is exactly pi!"
It wasn't a conclusion as such, but more of a process in the context of group theory of how i*i is -1. Well, i*i=-1 is the very equation by which i is defined, so he didn't prove anything new, but rather showed us the process of how it works. So people who would ask what's x*i or essentially, "what does multiplying by i do?" would find this illustration useful. Just saying i*i=-1 is a given is one answer, but more of a declarative one, and it raises plenty more questions than it solves. Giving an animation to explain the process helps people explore complex numbers. So it was the same thing as saying, "Just saying i*i=-1 is not satisfying. Here is something that you might find satisfactory and it will help you explore complex numbers as well."
Trust me when I say this: do NOT make spaghetti in the toaster. Don't ask me how I know, it's not important. Just don't do it.
But i^i is not - 1, it's ≈ 0.2
Nevermind, I mistook the * for a ^
This Channel is better than University. You are the man 3Blue1Brown
@Sophisticated Coherence but he does not teach everything else
@@jsutinbibber9508 What stage are you at in your education? Because these videos become absolutely indispensable at some point and fourth (not gonna get ya to the finish line - bad analogy - but gives some ideas about stamina (for example).
University has always been a joke. A scam
Im sorry to hear you didnt go to a good one.
In europe its very cheap and right now im studying at University of Twente in systems and control, it is very good. The teachers are competent and caring, our facilities are good. The campus promotes sports and social associations that help you develop skills outside of the core classes.
I might be lucky but it is not a scam.
They really aren't a scam, lol
ANY university in the world teach this kind of thing in mathematics related courses.
This channel started my love for calculus at a young age. Am currently pursuing Engineering at Berkeley. Thank you so much!
Good for you! I got my degree in geophysics from Berkeley, and I am so proud and grateful that I went there.
So your explanation of complex numbers with shifting and stretching and rotating has taught me more about complex numbers, in an intuitive sense, than any teacher.
So thank you
"Those who know do, those who understand teach." And your are one of the best examples of the second one.
The one I hear often is 'those who can, do. those who can't, teach' which is kinda funny. sorry about the four year old reply
Thank you for your work, I'm a PhD student in Electrical Eng. and wanted to go deeper in to the fundamentals of signal processing and linear algebra.. Your videos helped me think about these visualizations better, and you do a good job on them. I hope you continue inspiring and helping people all around the world. See ya. Kudos from Brazil.
I just want to say, Grant, that I really love this revisiting of the Euler formula. I didn't quite understand the whole idea you were trying to get across in the first video, about stretching, moving, and rotating being related to certain operations. But the group explanation has actually really helped me to understand it.
I love your channel. I usually end up watching your videos right when they come out and I tend to just go with the flow bc I hv no idea what's going on lol. But then I watch them a few more times, maybe not to completion, or with huge gaps of time in-between viewings, and I suddenly feel like switch go off in my head. And then once that happens and everything falls into place, it just feels beautifully awesome and I can extend my gratitude enough for making such abstract concepts relatively easy to digest and really comprehend. Because at the end of the day, I could read a textbook, but this gives so much more depth which is extremely helpful especially when starting out.
I think one of my favorite proofs I have found of Euler's formula was in a book I picked on relativity, where it starts with only the equations ds²=dx²+dy² and rθ=s, and ends up showing rθ=x+iy, without even defining the number π.
Cant wait for more complex analysis videos really...this video by the way was extremely thrilling to be watched and getting to atleast know that angle preseving or the analytic nature of the e to the z function isnt opaque but quiet enthralling for all if they stumble on this video and especially the point where the video closes off just vividly showing it...its a blessing to be a part of this channel...💙
Im mean and skip sponsors usally, but Cloud Lab is actually the first ad ive seen for something truly brilliant. cant wait to see what this idea becomes in the coming years
Has it really been only two years? Has it really been already two years! Congratulations!
You are legitimately one of my favorite channels. It's been fun to be along for this ride, hope it continues for years to come!
I haven't watched the other videos, but the argument at 19:30 seems to be somewhat circular: If you are already at the point where you are comfortable enough with the definition of complex exponentials to be able to reason which base "makes sense", then you already know "why e^(i*pi)=-1". In other words, this video was less about 'the why' of this relation, and more about how it could make sense if one considers the exponential function to be a mapping between two groups on the complex numbers, e^(i*pi)=-1. Not to take away from the rest of the video, which was obviously great :)
Edit: no pun intended with 'circular' :)
Agreed! The video is great, but this one step is not clear enough I think.
The explanation at 21:06 kinda touches on it, because it hints that the derivative of different exponentials would mean a different rate of change around the unit circle, meaning that Euler's formula only works for e. That said, he still didn't elaborate on it enough I think.
Edit: If you do the derivative with 2^x instead of e^x, you get i(ln(2)2^(i*t)) which might be the explanation we were looking for! Because the factor in the derivative is converted into a factor in the velocity around the circle. This explains the angle we get if we use 2^x instead of e^x, as well as e^x is special.
My favorite channel on UA-cam and really my favorite channel no matter what platform. Thank you so much. The mind expanding ideas here are so beautiful. I am so grateful that you take the time to share them. I love these journeys into the world of math so much. If math was like this in school I would have made it my career.
Phenomenal. I've been subscribed to your channel for two years now and every time I watch a new video of yours I am absolutely astonished at your work. Math made beautiful. Just wow. You are a gold mine of youtube
awesome !!!! when you uploaded the video about e^pi i two years ago, I couldn't understand it completely and this video helped me alot in gaining insight and complete my understanding of what "taking adders to multipliers" is-the phrase you used in that video. I am always thankful to you for making such amazing videos. I wish I could meet you and learn math directly from you.....keep up the great work of making people enthusiastic in math !! waiting for your essence of calculus series ........
I love this. It's perfect. I'm lulled by numbers and finding order in disorder, patterns of beauty in a chaotic place. It's beautiful how he describes it to make sense... I don't have the education to do calculus now but I see numbers how he describes it, exactly. It's like 0 is middle C on the piano. I love patterns. Music is math. I'm in awe.
Hey Grant, this explanation is has really done it for me. I am a junior at uni studying physics and I am so glad that you have made this video because I finally understand things that I didn't even think I didn't understand in the first place. Not just with euler's formula but with math in general. Thanks a lot.
Thanks! This is one of my new favorite videos. I took an abstract algebra course and learned all about homomorphisms but it never clicked until now to define exponentiation as the function that preserves the homomorphism between additional of exponents and multiplication of exponentiated values.
I think group theory and discussing graphs would fit well with your amazing visual style of presentation.
I would love love love to see a series on group theory build up to giving a sense of why in the world checking if two graphs are the same is so freaking hard. For example touching on graph isomorphism and Babai's work. It sounds like it has something to do with the symmetric group just being so large it doesn't fit well with our intuition, but it's hard to see. It just hurts my mind that something can be "easy" enough to do in _linear time_ vs graph size for almost all graphs, yet no one knows how to do it in even an arbitrarily large polynomial amount of time vs size if it must work for _all_ graphs!
I'd love that too. There are some textbook like introductions on youtube (check out Sarada Herke), but nothing to bridge jumping to any of Babai's lecture videos, and nothing really conveys to me the core difficultly they are fighting against. Linear in time for almost all graphs, I had no idea the gap was that big! I'd love to see a visualization of what that core difficulty is that somehow escapes almost all graphs. So mysterious, I bet there is something beautiful in there when explained well!
I think it has nothing to do with group theory, but instead just computer science. It's because the problem is NP-Complete as you can reduce the satisfaction problem to it somehow.
Does this mean the vertical axis of the additive group undergoes modulus arithmetic when its transformed? Like with e as the base, a vertical transformation of 2pi maps to a 360 degree turn, or the same as doing nothing? Do you "lose" information then when this is done?
Wow thats a pretty good catch. Indeed if you look back at the group of rotations of the square, this group is the same as the integers modulo 4, and the circle group (group of all rotations) is just the Real numbers modulo 2*Pi.
The loss of information you describe comes from the fact that exp(2*Pi*i*k)=1 for all integer k, so multiple points are mapped to 1 (adn thus multiple points are mapped to any point).
In general, "loss of information" like this are so important they are described through the fundamental theorem on homomorphisms. the most important theorem of grouptheory
You’re the best math teacher I never had. Thank you for making these videos. I can’t possibly ever express in words the true depths of my gratefulness. Thank you!!!!
It's difficult to appreciate just how amazing this video is until you've actually done a course on group theory. When I watched this a couple of years ago, I got the main gist of the idea and I was impressed. However, even though the idea in itself is beautiful, I appreciated how succinctly you summarized the actual rules of group theory so much more. Also, in my education, I didn't really look at group theory as symmetric in nature, so when you showed the different numbers as actions that preserve symmetry it blew my mind. Great video, probably one of the best on this channel (and that's saying something!) :)
Every time I learn something new and interesting in your videos I wan't to like it, but then I see that I already liked it. Keep up the good work!
10:51 Here, you say you're squishing by a factor 0.5, but you're actually *stretching* by a factor of 0.5, i.e., squishing by a factor of 2
The best thing about u is what you know??
U make an intuitive pictures of everything. U make us to think the abstractness of any mathematical topic.The same way I had learned maths in childhood and still learning. And I want to thank u a lot because this video helped me in writing my mathematical papers....
I've read/watched lots of information about Euler's Formula and imaginary numbers in general. This was the first explanation that left no doubt in my mind as to why imaginary numbers are so intrinsically related to rotation. Thank you.
Thanks for this and other amazing videos. I really like to learn to do such animations.
I found a small mistake at minute 13: the angle corresponding to 2+i is not 30° but rather arctan 1/2 = arcsin 1/√5 = arccos 2/√5 = 26°33'54"
This is, hands down, one of my favorite video's on UA-cam
I just rewatched the old video before this one, and oh my goodness. The sound quality is incomparable between them. Still loving your videos. Keep it up!
The extent with which you can wrap my brain around some of these identities and concepts is SO WORTH a commercial or two.
THANK YOU for feeding my visual learning preference. I am teaching myself Data Science and Machine Learning along with AnimateCC (Flash :) I have been trying to recreate the animation in my head as I learn - fascinating.
So in this view, adding 1 to both sides to 'beautify' the equation as e^(i*pi) + 1 = 0 actually obscures its true meaning?
All e^(i*pi) = -1 is saying is "rotation by 180 degrees is the same as a reflection".
And if we indulge the tau-ists, then all e^(i*tau) = 1 is saying is "rotation by 360 degrees is the same as doing nothing", which is pretty neat. Euler's formula almost seems like a tautology in this sense, in that this is the only natural way to define e^(i*x).
e^(i*tau) = 1 is the same as multiplying by 1. As for e^(i*pi) = -1, it is the same as e^(1/2*i*tau) = --1 or rotation of half turn. So, yes pi obscures its true meaning.
If e^(i*tau) is 1, doesn't that mean i * tau = 0?
@@linus6718 No, because the exponential function in this case is periodic. You see, if e^0 = 1 then e^i*tau = 1 too because the exponential is periodic with period i*tau (the same as saying one rotation by 360 degrees does nothing), so: e^(k+tau*i) = e^k for every number k
but you could say i*tau is congruent to 0 mod(i*tau)
@Linus Yes, it is. x^0 = 1 for all x's that are real numbers. The reals are rational, irrational and transcendental numbers (think any point you can choose on a continuous numberline). π is a transcendental number so it's included. e too (también!). So, yep, i*tau = 0. Another way to verify is with
e^iπ = -1 or
e^i*tau/2 = -1
Square both sides and you get
e^i*2π = (-1)^2 = 1 or
e^i*(tau/2)*2 = e^i*tau = 1.
Thus
e^i*tau = 1 = e^0
Now take the natural log of both sides
In(e^i*tau) = ln(e^0)
i*tau * ln(e) = 0 * ln(e)
and ln(e) = 1 so
i*tau = 0 Booyah!
@Daniel Lopes actually states the generalized formula for any value k an integer perfectly but denies his own equation for the valid k = 0.
cred:
I have an MS in Physics '85 and a Math minor, 30 years of scientific work experience, am left-handed, and have spoken with Doug Hofstadter personally about "Göedel, Escher, Bach, an Eternal Golden Braid."
The number line transformations remind me strongly of 1D matrix transformations. Especially as you illustrated them in your Essence of Linear Algebra series.
Thank you for helping me improve my understanding.
Fun fact: The transformations of the multiplicative group of th ecomplex numbers represents exactly those 2D lienar transformatiosn which are not just real linear transformations but even Complex linear transformations (meaning they are the linear transformations commuting with multiplication by complex numbers)
My Diff EQ class led me to your channel while looking for a certain integral. Even though that did not help that search, I have been interested ever since. Mostly because a lot of the math you cover is something I have seen or think I will see in the future. It's also because you explain everything so well. After watching certain videos I was confident enough to complete some practice problems I have never studied. That's due to good teaching from these videos.
Complex analysis is just glorious. Eternal gratitude to you for this and your entire UA-cam corpus.
This imo is the best Math channel on UA-cam
18:51 "so wouldn't you agree that [completely unjustified leap in an argument that relies 100% on intuition]?"
Completely agreed. It's so stupid how we just jump to that conclusion and then make more assumptions based on that with no explanations given.
This is by far is one of my favorite 3B1B videos, I come back to watch it again and again
Wow, what an enlightening video! I had previously held a certain intuition about multiplication on the complex plane as scaling and rotation, but I didn't really understand WHY we choose to think of it like that. This video explains very well how exponentiation is simply a homomorphism between sliding and stretching. So when we extend into the complex plane, we turn vertical sliding into rotation to encompass all 2D transformations.
This needs to be shown to more people. I hate when they use the taylor series expansion to explain this. This is so much more intuative!
It is intuition, but it isn’t proof. Both should be considered.
This man and his contributors deserves a worldwide recognition of mathematicians around the world.
This channel is SERVING the mathematics to everybody.
Excellent, 3B1B ... Loved this this take-two version and your original. What I didn't realise (as I have only recently discovered your channel) is that this subject was where it all started for you! ... even the thought of your very first [your # -e^(iπ)] video would be on this ... well done ... glad I found your channel (well, the UA-cam matching algorithm). Love your channel and your excellent communication and presentations skills to go with it !!!
Fantastic video. I dealt a lot with group theory in inorganic and quantum chemistry - this was a much better refresher than going through my old notes!
Currently studying for my complex analysis exam, and man am I ever grateful to you for this video! It was an 𝘪 opening experience for me!
How dare you make me read that pun with my own two i’s
@@sophiap.8859 i cannot unsee that
Did you pass bro?
@@boston0086 Hahah In the end I didn't even do it. The corona quarantine had just started and so I just got a passing grade.
So yeah, I guess.. Sorta passed :)
@@garlic7099 Congrats bro:) the most important thing is that you you were interested in it! The topic about complex analysis is so much, you will always learn new stuff about that :D
At 13:33 that is NOT a 30 degree rotation. It is approximately a 26.57 degree rotation.
Ooh! Good catch, thanks for that. Silly me, mixing up my sides.
Yup. Thought the same thing, immediately! :D
Omg you're right, i measured it with my protractor (because that's quiqer than calculating it) and I got exactly that
Lol it's just arrcos(2/sqrt(5)). Awesome video
is arrcos the pirate version of arccos?
New to the channel and a total casual, but your videos are highly therapeutic for me. I hope to regrow long lost math roots, but if nothing else, I'll be able to find my center with ease! Thank you for your content.
Thanks. This made a lot of sense to me. I was reminded of Napier's logarithm tables (which I saw in another video on the history of logarithms) where he multiplied by a tiny amount in one column and added a tiny amount in another and how the natural logarithms of the second column emerged in the first column (well, it was actually dividing so it was only related to the natural logarithm). That was a way to match up the multiplicative group to the additive group like you described. The rolling up, rotating, and stretching of the whole coordinate space at the end was very cool.
Wow.... this is the best introduction for group theory that i have ever seen.
Thanks a lot.
Thanks for the video. The analogy is really helpful. I have just one question:
In 20:00, you explain that the additive action maps to the multiplicative action, and that the action of vertical sliding maps to rotation as a result. How do you come up with the numbers for the rotation in radians? What is a more intuitive way to understand this scaling apart from using Euler's formula? (which is what we are trying to prove so it does not make sense to use the formula before proving it).
I have a similar question. Would love to see if anyone responds to this.
Me 3! At 19:40, he said "it happens to be 0.693 radians", which is the moment that made me really want to now *why*!
The explanation at 21:06 kinda touches on it, because it hints that the derivative of different exponentials would mean a different rate of change around the unit circle, meaning that Euler's formula only works for e. That said, he still didn't elaborate on it enough I think.
Edit: If you do the derivative with 2^x instead of e^x, you get i(ln(2)2^(i*t)) which might be the explanation we were looking for! Because the factor in the derivative is converted into a factor in the velocity around the circle. This explains the angle we get if we use 2^x instead of e^x, as well as e^x is special.
+
*3b1b:* turns ads off for better video experience
*UA-cam:* alright lets turn ads back on and keep all the profits
Sir, I am thankful for you and your channel today! Seriously. This is my first video of 2020 and a great way to start the new year! :)
"They are one example in a much larger category of groups"
Literally, haha
Is that a category theory joke? xd
Patrick
hehehehe The Joy of Cats.
Hey. At least it's locally small!
@@nasajetpropulsionlaborator8727 Lmao, projecting much?
Group theory has a TON of potential when it comes to optimizing machine code, and I'm disappointed that not more people are looking into it.
This really interests me as a student studying Computer Science. How can group theory be used to optimize machine code?
Incredible description of the subject. It motivated me to go to patreon for the second time in my life. The first time was after listening to Sam Harris and The Very Bad Wizard's discuss Partially Examined Life while referencing Robert Wright. In other words, this guy has a definite black belt in explaning complex ideas.
I finally understood this concept. I'm a math lover, although I'm a biologist.
I didn't quite undersand why, a teacher tried to explain it to me, but nothing; I read about the subject but nothing; I even watched other trying to explain it, but nothing. Finally I've found an explanation I can understand and it's beautiful, I mean it! Thank you so much!
are all these actions considered transformations, or does group theory make them something else distinct from geometry?
Ben Dover geometry is just a special case, and a transformation is just a word unique to geometry to describe elements of a group :)
Can I ask: what software do you use to create these videos? The animations are so smooth and elegant!
Thanks for sharing your knowledge. It is quite impressive to see how these complex concepts are so easy to understand with the proper teacher!.
This finally makes sense! By far the best video on this subject on UA-cam! This is phenomenal!
18:00 I Don't seem understand to how Grant(3b1b) is relating the two groups. I would highly appreciate it if someone helped me to understand the correlation. thank you
Mohith S N Raju all it means is that given the two actions, the result is the same for these two groups (so in this case -1 and 2 give the same result (but different paths to get to them, which is of course to be expected))
I just love how youtube sent me this video to recommended just to see that this 2 year anniversary happened 2 years ago
I've gotten through linear algebra and discrete math/proofs. I plan on taking the GRE sometime soon. This video was such an incredible introduction to the group theory I'm required to know for the test. Thank you so much!! :)
Incredible narration. Excellent animation sequencing. Thanks for all of your hard work!!
Excellent. My only quibble is that in discussing multiplication on the number line, you only referred to the "multiplicative group of POSITIVE numbers." And while it's pretty obvious what multiplication by negative numbers should do to the line, you didn't spell it out. And yet, when talking about i*i = -1, you referred to -1 as the "unique action" without having earlier made clear that negative numbers are also a valid part of the multiplicative group.
I actually found that quite genius of him. The point was that positive real numbers are pure stretchings while negative numbers also include rotations, which are a complex thing (and notice that the real exponential function only puts out positve numbers, so the real exponential function only gives you a relation between the additive real numbers and the multiplicative positve numbers)
And he did spell it out when he explained the complex multiplication and how it relates to rotation ;)
uhm.... it's genius of him because frankly multiplication by real negative number is just stretching and flipping through 0, it's not really a complex thing. In 1D, there is no need for rotation to involve. It happens that in complex, "flipping" through y-axis is 180 degree rotation.
Exactly. If he had talked about multiplying by negative numbers in 1D, it could have looked like flipping. But that would have created a misconception when extending to the complex plane because multiplying by negative 1 is not flipping in the complex plane but just rotation.
It's 'cause only the positive reals are in the range of the exponential map e^x (where x is real), but all complex numbers other than zero are in the range of the exponential map e^x (where x is complex).
does this idea of thinking of numbers as actions carry the connection between addition and multiplication like basic arithmetic does? I mean multiplication if seen purely logistically is a lot of additions. 5 * 2 = 5 + 5 how does that translate in terms of sliding and squishing the line. I think the proper question would be whether there is a connection between different action groups in general. Any responses would be very appreciated!
Well, I think of it a little differently than squishing and stretching. When thinking of a group, which is a set and corresponding operation, for example in the additive group 5 + 5, is the square of five or better stated multiplication are the powers of the addition operation (it even follows all the exponent rules). In the same way stretching would be the powers of the sliding motion. So sliding over 5 and then 5 again would be equivalent to stretching by 5 and then again by 2.
I think you just shattered my understanding of numbers forever. I love your videos. Keep up the good work!
This is just so beautiful. I love that at one point I was stunned by an idea appearing ... and then 2 minutes later I was lost and had to rewind !
0:48 "so here, two years later" *whince* This much time already? D:
After checking, I'm relieved, that for me at least, it's only a little bit more than one year. But still, time passes! :/
You're telling me. I just kept thinking "2 years? That can't be right, surely that's not right".
for me it was more like: _only_ 2 years? this channel feels like such a classic and is has so many great things in it already.. :D
Odd how your vocalization has slowed slightly over two years. Is the aging process exponential or linear? Will your voice be twice as slow in another 2 years or slowed to a barely audible rumble? ;-))
Wish we had vids this back in the Sixties. Nice!
Please do another video about the Riemann Hypothesis and Ramanujan Sums!
You should market these videos, especially this one, to all colleges offering group theory. Just wonderful. Thanks so much!
Congratulations to your anniversary! I am a long standing subscriber to your fascinating content!
Thank you for the many subtitles .
What application do you use for this high quality illustrations?
He programs in python, custom code for the presentations. He has made his library available as open source, look for it on his web.
So great ! I've used complex numbers and exponents for years without understanding them, but now it finally makes sense. Thank you!
I normally prefer to read my math (old school) but this series of videos is always enjoyable and offers a different perspective on a lot of otherwise dry topics. The videos on the uncertainty principle with Fourier Transforms was wonderful.
EmeraldCloudLab looks amazing
I am still confused. All is good until 19:00, where we jump to exponentiating by complex numbers.
What was covered: adding as shifting and multiplying as stretching. Also, exponentiating by WHOLE numbers as translating a shift to a multiplication.
But we still do not know how to exponentiate by all real numbers, not to mention complex numbers.
Did I miss something?
agreed, got stuck at the same point
Me too, got stuck there. Why does exponentiation by complex number correspond to rotation of the plane? It can be verified mathematically, but I'm not getting the intuition behind it.
You can think of exponentiation by reals as a way of turning a discrete function into a continuous one - it still has to go through the same discrete points. That can be one starting point towards understanding. It turns out that when you do a series expansion of a real exponential then it usually works just fine in the complex domain, and you can then look up the sine and cosine in the same series expansion and you’ll see the Euler’s formula that way as well. Again: that’s just one of many approaches. But going from discrete to continuous exponentials requires a better definition of an exponential than the elementary one - whether you look at a series expansion or something involving logarithms doesn’t quite matter.
He didn't actually explain it, he just asserted it. At 18:49 he said "So wouldn't you agree that it would be *reasonable* for this new dimension of additive actions, slides up and down, to map directly to this new dimension of multiplicative actions, pure rotations?"
I completely understand how multiplying by 2^(real number) will stretch the space, but he never said why multiplying by 2^i would rotate it, he just made a comparison to how multiplying by i made the space rotate. I agree with @Mithilesh Hinge, I can see it algebraically, using Euler's formula ( e^ix = cos( x ) + i sin( x ) ), but I don't get the same intuitive feel as Grant/3B1B provided for how multiplying by a complex number can rotate a space in the complex plane.
Can someone give an intuitive, geometric reason as to why 2^i causes a rotation? Maybe there isn't one, which is acceptable, but I was hoping for something as elegant as his earlier explanation of rotations due to multiplying by complex numbers.
And, as some others have mentioned, even if 2^i = 0.769 + 0.639 i, that looks like a stretch and a rotation, which is not the "pure rotation" he mentioned.
Otherwise, though, this video is wonderful. 😊
@@tonylopez5937 if you multiply the complex number z= r*exp(it) by the complex number exp(ix), you get r*exp(i(t+x)). You are just rotating z by x radians because the angles add. The author of the video is not explaining what is really happening here. He is assuming Euler’s formula and the polar form of a complex number. He is just saying that the image of pi*i under the exponential map (homomorphism) is -1 because Euler’s formula is true. His graphics are nice, but he is not using group theory to explain why Euler’s formula is true. So the title of this video is a bit misleading.
Thanks for sharing! It is like a kind of encapsulation. You can use this formula not really understanding why it works, as like as you can drive a car knowing nothing about of the Laws of thermodynamic. Your wonderful explanation allows to look under the hood of the Universe.
polar coordinates are such a nice way to describe complex numbers, and better highlight how complex numbers, though described with 2 values, represent a single number.
positive reals are rotated 0 radians, negative reals are rotated pi radians, making the real axis. these are all the numbers we know now. rotations other than 0 or pi radians are numbers that arent entirely on the real axis, and are called lateral numbers. in this system, numbers are defined by a magnitude and rotation. 1 is 1