Holograms! (Early view)
Added 2024-10-01 01:47:20 +0000 UTCThis is one of the most fun projects I've worked on. This early draft I'm sharing is already one of the longest pieces I've posted, but there's still more to do.
As always with these early releases, let me know what errors you catch, and which parts of the lesson could be clearer. For this particular project, I also have a more targeted question. I'm debating whether to add the final piece of the explanation within this video or pull it out as a supplemental lesson. I'm not looking for guesses about what the YouTube algorithm is more inclined to recommend regarding video length, what I'm trying to figure out is what's best for the viewer.
My essential question for you is whether at the end of this draft, you find yourself mentally full, preferring a break (say until tomorrow) before seeing more, or whether you find yourself both energized and hungry for more.
The final piece of the explanation will not be too long, perhaps around 8-10 minutes depending on how I pace it. The main conceptual jump is to start modeling the waves with complex numbers, but after that, carrying out the appropriate algebra and pointing to the right set of terms offers a more powerful explanation of why holography works.
On the one hand, minute 40 of a YouTube lesson is perhaps not the best time to up the level of abstraction. On the other hand, keeping everything packaged together and preventing the need for a recap has an appeal, and there's room to tighten up the existing draft. I could easily go either way, and I don't think there's a wrong answer, but I am curious to gather information on where people's heads are just from what's presented here.
Comments
Watched the full version and I first just wanted to say wow! What a stunner! But (more importantly) I work in radio astronomy, and some of these animations, especially the whole bit on expanding from the single slit to the grating, would be immensely helpful in describing/explaining how/why we need a whole bunch of antennas spaced at different distance to make pictures of black holes and solar flares and such.
Brian O'Donnell
2024-10-06 00:15:54 +0000 UTCThe diffraction grating part is so cool, we talked about this formula for diffraction gratings used as monochromaters and the resulting angles different wavelengths are diffracted at given d in Instrumental Analysis, and I think the derivation in the textbook was probably similar to what you did, but it really just clicked with the animation, thank you!
Sara K
2024-10-05 22:56:16 +0000 UTCMine too! It's too bad it's not free anymore like it was when I grew up and when I worked there, but then again, what is these days?
David Terr
2024-10-04 20:24:56 +0000 UTCFair enough! Perhaps the justification for using the superposition principle is more complicated than I thought - just a suggestion!
David Terr
2024-10-04 20:21:32 +0000 UTCNoted, thanks!
3blue1brown
2024-10-04 18:27:09 +0000 UTCFor some viewers, that will absolutely be the right thing to say. One of my hopes for this project is that it can be satisfying even to those beyond the usual very-math-literate inner audience, so I was trying to opt away from Fourier references.
3blue1brown
2024-10-04 18:25:36 +0000 UTCI feel like a bit more justification is needed to invoke the superposition principle since you need to explain why the exposure pattern from multiple dots (which is not a sum of the individual exposure patterns each would produce) has a diffraction effect such that the wave on the other side is a sum. You certainly can justify it, but for this project I thought it'd be better to just get to the more general explanation (not in the draft, but it will be in the final version published tomorrow)
3blue1brown
2024-10-04 18:23:37 +0000 UTCThank you for the offer, if I ever tackle that topic, I'll let you know. For now, I was just planning to do this one (large) project on Holograms and move on to a few other mathematical topics for the rest of the year. Very neat that you got to meet Frank Oppenheimer! The Exploratorium is one of my all-time favorite museums.
3blue1brown
2024-10-04 18:21:12 +0000 UTCAnother way that it feels like more efficient encoding is how noisy the exposed film looks. If you think of all possible exposure patterns, the vast majority look like random noise, so from an information theoretic perspective, if you wanted to fill the space of all such patterns more efficiently, you'd expect to see more random-looking encodings like this. Holography involves a remarkably simple setup for such an information-rich recording, so to your point, the analog processes seem on the inventor's side here.
3blue1brown
2024-10-04 18:19:16 +0000 UTCThat's great to hear, thanks. In the final edit (to be published tomorrow) I tightened up that section a little, and I think it all fits a bit better as a coherent whole.
3blue1brown
2024-10-04 18:16:41 +0000 UTCThis fact will come up later in the full version. I can see the case for keeping such facts out if they're not immediately relevant, but personally, I like the idea of being able to instill a sense of familiarity in a viewer for things that matter later on. In this draft, it didn't really make sense without the payoff, but I suppose we can see what people think in the final one.
3blue1brown
2024-10-04 18:15:48 +0000 UTCOne didactic question I had - when you do "forward references" (e.g. intensity ~ amplitude ^ 2), do you think this is generally good? I am thinking of it in a very naive story telling perspective, where I find that if I do this with stories about the world, it tends to distract rather than add to it, but maybe it's different in a more informative environment as you are instead shaping the viewer's ways of thinking. [Also, and maybe this is my bad memory - did we need that fact later? Or is that going to come up in the full video?]
_ericBG
2024-10-04 09:33:30 +0000 UTCThe video absolutely flew by, that was a joy to watch. As others, I really liked the section on diffraction grids. I would think that it'd be nice to have it be a separate video, but only in the sense of wanting to potentially space it out... If you're honestly not worried about Youtube performance etc, I'd try and release both at the same time. It did not feel like 40 minutes at all, but maybe I was in a good learning mood.
_ericBG
2024-10-04 09:31:18 +0000 UTCIncredible work, and very satisfying to follow along - I never took it upon myself to learn how holograms work, despite them being so magical. I think I was shying away from what I thought must be a daunting task. This presentation has been another wonderful revelatory experience I've come to cherish from your videos. I'd be happy with one big video, or an additional one, with a slight preference towards the latter. I will say that I'm very excited to learn about the more abstract principle! One thing that intrigues me is that this seems to be yet another example of the uncanny way in which encoding and decoding of information seems to occur very naturally using analogue processes. For example, in vinyl, the pattern of sound waves is encoded as a groove pattern, and that very groove pattern can naturally reproduce that original sound when a stylus traverses it (in holography, the stylus is the reference light, and the film is the groove). I feel there's a deeper principle at play here that may be worth exploring about the way in which nature provides convenient ways to encode and decode information, in particular using the same mechanism that was used to encode it, but in reverse/inverse.
spacediver
2024-10-04 02:00:42 +0000 UTCI love this, I think that's definitely the right place to stop for now, but I also wanted to mention that the animations, towards the end, of the interference patterns for multiple points gave me a bit of a headache, especially when moving, and might be a serious no-go for some photosensitive viewers.
Benjamin Newman
2024-10-03 21:36:55 +0000 UTCHere's another suggestion. If you plan on making a series of videos on holography, make sure to also make one on the holographic principle, which hypothesizes that the universe itself is a hologram! If you like, I can help you with that one since I already know quite a bit about it, but if you do want my help, I'd like to be compensated. (Incidentally, I've visited The Exploratorium in San Francisco many, many times, and in fact, I was an explainer there during the summers of 1980 and 1981. I even got to meet Frank Oppenheimer, who was then the director.)
David Terr
2024-10-03 03:14:25 +0000 UTCWow, another excellent video! I never understood how holograms work before, despite watching about 5 or 6 explanations, but I was finally able to understand this one, so that now I can safely say I understand holograms! One suggestion though: Isn't the superposition principle the explanation of why we still get a reliable reconstruction of a set of points, since light is an electromagnetic wave, whose contributions from each point source in the object add up, and hence the reconstructed image similarly adds up? I don't know if there's a nice, simple way to say this at the end of the video, but if you can think of one, then please do so!
David Terr
2024-10-03 03:11:28 +0000 UTCOutstanding! I’m in agreement with Nabeel. The diffraction grid section is excellent on its own and can easily be a *useful* stand-alone video; maybe sprinkling a bit more details on the CD as a diffraction grid. And it works great as a teaser for the holography one. I also agree that (based on your description) the final section (not in the draft) is probably too deep of a dive by the end of this one. The current end is a very satisfying stopping point.
Euro Micelli
2024-10-03 00:11:20 +0000 UTCGreat video! I felt happy with the conclusion of this one and being allowed/encouraged to mull that over for a bit before taking it to the next level. I'm somewhat familiar with the basics of holograms, and I suspect someone completely new to them would feel even more so. So two videos definitely has my vote.
Martin S
2024-10-02 22:03:33 +0000 UTC3b1b already has some excellent explainers of Fourier transforms. Perhaps it's time for a callback and/or extension of that series?
darkwater4213
2024-10-02 19:36:14 +0000 UTCThis has been one of the biggest projects I've ever worked on. The bulk of animating and video editing has been in the last month, but there was a lot of research, setup, filming, etc. throughout the year.
3blue1brown
2024-10-02 16:53:39 +0000 UTCCertainly, all the code I use for videos is always visible in https://github.com/3b1b/videos
3blue1brown
2024-10-02 16:53:00 +0000 UTCnanometer sized LCDs crammed tightly together and individually addressed by software will be fantastic (when they are invented and produced)!
Gregor Shapiro
2024-10-02 14:49:56 +0000 UTCSupercool! The reason for the higher order beams to not be there for Fresnel zones is that the diffraction pattern is actually a Fourier transform of the grating. For a blocky pattern, this includes higher order lobes, but for the sine-wavy Fresnel function, it does not. Adding this small fact might improve intuition.
Ahgversluis
2024-10-02 08:16:58 +0000 UTCTheoretically, we should be able to have full motion holography: run a film at (say) 60 frames per second, and we should be able to watch a moving image from a variety of angles. Even more theoretically, we don't need this to be done with physical film, but could have holographic LED matrices to allow digitally recorded holographic images.
Stacey Greenstein
2024-10-01 23:23:29 +0000 UTCI Kinda knew it had to do with phase and could only be in the color of the lazer. Great presentation. I would love to learn how much time you spend on producing these amazing videos. I assume it's a lot. Do you delegate this task to your students for Xtra credit?
John T. Draper
2024-10-01 21:02:19 +0000 UTCI agree with @Bob. Breaking it into 2 or 3 similar to what was done in explaining transformer NNs would compartmentalize various pieces such that we can ponder them as we step through the series.
KirkDCO
2024-10-01 21:02:13 +0000 UTCWill the Maxim code used in your presentation be put on GitHub? This would be an excellent example of using Maxim.
John T. Draper
2024-10-01 20:58:28 +0000 UTCMaybe against the grain but I think I’d like it broken into a playlist of a few videos. When I got to the diffraction grating part I found myself wishing it was a new video. But I loved it — wish I had this during my optics classes many years ago!
Nabeel Sherazi
2024-10-01 20:41:54 +0000 UTCThis is absolutely amazing. I've always wanted to have *some* understanding of how holography works, and this is exactly what I needed. It's incredibly understandable (classic 3B1B), and I think it ends at just the right point: the basic principles have been made clear, and it lays out the missing complications to come. I vote for putting the rest in a separate follow-up. I will be eagerly awaiting it, although I'm pretty sure I'm going to have trouble following it. TYPO ALERT with apologies: at 35:34, PolOroid should be PolAroid. (Wikipedia tells me Poloroid is a musician from Essex!) I've got a friend who worked heavily in optics and holography for many years. I can't wait to see how he likes this one.
Matthias Ferber
2024-10-01 20:05:55 +0000 UTCThis is excellent, but a bit long. Might I suggest splitting the physical holography start as a 10-15 minute teaser and having the mathemtical bulk of the video as a second one?
Bob Dowling
2024-10-01 19:30:42 +0000 UTCI loved the video and wouldn't mind one bit if it was 8-10 minutes longer. Thanks!
Peter Bonem
2024-10-01 17:14:00 +0000 UTCIncredibly clear explanation (but I have only view half of this draft). What stuck me most is that the 'magic' of holograms is simply based on ordinary light, but was hidden from our perception since the dawn of time ...until lasers (monochromatic light) was invented.
Richard Hackathorn
2024-10-01 15:54:27 +0000 UTCOK, after watching the video, I agree that you could put the general derivation in a separate video.... but, sigh, you will have to recap this video. I still am so grateful, and impressed by the amount of time you're willing to take to describe these complex subjects so thoroughly and clearly. it looks like SO much work... but it is so intellectually pleasing to see in one video.
EngyRMP
2024-10-01 15:28:52 +0000 UTCExcellent explanation and visuals, as always. The length was ok for me, even though I did step out for a few minutes. Now, I am desperate for the ending piece.
Paul Mario Koola
2024-10-01 14:33:11 +0000 UTCIt’s a great question, which I wanted to address at the end. For white light reflection holograms, the thickness does matter, as it determines which wavelengths get reflected. For monochromatic transmission holograms, the thickness matters less, in that film thinner than the wavelength could work fine (at least in theory, if it could become opaque enough)
3blue1brown
2024-10-01 12:35:46 +0000 UTCAwesome work! and fascinating topic! In the interests of perfection: At 16:31 you move on to the next part and say "but how does reconstruction work..." there should be a longer pause before this, as it feels janky
Alex Jonathan Henderson
2024-10-01 12:19:30 +0000 UTCThanks, This is a topic I was hoping you would cover some time! In my opinion, you can omit the development of the interference pattern from slits. Better include that final explanation you want to add.
Dan Steinitz
2024-10-01 12:00:59 +0000 UTCThis is very interesting, learned a good bit about light, thank you for sharing!
Luke de Wet
2024-10-01 10:35:54 +0000 UTCThis was really interesting, and I finally feel like I almost understand holograms! Thanks! You're already spending about 2 minutes at the end leading up to the more complex explanation, and some of that might not be necessary if you jump right into the explanation. I think another 8-10 minutes wouldn't hurt, and it'd be nice for the video to be a complete, all-in-one guide. As a side note, at 32:49, when you mentioned that only the binary diffraction grating has higher-order beams, I got pretty excited. It reminded me of how an ideal square wave is the sum of a sine wave and all of its odd harmonics. Is this an actual ah-hah moment, or just a coincidence?
Anonymous
2024-10-01 10:25:20 +0000 UTCAt some point, it would be interesting to learn the impact of thickness of the film. The theoretical models assume zero thickness, but the actual piece of glass demoed here is quite thick. So this thought lingers in mind all the time, and messes with the intuition: it kind of feels maybe those fancy diffraction patterns work because they are encoded in 3d rather than 2d.
Pāvils Jurjāns
2024-10-01 09:41:44 +0000 UTCHaven’t had time to watch it yet, but I will vote for the “all in one” format. I can easily pause & bookmark if my brain gets full, but I can’t always navigate the YouTube universe to find additional episodes.
David B. Hill
2024-10-01 08:17:49 +0000 UTCTerrific! I knew a bit about holograms, but this goes beyond! Little issue: at 28:10, "First-order Taylor expansion" becomes "First-order Taylor's expansion" (added 's), this flicks in the viewer eye like a laser. Is it worth adding a few seconds of video to explain why holograms always seem to have the same kind of color? I mean, we don't need a full explanation, just a "obviously it depends on the wavelength and therefore the color, which is why..." that literally takes 5 seconds. Again, amazing video! More practical that some of your older ones with perfect boxes that produce pi * 10**n collisions, this new way of approaching math could bring in viewers who hate abstraction (and then trick them into liking math 🤪) In that matter, it is way less intense than some shorter videos, the length is good because we have a real goal towards we tend, at no point did I think "where the heck are we going to end up?", so no, no shorter for me.
Oltarus
2024-10-01 07:13:56 +0000 UTCI found myself pretty hungry for the rest of the explanation. The video didn’t feel as long as it actually was and I think one 50+ minute video would be completely fine.
Zachary Bills
2024-10-01 06:22:24 +0000 UTCThis is fantastic, and I cannot wait to see the final piece! The length felt about right to me, and I certainly could go another 10-15 minutes of complex-number math for that final piece. But on the other hand, I did have a fairly good high-school physics class some 40+ years ago, and I do remember my trig, so a lot of this feels familiar, which lessens the cognitive load. For someone without this background, the answer might be different.
Alexander Klaiber
2024-10-01 05:29:01 +0000 UTCAlmost everyone is mesmerized by a hologram when they see one. Everyone wants to know the magic behind it. Great job handling it. To answer your question - Although it is long, I did not feel any lag. And yes, it was heating up my brain cells for sure. Of course there is a lot to catchup by the viewer to truly understand why it works. I like that you took your time to form the questions properly, before going on to explain the details. I liked how you broke the challenge into bite-sized pieces with 1-point, 2-point, multi-point sources. That phase shift animation started the 'aha!' in me. Great explanation! I'm glad you made this video and I certainly learnt so much from this one.
Victor
2024-10-01 03:22:20 +0000 UTCThis was a really fun video, definitely left me "hungry for more"! Absolutely amazing how much is going on here! I'm a big fan of Mathologer, who often has "masterclass" videos, and I feel like something along those lines could be good for this video (i.e. some sort of "chapters" with a holistic path through the lesson of the video, allows viewers to take their own breaks and schedule watch time as they see fit) One minor point: ~9:25 - I was getting dizzy motion sickness from this visual, might just be me.
Michael Kokosenski
2024-10-01 03:07:40 +0000 UTCThis seems like just about the right length, to me. Very nice explanation -- now I understand holograms a lot better!
M. Eric Carr
2024-10-01 02:31:40 +0000 UTCI am definitely in the “energized and hungry for more” camp. The video is fascinating and easy to follow, and an extra 10 minutes shouldn’t be a problem at all. I did watch it at 2x speed though, so it was a 20-minute video for me. Not sure if that changes things.
Sergey K
2024-10-01 02:26:40 +0000 UTCStill early in the watch, but one thing that felt like sweeping a basketball ball under the rug was the definition of "light field". I think I might understand the choice of not diving too deep into the definition so early in the video, but since the idea of 'light field' is so recurrently used, it gives the taste as if something is missing.
ILim
2024-10-01 02:12:02 +0000 UTC
