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64 Responses to “Richard Feynman, the Challenger Disaster, and Software Engineering”

  1. John Ingle on February 20th, 2008 11:27 am

    You’ve written a fantastic article! I enjoyed reading it and am now excited about reading the full report. It’s amazing what we can learn from history. :) If you know of any similar documents doing post-mortems on the solutions to hard problems, I would be very interested in hearing about them. Especially if they’re written by anyone as engaging as Dr. Feynman!

  2. V-dawg on February 20th, 2008 12:57 pm

    Great Article Gustavo, I couldn’t agree with you more. Fundamental good design practices apply to any engineering discipline.

  3. mantrid on February 21st, 2008 4:36 pm

    Excellent article! I just had a thought that there is nothing bad in top-down approach in some circumstances. We’d like to build systems in top-down manner because it’s simpler than bottom-up and easier to manage. We’d like to build software as easy as we build houses. Perhaps we use top-down approach too early? I mean, top-down is good when we have reliable building blocks and we know almost every assosiations and implications between those bricks. But with today’s software engineering the problem is that we do not have such reliable blocks. As long as we’re discovering design problems and reliable solutions, we should stick to bottom-up approach, what will eventually let us shape those bricks and lead us one day to common building blocks for software. Only then it would be safe to ease the development process with top-down attitude. 10 years ago a developer had to consider hardware specific and low-level OS issues. But in time we learned how to address those problems and came up with hardware abstraction, common protocols, interafces, APIs, patterns, do-s and don’t-s. Today we don’t have to start bottom-up on such a low level as 10 years ago. We can start in a little bit higher level. Perhaps in time we will go higher again? How much higher will we be able to start from?

  4. Paul Wassmund on February 21st, 2008 7:04 pm

    I think it’s largely a matter of finding the correct balance. There IS a place for top-down design – it lets us consider the overall structure of the software, rather than just patching together a bunch of small pieces; it lets us address non-functional requirements such as reliability, extensibility, etc.; it allows us to make use of architectural patterns and design patterns that have been proven to be effective in other real-world applications. However, once we’ve established a design framework, we can build it from the bottom up, following the incremental approach (with testing at each step of the way) advocated here. Even during the top-down phase, we can do deep dives into areas in which there aren’t well-defined patterns to guide us, or where we don’t have experience with new hardware (this is a form of risk mitigation). It’s up to the engineers (and management) to determine what’s appropriate for a given situation, but to state that top-down is inherently bad is, I think, inaccurate.

  5. Austin on February 21st, 2008 7:07 pm

    Hogwash. The point of your article seems to be that top-down design leads to problems. I get this impression from “…’top down’ design, made in ignorance of detailed bottom-up knowledge, leads to problems.” Yet, the stuff you later cite from Feynman doesn’t support this. The quote relating a desire for a “step-by-step increase in scope” isn’t about design, it’s about _implementation_. Design and implementation happen in SEPARATE PHASES OF PROJECTS. Top-down design, bottom-up coding. This is the way every software company in America writes software. You can’t design a system from the bottom up. Go ahead and try, I dare you… it doesn’t work out better.

  6. Gustavo Duarte on February 21st, 2008 7:20 pm

    Thank you all for the kind words.

    @John: Feynman’s appendix is by far the coolest thing I know in this regard. I’m glad this thing got Slashdotted so more people got to know it. I don’t know of anything like this off-hand.

    @Mantrid, Paul: I agree _completely_ with what both of you are saying. I’m going to write a follow up clarifying some of these things and what exacly I mean by ‘bottom up’. I’ve had the same discussion over email with someone at NASA. But I think you’re exactly right.

    @no no: Did you read Feynman’s appendix? What did you think of it? Do you think I interpreted it incorrectly?

  7. Austin on February 21st, 2008 9:12 pm

    I did read the appendix, and I don’t think the section you’ve cited is quite relevant. My point is you’re conflating the design and implementation phases in your article here. It’s one thing to criticize big up-front design/waterfall style project management, but another entirely to propose that “top-down” design is bad. Every engineering project is fundamentally top-down: you start with a goal (get a rocket into orbit, say) and figure out the details of how to make that work later. Design _has_ to be top down. Big up-front design, as mentioned by Feynman, is the idea that you can plan everything about a project and then put everything together in a minimal implementation phase. I think you meant to criticize this method of project management, since designs like this fail. But the fact remains, you must have a high-level design phase before you try to implement anything. You can’t design “bottom-up”.

  8. cjones on February 21st, 2008 10:10 pm

    Fascinating article and I think it explains very clearly the common differences involved between those who manage a project and those who actually are getting the job done. This is a classic problem in most development shops where the people managing the developers/engineers have never actually coded anything themselves. Austin, stop being such a nerd and enjoy the damn article. You wanna show how much you know go to Slashdot and run your mouth know-it-all.

  9. Steve P. on February 21st, 2008 10:21 pm

    Good article, though you might have emphasized more that Feynman himself did not discover the temperature problem with the O rings. Here the true mark of his independence and basic honesty was that he was willing to publicly and very convincingly demonstrate it in front of cameras after being tipped off about the problem. A lesser person would have allowed the result to have been buried in the report to minimize the embarrassment to NASA and the US government. Feynman correctly realized magnitude of the engineering failure of which the O ring problem was just one symptom, and was not willing to let anybody get off lightly.

  10. Merlin Silk on February 22nd, 2008 12:08 am

    Richard Feynman was a little bit too difficult for when I was in college studying physics, or maybe he was too simple – – thinking about it, it must have been the latter. Because everything else in the lectures and classes was so darn difficult that what he had to say could not be so easy. I still have his Feynman lectures on Physics here on my book shelf, maybe it’s time to try to read them now. And with his ability to see things in simple ways he also impressed me in his biography, “Surely, you must be joking, Mr. Feynman” – so, yes, this guy can think, but what’s more important, he has the ability to live life to the fullest. In software development I have always followed the bottom up approach and caused some nervous break downs in managers because to them it seemed very slow. I was always vindicated because my stuff never needed any big fixes later, while the top-downers were later re-inventing bigger part of their work. So, yes, great article! Merlin http://www.MerlinSilk.com

  11. Gustavo Duarte on February 22nd, 2008 1:18 am

    Thanks again for the compliments.

    @Austin: I do see your point. Here’s what I wrote to someone about this: “I completely agree. That is one thing I do wish I had made clearer. I don’t interpret Feynman’s “bottom up” at all as meaning the chaotic, directionless processes we sometimes see in the industry. As he talks about “preliminary study of materials and components” in relationship to the engine, it’s clear to me that such a study would take place within the context of a plan and a preliminary design. After all engineers can’t randomly test materials until a space shuttle engine crystallizes in front of them :)

    “ I am going to have a follow up entry addressing some of these points. However, I do think that many thoughtful teams are top-heavy, and would benefit from de-emphasizing the schism between design and build. I think you and I do differ in that I do not see the phase rigidity you do. I’m ignoring the chaotic crap shooters in this discussion though, I wouldn’t call them ‘bottom up’, just ‘a mess’.

    @Steve: that’s also a good point. I didn’t want to get too much into the o-ring history though. If I had known this would be read more widely than by my mom and dog, I might have talked some more about the history. So it goes. I’m just really happy that a lot of people got exposed to Appendix F, so all in all I’m happy.

  12. ranjix on February 22nd, 2008 7:47 am

    tried to read earlier but was slashdotted. Anyway. Tried to read the little parallel between the avionics engineering and software. Not very good. Tried to read the appendix from mr. Feinman. I find it boring, irelevant, unconvincing, hiding behind the words. Sorry. Literature, not engineering. Too polite. “Let us make recommendations to ensure that NASA officials deal in a world of reality in understanding technological weaknesses and imperfections well enough to be actively trying to eliminate them.” How about “these bulleted list is what I recommend and why: …”? Leave the fluff for the school play. Further. Somehow the texts (above and the appendix) leave impression that top-down=bad and bottom-up=good. Hardly believable. Reader Austin above remarks are right on the spot. Most of the projects start with a goal, followed by a top-down analysis and design. When starting writing code, the process automatically becomes bottom-up. Bottom-up design would mean “hey, I have this screw and this nut, let’s put them together, what do I see? Yeah! It looks like a part of a rocket!” Sorry for the stretched example, but that’s bottom-up for you. Also, there is a tendency to compare software with any other kind of engineering. Frankly I’m not sure it applies. In “normal” engineering, the materials are usually well tested, and the number of “moving pieces” is fairly limited. A bridge has fewer pieces than a car (probably) which has fewer pieces than a rocket. Also, the results of the “normal” engineering are visible, it’s easier to spot a screw with the wrong dimension than one of the 6 constructors with 2 parameters in the wrong order. To make it more like “software engineering”, one has to add an unknown number of uncontrollable variables (os, dbs, messaging systems, firewalls, etc, none of them thoroughly tested), would have to make the engineers work in semi-darkness, and would have to make one feel like crap when the project is “done”. I guess a question would be – at which point any project becomes unmanageable? be it a rocket or an os. It looks to me like there is a hard (human) limit. but enough for now

  13. Mike Petry on February 22nd, 2008 6:01 pm

    Great post! I appreciate this work and I am definitely a fan of the late Dr. Feynman, but I am a proponent of software design. As a advocate for top-down software design, I typically find myself in the minority and have been meaning to blog on this topic myself. I found this posting to be a compelling counterexample to my own take on the subject and was motivated to post to my own blog. Although a fan of top-down design, I also believe in incremental development and find agile methods to be valid. I just happen to have had a lot of success developing very complex systems using UML. Of course UML is not a silver bullet and must be used in conjunction with good old exploratory hacking or the management friendly term “risk reduction prototyping”. Thanks for the compelling and controversial posting.

  14. otter on February 29th, 2008 5:23 am

    Ranjix, you said that [quote]In “normal” engineering, the materials are usually well tested, and the number of “moving pieces” is fairly limited.[/quote] But in the case presented, Feynman stated [quote]The engine was designed and put together all at once with relatively little detailed preliminary study of the material and components.[/quote] Anyways, I thought it was a great article and the opposing comments also gave a lot to think about. I guess that in the end the success of every project, be it software or engineering, will depend on striking the right balance between top-down, bottom-up, and management-worker relations.

  15. mentalmodel on March 8th, 2008 11:18 am

    I think what makes the space shuttle example appropriate for software engineering is that both are systems that are fairly new, unknown, and complex. We haven’t evolved a professional discipline dedicated to space shuttle design and manufacture, so a lot of the problems encountered in the development of a reusable re-entry space vehicle are novel. To me, computer science is to software engineering as physics is to space shuttle design. It’s amazing to reflect on how little we know about software development. That said, I’m sure there was no shortage of self-proclaimed experts in space shuttle design inside of NASA at the time of the Challenger disaster. Will a similar event be necessary in order for there to be a reassessment of how software gets made?

  16. AVEng on March 13th, 2008 3:06 am

    I have worked in the avionics field for 15 years, as a system engineer, a software engineer and a technical lead. I’ve worked on the control systems for commerical jets, for small business jets and for UAVs. I’ve worked on collision avoidance systems, on performance/prediction systems and on flight/navigation sytems. Richard Feynman’s observations are brilliant and exactly on target. He illustrates perfectly the problems I’ve encountered throughout my entire career. The TQM top-down approach does not work, and never has. Plus, the “UML as blueprint” model is an absolutely catastrophic addendum to this already flawed approach, because not only does it abstract the design even further, in the cases where I’ve seen it employed it utterly fails to consider failure modes. No, the top-down approach is only good for one thing – frameworking. You use a top-down approach to design a system’s skeleton. After that, you immediately switch to a rapid prototyping paradigm to backfill the system’s details. That’s the only approach that works, and ALL systems are built this way, whether they official recognize it or not.

  17. Reid Peryam on March 14th, 2008 1:09 pm

    A text book example of Déformation professionnelle ;)

  18. Gustavo Duarte on April 2nd, 2008 9:21 am

    @mentalmodel: that’s a good point, and Feynman explicitly states this in the report (“It is built at the edge of, or outside of, previous engineering experience.”). But there’s a lot of engineering that happens where boundaries are being pushed, enough that I don’t think it’s fair to say “standard” engineering is about solving previously solved problems. Civil engineering, at least from the outside, is one where it does look like things are pretty formulaic by now – after all we’ve had buildings for a few thousand years (though things aren’t so clear, as per the Steve McConnell’s articles above). But in most branches I think the envelope is pushed more often than not. So the techniques for dealing with the new are fundamental to the field of engineering as a whole, and here there’s a lot of common ground with software.

    @AVEng: thanks for the feedback, it’s always interesting to hear from people doing the kinds of systems Feynman talked about. Your take on top/down is exactly what I do in my own projects: use top/down for a general skeleton, and then switch to reality: experimentation and prototyping.

  19. Me, myself and I on June 19th, 2008 12:37 am

    IMO, there’s nothing wrong with a top-down approach at the right place.

    More exactly: you should use a top-down approach to detail the problem to be solved and to chop it into many more smaller problems, and then use a bottom-up approach to solve the individual problems.

    I always make a diference between architecture and design/engineering. Architecture is a direct result of requirements, and IMO transforming requirements into architecture is OK, since it is a safe way to create a vision of a product which matches the customer requirements. Nevertheless, it just creates a vision, one that may be proven unrealistic by engineers.

    However, letting engineers design the whole system bottom-up, starting from whatever they think is right and trying to adapt to each and every customer requirement incrementally, is IMO a bad approach, potentially yielding an extraordinary product from a technical point of view, but which no customer/end user would want to use, and p[otentially investing a lot more effort than appropriate.

    Of course, it greatly adds to the quality of design if architects are good programmers, and if engineers have direct contact to customers and are given a chance to train in understanding customer and end-user requirements – as a programmer, really putting yourself in an end-user’s shoes is harder than you may think.

    What do you have against UML? It’s a perfectly valid documentation tool, mostly for allready written code, even if when used to it you start by creating your code skeleton in UML – the blueprint. Of course, there are potentially many wrong uses of UML, but IMO it is a wonderful tool for documentation – of course, a bad designer will do a bad design with or without UML, but a good designer will do a good design easier using UML. Besides, no respectable engineering discipline works without blueprints, therefore I suppose UML is rather a part of the solution than a part of the problem.

    As for prototyping, it is IMO the worst approach. It should be used only when a completely new problem has to be solved, one for which there is nothing related ever done before, for which even requirements need to be defined by prototyping. It is the most expensive solution to drive a SW project. (We just finished such a project, where prototying was a customer requirement. The product is incomplete, it took at least twice as much time to build, and it is our estimation that by using our traditional approach we could have delivered the same product, with more features, with a three times lower budget.)

  20. Gustavo Duarte on June 19th, 2008 10:28 pm

    @Me, myself and I:

    Thanks for the well written comment.

    You know, these discussions are hard because the terms are so ill-defined. It’s not as if we’re looking at a concise, well-defined description of a process and then analyzing that. With that in mind, here’s my answer to some particular points. So here we go:

    Yes, you do need some top down analysis to be sure.

    Regarding vision, it can both help and hurt. It often means people stick to an idea or plan, and start ignoring reality and failing to adapt. This happens in many spheres of life, far beyond just software. It’s like CEOs whose “visions” get companies stuck in an ill-fated trail, ignoring markets, ignoring new evidence, pursuing grand plans full of risk rather improving incrementally on the fundamentals. Then blowing the company up.

    In software, what you get is a vision that more often than not:

    1. Comes from people who are technically incompetent, ignorant, and haven’t done software for years

    2. Is set in stone, due to organizational realities. Leading to:

    3. One hell of a mess where programmers need to work around brain-dead architectures.

    Does that mean that architecture is bad? No, of course not. You can do it right, but imho doing it right means realizing that architecture is a _proposed_ way to handle things, a sort of “hmm, let’s start going over here” rather than a detailed map to crapdom.

    However, here the lack of any rigor in definitions bites us. It seems we’re saying something similar, since you say that it “may be proven unrealistic by engineers”. I suspect we’re more in agreement than not regarding this pont.

    I completely agree with the cost thing.

    I think architects who are not good programmers should be shot. The ones who don’t program at all should be impaled. This idea of the “non-programming architect” is one of the most stupid things going on in enterprisey development imho.

    I totally agree on the user’s shoes thing. That’s one of the big failures of software development, the lack of attention to this. I think _every_ developer on a team should spend time _living the user’s day_ at some point, as early as possible, truly understanding – and hopefully doing, briefly – the job that will be impacted by the software.

    Regarding UML, I don’t have anything against UML itself, it’s a tool as you point out. Can be used well or poorly. Trouble is the latter is far more frequent. I’ve done much UML over the years, used several tools: Poseidon, Enterprise Architect, Rational stuff, Visio, you name it. I can do diagrams pretty well and pretty fast. So I’d say I’m an “experienced” UML user.

    I’d say this:

    1. UML diagrams often communicate less effectively than a simple block diagram or English text. They’re also expensive to produce in many organizations.

    2. Since people don’t really read the books and the specs, UML is pretty loose. I’ve seen so many non-sensical package, component, and class diagrams, gosh, it’s crazy. Is that UML’s “fault”? Well, yes and no, but we must evaluate UML in terms of its real-world usage, not some ideal UML-conforming paradise.

    3. Designing software classes graphically is silly. Whiteboarding with UML to get ideas going? Sure. Sitting down and “designing” software in UML? I think that’s a very bad way to go, often used by the non-coding architect types.

    4. The blueprint of the software engineering discipline is code. For software, code _is_ design. This is a fundamental point for me, something I believe deeply in. Diagrams are aids to _understanding_ the blueprint. It’s like looking at diagrams of an aircraft design that give you a high-level overview of what’s going on, to help you make out the forest Here UML can indeed help.

    5. Again, your usage of UML sounds very sane to me. Using it as a documentation tool for already written code: perfect. Using it as a tentative skeleton: perfect, though for me it’s more efficient to just use code for that. But the “UML as blueprint” crowd belabors under the illusion they can nail down every aspect of a “design”, every class and field and method, and then hand it down to programmers. _That_ is insanity imho.

    Nowadays I use UML in three primary ways: light whiteboarding, as understanding aids in architecture documents (my role is often of “architect”), and as documentation for a built system. But I must say in general I think UML has been more of problem than solution for software.

    Regarding the prototyping, I fully agree that decent requirements and good high-level direction at the start can reduce cost.

    This is an interesting discussion, I love to talk about this stuff. Thanks again for the well-made points, I wish we had more time to define things properly and speak more precisely about all this. I hope to start posting more often, then I’ll elaborate on some of these points.

  21. Webyantra  » How software bugs can lead to national catastrophic disasters? on August 24th, 2008 6:07 am

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  22. Richard Feynman’s Modest Science : Gustavo Duarte on August 25th, 2008 4:40 am

    […] time off and hit physics again. If you want to read more of his stuff, Feynman wrote an insightful essay on engineering and there’s the classic Cargo Cult Science, both online. Amazon has the lectures along with […]

  23. Iterative & bursty v.s Upfront & serialzed « Computing Life on September 15th, 2008 5:36 am

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  24. william on September 27th, 2008 3:27 am

    I wish Doctor Feynman were still alive so that he could analyze the alleged necessity of the “Bernanke/Paulson bailout!”

    I know economics is not his field in a sense but even as I write that I realize that his way of thinking is open to anything which needs to be understood.

    Isn’t it curious that Bernanke comes rushing to Bush to warn him in an authoritative manner that their is a crisis which demands immediate action or else terrible things will happen. Bush so readily agrees to the Bernanke proposal without any attempt to question or understand.

    I have always been an admirer of Richard Feynman as a hero of science. There have been many others throughout the history of science, men and women of independent mind. Galileo and Giordano Bruno come to mind, Darwin and Mendel, Maxwell and Tesla. In the realm of economics, which is not my field either, I will name Carl Menger, Eugen von Bohm-Bewerk, Friedrich von Hayek and Ludwig von Mises.

    I want you to know that when I was stationed in the military in Korea in 1970 I encountered two officers who were both Ph.D.’s in Economics from Harvard who were finishing their tours of duty in Korea and about to return to the states. I asked them if they had heard of Samuelson, Keynes, Galbraith and Heilbroner, who were the writers of the textbooks or exponents of the theories being taught in Economics throughout the American universitiesa and colleges. Of course they knew them all. But neither of them were at all familiar with Menger, Bohm-Bawerk, Hayek or Mises!

    I only knew of them because I had read Ayn Rand’s The Objectivist Newsletter after Atlas Shrugged, her insightful novel. In the Objectivist Newsletter Rand had book reviews including reviews of a few of the works of Ludwig von Mises, the great Austrian economist, who was a student of the founder of the Austrian school of economics, Carl Menger. Menger was an academician who lived in the Nineteenth Century and set out to discover the Laws of the Marketplace, how the market operated when the government did not intervene, rather made sure no one violated contracts or used force or fraud.

    The Austrian school of the free market is one of the best kept secrets in academia by those who have an agenda! There are those who do not want it widely taught or understood. It does provide insight into the happenings throughout our history of such events as the Great Depression. We are led to believe that the Great Depression was caused by a failure of the free market and that Roosevelt rescued the country by his brilliant interventions.

    The Federal Reserve System was created in 1913 for the purpose of maintaining the stability of the dollar. Notice that it now takes one dollar to have the purchasing power of just four cents of the 1913 dollar!\ Is it possible that interventions by the Federal Reserve System set the stage for the depression by causing the easy credit throughout the Twenties and that Roosevelts interventions prolonged the Great Depression? Is it possible that Bernanke’s Federal Reserve is responsible for the credit collapse now and that his solution would gloss over the Federal Reserve’s responsibility in causing the crisis in the first place and perpetuate the problem and exacerbate it in the process?

    There is a website entitled Ludwig von Mises Institute where you might find discussion of these issues in a most lucid and rational fashion as well as books which provide the understanding of the issues involved. http://www.mises.org

    Murray Rothbard has written The Case Against the Fed which provides insight into the origins of the Federal Reserve System and its operations and role in history.

    Ron Paul is an advocate of the Austrian theory of economics and has argued for all his years as a Congressman for abolition of the Federal Reserve System and introduction of sound money as a competing currency to the Federal Reserve Notes wer are obliged to use by the legal tender laws.

    http://www.ronpaul.com\ http://www.campaignforliberty.com

    Enjoy! Join us in restoring our Constitutional Republic. I don’t agree with Ron Paul on everything. For example I am pro choice and unfortunately his religious views interfere with his thinking on that issue.

    http://www.fff.org\ http://www.fee.org

    Here is a link to the Atlas Society which promotes the ideas of Ayn Rand. I searched and found references to Richard Feynman there:

    http://tinyurl.com/3k8egc

    Enjoy and discover!

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  26. Ahmed on November 4th, 2008 3:25 pm

    The key point here is an attitude of ‘highest quality’\ Process is testing are useless without it.

    I once worked for a major telecom vendor which had all kinds of code reviews, unit testing, system testing… but they started treating engineers like replaceable parts. As if any engineer can work on a system they haven’t even worked on and make changes. Oh how it all collapsed from there.

    There is actually one big item that actually come from academia itself which lend to this behavior.

    ​1. design vs implementation. Now I know what this means in the academic sense. I can ‘design’ an algorithm in pseudo-code or flowcharts… and then implement it in a specific language like C. However, far too often, this seems to get misinterpreted as the implementation is like construction. A dummy’s job. When in fact, the compiler is the implementor and every thing is design. One is just abstract design, the other is low-level design. I always say, if you can write a design so specific that any idiot can implement it, you have something just as complicated as code.

    The other is people not valuing experience in a specific domain / area of code. This is largely a consequence of a hacker mentality. Some pieces of software are literally millions of lines long. They have the complexity that probably outweighs the human body. Yet, we send doctors to school for years upon years to specialize in only one area of the human body. For engineers, many places throw them in and they’re doing ‘surgery’ within a week. Ponder that for a second. Sometimes you have to pay someone just to know the code/domain even if there is not that many changes. So that when changes need to be made, they are ready and know the system inside out.

    I’ll use the analogy of the bomb with wires. Which wire do you cut to diffuse the bomb? Leave it up to a rookie and maybe they will figure it out, maybe they won’t. All the while, the clock is ticking and maybe the bomb will actually explode! Or you can pay an expert who knows about that bomb so that when a bomb shows up, they know exactly which wire to cut and you know there will be no issue.

    Payment is like this:\ 1 dollar for me to cut the wire\ 10000 dollars for me to know which wire to cut.

    Often times business only value the time you’re cutting wires.

  27. Thinking Like an Engineer « Pari’s TechBlog on December 17th, 2008 1:34 am

    […] Richard Feynman, the Challenger Disaster, and Software Engineering […]

  28. ref on December 31st, 2008 8:50 am

    It’s interesting how many different areas of thought Richard Feynman has influenced

  29. Abhijith on January 28th, 2009 8:46 am

    Great post! I came across you blog today and I am not able to move away from the page :) . Looking forward to read all your articles.

  30. Gustavo Duarte on January 28th, 2009 9:02 am

    Abhijith: thanks :)

  31. Luiz Carlos de Almeida on March 23rd, 2009 11:09 am

    Luiz Carlos de Almeida – luiz1611@hotmail.com\ ANÁLISE DOS DIAGRAMAS DE FEYNMAN

    Diagramas de Feynman (Baseia os cálculos na Teoria de Campos):\ “Os Diagramas de Feynman são um método para se fazer cálculos na Teoria quântica de campos, criados pelo físico norte-americano Richard Feynman. Também são conhecidos por Diagramas de Stückelberg. As linhas representam partículas interagindo e termos matemáticos correspondem a cada linha e vértice. A probabilidade de uma determinada interação ocorrer é calculada desenhando-se os diagramas correspondentes à interação, e através deles se chega às expressões matemáticas corretas. Os diagramas fornecem uma interpretação visual do fenômeno.”

    Críticas aos Diagramas de Feynmam (Teoria de Campos da Física Quântica):

    A matemática consegue provar muitas coisas que não são realidade, basta para isto, serem criadas constantes, ocorrerem deduções, renormalizações, sendo que, não basta ser real, para que alguma fórmula o torne explicável. É o que acontece com os Diagramas de Feynman, consegue-se prová-los matematicamente, somente não se consegue provar o que eles tentam representar.\ Não é de se estranhar que houve uma explosão de fórmulas para explicar formalismos. Os Diagramas de Feynmam, não são representativos da realidade. Analisando todos os Diagramas de Feynmam, todos se mostram equivocados. Será demonstrado, os enganos do diagrama (interações elétron/posítron). Outros diagramas estão sendo contestados pelas demais explicações, baseadas no novo modelo nuclear.

    Diagrama de Feynman para a interação elétron/posítron:

    A explicação da Teoria quântica de campos:\ “Neste diagrama de Feynman, um Elétron e um Posítron anulam-se, produzindo um fóton virtual, que se transforma num par quark-antiquark. Depois, um deles radia um Gluón. (O tempo decorre da esquerda para a direita.)”

    Críticas a este Diagrama de Feynman e à sua explicação:

    Como os princípios da Teoria da Eletrodinâmica estão equivocados, os diagramas correspondentes às interações que elas representam, para se chegar a expressões matemáticas corretas, só podem chegar, também, a conclusões equivocadas da realidade destas interações das partículas, pois, é de se observar que a explicação para o Diagrama de Feynman não condiz com o que ocorre na realidade.

    A Nova Explicação:\ O termo “Aniquilação” não é apropriado para este evento, pois as energias elementares, tanto positiva quanto negativa, não se aniquilam e também não se perdem, apenas se transformam.\ Como o elétron e o posítron são partículas duais (cada um com 02 energias magnéticas), ocorre uma interação em que o elétron perde 01 energia magnética com seu campo de massa (neutrino) e o posítron perde 01 energia magnética com seu campo de massa (antineutrino), cada um com uma energia cinética de 0,255 MeV (com um total de 0,511MeV de energia Cinética).\ Restando 01 Energia magnética negativa do elétron e 01 energia magnética positiva do positron (sem seus campos de massa), que forma a radiação eletromagnética (y) de 0,511 MeV de Energia cinética.\ Quando esta radiação eletromagnética choca-se com o núcleo, atinge metade do elétron e metade do posítron que estão na formação dos Nêutrons e Prótons do Núcleo atômico, ocorrendo o processo de Reflexão das Radiações eletromagnéticas de alta velocidade.\ Assim, não ocorre a Anulação (Aniquilação) do elétron e do posítron, não ocorre a formação de um fóton virtual, não ocorre a sua transformação em um quark e em um anti-quark, e depois um deles não irradia um Gluón como prediz a explicação do Diagrama de Feynman.

    Esquematização do evento das interações elétron/posítron, pelo Novo Modelo Nuclear:

    A TEORIA DA ELETRODINÂMICA QUÂNTICA (E.Q)\ A teoria:\ “As forças eletromagnéticas entre dois elétrons surgem pela emissão de um fóton por um dos elétrons e a sua absorção por outro elétron.\ Como um elétron emite um fóton, isso significa a violação do princípio da conservação das energias ou da conservação dos momentos; o mesmo vale para a absorção de um fóton. Todavia, pela a mecânica quântica, a conservação de energia não é necessariamente válida em pequenos intervalos de tempo. O sistema pode “pedir emprestada” alguma energia para o elétron emitir o fóton; a energia é devolvida quando o outro elétron absorve o fóton. Este processo é chamado de troca virtual de um fóton entre elétrons.\ Neste processo, chamado de espalhamento de elétrons, ocorre mudanças na trajetória dos elétrons pela simples “troca de um fóton”. Esta é uma das idéias básicas da eletrodinâmica quântica.\ Este fenômeno é representado pelo diagrama de Feynman e explicado por expressões de matemática corretas, baseadas neste diagrama”.

    Críticas à Teoria da Eletrodinâmica Quântica (E.Q.)\ As radiações eletromagnéticas não surgem por acaso, pois, surgem da união entre um posítron e um elétron e este processo acontece em quase sua totalidade em núcleos de átomos, e também, as radiações eletromagnéticas não são absorvidas, pois a energia elementar negativa unida à energia elementar positiva, durante os processos de propagação e de reflexão não se altera, somente altera a sua energia cinética (sua velocidade).\ O elétron da eletrosfera não emite, por si só, qualquer energia eletromagnética, ele apenas interage nos processos de propagação destas radiações, então, quando a teoria eletrodinâmica diz que, na física quântica o princípio da conservação da energia ou da conservação dos momentos, não é necessariamente válida, em pequenos intervalos de tempo, e que o sistema pode pedir emprestado alguma energia para o elétron emitir o fóton e que a energia é devolvida, quando outro elétron absorve o fóton, em um processo de troca virtual de um fóton entre elétrons, fica claro, que esta idéia básica da Física Quântica, além de não ser a realidade dos fatos, como explanado neste trabalho sobre como acontece a propagação e a reflexão das radiações eletromagnéticas, ainda colocou como sua base científica, uma interpretação equivocada da realidade dos acontecimentos a nível atômico, elegendo os elétrons como emissores das radiações eletromagnéticas. O diagrama de Feynmam, para este evento, também está errado.

    TEORIA DA CRONODINÂMICA QUÂNTICA (C.D.Q)\ A Teoria:\ “A Teoria da Cronodinâmica Quântica é parecida com a Teoria da Eletrodinâmica Quântica em alguns aspectos (as interações se dão através da troca virtual de quanta). No entanto, existe uma diferença fundamental: o fóton, mediador da interacão eletromagnética, é eletricamente neutro; já o glúon, mediador da força nuclear forte (força colorida), é colorido. Por isso, eles interagem entre si, o que dá origem, nas equações da C.D.Q, a termos que não têm análogos na Eletrodinâmica Quântica. A Cronodinâmica Quântica comporta-se, então, de forma diferente de qualquer força conhecida.\ A Cronodinâmica Quântica solucionou, então, o mistério do caráter da força entre os quarks, de uma forma que apresenta grande simplicidade, o que é fundamental para o sucesso de uma teoria.\ Durante muito tempo pensou-se que entre as partículas da lista dos férmions fundamentais estariam o próton e o nêutron. Mas isso se revelou falso: os prótons e os nêutrons são formados por partículas mais básicas – os quarks.\ Os prótons são formados por dois quarks up e um quark down, enquanto os nêutrons são formados por um quark up e dois quarks down. Os quarks up têm carga elétrica +2/3 enquanto os down têm carga -1/3.\ Assim como a força entre os elétrons se dá através da troca virtual de fótons, os quarks estão ligados por uma força que surge da troca de glúons. Os glúons são indiferentes ao sabor, mais muito sensíveis à cor. Os glúons interagem com a cor assim como os fótons interagem com o sabor. Note que existem vários tipos de glúons, um para cada situação de cor.” 1-

    1-Explicação Original para este Diagrama de Feynman:\ Neste Diagrama, um quark vermelho se torna azul com a emissão virtual de um glúon vermelho-azul, que é absorvido por um quark azul que se torna vermelho!!!.

    2-

    2-Explicação Original para este Diagrama de Feynman:\ Neste Diagrma, um quark azul se torna verde com a emissão virtual de um glúon azul-verde. Este glúon é absorvido por um quark verde, que se torna azul!!!.

    Críticas à Teoria da Cromodinâmica Quântica (C.D.Q)

    Como na explanação anterior, esta troca virtual de fótons, não acontece na realidade.\ Quanto ao Gluón, não exite emissão virtual de gluón, pois, a força de união (força forte), que ocorre entre os pósitrons e elétrons nos Nêutrons e Prótons não dependem de mediador, já que é uma força de natureza magnética elementar, entre as partículas magnéticas negativas e as partículas magnéticas positivas.\ Na realidade não existem Quarks. Existem elétrons e posítrons em união na formação dos Prótons e Neutrons. Esta união não ocorreu sem que houvesse muita força, para que não ocorresse o processo de “aniquilação” entre a matéria e antimatéria, e esta força foi a força gravitacional no interior de estrelas, onde estes prótons foram formados e a partir destes prótons, os nêutrons e assim todos elementos químicos, com um número bastante elevado de massa nuclear.\ Como não há realidade na emissão virtual de gluóns, também os quarks foram uma criação, para explicar o que, ainda, não se tinha uma explicação. A teroria da cronodinâmcia é uma teoria baseada em idéias sem realidade, quando busca relação entre +2/3 de carga e –1/3 de carga e em trocas virtuais de gluóns.

  32. Jim Patrick on September 4th, 2009 11:48 am

    I am having a difficult time understanding why the following is used to characterize top-down:

    The Space Shuttle Main Engine was handled in a different manner, top down, we might say. The engine was designed and put together all at once with relatively little detailed preliminary study of the material and components.

    Why didn’t the designers go into more in depth study of the parts during top-down design? Top-down design does not preclude this. In a ‘pure’ top-down design the various parts would have been fabricated to meet specifications. In a mixed top-down/bottom-up design the analysis from the top-down would be used to select appropriate parts that met specifications. So it appears to me that they both are important. Good article nevertheless.

  33. alan borcic on October 9th, 2009 3:32 pm

    that was so cool what u did

  34. Kevlin Henney on November 1st, 2009 2:31 am

    One of the most important observations here is that your conclusions and observations are known, but commonly ignored. It is often said that software development is an immature discipline. However, what is normally meant by this is that software development is a youthful discipline lacking experience and knowledge. On the contrary, its pervasiveness and growth into all walks of life over many decades have ensured that there is a great deal of experience and accumulated wisdom. The immaturity is not in what we know, but in our failure to pay attention to and apply what we know. The immaturity is like that of an adolescent, not that of an infant.

  35. anyone on November 1st, 2009 3:32 am

    forward chaining (bottom-up) VS backward chaining (top-down)?

  36. Jan on November 1st, 2009 4:21 am

    Richard Feynman is my all time favorite scientist. His work on the Challenger investigation is documented in his book “What Do You Care What Other People Think”, a highly recommended read. Also check out “The Pleasure of finding things out” and the BBC documentary “No Ordinary Genius”.

  37. Jan on November 1st, 2009 4:26 am

    Oh and Thanks for this excellent post!

  38. gsempe on November 1st, 2009 6:11 am

    Great post. Fantastic post. A must read

  39. Erin Ptacek on November 1st, 2009 8:05 am

    This is a truly excellent article. In my mind, I’ve often made the same comparisons using many years of experience in making clothing and costumes. To get a perfect garment, it’s necessary to make a muslin first, which is the top down part of the design. Then you take the muslin apart and use that as your base pattern for the finished garment — that’s the bottom up design. Obviously muslin is cheap, and rocket engine parts are not.

    My experience just doesn’t have the same cred as Feynman — who is a life long hero of mine, and you’ve just reminded me of one reason: genius is something of recognizing fundamental patterns that can be applied to multiple disciplines (though, IMO, these disciplines are not as disparate as most people seem to think).

  40. realist on November 1st, 2009 11:02 am

    Many coders reflexively advocate bottom-up design because they are aware, either overtly or subliminally, that they are very low down on the pecking order within corporatocracies and bureaucracies. It’s a sad-but-true fact of life that those with real power within these organisations tend to be those from higher social classes than the bulk of programmers, with more family connections, and with a broader liberal education encompassing business, sales, marketing, law and politics. They are thus more equipped to engineer the real aspects of organisation success, which revolve around the development of power.

    I’ve worked in small organisations, like start ups, where coders have been, for a while, the driving force. An exclusively bottom-up approach works for a while but inevitably a point comes where the episteme encompassed by the organic code fails to scale beyond the narrow problem domain. That’s usually when the product managers step in (or are appointed as a new layer) to foist a top-down refactor/re-engineer approach. And everything gets paralysed for a couple of cycles. Apple’s been through this process with almost every wave of new products breakouts. Anyway, we need a smarter way to combine the strengths of both top-down and bottom-up, without just cycling through the weaknesses of both.

  41. Daily Links #118 | CloudKnow on November 1st, 2009 12:08 pm

    […] Feynman, Challenger Disaster, and Software Engineering […]

  42. links for 2009-11-01 at DeStructUred Blog on November 1st, 2009 6:38 pm

    […] Richard Feynman, the Challenger Disaster, and Software Engineering : Gustavo Duarte (tags: engineering software programming design history physics article feynman agile) […]

  43. Phil Brass on November 2nd, 2009 9:53 am

    The adversarial IV&V process for systems design verification was actually in use at NASA in the 60s during the Apollo program. Furthermore, they apparently often hired the second-lowest bidder to do the IV&V testing, so there really was an adversarial relationship. And they supposedly didn’t ship until there no IV&V findings. I think this is a very good example of the proper use of security economics. But crediting Feynman for discovering TDD in 1986 is a bit of a stretch IMHO. My source for this is the second edition of Ross Anderson’s book, Security Engineering.

  44. Richard Feynman, 挑战者号, 软件工程 | 酷壳 – CoolShell.cn on November 4th, 2009 1:19 am

    […] 源文:链接  (本文主要根据挑战者号的问题,以及Richard Feynman那对NASA严厉的批评报告,批评了不适当的“自顶向下”的设计方法,并总结了一下软件工程和其它工程的相通的一些观点。翻译水平有限,欢迎指正) […]

  45. Saulo Silva on November 4th, 2009 6:00 pm

    Great post, Gustavo. I’m glad I found your blog.

    Cheers

  46. Jon Court on November 18th, 2009 6:59 pm

    Hi,

    Got this blog from a comment on a blog on my site – very glad it was pointed out.

    Awesome content – well written too.

    Thankyou.\ Jon

  47. Manish on January 22nd, 2010 1:16 pm

    Let me start by saying I have recently started reading your articles which I stumbled upon while searching for something on memory segmentation. I found that article, and others, to be really interesting not only because they had the needed technical insights, but also because you try to weave them into a story like writing. Count me in as a newer addition to your readership :) I am probably too late to comment on this artcile, but I will still try. I find that the responses are really interesting. I think I do understand your point about bottom-up approach and Austin’s comments about top-down approach. I can almost ‘see’ the two sides as I felt the same confusion when I went back to school to do my MS in Computer Science after more than 13 years in industry – there was total lack of those processes. I am sure you will say that academia and industry are very different, but let me tell you that working with such an approach I really enjoyed doing stuff, and could also see how other partners in project thought about things. Sure some of those could be called wild ideas, and I would not have tried them in the industry (am I sounding like a manager here?), but I was pleasantly surprised with the results many times. Even though the ideas were not best or the ones we should have picked, but they showed me a completely different path that could not have ‘seen’ it through just analysis.

    I personally like that kind of approach as I feel that is more innovative (think out-of-box). However, I do agree with Austin that current industry it is most of the time Top-down for design and analysis for all software engineering models including Agile development (although it sounds different). The (most obvious) reason I think lies in the effort to try to eliminate the uncertainty. It is a reality that all business work with deadlines and targets, and a complete bottom up approach, in my opinion, does not fit there completely. Lets face it, most business are not about innovation (except for trying new spins around the concept of management) but to sell things to customers. You would say, aren’t the two linked -innovation leading to more selling? They are not many times. They can actually work against each other in many situations, and innovation takes a back seat against any arguments about selling.

    I agree with the basic idea behind this article that the analysis and design are very important not just to finish things with in deadline (do the projects still meet the deadlines anyway?), but to provide a direction to the project, and to have an idea about the timelines. It should not be over-used in lieu of experimentation (as that will stifle the innovation).

    That is the reason I think that small companies/startups are innovative with minimal procedural bottlenecks, but as the size grows, the procedural steps (necessarily or not) creep in.

    I see this happen all the time at my workplace (not that we are a big corporation, but we would like to be one:)), when the ‘project’ becomes the focus instead of the end product (although the managers will never accept that).

  48. Challenger Disaster & Software Engineering « DailyDigital on February 9th, 2010 12:51 pm

    […] Link […]

  49. Sarah on April 27th, 2010 7:38 pm

    Yes, this tradgic disaster was very heart breaking for many, and devastating to everyone. I bet all the people who had designed and made the shuttle Cahllenger had beat themselves up inside, blaming theirselves for the terrifyingly horrible accident.

  50. Anablog » Blog Archive » Nasa space exploration slideshow on May 27th, 2010 10:42 am

    […] trick where you looped the yo-yo around three times—it was called the John Glenn. Here is a good blog regarding the first Shuttle disaster. Here is more on the great physicist Richard Feynman’s observations on the crash, and why the […]

  51. http://duartes.org/gustavo/blog/post/richard-feynman-challenger-disaster-software-engineering » andrewsavikas.com on September 2nd, 2010 5:53 pm

    […] http://duartes.org/gustavo/blog/post/richard-feynman-challenger-disaster-software-engineering […]

  52. Lastactionseo on September 27th, 2010 3:00 am

    Lastactionseo…

    Vielen Dank für das freischalten des Kommentars….

  53. Jane Qiu on September 29th, 2010 2:48 am

    Great articles!\ I’m looking for some info about linux process management, and jumps to your blog. Your articles are the best I have ever seen, they are so intreasting and smart. Thanks for sharing them with us:)

  54. Lalitkumar Bhamare on January 26th, 2011 12:51 pm

    This is a wonderful blog I have come across while trying to analyse The Appendix of Challenger Report by Mr.Richards Feynman.

    Appreciate the brilliancy of the way it has been explained in terms of software testing. Thanks.

    Regards,\ Lalit

  55. L’approche ascendante versus ascendate « Projet dans un environnement graphique on March 1st, 2011 8:55 am

    […] où on part en permanence de ce qui est bien connu et solidement maîtrisé. (Wikipedia).  Voici un article qui applique les conclusion de Feynman à l’ingénierie logicielle. Voici le rapport de Feynman en texte […]

  56. Ler e aprender « Bit is Myth on March 25th, 2011 6:00 pm

    […] as duas dicas que vieram e se encaixaram como luva, estão na lousa do Richard Feynman que estão neste artigo. Coloco-as aqui por enquanto, mas estou pensando em mandar […]

  57. Brandon Frost on May 4th, 2011 6:41 am

    […] as duas dicas que vieram e se encaixaram como luva, estão na lousa do Richard Feynman que estão neste artigo. Coloco-as aqui por enquanto, mas estou pensando em mandar […]\ Link […]\ Sarah on April 27th, 2010 7:38 pm\ Yes, this tradgic disaster was very heart breaking for many, and devastating to everyone. I bet all the people who had designed and made the shuttle Cahllenger had beat themselves up inside, blaming theirselves for the terrifyingly horrible accident.\ Anablog » Blog Archive » Nasa space exploration slideshow on May 27th, 2010 10:42 am\ […] trick where you looped the yo-yo around three times—it was called the John Glenn. Here is a good blog regarding the first Shuttle disaster. Here is more on the great physicist Richard Feynman’s observations on the crash, and why the […]\

    http://duartes.org/gustavo/blog/post/richard-feynman-challenger-disaster-software-engineering » andrewsavikas.com on September 2nd, 2010 5:53 pm\ […] http://duartes.org/gustavo/blog/post/richard-feynman-challenger-disaster-software-engineering […]\ Lastactionseo on September 27th, 2010 3:00 am\ Lastactionseo…\ Vielen Dank für das freischalten des Kommentars….\ Jane Qiu on September 29th, 2010 2:48 am\ Great articles!\ I’m looking for some info about linux process management, and jumps to your blog. Your articles are the best I have ever seen, they are so intreasting and smart. Thanks for sharing them with us:)\ Lalitkumar Bhamare on January 26th, 2011 12:51 pm\ This is a wonderful blog I have come across while trying to analyse The Appendix of Challenger Report by Mr.Richards Feynman.\ Appreciate the brilliancy of the way it has been explained in terms of software testing. Thanks.\ Regards,\ Lalit\ L’approche ascendante versus ascendate « Projet dans un environnement graphique on March 1st, 2011 8:55 am\ […] où on part en permanence de ce qui est bien connu et solidement maîtrisé. (Wikipedia). Voici un article qui applique les conclusion de Feynman à l’ingénierie logicielle. Voici le rapport de Feynman en texte […]\ Ler e aprender « Bit is Myth on March 25th, 2011 6:00 pm\ […] as duas dicas que vieram e se encaixaram como luva, estão na lousa do Richard Feynman que estão neste artigo. Coloco-as aqui por enquanto, mas estou pensando em mandar […]

  58. Lars Falk on May 4th, 2011 7:25 am

    Do you know who owns the copyright of the picture of Feynman’s blackboard?

    Best wishes,

    Lars

  59. Elegant Code » Book Review: The Clean Coder on September 6th, 2011 2:58 am

    […] disaster. This has been applied to the field of software engineering many times already (check out this blog post from Gustavo Duarte which is one of my all-time favorites), but still, it definitely never wears […]

  60. Shannon on December 11th, 2012 6:02 pm

    To revive this old thread, there is one thing I see in Feynman’s writings about the Challenger investigation from his book “What Do You Care what Other People Think?” that I believe touches on something important to testing, but that I seldom see cited in software testing articles that refer to the Challenger incident, or Feynman’s report.

    If I have it right, Feynman suspected that the O ring failure occurred where the technicians were testing the rings! That is, the leak occurred around the test port. This isn’t to say he faulted testing, and there are perhaps some issues that don’t translate neatly from the domain of physical manufacture to digital development. But I do think it is a cautionary tale to remember to account for test code, performance probes, etc that pass from the development into production. I could see how remnants of these things could potentially work against product quality.

  61. Gustavo Duarte on December 13th, 2012 5:32 am

    @Shannon: that’s really interesting. I haven’t read that book yet, I’ll add it to the queue here. Thanks for your comment.

  62. Richard Feynman, 挑战者号, 软件工程 | multiprocess on November 10th, 2013 1:29 am

    […] 源文:链接  (本文主要根据挑战者号的问题,以及Richard Feynman那对NASA严厉的批评报告,批评了不适当的“自顶向下”的设计方法,并总结了一下软件工程和其它工程的相通的一些观点。翻译水平有限,欢迎指正) […]

  63. Corey Bayless on November 16th, 2013 8:47 pm

    This is why I freaking love the Internet. I am currently watching “The Challenger Disaster” right now. The disaster happened when I was a junior in high school, in drafting class. Most people in the class were crying and our teacher said, “I was in class in high school when Kennedy was assassinated. I never thought I’d have the same experience in a classroom 23 years later…”

    What a wonderful article to read. I know I’ll be reading about Feynman for the rest of the night. Thank you for the great read…

  64. Randy on December 15th, 2013 4:14 pm

    As a licensed engineer in control systems and now a project manager; I have put software to work to solve many control problems. I agree with Dr. Feynman if you do not understand the problem you cannot solve it. To that end one must first understand the problem, define the scope or goal… the top, to achieve the goal you must bring to the detail knowledge to bear to build the solution… the bottom, without one you cannot have the other. When one out weights the other the solution achieves neither.

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