You’ve played Flexbox Froggy before, right? Or maybe Grid Garden? They’re both absolute musts for learning the basics of modern CSS layout using Flexbox and CSS Grid. Thomas Park made those and he’s back with another game: Anchoreum.
Anchoreum: A New Game for Learning Anchor Positioning originally…
Let’s spend some time looking at disclosures, the Dialog API, the Popover API, and more. We’ll look at the right time to use each one depending on your needs. Modal or non-modal? JavaScript or pure HTML/CSS? Not sure? Don’t worry, we’ll go into all that.
The Different (and Modern)…
The State of CSS 2024 survey wrapped up and the results are interesting, as always. Even though each section is worth analyzing, we are usually most hyped about the section on the most used CSS features. And if you …
Popping Comments With CSS Anchor Positioning and…
When Nikola Tesla predicted we’d have handheld phones that could display videos, photographs, and more, his musings seemed like a distant dream. Nearly 100 years later, smartphones are like an extra appendage for many of us.
Digital fabrication engineers are now working toward expanding the display capabilities of other everyday objects. One avenue they’re exploring is reprogrammable surfaces — or items whose appearances we can digitally alter — to help users present important information, such as health statistics, as well as new designs on things like a wall, mug, or shoe.
Researchers from MIT’s Computer Science and Artificial Intelligence Laboratory (CSAIL), the University of California at Berkeley, and Aarhus University have taken an intriguing step forward by fabricating “PortaChrome,” a portable light system and design tool that can change the color and textures of various objects. Equipped with ultraviolet (UV) and red, green, and blue (RGB) LEDs, the device can be attached to everyday objects like shirts and headphones. Once a user creates a design and sends it to a PortaChrome machine via Bluetooth, the surface can be programmed into multicolor displays of health data, entertainment, and fashion designs.
PortaChrome: A portable light system that can digitize everyday objects
Video: MIT CSAIL
To make an item reprogrammable, the object must be coated with photochromic dye, an invisible ink that can be turned into different colors with light patterns. Once it’s coated, individuals can create and relay patterns to the item via the team’s graphic design software, or use the team’s API to interact with the device directly and embed data-driven designs. When attached to a surface, PortaChrome’s UV lights saturate the dye while the RGB LEDs desaturate it, activating the colors and ensuring each pixel is toned to match the intended design.
Zhu and her colleagues’ integrated light system changes objects’ colors in less than four minutes on average, which is eight times faster than their prior work, “Photo-Chromeleon.” This speed boost comes from switching to a light source that makes contact with the object to transmit UV and RGB rays. Photo-Chromeleon used a projector to help activate the color-changing properties of photochromic dye, where the light on the object’s surface is at a reduced intensity.
“PortaChrome provides a more convenient way to reprogram your surroundings,” says Yunyi Zhu ’20, MEng ’21, an MIT PhD student in electrical engineering and computer science, affiliate of CSAIL, and lead author on a paper about the work. “Compared with our projector-based system from before, PortaChrome is a more portable light source that can be placed directly on top of the photochromic surface. This allows the color change to happen without user intervention and helps us avoid contaminating our environment with UV. As a result, users can wear their heart rate chart on their shirt after a workout, for instance.”
Giving everyday objects a makeover
In demos, PortaChrome displayed health data on different surfaces. A user hiked with PortaChrome sewed onto their backpack, putting it into direct contact with the back of their shirt, which was coated in photochromic dye. Altitude and heart rate sensors sent data to the lighting device, which was then converted into a chart through a reprogramming script developed by the researchers. This process created a health visualization on the back of the user’s shirt. In a similar showing, MIT researchers displayed a heart gradually coming together on the back of a tablet to show how a user was progressing toward a fitness goal.
PortaChrome also showed a flair for customizing wearables. For example, the researchers redesigned some white headphones with sideways blue lines and horizontal yellow and purple stripes. The photochromic dye was coated on the headphones and the team then attached the PortaChrome device to the inside of the headphone case. Finally, the researchers successfully reprogrammed their patterns onto the object, which resembled watercolor art. Researchers also recolored a wrist splint to match different clothes using this process.
Eventually, the work could be used to digitize consumers’ belongings. Imagine putting on a cloak that can change your entire shirt design, or using your car cover to give your vehicle a new look.
PortaChrome’s main ingredients
On the hardware end, PortaChrome is a combination of four main ingredients. Their portable device consists of a textile base as a sort of backbone, a textile layer with the UV lights soldered on and another with the RGB stuck on, and a silicone diffusion layer to top it off. Resembling a translucent honeycomb, the silicone layer covers the interlaced UV and RGB LEDs and directs them toward individual pixels to properly illuminate a design over a surface.
This device can be flexibly wrapped around objects with different shapes. For tables and other flat surfaces, you could place PortaChrome on top, like a placemat. For a curved item like a thermos, you could wrap the light source around like a coffee cup sleeve to ensure it reprograms the entire surface.
The portable, flexible light system is crafted with maker space-available tools (like laser cutters, for example), and the same method can be replicated with flexible PCB materials and other mass manufacturing systems.
While it can also quickly convert our surroundings into dynamic displays, Zhu and her colleagues believe it could benefit from further speed boosts. They’d like to use smaller LEDs, with the likely result being a surface that could be reprogrammed in seconds with a higher-resolution design, thanks to increased light intensity.
“The surfaces of our everyday things are encoded with colors and visual textures, delivering crucial information and shaping how we interact with them,” says Georgia Tech postdoc Tingyu Cheng, who was not involved with the research. “PortaChrome is taking a leap forward by providing reprogrammable surfaces with the integration of flexible light sources (UV and RGB LEDs) and photochromic pigments into everyday objects, pixelating the environment with dynamic color and patterns. The capabilities demonstrated by PortaChrome could revolutionize the way we interact with our surroundings, particularly in domains like personalized fashion and adaptive user interfaces. This technology enables real-time customization that seamlessly integrates into daily life, offering a glimpse into the future of ‘ubiquitous displays.’”
Zhu is joined by nine CSAIL affiliates on the paper: MIT PhD student and MIT Media Lab affiliate Cedric Honnet; former visiting undergraduate researchers Yixiao Kang, Angelina J. Zheng, and Grace Tang; MIT undergraduate student Luca Musk; University of Michigan Assistant Professor Junyi Zhu SM ’19, PhD ’24; recent postdoc and Aarhus University assistant professor Michael Wessely; and senior author Stefanie Mueller, the TIBCO Career Development Associate Professor in the MIT departments of Electrical Engineering and Computer Science and Mechanical Engineering and leader of the HCI Engineering Group at CSAIL.
This work was supported by the MIT-GIST Joint Research Program and was presented at the ACM Symposium on User Interface Software and Technology in October.
We can apply the concept of fluid typography to almost anything. This way we can have a layout that fluidly changes with the size of its parent container. Few users will ever see the transition, but they will all appreciate the results. Honestly, they will.
Fluid Everything…
As educators are challenged to balance student learning and well-being with planning authentic and relevant course materials, MIT pK-12 at Open Learning developed a framework that can help. The student-centered STEAM learning architecture, initially co-created for Itz’at STEAM Academy in Belize, now serves as a model for schools worldwide.
Three core pillars guide MIT pK-12’s vision for teaching and learning: social-emotional and cultural learning, transdisciplinary academics, and community engagement. Claudia Urrea, principal investigator for this project and senior associate director of MIT pK-12, says this innovative framework supports learners’ growth as engaged and self-directed students. Joining these efforts on the pK-12 team are Joe Diaz, program coordinator, and Emily Glass, senior learning innovation designer.
Now that Itz’at has completed its first academic year, the MIT pK-12 team reflects on how the STEAM learning architecture works in practice and how it could be adapted to other schools.
Q: Why would a new school need a STEAM learning architecture? How is this framework used?
Glass: In the case of Itz’at STEAM Academy, the school aims to prepare its students for careers and jobs of the future, recognizing that learners will be navigating an evolving global economy with significant technological changes. Since the local and global landscape will continue to evolve over time, in order to stay innovative, the STEAM learning architecture serves as a reference document for the school to reflect, iterate, and improve its program. Learners will need to think critically, solve large problems, embrace creativity, and utilize digital technologies and tools to their benefit.
Q: How do you begin developing a school from scratch?
Urrea: To build a school that reflected local values and aspired towards global goals, our team knew we needed a deep understanding of the strengths and needs of Belize’s larger education ecosystem and culture. We collaborated with Belize’s Ministry of Education, Culture, Science, and Technology, as well as the newly hired Itz’at staff.
Next, we conducted an extensive review of research, drawing from MIT pK-12’s own work and outside academic studies on competency-based education, constructionism, and other foundational pedagogies. We gathered best practices of innovative schools through interviews and global site visits.
MIT’s collective team experience included the creation of schools for the NuVuX network, constructionist pedagogical research and practice, and the development of STEAM-focused educational materials for both formal and informal learning environments.
Q: Why was co-creation important for this process?
Urrea: MIT pK-12 could not imagine doing this project without strong co-creation. Everyone involved has their own expertise and understanding of what works best for learners and educators, and collaborating ensures that all stakeholders have a voice in the school’s pedagogy. We co-designed an innovative framework that’s relevant to Belize.
However, there’s no one-size-fits-all pedagogy that will be successful in every context. This framework allows educators to adapt their approaches. The school and the ministry can sustain Itz’at’s experimental nature with continual reflection, iteration, and improvement.
Q: What was the reasoning behind the framework’s core pillars?
Glass: MIT pK-12 found that many successful schools had strong social-emotional support, specific approaches to academics, and reciprocal relationships with their surrounding communities.
We tailored each core pillar to Itz’at. To better support learners’ social-emotional well-being, Belizean cultural identity is an essential part of the learning needed to anchor this project locally. A transdisciplinary approach most clearly aligns with the school’s focus on the United Nations Sustainable Development Goals, encouraging learners to ask big questions facing the world today. And to engage learners in real-world learning experiences, the school coordinates internships with the local community.
Q: Which areas of learning science research were most significant to the STEAM architecture? How does this pedagogy differ from Itz’at educators’ previous experiences?
Urrea: Learning at the Itz’at STEAM Academy focuses on authentic learning experiences and concrete evidence of concept mastery. Educators say that this is different from other schools in Belize, where conventional grading is based on rote memorization in isolated academic subjects.
Together as a team, Itz’at educators shifted their teaching to follow the foundational principles from the STEAM learning architecture, both bringing in their own experiences and implementing new practices.
Glass: Itz’at’s competency-based approach promotes a more holistic educational experience. Instead of traditional subjects like science, history, math, and language arts, Itz’at classes cover sustainable environments, global humanities, qualitative reasoning, arts and fabrication, healthy living, and real-world learning. Combining disciplines in multiple ways allows learners to draw stronger connections between different subjects.
Diaz: When the curriculum is relevant to learners’ lives, learners can also more easily connect what happens inside and outside of the classroom. Itz’at educators embraced bringing in experts from the local community to enrich learning experiences.
Q: How does the curriculum support learners with career preparation?
Diaz: To ensure learners can transition smoothly from school to the workforce, Itz’at offers exposure to potential careers early in their journey. Internships with local businesses, community organizations, and government agencies provide learners with real-world experience in professional environments.
Students begin preparing for internships in their second year and attend seminars in their third year. By their fourth and final year, they are expected to begin internships and capstone projects that demonstrate academic rigor, innovative thinking, and mastery of concepts, topics, and skills of their choosing.
Q: What do you hope the impact of the STEAM architecture will be?
Glass: Our hope is that the STEAM learning architecture will serve as a resource for educators, school administrators, policymakers, and researchers beyond Belize. This framework can help educational practitioners respond to critical challenges, including preparation for life and careers, thinking beyond short-term outcomes, learners’ mental health and well-being, and more.
Artist and designer Es Devlin is the recipient of the 2025 Eugene McDermott Award in the Arts at MIT. The $100,000 prize, to be awarded at a gala in her honor, also includes an artist residency at MIT in spring 2025, during which Es Devlin will present her work in a lecture open to the public on May 1, 2025.
Devlin’s work explores biodiversity, linguistic diversity, and collective AI-generated poetry, all areas that also are being explored within the MIT community. She is known for public art and installations at major museums such as the Tate Modern, kinetic stage designs for the Metropolitan Opera, the Super Bowl, and the Olympics, as well as monumental stage sculptures for large-scale stadium concerts.
“I am always most energized by works I have not yet made, so I am immensely grateful to have this trust and investment in ideas I’ve yet to conceive,” says Devlin. “I’m honored to receive an award that has been granted to so many of my heroes, and look forward to collaborating closely with the brilliant minds at MIT.”
2025 McDermott Announcement
Video: Arts at MIT
“We look forward to presenting Es Devlin with MIT’s highest award in the arts. Her work will be an inspiration for our students studying the visual arts, theater, media, and design. Her interest in AI and the arts dovetails with a major initiative at MIT to address the societal impact of GenAI [generative artificial intelligence],” says MIT vice provost and Ford International Professor of History Philip S. Khoury. “With a new performing arts center opening this winter and a campus-wide arts festival taking place this spring, there could not be a better moment to expose MIT’s creative community to Es Devlin’s extraordinary artistic practice.”
The Eugene McDermott Award in the Arts at MIT recognizes innovative artists working in any field or cross-disciplinary activity. The $100,000 prize represents an investment in the recipient’s future creative work, rather than a prize for a particular project or lifetime of achievement. The official announcement was made at the Council for the Arts at MIT’s 51st annual meeting on Oct. 24. Since it was established in 1974, the award has been bestowed upon 38 individuals who work in performing, visual, and media arts, as well as authors, art historians, and patrons of the arts. Past recipients include Santiago Calatrava, Gustavo Dudamel, Olafur Eliasson, Robert Lepage, Audra McDonald, Suzan-Lori Parks, Bill Viola, and Pamela Z, among others.
A distinctive feature of the award is a short residency at MIT, which includes a public presentation of the artist’s work, substantial interaction with students and faculty, and a gala that convenes national and international leaders in the arts. The goal of the residency is to provide the recipient with unparalleled access to the creative energy and cutting-edge research at the Institute and to develop mutually enlightening relationships in the MIT community.
The Eugene McDermott Award in the Arts at MIT was established in 1974 by Margaret McDermott (1912-2018) in honor of her husband, Eugene McDermott (1899-1973), a co-founder of Texas Instruments and longtime friend and benefactor of MIT. The award is presented by the Council for the Arts at MIT.
The award is bestowed upon individuals whose artistic trajectory and body of work have achieved the highest distinction in their field and indicate they will remain leaders for years to come. The McDermott Award reflects MIT’s commitment to risk-taking, problem-solving, and connecting creative minds across disciplines.
Es Devlin, born in London in 1971, views an audience as a temporary society and often invites public participation in communal choral works. Her canvas ranges from public sculptures and installations at Tate Modern, V&A, Serpentine, Imperial War Museum, and Lincoln Center, to kinetic stage designs at the Royal Opera House, the National Theatre, and the Metropolitan Opera, as well as Olympic ceremonies, Super Bowl halftime shows, and monumental illuminated stage sculptures for large-scale stadium concerts.
Devlin is the subject of a major monographic book, “An Atlas of Es Devlin,” described by Thames and Hudson as their most intricate and sculptural publication to date, and a retrospective exhibition at the Cooper Hewitt Smithsonian Design Museum in New York. In 2020, she became the first female architect of the U.K. Pavilion at a World Expo, conceiving a building which used AI to co-author poetry with visitors on its 20-meter diameter facade. Her practice was the subject of the 2015 Netflix documentary series “Abstract: The Art of Design.” She is a fellow of the Royal Academy of Music, University of the Arts London, and a Royal Designer for Industry at the Royal Society of Arts. She has been awarded the London Design Medal, three Olivier Awards, a Tony Award, an Ivor Novello Award, doctorates from the Universities of Bristol and Kent, and a Commander of the Order of the British Empire award.
While working as a lecturer in MIT’s Department of Architecture, Skylar Tibbits SM ’10 was also building art installations in galleries all over the world. Most of these installations featured complex structures created from algorithmically designed and computationally fabricated parts, building off Tibbits’ graduate work at the Institute.
Late one night in 2011 he was working with his team for hours — painstakingly riveting and bolting together thousands of tiny parts — to install a corridor-spanning work called VoltaDom at MIT for the Institute’s 150th anniversary celebration.
“There was a moment during the assembly when I realized this was the opposite of what I was interested in. We have elegant code for design and fabrication, but we didn’t have elegant code for construction. How can we promote things to build themselves? That is where the research agenda for my lab really came into being,” he says.
Tibbits, now a tenured associate professor of design research, co-directs the Self-Assembly Lab in the Department of Architecture, where he and his collaborators study self-organizing systems, programmable materials, and transformable structures that respond to their environments.
His research covers a diverse range of projects, including furniture that autonomously assembles from parts dropped into a water tank, rapid 3D printing with molten aluminum, and programmable textiles that sense temperature and automatically adjust to cool the body.
“If you were to ask someone on the street about self-assembly, they probably think of IKEA. But that is not what we mean. I am not the ‘self’ that is going to assemble something. Instead, the parts should build themselves,” he says.
Creative foundations
As a child growing up near Philadelphia, the hands-on Tibbits did like to build things manually. He took a keen interest in art and design, inspired by his aunt and uncle who were both professional artists, and his grandfather, who worked as an architect.
Tibbits decided to study architecture at Philadelphia University (now called Thomas Jefferson University) and chose the institution based on his grandfather’s advice to pick a college that was strong in design.
“At that time, I didn’t really know what that meant,” he recalls, but it was good advice. Being able to think like a designer helped form his career trajectory and continues to fuel the work he and his collaborators do in the Self-Assembly Lab.
While he was studying architecture, the digitization boom was changing many aspects of the field. Initially he and his classmates were drafting by hand, but software and digital fabrication equipment soon overtook traditional methods.
Wanting to get ahead of the curve, Tibbits taught himself to code. He used equipment in a sign shop owned by the father of classmate Jared Laucks (who is now a research scientist and co-director of the Self-Assembly Lab) to digitally fabricate objects before their school had the necessary machines.
Looking to further his education, Tibbits decided to pursue graduate studies at MIT because he wanted to learn computation from full-time computer scientists rather than architects teaching digital tools.
“I wanted to learn a different discipline and really enter a different world. That is what brought me to MIT, and I never left,” he says.
Tibbits earned dual master’s degrees in computer science and design and computation, delving deeper the theory of computation and the question of what it means to compute. He became interested in the challenge of embedding information into our everyday world.
One of his most influential experiences as a graduate student was a series of projects he worked on in the Center for Bits and Atoms that involved building reconfigurable robots.
“I wanted to figure out how to program materials to change shape, change properties, or assemble themselves,” he says.
He was pondering these questions as he graduated from MIT and joined the Institute as a lecturer, teaching studios and labs in the Department of Architecture. Eventually, he decided to become a research scientist so he could run a lab of his own.
“I had some prior experience in architectural practice, but I was really fascinated by what I was doing at MIT. It seemed like there were a million things I wanted to work on, so staying here to teach and do research was the perfect opportunity,” he says.
Launching a lab
As he was forming the Self-Assembly Lab, Tibbits had a chance meeting with someone wearing a Stratasys t-shirt at Flour Bakery and Café, near campus. (Stratasys is a manufacturer of 3D printers.)
A lightbulb went off in his head.
“I asked them, why can’t I print a material that behaves like a robot and just walks off the machine? Why can’t I print robots without adding electronics or motors or wires or mechanisms?” he says.
That idea gave rise to one of his lab’s earliest projects: 4D printing. The process involves using a multimaterial 3D printer to print objects designed to sense, actuate, and transform themselves over time.
To accomplish this, Tibbits and his team link material properties with a certain activation energy. For instance, moisture will transform cellulose, and temperature will activate polymers. The researchers fabricate materials into certain geometries so they can leverage these activation energies to transform the material in predictable and precise ways.
“It is almost like making everything a ‘smart’ material,” he says.
The lab’s initial 4D printing work has evolved to include different materials, such as textiles, and has led the team to invent new printing processes, such as rapid liquid printing and liquid metal printing.
They have used 4D printing in many applications, often working with industry partners. For instance, they collaborated with Airbus to develop thin blades that can fold and curl themselves to control the airflow to an airplane’s engine.
On an even greater scale, the team also embarked on a multiyear project in 2015 with the organization Invena in the Maldives to leverage self-assembly to “grow” small islands and rebuild beaches, which could help protect this archipelago from rising seas.
To do this, they fabricate submersible devices that, based on their geometry and the natural forces of the ocean like wave energy and tides, promote the accumulation of sand in specific areas to become sand bars.
They have now created nine field installations in the Maldives, the largest of which measures approximately 60 square meters. The end goal is to promote the self-organization of sand into protective barriers against sea level rise, rebuild beaches to fight erosion, and eliminate the need to dredge for land reclamation.
They are now working on similar projects in Iceland with J. Jih, associate professor of the practice in architectural design at MIT, looking at mountain erosion and volcanic lava flows, and Tibbits foresees many potential applications for self-assembly in natural environments.
“There are almost an unlimited number of places, and an unlimited number of forces that we could harness to tackle big, important problems, whether it is beach erosion or protecting communities from volcanoes,” he says.
Blending the radical and the relevant
Self-organizing sand bars are a prime example of a project that combines a radical idea with a relevant application, Tibbits says. He strives to find projects that strike such a balance and don’t only push boundaries without solving a real-world problem.
Working with brilliant and passionate researchers in the Self-Assembly Lab helps Tibbits stay inspired and creative as they launch new projects aimed at tackling big problems.
He feels especially passionate about his role as a teacher and mentor. In addition to teaching three or four courses each year, he directs the undergraduate design program at MIT.
Any MIT student can choose to major or minor in design, and the program focuses on many aspects and types of design to give students a broad foundation they can apply in their future careers.
“I am passionate about creating polymath designers at MIT who can apply design to any other discipline, and vice-versa. I think my lab is the ethos of that, where we take creative approaches and apply them to research, and where we apply new principles from different disciplines to create new forms of design,” he says.
Outside the lab and classroom, Tibbits often finds inspiration by spending time on the water. He lives at the beach on the North Shore of Massachusetts and is a surfer, a hobby he had dabbled in during his youth, but which really took hold after he moved to the Bay State for graduate school.
“It is such an amazing sport to keep you in tune with the forces of the ocean. You can’t control the environment, so to ride a wave you have to find a way to harness it,” he says.
Can we recreate a JavaScript library for scrolling animations with a modern CSS approach using CSS Scroll-Driven Animations? Yes. Yes, we can.
Web-Slinger.css: Like Wow.js But With CSS-y Scroll Animations originally published on CSS-Tricks, which is part of the DigitalOcean family. You should get the newsletter….
Getting to the heart of causality is central to understanding the world around us. What causes one variable — be it a biological species, a voting region, a company stock, or a local climate — to shift from one state to another can inform how we might shape that variable in the future.
But tracing an effect to its root cause can quickly become intractable in real-world systems, where many variables can converge, confound, and cloud over any causal links.
Now, a team of MIT engineers hopes to provide some clarity in the pursuit of causality. They developed a method that can be applied to a wide range of situations to identify those variables that likely influence other variables in a complex system.
The method, in the form of an algorithm, takes in data that have been collected over time, such as the changing populations of different species in a marine environment. From those data, the method measures the interactions between every variable in a system and estimates the degree to which a change in one variable (say, the number of sardines in a region over time) can predict the state of another (such as the population of anchovy in the same region).
The engineers then generate a “causality map” that links variables that likely have some sort of cause-and-effect relationship. The algorithm determines the specific nature of that relationship, such as whether two variables are synergistic — meaning one variable only influences another if it is paired with a second variable — or redundant, such that a change in one variable can have exactly the same, and therefore redundant, effect as another variable.
The new algorithm can also make an estimate of “causal leakage,” or the degree to which a system’s behavior cannot be explained through the variables that are available; some unknown influence must be at play, and therefore, more variables must be considered.
“The significance of our method lies in its versatility across disciplines,” says Álvaro Martínez-Sánchez, a graduate student in MIT’s Department of Aeronautics and Astronautics (AeroAstro). “It can be applied to better understand the evolution of species in an ecosystem, the communication of neurons in the brain, and the interplay of climatological variables between regions, to name a few examples.”
For their part, the engineers plan to use the algorithm to help solve problems in aerospace, such as identifying features in aircraft design that can reduce a plane’s fuel consumption.
“We hope by embedding causality into models, it will help us better understand the relationship between design variables of an aircraft and how it relates to efficiency,” says Adrián Lozano-Durán, an associate professor in AeroAstro.
The engineers, along with MIT postdoc Gonzalo Arranz, have published their results in a study appearing today in Nature Communications.
Seeing connections
In recent years, a number of computational methods have been developed to take in data about complex systems and identify causal links between variables in the system, based on certain mathematical descriptions that should represent causality.
“Different methods use different mathematical definitions to determine causality,” Lozano-Durán notes. “There are many possible definitions that all sound ok, but they may fail under some conditions.”
In particular, he says that existing methods are not designed to tell the difference between certain types of causality. Namely, they don’t distinguish between a “unique” causality, in which one variable has a unique effect on another, apart from every other variable, from a “synergistic” or a “redundant” link. An example of a synergistic causality would be if one variable (say, the action of drug A) had no effect on another variable (a person’s blood pressure), unless the first variable was paired with a second (drug B).
An example of redundant causality would be if one variable (a student’s work habits) affect another variable (their chance of getting good grades), but that effect has the same impact as another variable (the amount of sleep the student gets).
“Other methods rely on the intensity of the variables to measure causality,” adds Arranz. “Therefore, they may miss links between variables whose intensity is not strong yet they are important.”
Messaging rates
In their new approach, the engineers took a page from information theory — the science of how messages are communicated through a network, based on a theory formulated by the late MIT professor emeritus Claude Shannon. The team developed an algorithm to evaluate any complex system of variables as a messaging network.
“We treat the system as a network, and variables transfer information to each other in a way that can be measured,” Lozano-Durán explains. “If one variable is sending messages to another, that implies it must have some influence. That’s the idea of using information propagation to measure causality.”
The new algorithm evaluates multiple variables simultaneously, rather than taking on one pair of variables at a time, as other methods do. The algorithm defines information as the likelihood that a change in one variable will also see a change in another. This likelihood — and therefore, the information that is exchanged between variables — can get stronger or weaker as the algorithm evaluates more data of the system over time.
In the end, the method generates a map of causality that shows which variables in the network are strongly linked. From the rate and pattern of these links, the researchers can then distinguish which variables have a unique, synergistic, or redundant relationship. By this same approach, the algorithm can also estimate the amount of “causality leak” in the system, meaning the degree to which a system’s behavior cannot be predicted based on the information available.
“Part of our method detects if there’s something missing,” Lozano-Durán says. “We don’t know what is missing, but we know we need to include more variables to explain what is happening.”
The team applied the algorithm to a number of benchmark cases that are typically used to test causal inference. These cases range from observations of predator-prey interactions over time, to measurements of air temperature and pressure in different geographic regions, and the co-evolution of multiple species in a marine environment. The algorithm successfully identified causal links in every case, compared with most methods that can only handle some cases.
The method, which the team coined SURD, for Synergistic-Unique-Redundant Decomposition of causality, is available online for others to test on their own systems.
“SURD has the potential to drive progress across multiple scientific and engineering fields, such as climate research, neuroscience, economics, epidemiology, social sciences, and fluid dynamics, among others areas,” Martínez-Sánchez says.
This research was supported, in part, by the National Science Foundation.
