Tanja Döring, Axel Sylvester, Albrecht Schmidt
When we started to explore the use of unusual materials for human-computer interaction (HCI) some time ago, we came across soap bubbles as handles for interaction. We subsequently built the Soap Bubble Interface, an installation that drops soap bubbles onto a liquid surface, where the bubbles control sound and light when moved . We presented this project at 2010 International Conference on Tangible, Embodied and Embedded Interaction (TEI 2010) and at a variety of venues afterward (see Figure 1).
We always found that people were attracted to the bubbles and really enjoyed playing around with them, experiencing their bursting and exploring possible interaction techniques and mappings to control sound and light. By using soap bubbles for interaction, we applied a material that on the one hand comes with a wealth of nice propertiessuch as the bubbles' perfectly round shapes, the beautiful reflections on their thin skins, and their tendency to burst after a short whileand on the other hand has strong connotations and meanings, from playfulness to a vanitas symbol for the transience of human life. All of these properties and semantics were available to be used for the interaction. We especially liked the idea of having UI elements that could be generated whenever we wanted, in different sizes, with or without smoke inside, and that did not last. Motivated by this experience, we started to explore the design space of user interfaces that use unusual and natural materials like water, fog, plants, or soap bubbles for interface components. We believe this is important in three ways. First, the ephemeral (i.e., transient) is a natural phenomenon that yields potential for application in HCI but that has not yet been thought of as part of reality-based interaction . Second, this is an important topic for the research field of tangible user interfaces (TUIs), which deal with diverse materials and rich textures for interaction. And third, ephemerality as a design concept has the potential to address the problem of cognitive overload due to the huge amount of data that gets represented in ubiquitous computing systems nowadays. This also leads to the question of how ephemerality can be designed into the digital. Thus, it is timely to systematically explore the design space for user interfaces that focus on ephemerality as a design conceptwe call them ephemeral user interfaces. By taking a material perspective, we also address questions around the role of materiality in HCI, a current research topic in interaction design .
The word ephēmeros is originally Greek and means "lasting only one day." While most often it is used to express transience, the word ephemeral contains further meanings that make it a very suitable umbrella term for the class of user interfaces we focus on (see sidebar). Ephemerality is an important aspect of human lifeon a large scale, regarding our own lives (e.g., childhood, youth), and on a small scale, regarding all the special moments and experiences we have . People generally love the ephemeral as an event and a sensation, for example, in the form of performances or fireworks. When something is there for only a limited time, experiencing it is special.
Within art, integrating ephemeral materials started as part of movements such as arte povera, land art, and pop art, where cheap, natural, and industrial materials were used to broach the issue of everyday contexts. Materials such as earth, trash, or clothes became part of artworks, which explicitly used the materials' connotations for their meanings. This also included a number of ephemeral materials such as ice, food, and fire. Important for regarding something as an artistic material in this broader context of contemporary art is the existence of certain meanings of the material in a cultural context, as well as the evocation of a specific, often multisensory perception of the material. Even fire, air, or light can be regarded as materials of art if used in a meaningful way. In our discussion of ephemeral UIs, we are following this approach: An interaction material can be any material that is used in a meaningful way for the interaction, that has certain meanings in a cultural context, and that evokes a multisensory perception. Here, we are specifically interested in ephemeral interaction materials.
Ephemeral user interfaces constitute an approach to bringing the described aspects of ephemerality and related aesthetic experiences into human-computer interaction.
We define ephemeral user interfaces as "a class of user interfaces that contain at least one UI element that is intentionally created to last for a limited time only. The durability of the UI element is determined by its intrinsic material properties in combination with its surrounding ecosystem. While their ephemeral UI element(s) exist(s), ephemeral user interfaces provide a rich and multisensory user experience. They may deliberately be designed to offer only partial or imperfect user control" .
Ephemeral UI elements are characterized by two important features. First of all, they are time-based. This means that parts of the interface are designed not to last. How long they last varies depending on their material, their surrounding ecosystem, and what determines their disappearance or degradation. Ideally, the disappearance of UI elements fits the intended interaction with the interface and its user experience. This could be due to the fact that UI elements are needed for only a short time or that users should be engaged in destroying them and creating new ones. UI elements might also disappear to simply raise attention or to limit the user's mental load by presenting information unobtrusively in the background for a limited time. With ephemeral user interfaces, temporality becomes part of the meaning of the interaction. A second focus of ephemeral UI elements lies on the qualities and aesthetics of the materials used for interaction. While this generally might be true for any user interface, ephemeral user interfaces contain materials that carry special embedded meanings from other contexts, often ones deeply inscribed into the cultural context of their users (e.g., the elements water, air, earth, and fire). Alongside using the semantics of the materials, one central idea of ephemeral UIs is that the intrinsic properties of the used materials are directly applied to the interaction, beyond their use as passive decoration in backgrounds, covers, or shells. Ephemeral UI elements can be realized by directly applying ephemeral materials like soap bubbles or fog that disappear by themselves due to their physical properties or by integrating materials with certain properties into an ecosystem that enables ephemerality.
To get a deeper understanding of the design space for ephemeral UIs, we collected and analyzed user interfaces that we regard as falling into this research area (see Figures 3-5 for examples; the collection is accessible on www.ephemeral-uis.org). In our design space, we focus on three aspects of ephemeral UIs: materials far ephemeral UI elements, interaction, and ephemerality (see Figure 2; for a discussion in more detail, see ).
Materials for ephemeral UI elements. Example materials for ephemeral user interfaces could be, among others, water, ice, fog, air, soap bubbles, sand, clay, fire, light, plants, wax, perfume, or food. One relevant aspect of materials for user interfaces is the purpose of their selection. Analyzing the set of UIs and their descriptions and design rationales, we found that on the one end of a continuous spectrum, the properties of a certain materialfor example, its physical, mechanical, electrical, optical, eco-, thermal, or acoustic propertiesled to its usage within a user interface. On the other end of this spectrum is the material semanticsa material's meaning, history, and typical ways of use in a certain cultural context or environment. A further way to discuss and structure ephemeral user interfaces is to group them by the states of matter of the dominating interaction materials: solid, liquid, or gas. This yields the potential to cluster interaction techniques based on the states of matter.
Interaction. We distinguish between interfaces where the ephemeral material is used for output only, those that use the ephemeral material for input only, and those that use one ephemeral material for both input and output. Many prototypes and installations use ephemeral materials for output only, for example, ambient displays (see Figure 3). These UIs receive their input either from a computer or from a user. If the input comes from a computer system, it can either involve no interaction by usersfor example, when displaying digital informationor include implicit interactioninput based on tracked human behavior, often without the users realizing this. In a further category, ephemeral materials are used for output and the system allows user input, but the input and output spaces are not the same (indirect interaction). The next class of user interfaces uses ephemeral materials for input only; among these are a number of tangible music instruments that use clay, jelly, or water for input (see Figure 4). UIs that use ephemeral materials for input and output ideally unify the input and output space and often are realized by gestural interaction with and projections onto ephemeral materials like soap bubbles, ice, or fog (see Figure 5).
Ephemerality. One of the characteristics of ephemeral user interfaces is that parts of the UIs are not designed to last. This leads to two design parameters: first, how the disappearance or degradation of ephemeral UI elements is determined, and second, the class of durability of ephemeral UI elements. Depending on the material, different mechanisms can be used that determine the disappearance of the ephemeral UI element. We identified three different mechanisms: natural phenomena (e.g., gravitation, phase transformation, disappearing sunlight, bubbles that naturally burst), user interaction (e.g., bursting a bubble by touching, eating food), and system trigger (e.g., as applied in ferrofluid interfaces). Different ephemeral materials offer different durations. Looking at the natural materials used in user interfaces, we distinguish six classes of durability that can be used for the design of ephemeral UIs, from ultrashort durability (elements that last only seconds, e.g., water drops) to long durability (elements that can last up to months or even years, e.g., plants or food). Additionally, one class addresses materials that do not have a self-determined durability but that rather depend on other conditions, such as temperature or their amount (flexible durability). Ice is an example of a material that can last forever if the temperature is low enough but that can also melt from one moment to another.
The concept of the ephemeral user interface leads to a number of areas for future research. We believe the following three areas are especially interesting for the HCI community: First, design tools for material-focused user interfaces is a promising research direction to elaborate on the physical materials' aspects and meanings for interaction. Second, ephemeral smart materials focuses on the application of novel and artificial materials for interaction. And third, as natural materials and tangible interaction are not necessarily suitable for all user interfaces, nature and ephemerality as metaphor for hardware and software design forms another strand of research.
Design tools for material-focused user interfaces. In our design space, we have begun to structure the aspects of material selection for ephemeral user interfaces. This process could be supported by a catalog of example materials and prototypes, as well as their material properties and semantics in certain cultural contexts. Additionally, the design space for interaction techniques with ephemeral UIs starting from gas, liquid, and solid materials should be further explored and could be developed into a material-focused interaction vocabulary for ephemeral UIs. An important area of future work will be toolkits that support the integration of a variety of different materials for interaction. Furthermore, our approach to talking about ephemeral UIs from a material perspective could be extended to TUIs in general. If we design UIs starting from material semantics and properties, this would most likely lead to much richer textures for interaction and an integration of the fascinating phenomena nature offers.
Ephemeral smart materials. Thinking about all the qualities of natural materials and how they can be used for interaction leads to the question of how we could design materials with exactly the properties we wanted for a user interface. Current activities in nano- and material sciences already focus on the invention of materials with novel features. In the future, a typical UI design task might focus on the design and invention of a new material instead of selecting an existing one. Ephemeral natural materials could provide a valuable starting point to think about the features and possible interaction techniques future smart materials should provide from a user experience point of view (rather than a technical definition of requirements). For example, one focus could be on the aspects of ephemerality as introduced in our design space: How could we design an ephemeral smart material with a certain durability span that was perhaps computationally controlled? Could a material be reactivated, as is already possible with ferrofluid sculptures? What interaction techniques are possible for a certain set of novel materials? These open questions are related to current research programs such as radical atoms .
Nature and ephemerality as metaphor for hardware and software design. Analyzing the values that the integration of natural and ephemeral physical materials have for UI design can also help to improve the design of digital systems. This is in line with the framework of reality-based interaction that suggests starting to think from real-world phenomena when designing interaction . The designer's challenge lies in balancing computational power and reality. Taking nature only as a model and transferring insights back to the digital domain can be useful in some cases. A few examples of such nature-inspired UIs (e.g., robotic plants) or applications that implement transience by letting content disappear after a short moment (e.g., the picture-sharing platform Snapchat) have already been designed, but the potentials have not been fully utilized. How could hardware and software elements grow, get older, degrade, or even decay as things in nature do? In this sense, ephemerality could also be a strong concept for software design.
With our introduction to ephemeral user interfaces, we hope to have inspired you to value the aesthetics of interface components that do not lastand to contribute to this exciting new research focus! Further information on ephemeral user interfaces can be found on www.ephemeral-uis.org.
We are thankful for permissions to use images of ephemeral user interfaces. Part of this work was funded by the German Research Foundation (DFG).
9. Cauvard, M. and Pluvingae, R. Noisy Jelly Press Kit; http://pluvinage.eu/NOISYJELLY_presskit.pdf
Tanja Döring is a research associate and Ph.D. candidate at the University of Bremen, Germany. Her research focuses on novel ways of HCI including tangible and gestural interaction. She is especially interested in leveraging the potential of material diversity for interaction. She has a master's degree in computer science from the University of Hamburg, Germany.
Axel Sylvester is a self-employed IT consultant, independent researcher, and manager of the Fab Lab Fabulous St. Pauli in Hamburg, Germany. His research interests include a variety of topics, from unconventional user interfaces to means for personal production to educational aspects of Fab Labs. He has a master's degree in information systems from the University of Hamburg.
Albrecht Schmidt is a professor of human-computer interaction at the University of Stuttgart, Germany. His research interests include pervasive computing and HCI beyond the desktop. He has chaired several HCI-related conferences and is one of the technical program chairs of CHI 2014. He has a Ph.D. in computer science from Lancaster University.
Literally meaning "lasting only one day," the word ephemeral generally depicts something that is temporally restricted. For example, the mayfly, a fly with a very short life span, is called ephemeroptera. Beyond this meaning of something that is transient, the ephemeral is often connected to a certain aesthetic, which in many cases involves multisensory perception. In this sense, a butterfly or a flower, for example, is a strong metaphor for ephemerality, as often applied in poems. Experiencing things or moments that do not last is often valued as precious, because it is likely to be a unique or rare experience. Within cultural studies, the term ephemeral is used to describe phenomena that arise and disappear again, for example, in the context of new media, and for the triviality of everyday life, as captured by diary literature, for example. In this sense the term ephemeral is also used to indicate the generally low-valued, the peripheral. Other interesting aspects of the ephemeral are vagueness and fluidityfor example, as represented by soap bubbles, which are "in between" spaces, "neither virtual nor real" , lacking permanence or solidity. The French philosopher Christine Buci-Gluckmann, who wrote about the aesthetics of the ephemeral, described water as the ephemeral material par excellence. She described the "spirit of the vagueness" as playing an important role for the ephemeral . Outlining these meanings of the word ephemeral, we believe that human-computer interaction should care about integrating aspects of ephemerality into user interfaces. Transience, the aesthetics of the unique moment connected to a multisensory experience, the trivial and peripheral, as well as vagueness, are all aspects of life that have yet only very rarely been addressed and represented in computing. Ephemeral user interfaces provide an approach to integrating time-based phenomena into HCI and to offering strong sensual experiences by using ephemeral natural materials. Furthermore, ephemeral UIs have the potential to be especially suited to present the trivial, for example, as information at the periphery. The "spirit of the vagueness" could support the presentation of ambient information or allow "input on demand" as well as input mechanisms that are purposely not precisely controllable
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