Despite the title of Robert Bryce's recent book, Smaller, Faster, Lighter, Denser, Cheaper, miniaturization is only one half of the story of technology—and of nature. Making components of things smaller, lighter and denser indeed enables the things composed of those parts to be faster, yes, but also larger. And although it is hard to witness this evolution as it applies to natural things, like birds, the same dynamics are clearly visible in the technological analog to birds, aircraft. A new paper by Adrian Bejan, professor of mechanical engineering at Duke University, clearly shows both how airplanes have increased their size, speed and range over time and how wingspan, fuselage length and engine size have remained proportional in the majority of these aircraft as they have grown.
As with birds and planes, so with iPhones, apparently. Finally, it seems that Apple will catch up to Samsung in the screen size of their smartphones (at least at the phablet end of the spectrum.) Is this a case where Samsung has had a clearer sense of natural design evolution than Apple? Not completely. Tim Cook may have been hamstrung by Steve Job's vestigial bias against smartphones that are not completely one-handed, but Apple was also legitimately reluctant to make an iPhone larger until it could make it lighter and faster as well. And similar to the evolutionary tendency of larger birds or planes to have longer range, Apple has not wanted to increase screen size at the expense of battery life. The rumored 2mm thin battery on the reported 7mm thin iPhone 6 may not increase the device's battery life over previous models, but it is unlikely to reduce it.
From The Evolution of Airplanes, Adrian Bejan et al., Journal of Applied Physics
Before we get any deeper in why screen size matters in the design evolution of the iPhone, let's look at what Bejan found in his research on airplanes. The chart above, from his article with collaborators J.D. Charles and Sylvie Lorente in Journal of Applied Physics, "The Evolution of Airplanes," shows the trend over time towards larger, heavier planes capable of going faster for longer distances. But just as in the world of mobile devices, the rule is diversity. Counterbalancing trends towards large, integrated systems, like the Airbus 380 (the largest passenger aircraft) and miniaturization like the Robo-Fly (the smallest drone to date) lead to a large solution space that, in aggregate, moves more things, farther and faster with greater energy efficiency. At the same time, this profusion of solutions leads to a dramatic increase in overall flow through terrestrial airspace and greater energy demands overall.
This, to Bejan, is the implicit goal of design evolution, the vascularization of space, the churning of the earth's surface and atmosphere, the utilization of more and more of the ambient energy captured by the earth from the sun. As coherent as his findings are of the parallels between the evolution of creatures and of technology, it is the outliers that make the case clearest. In the present paper, Bejan talks about the Concorde supersonic airplane as an example of an aircraft that "In chasing an 'off the charts' speed rating… deviated from the evolutionary path traced by successful airplanes that preceded it." Commercially successful passenger airplanes from Boeing and Airbus sell in the thousands while only 20 Concordes were ever built. Bejan told Sci-News, “The Concorde was too far off from the ratios that evolution has produced in passenger jets.” Prof Bejan said. These proportions include the proportion of the wingspan to fuselage length as well as fuel efficiency and mass-to-velocity ratio.
The net effect, Bejan writes, is that, "What works is kept. Flow architectures that offer greater access persist, and are joined by even better ones. Together, the vascular tapestry of old and new carries the global human flow easier and farther than the old alone. Air mass transport with new and old airplane models mixes the global sphere more effectively than in the absence of new models."
I have been following Bejan's work particularly with an eye to what it might tell me about Apple's design evolution. The combination of the move to larger iPhone screens on the one hand and some number of iWatch solutions that will capture iOS functionality on smaller screens on the other, does seem to follow the patterns of the Constructal Law as described by Bejan. I spent some time this Spring down at Duke meeting with Bejan and his students. (Thanks to the Duke Network Analysis Center for hosting my talk, "Design Everywhere: Natural Machines and the Success (and Failure) of Emergent Networks." It was hands-down the least technical talk they had ever had, but I would like to think that it had the most well-designed slides! You can see them here.) One thing that became clear to me from that experience is how every thing can be seen as a component of a containing physical flow system and as such has a characteristic scale. This is to say that the iPhone evolves in the context of the human hand as well as the capacities of the human eye. The iWatch must evolve in relation to the scale of the human wrist, etc.
As you can see in the figure above from Design in Nature (Bejan and Zane, Doubleday, 2012), component size, whether it is a human heart or a mechanism on an airplane, is a two-factor optimization. If the component is too small, it does not allow for enough internal flow, but if it is too large the carrying of the element itself reduces the overall flow of the creature or machine itself. Bejan's research has shown that design evolves to find a balance between these two in order to arrive at a characteristic size. When we look at this phenomenon in the world of technology, especially in an area as fast moving as mobile devices, we can see the work of evolution happen before our eyes.
With the iPhone we can say that the larger the screen gets the easier the flow of information between the user, the screen and the internet beyond. But if the screen gets too large it is no longer a phone but some sort of tablet. Similarly, if the device gets too heavy or thick as it grows larger or if its battery will no longer suffice for a full-day's use, it begins to climb the optimization curve in the wrong direction. So Apple's apparent move to larger-screened iPhones have to do with customer demand, as demonstrated so well by Samsung, but also with technological innovations regarding the lightness and thinness of components and the miniaturization of batteries and other electronics. I have not yet determined exactly which ratios are at play in the success of the iPhone (though I will be asking Bejan and his team for suggestions) but it is clear that Apple understands what these proportions are and that they must guide its design decisions.
Every flow system has a limit where the S-curve of its growth levels off. Passenger airplanes cannot get infinitely large. The Russian An-225 is the world's largest and heaviest passenger aircraft, but only a single plane was ever produced. It is not only physical limitations that affect the size of things. Every thing is but a component in a larger containing flow system. So in the case of passenger airplanes, there are only so many people who want to go from one place to another at the same time to fill these increasingly enormous Airbuses and Boeings. The same problem affected the Concorde but for different reasons. It had a very limited seating capacity and low fuel efficiency so it was very expensive. Finding enough passengers that were willing to pay $10,000 to fly from Paris to New York at the same time proved an insurmountable challenge.
I suspect that the flow dynamics of smartphones are such that something like the Samsung Galaxy Note may be the largest device that people are willing to carry everywhere and thus use as a phone. iPads require something other than a pocket and thus must make their success, or not, on the basis of other use cases (enter IBM, for instance.) But if Samsung were to respond to Apple by making ever-larger smartphones or if it increased the price of those phones beyond accepted ratios, it might find itself in Concorde territory. It will be interesting to see if, indeed, the 5.5-inch screen device is the optimal smartphone size or if the 5.1" Galaxy S5 or even the 4.7" iPhone 6 turn out to be the most popular. Certainly lighter and more flexible screens will make their size less of a limiting factor for usability. The question will be what the most relevant limiting factor is on increased screen size. If it is human factors, like hand size, we may well be close to arriving at equilibrium. But if weight, or thinness, voice control or even foldability open flow possibilities beyond hand scale we may see many further generations of smartphone design evolution.
