As Descartes pointed out that the reasoning is an interpretive process dealing with complexity analytically and synthetically, proper scientific theories of cities are needed for our rapidly changing cities. However as I mentioned, the validity of scientific theory only exists within a certain time and space, and often evolves with the increasing complexity. Therefore urban scientists need to be extremely cautious and sensitive when creating such a ‘universal theory of cities’ and understand its validity regarding time, scope, scale and context in each individual research question. Before creating a ‘theory of cities’, it is essential to understand urban dynamic complexity and its driving forces. The nature of cities as agglomerations of human settlement defines three elements: human, nature, and settlement. These three elements serve as building blocks of urban complexity, intertwining with each other structurally or organically. The challenge is that we are not only facing rapidly increasing complexity in each individual element (for example, human genome, astrophysics and communication technology), but more importantly, a geometric growth of urban complexity in the age of big data. Therefore there will be some universal theories of cities, but they would be replaced fairly quickly by the new ones because the fast growth of complexity.
Furthermore, it is difficult to adopt a universal theory of cities because every city is different. There is no city built purely based on a utilitarianism principle, because as the vessel of human settlement and symbol of prosperity, city is also often shaped by history, culture and philosophical views of human-nature relationship and human society. The cultural difference still highly impact people’s settlement preference, social networks and life style. Historical factors also could have an influence on city development such as racial and social segregation in USA. Therefore, urban science would not be universal since cities were not built purely on scientific reasoning.
So would it be worth spending time and resource to develop such a science of cities? The answer is affirmative and we need learn from other established paradigms such as biology and ecology to better understand cities. It is necessary to study cities beyond empirical observation and determinism composition to truly understand the mechanism of urban system. Just like biologists studying animals’ digestive system, it requires urban scientist look though the skin and feature of cities to see how they consume energy, its metabolism and how it adapts to climate and survive from disaster. The universal theory of urban equilibrium is valuable because many cities are facing universal issues such as energy consumption, water shortage, environmental degradation and disaster resilience. Beyond study each individual cities, we need to consider cities as different ecosystems to understand urban dynamic regarding allocation and competition. Moreover, the fact that city as a human agglomeration means there will be potential organizational benefit such as innovation and collaboration which beyond equilibrium and adaption.
City is a relatively recent product of human civilization and in last century human society experienced a mix of architectural determinism and social administration in cities, which brought us modern urban prosperity but also long-term social and environmental issues. Development of information technology and data science brings us to a new era that cities are increasingly mediated by digital technology. The large amount of city data enables us to study city with more scientific approaches to experiment and analyze urban phenomenon. New research topics such as social physics, collective intelligence and data driven society are emerging.  More importantly, data and science are no longer kept in labs but exist in everyone’s daily life, and people are engaging with city more actively and spontaneously. With careful calibration and proper approaches, this transition will eventually enable us to have a more responsive city and collaborative society.
 Ali Madanipour, Designing the City of Reason, Foundations and Frameworks (Routledge, 2007), 3
 Michael Batty, The New Science of Cities (The MIT Press, 2013), 25-27
 “The Surprising Math of Cities and Corporations,” TED Talk by Geoffrey West in 2011, accessed Sept. 21, 2015, http://www.ted.com/talks/geoffrey_west_the_surprising_math_of_cities_and_corporations?language=en
 Kingsley Davis, The Origin and Growth of Urbanization in the World, American Journal of Sociology,1995, 60:5, 429-437
 Arup and Royal Institute of British Architects, Designing with data: Shaping our future cities, 2015. https://www.architecture.com/Files/RIBAHoldings/PolicyAndInternationalRelations/Policy/Designingwithdata/Designingwithdatashapingourfuturecities.pdf
 Alex Pentland, Social Physics, How Good Ideas Spread- The Lessons from a New Science (The Penguin Press, 2014)