Zoning codes are a century old, and the lifeblood of all major U.S. cities (except arguably Houston), determining what can be built where and what activities can take place in a neighborhood. Yet as their complexity has risen, academics are increasingly exploring whether their rule-based systems for rationalizing urban space could be replaced with dynamic systems based on blockchains, machine learning algorithms, and spatial data, potentially revolutionizing urban planning and development for the next one hundred years. These visions of the future were inspired by my recent chats with Kent Larson and John Clippinger, a dynamic urban thinking duo who have made improving cities and urban governance their current career focus. Larson is a principal research scientist at the MIT Media Lab, where he directs the City Science Group, and Clippinger is a visiting researcher at the Human Dynamics Lab (also part of the Media Lab), as well as the founder of non-profit ID3. One of the toughest challenges facing major U.S. cities is the price of housing, which has skyrocketed over the past few decades, placing incredible strain on the budget of young and old, singles and families alike.

You don't need to be a chemist to make triacetone triperoxide, or TATP, the homemade explosive used in the bombs which killed 35 people and injured hundreds more last week in Brussels, according to one expert. Another calls the process "worryingly easy." The recipe can be found on the Internet, the ingredients -- hydrogen peroxide and acetone -- can be found at any drugstore, and can be mixed using regular kitchen equipment. "For the most part, IED components are commercial goods that are not subject to government export licences and whose transfer is far less scrutinised and regulated than the transfer of weapons," said a February report from the London-based Conflict Armament Research group, which traced the origins of more than 700 components recovered from ISIS bomb factories. In an attempt to head off attacks like those in Brussels, Boston, and scores of other places, the United States government has quietly asked the general public -- from credentialed professionals to "skilled hobbyists" -- to find ways of weaponizing "easily purchased, relatively benign technologies."