"What would the world be if there were no hunger?" It's a question that Professor Crystal would ask her students. They found it hard to answer, she wrote later, because imagining something that isn't part of real life—and learning how to make it real—is a rare skill. It is taught to artists and engineers, but much less often to scientists. Crystal set out to change that, and helped to create a global movement. The result一an approach known as systems thinking—is now seen as essential in meeting global challenges.

Systems thinking is crucial to achieving targets such as zero hunger and better nutrition because it requires considering the way in which food is produced, processed, delivered and consumed, and looking at how those things intersect (交叉) with human health, the environment, economics and society. According to systems thinking, changing the food system—or any other network- requires three things to happen. First, researchers need to identify all the players in that system, second, they must work out how they relate to each other, and third, they need to understand and quantify the impact of those relationships on each other and on those outside the system.

Take nutrition. In the latest UN report on global food security, the number of undernourished (营养不良) people in the world has been rising, despite great advances in nutrition science. Tracking of 150 biochemicals in food has been important in revealing the relationships between calories, sugar, fat and the occurrence of common diseases. But using machine learning and artificial intelligence, some scientists propose that human diets consist of at least 26,000 biochemicals—and that the vast majority are not known. This shows that we have some way to travel before achieving the first objective of systems t hinking - which,in this example, is to identify more constituent parts of the nutrition system.

A systems approach to creating change is also built on the assumption that everyone in the system has equal power. But as some researchers find, the food system is not an equal one. A good way to redress (修正) such power imbalance is for more universities to do what Crystal did and teach students how to think using a systems approach.

More researchers, policymakers and representatives from the food industry must learn to look beyond their direct lines of responsibility and adopt a systems approach. Crystal knew that visions alone don't produce results, but concluded that "we'll never produce results that we can't envision".

Can a small group of drones（无人机）guarantee the safety and reliability of railways and, at the same time, help railway operators save billions of euros each year? That is the very likely future of applying today's "eyes in the sky" technology to making sure that the millions of kilometres of rail tracks and infrastructure（基础设施）worldwide are safe for trains on a 24/7 basis.

Drones are already being used to examine high-tension electrical lines. They could do precisely the same thing to inspect railway lines and other vital aspects of rail infrastructure such as the correct position of railway tracks and switching points. The more regularly they can be inspected, the more railway safety, reliability and on-time performance will be improved. Costs would be cut and operations would be more efficient（高效）across the board.

That includes huge savings in maintenance costs and better protection of railway personnel safety. It is calculated that European railways alone spend approximately 20 billion euros a year on maintenance, including sending maintenance staff, often at night, to inspect and repair the rail infrastructure. That can be dangerous work that could be avoided with drones assisting the crews' efforts.

By using the latest technologies, drones could also start providing higher-value services for railways, detecting faults in the rail or switches, before they can cause any safety problems. To perform these tasks, drones for rail don't need to be flying overhead. Engineers are now working on a new concept: the rail drones of the future. They will be moving on the track ahead of the train, and programmed to run autonomously. Very small drones with advanced sensors and AI and travelling ahead of the train could guide it like a co-pilot. With their ability to see ahead, they could signal any problem, so that fast-moving trains would be able to react in time.

According to the Solar Energy Industry Association, the number of solar panels installed(安装)has grown rapidly in the past decade, and it has to grow even faster to meet climate goals. But all of that growth will take up a lot of space, and though more and more people accept the concept of solar energy, few like large solar panels to be installed near them.

Solar developers want to put up panels as quickly and cheaply as possible, so they haven't given much thought to what they put under them. Often, they'll end up filling the area with small stones and using chemicals to control weeds. The result is that many communities, especially in farming regions, see solar farms as destroyers of the soil.

"Solar projects need to be good neighbors," says Jordan Macknick, the head of the Innovative Site Preparation and Impact Reductions on the Environment(InSPIRE)project. "They need to be protectors of the land and contribute to the agricultural economy." InSPIRE is investigating practical approaches to "low-impact" solar development, which focuses on establishing and operating solar farms in a way that is kinder to the land. One of the easiest low-impact solar strategies is providing habitat for pollinators(传粉昆虫).

Habitat loss, pesticide use, and climate change have caused dramatic declines in pollinator populations over the past couple of decades, which has damaged the U.S. agricultural economy. Over 28 states have passed laws related to pollinator habitat protection and pesticide use. Conservation organizations put out pollinator-friendliness guidelines for home gardens, businesses, schools, cities—and now there are guidelines for solar farms.

Over the past few years, many solar farm developers have transformed the space under their solar panels into a shelter for various kinds of pollinators, resulting in soil improvement and carbon reduction. "These pollinator-friendly solar farms can have a valuable impact on everything that's going on in the landscape," says Macknick.