What happens when an unstoppable force meets an immovable object is a question that has perplexed many philosophers for thousands of years. Today, this classic paradox makes a good metaphor for one of the world's most important issues. The "unstoppable force" is the continually increasing worldwide demand for energy. The "immovable object" is the world's rapidly diminishing fossil-fuel reserves and the growing acceptance that burning these fuels is causing climate changes that will have profoundly negative effects on future generations. Worldwide demand for electrical energy is increasing and all indications are that it will continue to increase for the foreseeable future. Even if we found enormous new reserves of fossil fuels, we would not be able to continue burning them because of their contribution to global warming. Unstoppable force meets immovable object. In the early 20th century, oil was a cheap and apparently inexhaustible resource, and nobody imagined our consumption could affect something so seemingly out of our control as the climate. Today, we know differently. And our present scenario is both horrible and unsustainable. Given the scale and complexity of the challenge, the key players necessarily must include governments and the major energy-producing and energy-consuming industries such as electricity providers and the automotive industry. However, one industry – semiconductors – will play a vital role in making the "unstoppable" force less unstoppable and making the "immovable" object more movable. As far as the unstoppable force is concerned, two paths offer hope. The first is to reduce the amount of power each electrical product and application consumes and to make the generation and distribution of electrical energy more efficient, while the second is to change consumers' energy-consumption patterns. Semiconductor technology has a crucial role to play in both. There are several ways in which the energy consumption can be reduced. One is via technology evolution. Replacing previous-generation transistors with state-of-the-art ( 技术最先进的 ) devices would save four to five terawatt-hours/year (TWh/yr) in power-supply applications – the equivalent of two 500MW nuclear power plants. A second way is "smart systems", which combine multiple functions to reduce power use in individual devices and systems. The effectiveness of this approach has already been proven in domestic appliances where the availability of powerful, low-cost microcontrollers replaces the traditional universal motor with a more efficient brushless motor, which is typically 30 percent more energy efficient. If all universal motors were replaced by brushless motors, we could save up to 50 TWh/yr of power by 2020. The second path – helping consumers change their energy-consumption patterns – is more challenging because its successful execution largely depends on local combinations of legislation and infrastructure. But enabling technologies such as smart systems, smart metering and smart grids are available and there is evidence that supplying consumers with detailed information about their energy usage patterns encourages them to conserve.