What accounts for Detroit’s failure to produce a commercially viable electric car? When I discuss this question with students, I sometimes get conspiracy theories. They cite the 2006 documentary film “Who killed the electric car.” The film attributes the demise of GM’s all-electric car, the EV-1, to collusion among the carmakers, the government, and oil companies.

Here’s how I ask students to sort this out. First, I ask them to employ the logic behind Ockham's razor, a principle attributed to the 14th-century English logician and Franciscan friar, William of Ockham. The most common statement of his principle is “When faced with two competing theories that make the same predictions, the simpler one is more likely correct.” Let’s apply Ockham’s razor to electric cars.

In 1990, California mandated that by 1998 two percent of cars sold in the state had to be zero-emission vehicles, increasing the number to 10 percent by 2003. In response, GM spent about $1 billion producing 1,000 EV-1s, a small, two-seat, all-electric car powered by a lead-acid battery. The EV-1 had serious shortcomings. Its range was less than 100 miles (cold weather or using the AC further reduced the range), it took 8-12 hours to recharge, had limited storage, and was expensive. Beyond a few rabid devotees, nobody wanted them. GM stopped production in 2000.

Consumers value not only fuel-efficiency, but also decent horsepower, attractive interior design, room for gear and kids, safety, convenience, and reliability. And they demand all this at a reasonable price. Further, we increasingly view our cars as extensions of our living and work spaces. Firmly imbedded in the digital age, we demand seamless connections between home, office, and car. GPS navigation systems and power for iPods, phones, and laptops are fast becoming standard features. Meeting these demands with batteries alone is a challenge.

Compared to gasoline, batteries suffer from relatively low energy densities (i.e., the amount of energy stored per unit of mass). For example, a 30-kilowatt battery, capable of powering a car for about 70 miles, weighs approximately 800 lbs. It contains as much energy as a gallon or two of gasoline, weighing between 7-15 lbs. Bill Ford used to drive an experimental electric Ranger pickup truck because he needed the entire bed to hold the lead-acid batteries.

EV-1's successors, for example the Chevy Volt, use smaller, lighter lithium-ion batteries. These take up one-third of the space of the EV-1's original lead-acid batteries, while providing the same energy density. The Volt’s battery can power the car for 40 miles (The average American drives about 33 miles a day.) For longer trips, a small gasoline-powered generator kicks in to recharge the battery and extend the Volt’s total range to 640 miles. Between trips, the battery can be recharged in six and a half hours at an ordinary wall outlet.

Developing safe, reliable, and affordable batteries to power vehicles consumers want is a huge challenge. Batteries must be able to survive extremes in temperature and the wear and tear of driving, while lasting long enough to meet our ever-growing expectations for vehicle life. And they must be safe. Last year millions of laptops were recalled because of the danger that their batteries would burst into flames. (A plug-in hybrid would have the equivalent of hundreds of these battery packs bundled together.) Despite this, several companies (e.g., Tesla Motors and A123 Systems) are working on the next generation of design and are making progress.

Detroit is desperate to sell cars. To claim that the Big Three (often portrayed by critics as “greedy, short-sighted profit seekers”) refuse to sell cars consumers “really want,” compared with the cars they actually purchase, is a stretch. If alternative vehicles like the Volt provide more value to consumers than traditional cars, then automakers could not keep enough on the lots. But it’s my hunch that GM is designing the Volt for the political rather than the consumer market. (GM has admitted it can’t sell the Volt profitably for less than $50,000 a car.)

Back to Ockham's razor and my answer to the question “who killed the electric car?” The simpler explanation seems to be that a conjunction of physics and consumers did.