Eating is so time-consuming. All that tedious mastication — couldn’t we just cram the stuff we need for survival into a Tylenol-sized tablet and be done with it? Well, no. It turns out that a food pill, while the essence of convenience, would violate the laws of physics. The average person needs to ingest around 2,000 calories a day. Carbohydrates and proteins provide about 4 calories per gram; fat provides about 9 calories per gram. If you put 2,000 calories’ worth of fat into pill form — the most efficient way to do it — you’d need to pop roughly half a pound of pills a day. That’s almost 450 standard-sized capsules. And you still wouldn’t be getting your other vital nutrients. But look, physics aside, dinner in a capsule is depressing; a burger is delicious. Think of it as a cheese-dripping, bacon-topped patty-sized pill in a bun. — Erin Biba

Despite these drawbacks, Richard Bishop, a former federal researcher and now an industry consultant, says that “low-speed automation” systems, which control vehicles in heavy congestion, could be in high-end autos by 2015. Translation: Traffic jams will be with us for a while. — Daniel McGinn

It’s not hard to make individual vehicles at least partly automatic — luxury automakers have recently introduced adaptive cruise control , which adjusts a car’s speed based on the position and speed of the vehicle ahead of it. But a completely driverless network requires pricey road sensors. Litigation risks are another concern — imagine the lawsuits that could stem from faulty autopilot systems.

To traffic-weary drivers, it sounded great: Let technology handle tedious tasks like accelerating, steering, and braking. Cars — linked to road sensors and controlled by computer — could drive closer together, increasing highway capacity and fuel efficiency while reducing accidents and the need for new roads. Home, Hal!

Nuclear Spaceships

Well before Neil Armstrong stepped onto the moon, scientists knew that chemical propellants could take us only so far — they just don’t offer enough pop per pound. The obvious solution is nuclear energy. Yet we still don’t have a working nuke ship.

The earliest attempt to develop such a craft was Project Orion, launched in 1958. The concept: Create a vessel that would eject small atomic bombs from its rear. These would explode near a “pusher plate” attached to the bottom of the ship, and the energy pulses from the detonations would propel the ship at incredible speeds — an Orion spacecraft could have achieved a top velocity of 5 percent the speed of light (more than 33 million miles per hour). A 258-day trip to Mars was scheduled for 1965. Why didn’t it happen? In 1963, the Partial Test Ban Treaty outlawed nuclear explosions in space. Project Orion died on the spot.

An option that’s more politically feasible than bomb-powered spaceflight is nuclear thermal propulsion. This approach involves an onboard fission reactor powered by highly enriched uranium-235. Once flicked on, the reactor would theoretically heat hydrogen up to 3,100 degrees Kelvin, then shunt superheated gas out the ship’s tail. Such a craft would have more than twice the power of a chemical rocket.

The basic feasibility of nuclear thermal propulsion was proven during the 1960s, when a fission-powered engine called Nerva was tested successfully in the Nevada desert. But the Nerva program was killed in 1973, when a budget crunch forced NASA to abandon its expensive Mars-mission dreams in favor of the more cost-efficient space shuttle. The agency never got a chance to solve the remaining technical hurdles, like how to fire up the reactor again and again without catastrophic failure.

Some folks might be a wee bit resistant to the idea of a fission reactor flying overhead, but advocates of nuclear thermal propulsion insist it’s safe, since the reactors wouldn’t kick in until the ships were far from Earth. True, in the case of an accident in the atmosphere (as a ship made its way into space), some uranium would fall on the planet. The chief concern isn’t contamination, though; it’s the fact that the U-235 could be recovered by bad guys. It’s great for making bombs. — Brendan I. Koerner