When a magazine's cover shows "the world's sexiest man," many of us cringe. Says who? By what criteria? Was every male on Earth vetted? Did they include me? But when science programs make equally ridiculous claims, most educated people lack the techno-background to refute them.

Science prognosticators have a miserable track record. World's Fairs provided quick demos. In the 1964 Fair in Flushing Meadows, Queens, the year 2000 was depicted as bringing the average family a 30-hour work week, a flying car and robotic servants. There would be bustling colonies on Mars. Do you see any of that? Meanwhile, those same science-predictors failed to foresee the internet, a computer in every home, global warming, cell phones, the Chinese production of most domestic products, DVDs, the obesity epidemic and most of today's realities. So when we flip on the Science or History channel, should we really take seriously any visions about the US circa 2040?

A major science channel recently did another show about terraforming. Well? Could we transform Mars into an Earth-like paradise? It's only half our diameter, but, with no oceans, it possesses exactly the same land area as our own planet.

The concept seems simple enough. Since Mars already has some of the essentials (ice below the surface, oxygen bound into the soil), why not "seed" that world? The process might take centuries, but eventually you end up with breathable air and Eden Two. If we can turn a barren outer space vacant lot into a prime plot, well, why not?

Here's why not. Martian gravity is just 38 percent of ours. You can't change this. Any thick, precious, Earth-like atmosphere we create would leak away into space.

With the rocketry equivalent of a caravan of U-Haul trailers, maybe we could drag machines 38 million miles to extract oxygen and water from Martian raw materials and thus supply a bubble-enclosed colony. But transform the entire atmosphere? This ignores the volume and scale of any global meddling. It would be like expecting a bathroom heater to keep North America toasty all winter.

Those fake but earnest TV scientists speculate that if we merely introduce a new substance it then catalytically causes the entire planet to undergo a self-sustaining chain reaction. In other words, it'll happen by itself once you start it going! But Martian chemistry doesn't work like that. Its oxygen-rich minerals are stable, not unstable. And even if it could work, what entity - public or private - would cough up 500 billion bucks to achieve iffy results 300 years in the future? Anyone?

Then there's solar and cosmic radiation. Earth is shielded by our powerful magnetosphere. Mars has none. There, cell-damaging radiation is the constant companion.

Science fiction is fond of offering intriguing concepts. In recent decades we've been presented with:

Bending space so that astronauts can "jump" to other sections of the cosmos without passing through any of the intervening territory.

Creating wormholes to tunnel back through time.

Visiting parallel dimensions.

And, terraforming planets.

Simple to grasp in the abstract, they suffer one shortcoming: Nobody has yet come up with the slightest clue about how one could even begin any of these processes. Like the perpetual motion machine or the square root of minus one, some ideas simply have no analog in real life. Except the world's sexiest man. He really exists - in Saugerties.