History is filled with wondrous inventions that have changed our lives forever: the light bulb, the car, penicillin, the Internet. This has led to a belief in many that innovation can and will accomplish anything, and that it’s only a matter of time before all the fantastic technologies and ideas we dream of become a reality. While it is true that progress is an amazing thing, there are limits, and there are certain ideas that will simply never come to pass, no matter how cool they seem.

The appeal:
There are few among us who’ve never felt the slightest insecurity about our weight. Whether you feel you need to lose a few pounds or a few dozen, we’d all like an easy way to achieve our ideal weight. The “easy” part is what has given rise to the endless streams of fad diets promising us miraculous results.
It sounds good. Lose weight by just a few special tricks. Many even offer seductive claims like “eat as much as you like as often as you like” or “you can still eat cake.”
Why it won’t work:
The trouble is that there’s just no easy way out. These diets never live up to their claims. They’re either based on bad science and can’t deliver on their promises, or they’re so restrictive that no sane being could stick to them, or perhaps both. In the end, the only solution to the weight problem is common sense. Cut down on junk food, exercise regularly, and don’t worry if you slip up now and then.

The appeal:
On paper, communism seems like the blueprint of an ideal society. Classes, borders, and all such artificial barriers between humanity are broken down. Everyone is equal, and no one wants for anything. In the communist ideal, the entire world would be one unified nation with everyone contributing to the greater good.
Sounds great, right?
Why it won’t work: 
Communism fails to take into account human failings, however. It makes little concession for things like greed or laziness. If every person on Earth was perfectly selfless and good-natured, communism would work, but that is not the case, and until it is, it’s unlikely communism will ever deliver on its grand promises.
Furthermore, the transition to communism is generally thought to require armed revolution against those currently in charge, and all that violence sort of runs counter to the “perfect world, love thy neighbor” philosophy communism espouses.

The appeal:
We all dreamed of jetpacks when we were kids. Strap a rocket engine to your back, press a button, and fly wherever you please — no one can deny the appeal of that. Aside from the obvious fun and cool factor, it’d be incredibly convenient. No traffic to worry about; it would just be you, the open sky, and the need for speed.
Jetpacks actually do exist, and they work, albeit in a very limited capacity. Daredevils use them for stunts, and a few very rare and very rich hobbyists use them just for fun.
Why it won’t work:
Unfortunately, the dream of everyone using a jetpack to fly to work is unlikely to ever come to pass. The concept suffers from several fundamental flaws. The chief among these is the problem that the more fuel you carry, the harder it is to get off the ground. For this reason, jetpack flights can never last more than a few minutes — nowhere near long enough to use them for anything practical. They’re also extremely difficult to control and just downright dangerous.

The appeal: 
Virtual reality is something nearly every piece of science fiction in recent history has promised us is coming. It offers countless opportunities for entertainment, training, and behavior study, and it’s something most would admit to wanting. It does already exist in some limited forms, as anyone who’s spent time in Second Life or World of Warcraft will tell you.
Why it won’t work: 
However, the fully immersive virtual realities we’ve seen from things like Star Trek’s holodecks or the Matrix are a bit of a trickier proposition. It’s not impossible that we might one day see them, but it seems very unlikely.
With our current understanding of technology, there are only two ways a true virtual reality could be created, and both are not likely to ever see widespread use. The first is to employ impractically large and complex hamster-ball like machines paired with helmets to provide sight, sound, and potentially scent. The trouble with these is their over-complication and high expense, as well as the lack of a good way to stimulate the sense of touch. The other option would be to devise a way to plug directly into our brains to deliver information, but aside from being outside the reach of current knowledge, this method is just downright creepy, and it’s hard to imagine anyone agreeing to it.

The appeal:
Few people relish the idea of growing old. This has led to an endless string of treatments down through the ages promising to at least give us appearance of youth even as we slip past our prime years. From herbal cures to creams and scrubs to cosmetic surgery, virtually every society down through history has practiced some form of this.
Why it won’t work:
Of course, some of these treatments do work, to a limited extent, but no one can hold back the ravages of time forever, and trying to do so can do more harm than good. We’ve all seen cases of aging celebrities botoxing themselves until their faces are as frozen and plastic as a department store mannequin.
In the end, one wonders if it might not be better to save ourselves all the heartache and expense and simply accept the inevitable.

The appeal:
“Ensign, set a course for the Centauri System, maximum warp!”
There’s not a geek alive who hasn’t dreamed about the possibility of space ships traveling to alien worlds faster than the speed of light. Aside from the obvious cool factor and scientific potential, there are practical benefits of FTL travel, as well. While it may seem like science fiction, the prospect of an asteroid impact or other cosmological disaster striking the Earth is all too real, and FTL travel would offer us a means of escape in such a doomsday scenario.
Why it won’t work:
The problem is that FTL is, strictly speaking, impossible. According to Einstein’s theory of general relativity, nothing can travel faster than the speed of light. Some scientists have theorized that a space-bending propulsion system similar to Star Trek’s warp drive may actually work, but it would require an amount of energy roughly equivalent to that of a few dozen suns to work, so it’s not something we’re likely to see any time soon.
Still, they said man would never fly, so there’s always hope.

The appeal:
We’ve all seen the Jetsons. We’d all like a robotic servant to clean the dishes, wash the bathroom, iron our clothes, and do all those tiresome little chores that fill up our lives.
Robots are tireless, and they would never complain. They have no dignity to offend, and no task is beneath them. They could do wonders for the average lazybones, but there’s also great potential for looking after the infirm and elderly.
Why it won’t work:
Of all the things on this list, robot servants probably have the best chance of becoming a reality. They already have to a very limited extent; we have automated vacuum cleaners, factory workers, and warplanes. But the dream of a humanoid robot to take care of every one of our chores is still a long way off. The human home is a surprisingly complex environment, and building a robot to handle all it can throw at them is a monumental task. Even if such a robot ever was perfected, it could take years for the price to be low enough for even the rich to afford.

The appeal:
Like jetpacks, flying cars are something we’ve dreamed about and been told to expect for decades. The appeal is obvious: they’d be quicker, more convenient, and more fun — at least in theory. No more traffic jams. Long car trips take far less time. You get to take in the beauty of the world from above.
Why it won’t work:
Many have tried to construct a flying car practical for everyone, but none have succeeded. There are countless technical hurdles to overcome. What makes a good car and what makes a good plane are very different.
But even if a sound, cheap design could be perfected, there are many reasons why flying cars will never be a good idea. There would need to be runways everywhere, and that would require a total revamp of all our urban centers. Instead of solving traffic problems, it would make them worse; the more crowded the skies get, the more infrastructure we’d need to keep them organized. And not everyone is a good driver. Imagine how much worse a problem drunk driving would be with wings attached.

The appeal:
There may be nothing more universally true of all humans than the hatred of the common cold. No one likes it. Not even the most bizarre masochist can find anything pleasant in the experience. It’s just irritating.
Why it won’t work:
With all the medical advancements we’ve made, it seems ridiculous at first glance that we haven’t cured something as ordinary as the common cold. The reason for this is that there’s really no such thing as the common cold. It’s actually an entire family of thousands of similar but different viruses.
While it would be relatively easy to inoculate against one strain, that still leaves thousands more. And even if some group of people were to spend the absurd amount of time and effort it would take to inoculate everyone against all known strains, dozens more new types of cold would mutate as they worked. There’s just no way to cure them all. In the end, the only solution is to grit your teeth, take some Robitussin, and get through it.

The appeal: 
Teleportation, the ability to instantly transport people or objects to any location, is the ultimate convenience. No more long commutes. No more overnight flights. No more getting stuck in traffic. No more crowded elevators.
Even beyond removing such annoyances from our lives, teleportation could change the world for the better. Goods and mail arrive instantly. The amount of greenhouse emissions saved from no longer needing cars or planes would be enormous. There is no end to the problems teleportation could solve.
And aside from this, teleportation is just darn cool, as any Trekkie will tell you.
Why it won’t work:
Sadly, much like faster than light travel, teleportation is physically impossible according to our current levels of scientific understanding. The closest scientists have been able to achieve is to perfectly recreate tiny particles at one side of the lab while simultaneously modifying the original particles, in effect teleporting the particles. It’s unlikely this could ever be scaled up to anything of significant size, such as a person, however. For one thing, creating a new human body instantly from scratch is a bit beyond current technology, and for another, who would be fool enough to agree to be dismantled so as to create a perfect copy of themselves at their destination?