Sometimes the pendulum of our belief swings too far. For example, our perspective on what's possible.
Before the Renaissance, there were plenty of things that were deemed absurd. If you told Henry the Eighth his descendants would one day carry a device allowing near-instant communication with anyone on the planet, he might break into a condescending smile and then have you committed to some fetid hoosegow where you wouldn't annoy his subjects.
Hank's attitude seems cramped and unimaginative today, and so naturally we're on guard about being too quick to condemn an outlandish idea. We've seen too many instances of fantasy becoming fact.
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The mantra that "anything is possible" is one you'll hear a lot - whether it's a comment on time travel or shrinking humans to fit inside a blood vessel. But let's get real: Not everything is possible.
If a phenomenon violates physics, don't count on it taking place, no matter how advanced the technology. And even some behavior that is permitted by physics might not occur before the universe runs out of steam. For example, there's a finite possibility that my Honda's carburetor could quantum mechanically tunnel to a street corner in downtown Beijing while I eat breakfast. But the odds are so close to zero that even if I wait trillions of years, this is one bit of car trouble I'll likely never see.
Ergo, to antagonize those who might be planning to write the definitive sci-fi novel or screenplay this weekend, I've compiled a short list of my favorite things that, even in this era of relentless surprise, I wager will never happen.
The first is faster-than-light travel, or warp drive. This is of such obvious utility to space opera that it's like corn nuts — hard to give up. But it violates general relativity except in circumstances so extreme they might never prove useful. Of course, if you travel just below the speed of light you can slow down your own aging.
Consequently, future manned travel to the stars might be possible if you can arrange to corral the prodigious amounts of energy required. That's an engineering problem, which — unlike a physics problem — is not a priori insurmountable. So even though I'd bet against warp drive (and a "Star Trek" future), I'd allow for the development of "bent drive" in which astronauts reach the stars, but lose permanent touch with their peers. I will be pleased for you to prove me wrong.
A second and highly trendy anticipated development is instantaneous communication. This, too, is a staple of sci-fi, and is essential if you're tasked with establishing a galactic empire. Many people think that being able to text or talk without the usual speed-of-light delay is in the offing because of the (demonstrated) existence of quantum entanglement. Unfortunately, while quantum entanglement is real, it doesn't allow instantaneous communication. I can hear you whinge, but it just doesn't.
Now here's another passel of phenomena that suggest really impressive results — so-called "exponential" trends, things that change geometrically with time, and that could rework society. These are often temporarily impressive, but are ultimately constrained by the finite extent of the visible universe.
The poster child for exponential trends is the growth in human population. Around the 1970s, world population had a doubling time of only forty years. In other words, the tally of people could increase by a factor of four between your birth and death. This ballooning of bodies produced a torrent of dire predictions about starvation, disease, and an irritating lack of personal space.
But no exponential trend can go on forever. Indeed, as Isaac Asimov pointed out years ago, the growth rate, had it continued unabated, would convert all the mass in the visible universe into human flesh in less than seven millennia. You could reliably call that a hard limit.
Similar arguments have been made for other exponential phenomena, such as the increase in computer power, also known as Moore's Law. It can't go on forever (and indeed, some claim it has already slowed).
In other words, the next time you hear a news story about exponential growth, improvement, or threat, keep in mind that whatever else you can say about it, it's definitely temporary. Although you might not like how or where it stops.
There are no limits to our imagination, but there are limits in the universe. Some things won't happen because they're just highly unlikely — such as Spiderman, the fountain of youth, or alien invasions. But if you're wont to do so, you could answer that these dramatic developments don't violate physics, and are therefore simply a matter of having patience or waiting for a nerdy development in someone's basement lab.
But the bottom line is this: Sure, there are more things in heaven and Earth than dreamt of in your philosophy. But don't confuse the possible with the precluded.
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