Impossible is a relative term, like all terms. It is a necessary term because it allows us to assess and communicate the feasibility of something. Some things appear more plausible than others, and thus those things with the lowest relative level of probability in a given context are described as impossible. But of course impossible is not absolute. Only one who has complete knowledge of life and the cosmos can state absolutely that something is impossible. I’ve never met any such person, and I doubt you have either, so we may both conclude that anything that was ever told to us to be impossible can be, in fact, possible.
Our notions of possibility are necessarily based upon our experience, but our experience is limited—perhaps infinitely limited. Thus our assessment of probability is infinitely imprecise and is infinitely likely to be entirely inaccurate.
Of course, our entire system of scientific understanding and prediction is dependent upon the requirement of isolated systems. No scientific conclusion could ever be made without isolated system assumptions. In a nutshell, an isolated system (or “closed system,” I use them synonymously here) is a finite system which is closed to any outside influence. An isolated system assumption means it is assumed that the system in question is closed.
We make isolated system assumptions all the time. For example, suppose I throw a frisbee across a field and then observe the frisbee hover in the air like any well made frisbee before hitting the ground. I have a clear view of the path of the frisbee the entire time and I conclude that it was the cushion of air created by the motion of the disk that kept it afloat for an extended period of time before gravity finally won out. I could be wrong in this particular instance, however. There could have been invisible multidimensional fashion-monkeys who saw me toss the frisbee and thought it was the gift of a new hat. One monkey could then have grabbed the flying hat and donned it atop its head and taken a stroll down the field until taking it off out of disinterest and placing it gently upon the ground. This is entirely possible, and I rightly recognize the presence of an infinite number of possible outside influences. But as a scientific observer I have no choice but to rule out all influences except those which can be perceived and measured. Thus, by definition, I must close the system. Only then can I make meaningful and useful scientific conclusions and gain results which can be predicted and intentionally repeated.
It is important to understand that just because a speculated scenario, such as the intervention of cosmic monkeys, seems exotic does preclude its possibility. As humans, our limitations have often caused us to and continue to cause us to make pretentious and immature proclamations about the nature of plausibility, probability, and possibility. We tend to positively correlate exoticness with unlikelihood. There is rationalization for this, but we must not fall captive to the fallacy that the limitations we put on the universe are anything more real than our own mental limitations. We must recognize the difference between our best guesses of emergent patterns and the actual powers of the universe. Who says that the universe cannot at any moment exercise its prerogative to re-scramble the laws of physics? We must approach science and understanding humbly.
I offer you some examples of how historically in error our judgements of possibility have been. This way you can begin to make you own reassessments of what lies within the realm of human possibility:
Imagine that you are a caveman from 100,000 years ago, alike in mental capacity to any modern day homo sapiens. There are many things which you know to be impossible. You believe you are quite reasonable and just in such opinions. You know that when you say something, the sound disappears and cannot be captured. You know it is impossible to encapsulate or transport a speech the tribe leader makes. You know that humans are destined to walk the face of the earth and cannot leave it, yet must return to it no matter how high one jumps. To leave the surface of the earth and journey past the clouds is without doubt impossible. If we were to accelerate forward in time until 200 years before the present, even as a leading scientist you would still know that things such as induced coherent light (lasers) and frameless eyeglasses (contact lenses) were impossible. If we catapulted you another 100 years forward to 1910 you might be more flexible, but you would still argue that if anything is known to be true it is that objects cannot pop in and out of existence (ie., that nothing can travel from point A to point B without traversing all of the distance in between on a single trajectory). Sadly, many of you may still believe this to be true today, oblivious to the wonders of quantum mechanics (you’ll want to watch the whole clip).
Our difficulty grasping the realm of possibility stems not only from the limits of our experience but, relatedly, from the limits of our perception, as will I expatiate in another post. We just don’t know any better much of the time. But the least we can do is to maintain an open and curious mind and a tolerance for unorthodox ideas. After all, what we know to be true and possible changes over time; hindsight is 20/20, as they say. The writers of “Men in Black” had something to say about this facet of the human condition. Consider carefully the elegant words of J’s partner, K, after he reveals to J that extraterrestrials are living in Manhattan:
“Fifteen hundred years ago, everybody knew that the Earth was the center of the universe. Five hundred years ago, everybody knew that the Earth was flat. And fifteen minutes ago, you knew that humans were alone on this planet. Imagine what you’ll know tomorrow.”