Knowing

It's impossible to know everything. That shouldn't be surprising to most people.

However, the next statement will probably flip out a few people: it's impossible to know not just everything but anything.

Well, for certain values of "know", anyway.

The fully qualified answer is this: it is impossible, within the confines of the universe, to be 100% certain that any knowledge or perceived knowledge is 100% representational of reality. There are countless - in fact, likely near-infinite - examples of this in history, where various folks (many quite brilliant) stumbled upon something and said, "Ah ha! At last we know for sure!" only to have some piece of data float on by later that doesn't fit their theory, leading to a new theory and a new "Ah ha! At last..."

One might argue that the single biggest obstacle to scientific advancement is the certainty that one is correct. That being said, one could also say that the single biggest boon to scientific advancement is the drive to legitimately prove it - which always, eventually, fails.

Now, there are a few arguments that challenge this, usually nuanced.

In the first: "But, our laws and theories and science have led us to do amazing things! They have to be true!" No, they don't. They just have to be consistent enough with reality within allowable tolerances. An excellent example of this is Aristotalean mechanics: the fundamental principles are flat-out wrong, as proven by thousands of years of study. However, they're "wrong" by details that don't arise in practical use, especially for Ancient Greek-level technology. So, while "wrong", they're decent enough approximations that amazing things could be done using them. Modern science is no different. Our tolerances in many situations are much smaller, so our theories tend to be consistent enough to a very low level of results. However, that doesn't mean the logic or reasoning behind them is accurate or that some random bit of data won't fall into our laps in the next few years to which they are horribly inconsistent. Just take a look at things like dark matter and dark energy if you want to see examples.

The second argument is far more layman: "Okay, so that kind of technical stuff may not be 'known', but real-world stuff is. Like, I know I'm standing here talking to you." No, you don't. This piece of the puzzle can get a little more philosophical, but it's true on the practical level as well: you can never state how something is, only how it is perceived. The difference is far from trifling. In scientific terms, we have Heisenberg's Uncertainty Principle, which states that the act of observing something inherently interferes with the observation. Combine that with limitations on observational speed, and it is easy to deduce that any statement we could make, technically, about something has a decent chance of being false by the time we make it.

There's another sort of "fuzziness" that gets introduced, especially with real-world examples. For one: no human is a thing; humans are collections or concepts to begin with. Each person is made up of multiple bits - billions or more, depending on the level we wish to examine - but even from a cellular level, the body has pieces constantly growing, changing, and dying. Matter is taken in, matter is excreted, and as a result the body itself changes. Even without that, individuals atoms or subatomic particles disappear and reappear according to quantum flux principles. You as an individual and everything around you that you recognize only exists as an average state of multiple bits that are constantly changing. Again, our level of "allowable tolerances" comes into play: nothing is known except to a certain degree of approximation, and that includes existence.

The final support for our lack of knowledge is both more technical and more philosophical: everything in the universe seems to be affected by everything else. And by "everything", I mean everything. Every electron, every microvolume of space, every spark of energy affects and is affected by everything else. It is, therefore, impossible to know everything about, for example, a proton without knowing how it is being affected by everything around it - which would require knowing everything about everything. Now, on a local level, the larger part of the universe affects everything evenly so that only local variations really "matter" for our purposes: for example, we don't need to know the locations of all the planets and their velocities to be able to determine (within practical tolerances) how fast a cannon ball will fall from a tower, because us, the tower, the ground, and the cannon ball are all being affected about the same way by the planets. However, that's just another level of approximation - if we wanted to know how fast the cannonball was travelling through space, we'd have to know everything.

It's ironic that, in a very real sense, one reason we've managed to accomplish so much is that we're egotistical enough to think that the levels of observation we can make are the only ones that matter.

If you want to try to work these ideas into your real life, you can answer "probably" instead of "yes" to questions. You can also try to work in E-Prime, though it might take people a while to notice the difference.

And, finally, I'll just say that while it's impossible to know everything, or even anything, that's far from a reason for us to stop trying. As the phrase goes, "A man's reach should exceed his grasp/else what's a heaven for?"