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?"


Gravity got you down?

(Oh yeah, this one's going to be fun...)

Well fret no more. I'm here to tell you that gravity doesn't exist!

There, feel better? No? Still tethered to your planet, at the bottom of a gravity well hundreds of miles deep (unless I have readers on the space station)?

Okay, then, let's back up a little. Gravity exists, but no one knows what it is or why.  If you go by the old rule of "if you can't define it's limits, it doesn't exist", we could argue that gravity doesn't.  (Hrm, still not floating...)

Gravity's a bit like time in that respect. We have it, we can measure it, we can even use it, but we have no way of describing it fundamentally. We have no real notion of what is taking place, other than a grade-school concept of "the attraction between two bodies".

First, let's give what we *do* know: gravity seems to be an attractive force. This doesn't mean it's pretty: I mean that it brings two objects together. The amount of gravity any one object "inflicts" on any other can be calculated based on their relative masses and separation distances. We also know that gravity is indistinguishable from acceleration.

That's pretty much it. We don't know how it works: most interactions between objects require a medium of interaction, and despite searches for the almighty graviton, no such particle has ever been detected. Einstein got around this by stating that the "medium" was spacetime itself, and while it's a neat little answer, it's a bit too neat - and too black-boxy - for most modern physicists. We also haven't really been able to determine whether gravity operates within discreet units like other forces; this is important, because discretion would imply a quantum nature whereas a lack of discretion would seem to imply - well, something else. We also know that gravity is related to mass, but we don't know *why* it's related to mass.

We also have to reconsider the whole "attraction between two bodies" concept, not because it's wrong but because it's a simple statement that really doesn't make its full impact apparent. When we say "between two bodies", we really mean "between two things that exist" - again, since gravity is related to mass, and mass is interchangeable with energy, and everything in the universe has mass and/or energy, everything inflicts some gravity. Also, everything is affected by gravity. So, our little "attraction between two bodies" really means "attraction between everything in the universe and everything in the universe". That's right, gravity is trying to pull together everything in the universe; most of the time the force is too small to be measured or effective, but it's always there (and yes, while this means you're technically being drawn however slightly towards that bag of potato chips, it doesn't explain why you had to eat the whole bag in one sitting).

There is also, noteably, no such thing as "anti-gravity", which is one more trait gravity shares with time: whereas most forces or actions have an opposition, gravity (like time) does not. Even antiparticles - which are just mass like anything else - are attracted to each other and to standard particles. We've never encountered anything that has a reverse gravitational effect - basically, a repulsion instead of an attraction - that isn't based on some other force.

That's not to say a lot of people aren't trying to solve the unknowns. Quantum gravity, quantum loop gravity, holographic theory - there are a lot of approaches to answering the big question of how gravity works. There are even a few that state that gravity, like centrifugal force, "doesn't really exist" and is instead just something else being (mis)interpreted as a separate force - usually acceleration (again!) or entropy.

We'll have to see where it all goes. Since much of our future scientific and cultural expression will rely on overcoming gravity efficiently (at least locally), I expect this area of study to be one of the biggest for the next 50-100 years or until a major paradigm shift takes place.

Until then, it helps to realize that even something as familiar as gravity isn't all that familiar and remember all the good things that gravity permits - like a nice day in the waves at the beach.