As featured in Douglas Adams' The Hitchhiker's Guide To The Galaxy, it's The Ultimate Question. The ultimate question of life, the universe, and everything. The characters Vroomfondel and Majikthise couldn't articulate it any better than that to Deep Thought: the giant supercomputer they had built with the sole purpose of answering this, the most important question one can ask. Of course you'll know already that Deep Thought's answer to the ultimate question -- after six million years' processing -- was "42", the only problem with that answer being that it could only be of value if one knew precisely WHAT the ultimate question was. But of course, they didn't and so were none the wiser.
It's a tough question to fit into a single question isn't it? The reason I mention it is that I have been contemplating it recently and taking my sixth and fourth attempts respectively to get to the ends of two famous books on the subject by Stephen Hawking: A Brief History of Time and The Universe in a Nutshell. In both books Hawking attempts to explain what we know about the universe and passionately describes the work going on in Physics right now to fill in the remaining blanks.
I've always had an interest in Physics and have been annoyed that, despite having owned both these books for years, I had not managed to get to the end of either of them. They start off accessibly enough for anyone who studied Physics at school, with Newton's laws of motion and Einstein's theories of relativity. I can get my head around gravity, the solar system, elliptical orbits, I can even accept huge-scale concepts such as the speed of light and black holes. But from there on things start to skitter down a very slippery slope of incomprehension, starting with there not being space, and time, but a single continuum in four dimensions called spacetime, and that spacetime is curved and not flat, and that if the universe is even now continuing to expand (as has been proven) like the debris of an explosion, then there must have been an event long ago -- the explosion itself -- where all the matter in the universe was compressed into an object of zero size yet infinite mass and infinite density. This concept is known as a singularity and we call the explosion that marked the origin of the Universe "The Big Bang". From there the slope steepens as Hawking turns his attention to the branch of Physics that everyone is depending on to complete the jigsaw: Quantum Mechanics. I won't go into detail (I can't!) but Quantum Mechanics has to do with the very, very small, dealing with subatomic particles and moving on from there to matter and antimatter (ANTIMATTER!), particles existing in pairs and annihilating each other when they meet up.
Well I am proud (or should that be relieved?) to say that I have finally managed to finish A Brief History Of Time, and am close to finishing The Universe In A Nutshell, having promised myself to plough on through both whether I could grasp all the concepts or not. This is actually a worthwhile thing to do, because there are clear, lucid and important points in among the quarks, photons and gravitons, and it's also the only way of getting through them unless you yourself are a Quantum Physicist. I'm sure there must be many many people who are not professional scientists but who nevertheless have a burning curiosity to understand how we got here on Planet Earth, and to hear a rational explanation for the existence of everything we see around us, on the earth and in the sky. The problem with these books is that they are so technical as to put off all but the most determined truthseeker, despite being marketed as having been written for the layperson. What we need is, "Life the Universe and Everything for Dummies": anyone seen that on the bookshelves? Maybe I'll write it one day.