INTRODUCTION Science asks the fundamental questions about why the world is the way it is. And over the course of history the world's greatest scientific minds have provided many of the answers. It's because of science that we now know the Universe began around 13.7 billion years ago in a superheated fireball known as the Big Bang. It's because of science that we know all living things in the world encode their biological blueprint on a chemical molecule known as DNA, which serves as the vehicle by which we pass our traits and characteristics down to our offspring. It's because of science that we know our planet was once ruled by supersize reptiles and that one day 65 million years ago they were wiped out by the impact of a vast comet or asteroid with the Earth. And it's because of science that we have computers in our homes that are more powerful than the fastest university supercomputers of just ten years ago. Science probably encompasses the biggest areas of human intellectual endeavor.

Fitting, then, that it should get billed alongside a suitably big number -- 1001. Yet when it comes to dividing up the whole of scientific progress from the last 5,000 or so years into 1001 bite-size nuggets, suddenly it seems woefully small. That's about one entry in this book for every five years -- fine for the Dark Ages perhaps, but something of a squeeze for years like 1996 when we had Dolly the sheep (the worlds first cloned mammal), claims to have found life on Mars (as fossilized bugs inside a meteorite), and the Deep Blue chess computer won its first game against Garry Kasparov (who was at the time the reigning world chess champion). In fact, if this book was arranged chronologically I'd probably have run out of space somewhere in the middle of the Renaissance. So instead you'll find the pages within organized by subject. I've taken modern science as it's currently understood and partitioned it into ten major sections: physics; chemistry; biology; the Earth; space; health and medicine; social science; knowledge, information and computing; applied science; and the future. Each of these categories then splits down again into subsections on key topic areas, and within each you'll find, on average, 12 entries to cover that particular topic. So, physics has subsections on heat, relativity and quantum theory, to name a few.

And, for example, the quantum theory subsection has entries on ideas such as Schrödinger's cat, the uncertainty principle, and the 'many worlds' interpretation of quantum theory. My aim as a writer was to combine the breadth of a reference book -- for example, a dictionary of science -- with the accessibility and sense of fun that you get from a piece of popular science writing. That was my guiding principle in turning what could have easily been 'Science 100,001' into what you have here. Out went the abstruse and the arcane -- topics that the lay reader will neither need nor care about. And what was left I condensed, distilled and clarified into what's hopefully the ultimate balancing act between readability and comprehensiveness. The entries are written in plain and concise English. Often they are self-contained: but when they aren't there are references in bold type to other entries and subsections that either aid understanding or provide further information. If you aren't sure which subsection the entry you are looking for is in, there's a comprehensive index to guide you straight to it.

Subsections themselves, meanwhile, are written with as much continuity as possible, so if you're after the complete overview of quantum theory, then that subsection of physics will work as an essay that can be read from start to finish. Science 1001 is a big book about the biggest subject. I hope you enjoy it. Paul Parsons.