Thank you for the time and effort you have made to read this book. I hope you have found it profitable. Like every science textbook, it reflects the work of thousands, as every idea in this book was discovered by somebody. Discovering something new, even if it is just new to you, is very satisfying. When I am working on a new idea, I see it as a many-sided physical object in my mind, changing in shape, color and texture, rotating in all directions, until I can see the edges are parallel. When they are, I have the answer. I don’t know why my mind works like this, but it does. Sometimes the problem percolates for days or weeks, but sometimes it can take on-and-off thinking for years. Looking for confirmation of an idea means thinking up original experiments and making them work. When you do a novel experiment, you have to have so much trust in and understanding of your equipment that if you get an unusual result, you can believe the result is correct because you know the equipment is working properly, and therefore the hypothesis is true. This moment of discovery of something really original is thrilling: you know that you know something new, you know that it is important, and you know that no one else in the whole world knows it. It is a great gift to have that flash of insight when an experiment confirms an original idea. In over 35 years in science, I have been lucky enough to have this happen exactly four times. Each time, it is a golden moment, a glimpse of nature never seen before. In the spirit of discovery, I have climbed a hill to the west, away from a settled valley, and seen the dawn illuminate a new, unknown valley before me. Many scientists make that same climb, find a new valley and settle there, plowing the fields, building the towns, and leading others to the benefits of their discovery. Others, and I count myself lucky to be one of them, go into that new valley, stay for a while, and whether others come behind or not, set their restless mind on the new, undiscovered land over that next hill.