Warped Passages - Lisa Randall [41]
Extra-dimensional models address such particle physics problems, but they also use ideas from string theory. After discussing the basics of particle physics, we’ll introduce the fundamental motivation and concepts in string theory. We won’t derive models directly from string theory, but string theory contains some of the elements that are used when developing extra-dimensional models.
This review covers a lot of ground because research on extra dimensions ties together many theoretical advances in the two major strands of particle physics—model building and string theory. Some familiarity with many of the most interesting recent developments in these fields will help you to better understand the motivations and the methods underlying the development of extra-dimensional models.
However, in case you want to jump around, I will end each of the review chapters with a bulleted list of vital concepts that we will refer to later on when we return to extra-dimensional model building. The bullets will serve as a short cut, a summary, in case you want to skip a chapter or if you want to focus on the material we’ll turn to later on. I might occasionally refer to points that aren’t in the bullets, but the bullets will review the key ideas that are essential to the major results in the later part of the book.
In Chapter 17 we’ll start to explore extra-dimensional braneworlds—theories that propose that the matter of which our universe is composed is confined to a brane. Braneworld ideas have provided new insights into general relativity, particle physics, and string theory. The different braneworlds I’ll present make different assumptions and explain different phenomena. I’ll summarize the distinctive features of each model with bullets at the end of these chapters as well. We don’t yet know which, if any, of these ideas correctly describe nature. But it’s entirely conceivable that we’ll ultimately discover that branes are a part of the cosmos, and that we—along with other, parallel universes—are confined to them.
One thing I have learned from this research is that the universe often has more imagination than we do. Sometimes its properties are so unexpected that we stumble across them only by accident. Discovering such surprises can be amazing. Our known physical laws turn out to have startling consequences.
Let’s now begin our exploration of what those laws are.
5
Relativity: The Evolution of Einstein’s Gravity
The laws of gravity are very, very strict.
And you’re just bending them for your own benefit.
Billy Bragg
Icarus (Ike) Rushmore III couldn’t wait to show Dieter his new Porsche. But as proud as he was of his car, he was even more excited about his Global Positioning System (GPS) that he had recently designed and installed himself.
Ike wanted to impress Dieter, so he convinced his friend to drive with him to the local track. They got in the car, Ike programmed in their destination, and the two of them set off. But to Ike’s chagrin, they ended up in the wrong place—the GPS system didn’t work nearly as well as he had thought it would. Dieter’s first thought was that Ike must have made some ridiculous error, like confusing meters and feet. But Ike didn’t believe he could have made such a stupid mistake, and he bet Dieter that wasn’t the problem.
The next day, Ike and Dieter did some troubleshooting. But to their dismay, when they went for a drive the GPS was even worse than before. Ike and Dieter searched again for the problem and finally, after a frustrating week, Dieter had an epiphany. He