The Road to Reality Study Notes

Each week, as we go through each chapter in The Road to Reality Book Club, we use that as an opportunity to write down what we think are the major points to be taken from our reading. In this page we sum up what we believe Penrose was trying to convey and why. The hope is that these community-generated reading notes will benefit people in the future, as they go on the same journey.

Chapter 1

• Add a summary here

Chapter 2

• summary

Chapter 3

• and so on

Chapter 4

Penrose introduced the complex numbers, extending addition, subtraction, multiplication, and division of the reals to the system obtained by adjoining i, the square root of -1. Polynomial equations can be solved by complex numbers, this property is called algebraic closure and follows from the Fundamental Theorem of Algebra. Complex numbers can be visualized graphically as a plane, where the horizontal coordinate gives the real coordinate of the number and the vertical coordinate gives the imaginary part. This helps understand the behavior of power series; for example, the power series 1-x²+x⁴+… converges to the function 1/(1+x²) only when |x|<1, despite the fact that the function doesn't seem to have "singular" behavior anywhere on the real line. This is explained by singularities at x=i,-i.

Finally, the Mandelbrot set is defined as the set of all points c in the complex plane so that repeated applications of the transformation mapping z to z²+c, starting with z=0, do not escape to infinity.

Other Resources

• The Portal Book Club - We have a weekly group that meets to talk about this book. Come join us in Discord!
• Chronological guide to concepts introduced in TRTR Google Doc
• Book Club Resources in Google Drive