(in order of appearance)

Gian-Francesco Giudice
Head of the theory division at CERN, Geneva, and one of the first to propose a method to quantify how “natural” a theory is.

Michael Krämer
Professor of Physics at the University of Aachen, Germany and leader of the DFG research group “New physics at the LHC.” 

Gordon Kane
Professor of Physics at the University of Michigan and Director Emeritus at the Michigan Center for Theoretical Physics. Author of several popular science books and known for this predictions that supersymmetry would be found at the Large Hadron Collider (LHC).

Keith Olive
Professor of Physics at the University of Minnesota and director of the William I. Fine Theoretical Physics Institute. Known for this calculations that detail how supersymmetric particles would appear at the LHC.

Nima Arkani-Hamed
Faculty member of the Institute for Advanced Study in Princeton and director of The Center for Future High Energy Physics in Beijing, China. Winner of the inaugural Breakthrough Prize in Fundamental Physics. 

Steven Weinberg
Winner of the 1979 Nobel Prize in Physics. Author of several popular science books and textbooks on quantum field theory, quantum mechanics, and gravity. Weinberg holds the Josey Regental Chair in Science at the University of Texas, Austin.

Chad Orzel
Professor of Physics at Union College in Schenectady, New York. Author of several popular science books about how to teach physics to dogs and blogger par excellence.

Frank Wilczek
Professor of Physics at MIT and Stockholm University. Won the 2004 Nobel Prize in Physics together with David Gross and David Politzer. Author of several popular science books.

Garrett Lisi
Director of the Pacific Science Institute and avid surfer. Inventor of an exceptionally simple theory of everything.

Joseph Polchinski
Professor of Physics at the University of California, Santa Barbara, and member of the Kavli Institute for Theoretical Physics. Known for his seminal contributions to string theory.

Xiao-Gang Wen
Professor of Physics at MIT. Studied string theory under Edward Witten and now proposes that the universe is made of qbits.

Katherine Mack
Astrophysicist and, at the time of writing, postdoctoral researcher at the University of Melbourne. Known for her proficient skills in science communication and public outreach. 

George Ellis
Emeritus distinguished professor of complex systems at the University of Cape Town. Known for his founding contributions to the field of cosmology and fondness for philosophy.

Doyne Farmer

Physicist turned economist. Director of the Complexity Economics program at the Institute for New Economic Thinking at the Oxford Martin School, UK.

What happened since...

Chad Orzel has a new dog. Katherine Mack went on to become a professor at North Carolia State University. Garrett Lisi split up with his girlfriend, Michael Krämer no longer works on supersymmetry, and Joseph Polchinski, sadly, passed away before the book was published.