Joji Monma thinks this is interesting: A small computation gives From 6. Relativistic strings from A First Course in String Theory, Second Edition by Barton Zwiebach Publisher: Cambridge University Press Released: January 2009 Note Use (\frac{\partial X}{\partial s})^2 = 1. Share this highlight http://www.safaribooksonline.com/a/a-first-course/288375/ Twitter Facebook Google Plus Email Get Instant Access Now Start a Free Trial Have an account? Sign in. Minimise Unlock the rest of A First Course in String Theory, Second Edition and 30,000 other books and videos By clicking this box, you confirm that you have read and agree to the terms and conditions of our Membership Agreement, and you understand that when your trial period ends, you will be required to provide billing information if you wish to continue using the service. Unlock the rest of this book Start a Free 10-Day Trial loading Learn about Safari for Business Have an account? Sign in.