Two friends of mine, Yuan Yao and Weiguang Cao, started to read the book, A First Course in String Theory by Barton Zwiebach, a few weeks ago. Barton Zwiebach is my good-old professor in 8.04x – 8.06x quantum mechanics course series. I like his lectures very much, so join my two friends.

## Course information and video lectures

This textbook is based on an undergraduate course Prof. Zwiebach gives in MIT (with course number 8.251). The syllabus, readings and assignments of the course can be found in MIT’s OCW website here. Although this OCW course does not provide lecture videos, perimeter institute has recorded Prof. Zwiebach’s lectures in PSI lectures of 2012 – 2013. This lecture videos can be found in the *review* tag of this website.

## First five video lectures

In the first five lectures, Prof. Zwiebach starts from non-relativistic strings, then goes on to discuss how to find the Lagrangian for relativistic particles, and finally introduces relativistic strings. It is an exciting journey!

Non-relativistic string is the most familiar object, just imagine strings in guitars or violins. They vibrate when given an initial configuration by plucking them. Relativistic point particle is more peculiar, their velocity saturates if you keep accelerating them.

Relativistic strings are even more peculiar. If both end points are free, an open string will still vibrate in a crazy way, with its end points moving in the speed of light. You can also imagine creating a relativistic string by pulling it out from a D-brane (a very heavy thing) with constant force $T_0$ until it has length $l_0$. The rest energy of this string is $T_0 l_0$. All these interesting results come from the Nambo-Goto action. The only consideration when writing this action down is that the theory should satisfy the space-time symmetry of special relativity. It is amazing to see interesting physics coming out from a simple-looking action from geometric arguments.