An Introduction to String Theory

A Talk by Steuard Jensen, 11 Feb 2004

I'll begin with an explanation of the origin and audience of this talk, and then I'll give a full outline with links to the slides. The following pages contain snapshots of the overhead slides I used, together with explanations and comments similar to those I made in the talk itself. But if you want to jump straight to the talk right away, be my guest.

Assuming your browser supports style sheets, some of the explanatory comments will be indented and printed in a slightly different color like this. Those comments contain more "detailed" information that a casual reader could probably skip without missing much. The important bits are usually near the top and the details toward the bottom, but occasionally the final comment on a page is of general interest, too.

Background on the talk

This is a talk that I gave to the Chicago chapter of the MIT Alumni Association on 11 Feb 2004. The audience was about 40 people with a range of backgrounds, most of whom had taken a year or two of physics while at MIT (but for some of them, that was quite some time ago). Many of them had seen the NOVA series "The Elegant Universe" and were looking for a deeper level of understanding that took advantage of their physics experience.

As the original invitation to give the talk put it,

The challenge is to describe String Theory to our audience of engineers who have completed 1 or 2 years of undergraduate physics, perhaps 10 years ago, are used to dealing with equations but do not have a math background beyond differential equations, and are not aware of the concepts used in Quantum Field theory or String Theory.

The group was eager to see at least a few of the equations of the theory, which I think is precisely the right instinct to have if you want to learn a new scientific concept. But that prospect was daunting to me, because I know just how painful it can be when a speaker tries to push an audience through a lot of unfamiliar math in a short period of time. Complicated equations belong in classrooms, not in general talks. So I did my best to balance those competing desires: I kept the equations to simple algebra, and most of the important ones were variations on a single theme so that the audience could get at least a bit comfortable with it (that "theme" was essentially "energy spectra").

I organized the talk more or less historically, beginning with a review of relevant concepts in 20th century physics and then showing how those concepts are modified in string theory, with a final "payoff" as we discovered the beauty of T-duality (in the actual talk, I didn't have time for the material on open strings and D-branes). In retrospect, this may not have been the best approach, simply because there was a lot of pre-string material to review. While quite a few people in the audience were actively involved from start to finish (there were many good questions throughout the talk), I think some others might have enjoyed it more if I'd gotten to string theory itself faster. In more recent talks of this sort, I have made an effort to introduce the novel ideas of string theory side by side with the physics that came before. But for a web version like this, I feel like the existing format works pretty well (feel free to let me know if you think I'm wrong!).

And for the record, I have no clear idea why my (very obsolete) presentation software decided to print some letters darker than others, and there's certainly no point in me trying to debug it now. (I've now upgraded to Apple's excellent Keynote 3 program, which works beautifully and is a real joy to present with.)


  1. Introduction
  2. Theoretical physics before String Theory
  3. Gaps in the Theories and String History
  4. The Basics of String Theory
  5. T-duality and its implications
  6. Conclusions

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Copyright © 2004 by Steuard Jensen.