string endpoints move at light speed--?

gabeeisenstei

In Zweibach's introduction to string theory I encounter the assertion that the endpoints of an open string move at the speed of light. A few other sources on the web agree with this. But nobody bothers to tell me what the heck it means (not even in http://www.physicsforums.com/archive...p/t-49119.html , where it is stated that only the endpoints move at light speed, not the rest of it).

Where are the endpoints going so fast? Are they just vibrating in a tiny space? Are the endpoints massless, so as not to violate relativity?
What am I missing?

haushofer

It's a nice question. Remember that "mass" is a property of the string vibrations, not of the string itself (perhaps something like that is defined in string field theory, but I'm not acquinted with that)! So I'm not sure what "massless endpoints" would mean.

But can't you ask the same question for, e.g. gravitons? It's a consequence of the dynamics, so I'm not even sure what the "why"-question means.