I have been wondering if strings in string theory can go faster than light, as it is one dimensional when it does not vibrate? So do the same limits apply to it, I googled it but could not find a straight answer, does anyone have an answer or article?

  • $\begingroup$ Point particles are zero-diemtioal and cannot go faster than light. There is not reason strings should be able to. $\endgroup$ Dec 8, 2016 at 10:54
  • $\begingroup$ A massless string, such as the graviton that is a closed string, can travel the speed of light. $\endgroup$ Dec 8, 2016 at 11:04
  • $\begingroup$ I apreciate that, thanks alot! Do you perhaps have a link that supports this? $\endgroup$ Dec 8, 2016 at 11:05

1 Answer 1

  1. The longitudinal speed of a string is not a physical observable, due to reparametrization invariance, i.e. the points on a string are not material.

  2. The transversal speed of a string does not exceed the speed of light $c$.

  3. Free endpoints of an open string move with the speed of light $c$.

  4. Concerning the presence of tachyonic fields, see e.g. this Phys.SE post.


  1. B. Zwiebach, A first course in String Theory, 2nd edition, 2009; Chapter 6.
  • $\begingroup$ Is there a reference/explanation for the third point? $\endgroup$ Dec 25, 2016 at 11:29
  • 1
    $\begingroup$ The third point is explained in Ref. 1. $\endgroup$
    – Qmechanic
    Dec 25, 2016 at 14:38

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