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So I'm a bit confused about why strings can't move at the speed of light. I understand that the end points do if the string is open, but the rest of it doesnt.

To paraphrase, really I want to know why you must have timelike and spacelike tangent vectors to a point on the world sheet of a string. Why is it unphysical to have all tanget vectors point in spacelike directions, with just a single lightlike one pointing in the direction of travel?

To paraphrase a final time: I know that if the string moves at the speed of light, then a point on the string at time t = 0 is mapped exactly to a point at time t = t, which we can keep track of. So: traveling at the speed of light means we can keep track of each point on the string. But this is not allowed. Why?

I'm a noob with this stuff so please try to dumb your knowledge down as much as possible so I can understand. Thank you!