String Theory: Vibrations & Plank Lengths

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Discussion Overview

The discussion revolves around the implications of string theory, particularly concerning the concept of string vibrations and the Planck length. Participants explore the nature of vibrations in strings, the interpretation of lengths smaller than the Planck length, and the rigidity of strings as fundamental entities.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Paul questions whether vibrating strings could imply lengths smaller than the Planck length, suggesting that dividing a Planck length string into parts seems contradictory.
  • One participant asks what longitudinal vibration on a string would mean, indicating a need for clarification on the concept.
  • Another participant challenges the idea of strings changing length, questioning the implications for the physics described by string theory.
  • It is proposed that string theory encodes multiple ideas across different dimensions, and that transverse vibrations are preferred for representation.
  • A participant asserts that the Planck length is not the smallest possible length, arguing that shorter lengths could theoretically exist despite being unmeasurable with current technology.
  • Concerns are raised about the rigidity of strings if they are considered the smallest entities, questioning how they can vibrate if they are infinitely rigid.
  • A later reply references an earlier post to reinforce the idea that the Planck length is not definitively the smallest length, reiterating the uncertainty surrounding this concept.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the implications of the Planck length and the nature of string vibrations. The discussion remains unresolved, with no consensus on the interpretations of these concepts.

Contextual Notes

There are limitations regarding the assumptions made about the Planck length and the rigidity of strings, as well as the definitions of vibrations in the context of string theory. These aspects remain open to interpretation and further exploration.

pforeman
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In string theory, a string is at or near the plank length. If a string is vibrating, or if it is curved into something like a circle, aren't you having something smaller than a plank length?

With a vibrating string part of the string is inverted to the other part, this would mean that you could (and should?) divide a plank length string into parts Which I thought should be impossible.

Is there some reason that the vibration isn't thought to be "lengthwise" with the vibration being from one plank length to two plank lengths or some integer thereof?
Thanks,
Paul
 
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What would a longitudinal vibration on a string actually mean?
 
stretching from one length to another?
 
What is stretching from one length to another? You mean you are imagining the strings would change length?
What would it mean for the physics described by the string?

Basically string theory is set up to encode a lot of ideas at once as different dimensions.
The vibrations are transverse because it is difficult to draw a graph of longitudinal waves logitudinally.
So - how would it help to propose a string-model for fundamental interactions (etc etc) in which the strings carry longitudinal vibrations?

I'm taking this tack because I suspect you have been attempting to understand string theory based on your understanding of classical waves on a string. That approach will get you tied up i knots (could't resist).
 
pforeman said:
... aren't you having something smaller than a plank length?
l

You seem to have a belief that the Plank length is the smallest possible length. This is not true --- it's just the shortest length that we could ever even theoretically measure according to current theory. The fact that we could not measure shorter lengths doesn't mean they are physically impossible.

EDIT: and by they way, the Plank length using today's technology is MANY orders of magnitude smaller than anything that can be measured. But again, this does not rule out smaller lengths.
 
Assuming that a string is the size of 1 plank and thus the smallest possible entity. Also that it is not comprised of smaller particles then would it not be infinitely rigid? If so then how can it vibrate?
 
tanzanos said:
Assuming that a string is the size of 1 plank and thus the smallest possible entity.
... this question has been answered by phinds in post #5 when he said:
You seem to have a belief that the Plank length is the smallest possible length. This is not true...
 
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