Strings and the size of particles

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Discussion Overview

The discussion revolves around the relationship between string theory and the size of elementary particles, exploring theoretical implications, definitions, and the nature of particles as modes of vibration of strings or branes. The scope includes theoretical physics, conceptual clarifications, and critiques of string theory.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants propose that if elementary particles are modes of vibration of strings at the Planck length, it raises questions about how particles can be much larger, up to 10^20 times that length.
  • Others argue that in the Standard Model, particles are initially massless and acquire mass through the Higgs mechanism, with protons and neutrons being composite systems of quarks and gluons, which may also be viewed as vibration modes of strings.
  • Some participants assert that there is no established link between particles and strings, suggesting that discussions around string theory often lack empirical support.
  • Concerns are raised about the terminology of "string theory," with some stating that it should be referred to as "brane theory" due to the current focus on branes in research.
  • Participants note that the only well-known vibration modes in string theory are massless supersymmetric modes, with no confirmed non-supersymmetric modes corresponding to known particles in the Standard Model.
  • There is uncertainty expressed regarding the actual size of strings or branes, with some suggesting that theorists assume a spacetime continuum that may not align with Planck scale dimensions.
  • Some participants highlight that in cosmological contexts, strings or branes are theorized to be of cosmological scale, which contrasts with popular representations of string theory.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the validity and implications of string theory, with no consensus reached on the relationship between strings and particles or the appropriate terminology for the theory.

Contextual Notes

Limitations include the lack of empirical evidence linking strings to known particles, the dependence on theoretical definitions, and the unresolved nature of the size of strings or branes in various contexts.

Moneer81
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Hi,

If elementary particles are nothing but a mode of vibration of a string, and if strings are on the order of Planck's length, then how did we end up with particles that are as big as 10^20 times Planck's length?
 
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In the Standard Model the particles start out as massless and dimensionless. They acquire mass through the Higgs mechanism. The proton and neutron have size because they are multiparticle systems with lots of space between the three quarks and an "ocean" of massless virtual gluons flying around holding it all together. As quantum particles they are defined by their wave functions. So the quarks and gluons could well be vibration modes of tiny strings which BTW are not the size of the PLanck length but somewhat bigger.
 
Moneer81 said:
Hi,

If elementary particles are nothing but a mode of vibration of a string, and if strings are on the order of Planck's length, then how did we end up with particles that are as big as 10^20 times Planck's length?

Unfortunately

i) there is no link between particles and strings. Except methaphysical ones.

ii) string theory is a misnomer, since current theory work with branes and would be called brane theory. In fact, is callled brane theory in research papers but "string theory" in popular talks and books. Emphasizing the myth around string theory.

iii) The only "well-known" vibration modes are masless supersimmetric modes. There is a belief that would explain hypotetical particles like the graviton, but no prooof.

iv) Nobody has found nonsupersimmetric nonzero mass modes of vibrations that coincide with known particles of the standard model.

v) Nobody know if strings (or branes) are of the order of Planck's length.

vi) Etc
 
Juan R. said:
Unfortunately

i) there is no link between particles and strings. Except methaphysical ones.

ii) string theory is a misnomer, since current theory work with branes and would be called brane theory. In fact, is callled brane theory in research papers but "string theory" in popular talks and books. Emphasizing the myth around string theory.

iii) The only "well-known" vibration modes are masless supersimmetric modes. There is a belief that would explain hypotetical particles like the graviton, but no prooof.

iv) Nobody has found nonsupersimmetric nonzero mass modes of vibrations that coincide with known particles of the standard model.

v) Nobody know if strings (or branes) are of the order of Planck's length.

vi) Etc

(i) through (iv) are absolutely correct and I didn't deny them.


On (v), string (and brane and M-) theorists assume they have a spacetime continuum available to them and that motion, implied in the worldsheet, is unproblematical. Furthermore they (mostly) treat gravity as negligible. This implies their dimensions are large compared to the Planck length where the Compton radius equals the Schwartzschild radius.
 
I vote for (vi).
 
ohwilleke said:
I vote for (vi).

I think she's pretty cute too.
 
selfAdjoint said:
On (v), string (and brane and M-) theorists assume they have a spacetime continuum available to them and that motion, implied in the worldsheet, is unproblematical. Furthermore they (mostly) treat gravity as negligible. This implies their dimensions are large compared to the Planck length where the Compton radius equals the Schwartzschild radius.

Thanks!

Regarding (v) I mean that in proper formulation of string or brane theory there is nothing fixing really the scale of the string or branes. Whereas in other alternatives a Planck scale arise naturally, string or brane theorist choose the tension parameter which in last instance fix really the size of the string. The situation is similar to the status of 'hidden' dimensions, each author chooses a size: Planck scale (or several orders of magnitude larger, as you correctly note), mm range, cosmological, etc.

I also was expresing idea that in cosmology is supposed that strings (branes) are of cosmological scale. For example in brane cosmology is assumed that 4D spacetime is a brane of size more large that radius of observed universe. This is 'explained' from dualities.

I simply desired to express with my previous points that is said in popular books, talks, and magazines is very, very different is said in research articles on the topic.
 
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