What are the dimensions of strings?

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Discussion Overview

The discussion centers on the dimensions of strings in string theory, exploring whether they are confined to the Planck length or can vary in size, and how different types of strings might relate to fundamental particles and cosmological phenomena.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant questions if strings are Planck length in one dimension and zero in others, or if they can be more than Planck length in one dimension and exactly Planck length in others.
  • Another participant asserts that strings are exactly one-dimensional and suggests that their length is not strictly limited to the Planck scale, allowing for some variability.
  • A different viewpoint introduces the concept of QCD strings, which are significantly larger than fundamental strings, potentially up to 10^20 times longer, and discusses the relationship between different types of strings and branes.
  • One participant references Leonard Susskind's ideas about the immense strength of fundamental strings and their potential connection to black holes, suggesting that black holes might consist of a single string and that Hawking radiation could arise from quantum fluctuations in such strings.
  • Another participant mentions hints of cosmological scale strings that could stretch across the universe, proposing that strings might vary in size from just above the Planck scale to cosmological dimensions.

Areas of Agreement / Disagreement

Participants express differing views on the dimensions and sizes of strings, with no consensus reached on whether strings are strictly confined to the Planck scale or if they can vary significantly in size.

Contextual Notes

Some claims depend on specific interpretations of string theory and the definitions of different types of strings, which remain unresolved in the discussion.

ShadowVegan
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According to string theory, are strings Planck length in 1 dimension and 0 in all other dimensions? Or more than Planck length in 1 dimension and exactly Planck length in all other dimensions? Or something else? Thanks.
 
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The string is exactly 1-dimensional. I don't believe the length of the string is bounded to be at or below the Planck scale (obviously it must be close, but there is typically some wiggle room of an order of magnitude or so).
 
Presumably you are thinking of fundamental strings...that's what's usually discussed in these forums...there are a different "brand" of string that makes up elementary nuclear particles...called QCD strings and those are huge maybe 1020 times longer. Strings can also be thought of as 1 branes...one dimensional (length only) branes...particles would be zero branes (no dimensions). So strings are a special class of branes. (I think this depends on the particular string theory.)

The former are supposedly near the Planck scale, so one dimension and largr than Planck scale, yet there IS a type of unity between the two types of strings. Leonard Susskind says "you could suspend 1040 trucks from a fundamental string"...(gotta love THAT measurement unit!) they don't expand (extend) very easily.

Susskind points out that black holes, even the supersized giants at the center of galaxies, DO have the energy needed to extend strings to immense size..such that a black hole might consist of a single string! As an example, one theory posits the horizon of a black hole as a single tangled string with quantum fluctuations...when a bump in the string appears on the horizon, it appears to an outside observer as an open string...ends connected to the horizon...and when one breaks off due to quantum zero point energy...carrying gravitational energy, voila, Hawking radiation!
 
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Now that I think about it again, I know I read there are hints that cosmological scale strings that might stretch across the universe might be remnants of a big bang...don't recall the source...so "strings" might vary in size from just above Planck scale to cosmological size.
 

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