Is the closed string an unknot?

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Discussion Overview

The discussion revolves around the concept of whether a closed string can be classified as an unknot, exploring the definitions and implications of knots in mathematics and physics. Participants examine the nature of unknots, the potential for further knotting, and the relationship between closed strings and knots.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants propose that an unknot is essentially a circle or a 2-sphere, suggesting that a closed string is similar but may have irregularities.
  • Others clarify that an unknot is defined as a simple closed curve in 3D space that can be continuously deformed into a circle, raising questions about the criteria for identifying knots.
  • There is a discussion about whether an unknot can be knotted further, with some stating that if cutting and splicing are allowed, it can be done, while continuous transformations would not allow for further knotting.
  • One participant emphasizes that the definition of knots in mathematics differs from everyday understanding, noting that all closed curves are knots, but not all knots are equivalent in a topological sense.
  • Another participant questions whether the unknot serves as a primitive form of more complex knots, expressing uncertainty about this classification.
  • Concerns are raised about the utility of classifying closed strings as unknots in the context of mathematics and physics, as well as the possibility of combining closed strings like knots.

Areas of Agreement / Disagreement

Participants express differing views on the classification of closed strings as unknots and the implications of knotting operations. There is no consensus on whether the unknot is a primitive form of more complex knots, and the discussion remains unresolved regarding the relationship between closed strings and knots.

Contextual Notes

Participants note that the definitions of knots and unknots depend on specific mathematical criteria, which may not align with common language usage. The discussion also highlights the complexity of transformations and operations allowed in knot theory.

Master replies:
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A unknot is pretty much a circle or a 2-sphere, so is a closed string, maybe a bit more irregular but approximatly the same. Of course more is needed to identify the closed string as an unknot than the shape.
I assume that it is not so, yet I have no reason to deny it. I hope you may give me a reason.
Knots can also be added simply connecting the two knots. Is such a addition also possible with closed strings, if they are in fact unknots? Can, if it is a unknot, the closed string me knoted further?
 
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An unknot is a simple closed curve in 3D Euclidean space that is homotopic to a circle. Ie there must be a continuous deformation that maps it to, say the curve
##f:[0,1]\to\mathbb{R}^3:\ \ f(t)=(1,t,0)## where the latter representation is in spherical coordinates. Defining a knot is easy. The hard bit is working out whether any particular simple closed curve in ##\mathbb{R}^3## is a knot.

It's not clear what your question is. You ask whether an unknot can be knotted 'further'. That depends what operations you allow. If you allow cutting and splicing then yes - just cut it, do a granny knot, then splice the ends together. If not, and the 'knotting' transformation must be continuous, then the answer is no, because whatever transformation you do to try to knot it can be reversed to transform it back into the unit circle.
 
Master replies: said:
A unknot is pretty much a circle or a 2-sphere, so is a closed string, maybe a bit more irregular but approximatly the same. Of course more is needed to identify the closed string as an unknot than the shape.
I assume that it is not so, yet I have no reason to deny it. I hope you may give me a reason.
Knots can also be added simply connecting the two knots. Is such a addition also possible with closed strings, if they are in fact unknots? Can, if it is a unknot, the closed string me knoted further?

To a physicist or mathematician, a knots is defined as a closed curve. All closed curves are knots, all knots are closed curves. This is NOT the definition used in standard English. It is quite different from the "knots" encountered in everyday life, which we won't discuss here.

The only way to change a knot to a topologically different knot is to cut the string, move it around, then paste it back together. This is a definition of "topologically different."

The circle is called the "unknot" because in physics often it can dissipate by shrinking to a point. No other knot can do that. So the unknot is often less stable than the other knots.
 
andrewkirk said:
It's not clear what your question is. You ask whether an unknot can be knotted 'further'. That depends what operations you allow. If you allow cutting and splicing then yes - just cut it, do a granny knot, then splice the ends together. If not, and the 'knotting' transformation must be continuous, then the answer is no, because whatever transformation you do to try to knot it can be reversed to transform it back into the unit circle.

My question was not if the unknot may be knoted further, I apologize if that was unclear, but rather if the unknot is a primitve form of a higher more complex knot. I do not imagine so but...
But more importantly if the closed string may be considered as one and if it is any help to mathematics or the physics and if one may add two closed strings as one may do with knots.
 
Master replies: said:
My question was not if the unknot may be knoted further, I apologize if that was unclear, but rather if the unknot is a primitve form of a higher more complex knot.
No, it isn't.
But more importantly if the closed string may be considered as one and if it is any help to mathematics or the physics and if one may add two closed strings as one may do with knots.
I'm afraid I do not understand what you are trying to ask here.
 

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