What Sets Homeomorphic and Isotopic Knots Apart?

  • Thread starter ComputerGeek
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In summary, the difference between an isotopy and a homeomorphism is that an isotopy is a smooth path of embeddings between two manifolds, while a homeomorphism is just a single function between two manifolds. Additionally, a knot projection can only be considered isotopic to another if they can be deformed into each other via a sequence of Reidemeister moves.
  • #1
ComputerGeek
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What is the difference?
 
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  • #2
ComputerGeek said:
What is the difference?
Don't you mean "homeomorphic vs isotropic"?
The root words mean "same form" and "same change" (same difference?). Why not look them up in a scientific dictionary or on Google?
(I looked them up. Never mind, sorry!)
 
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  • #3
An isotopy is a smooth path of embeddings between two manifolds, while a homeomorphism is just a single function between two manifolds. Ie., a right circular cylinder centered at the origin with unit radius is a representation of an isotopy between the two circles at either end.
While the unlink of 2 components is homeomorphic to the Hopf link, the two are not isotopic.
 
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  • #4
hypermorphism said:
An isotopy is a smooth path of embeddings between two manifolds, while a homeomorphism is just a single function between two manifolds. Ie., a right circular cylinder centered at the origin with unit radius is a representation of an isotopy between the two circles at either end.
While the unlink of 2 components is homeomorphic to the Hopf link, the two are not isotopic.
So, it is appropriate to say:

If two knot projections can be deformed into each other via a sequence of Reidemeister moves then the knot projections are isotopic to one another.
 
  • #5
Yep. Each Reidemeister move produces an isotopic projection of a knot with respect to the original.
 

1. What is the difference between homeomorphic and isotopic?

Homeomorphic and isotopic are two terms used in topology, the branch of mathematics that studies the properties of geometric objects that remain unchanged under continuous deformations. Homeomorphic refers to two objects that can be transformed into each other by stretching, bending, and twisting without tearing or gluing. Isotopic, on the other hand, refers to two objects that can be transformed into each other by continuously deforming one into the other, without any cuts, punctures, or self-intersections.

2. Can two homeomorphic objects be isotopic?

Yes, two homeomorphic objects can also be isotopic. This means that if two objects can be transformed into each other without tearing, then they can also be deformed into each other without any cuts or punctures. In other words, homeomorphic implies isotopic, but the converse is not always true.

3. What is an example of two homeomorphic but not isotopic objects?

A classic example is a donut and a coffee mug. Both objects have only one hole, and can be transformed into each other by stretching or compressing, making them homeomorphic. However, a donut cannot be transformed into a coffee mug without making a hole in the donut or cutting the mug, so they are not isotopic.

4. Are homeomorphic and isotopic properties of the objects themselves, or of their representations?

Homeomorphic and isotopic are properties of the objects themselves, not their representations. This means that even if two objects have different shapes or appearances, they can still be homeomorphic or isotopic if they can be transformed into each other by continuous deformations.

5. How are homeomorphism and isotopy useful in science?

Homeomorphism and isotopy are useful in various scientific fields, including biology, physics, and chemistry. In biology, these concepts are used to study the shapes and structures of organisms, such as understanding how different species are related through their evolutionary history. In physics, they are used to describe the properties of space and objects, such as the behavior of particles or the topology of the universe. In chemistry, they are used to predict and understand the properties of molecules and their reactions. Overall, homeomorphism and isotopy help scientists to better understand and classify the complex structures and phenomena in our world.

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