Doubling a Cube: Can 3D Geometry Help?

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Discussion Overview

The discussion centers on the geometric problem of doubling a cube, specifically exploring whether extending geometry to three dimensions allows for this construction using basic solid geometry tools. Participants examine the implications of dimensionality on the problem and the limitations of traditional compass and straightedge constructions.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants assert that in plane geometry, it is impossible to construct a line equal to the cube root of 2 times the length of a side of a cube, thus making it impossible to double a cube with traditional tools.
  • Others argue that the impossibility is due to the restrictions of the allowed means rather than the dimensions themselves, suggesting that solid geometry might provide a different perspective.
  • One participant mentions that using a marked ruler allows for the construction of the cubic root of 2 and the trisection of angles, which could imply a different approach to the problem.
  • Another participant introduces origami as a method that can achieve the doubling of a cube, although it does not adhere to the compass and straightedge constraints.
  • A later reply references neusis construction as a method that could also achieve the goal, but notes that it similarly violates the traditional problem's spirit.
  • One participant suggests defining a three-dimensional equivalent of the problem, proposing that this could lead to innovative mathematical ideas, even if it does not resolve the classic problem.

Areas of Agreement / Disagreement

Participants express differing views on whether doubling a cube is possible in solid geometry, with some asserting it is not possible under traditional constraints while others propose alternative methods that do not conform to those constraints. The discussion remains unresolved regarding the feasibility of doubling a cube using solid geometry tools.

Contextual Notes

There are limitations regarding the definitions of allowed construction tools, as well as the implications of dimensionality on the problem. The discussion does not resolve the mathematical steps or assumptions involved in the various proposed methods.

Thecla
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In plane geometry it is impossible to construct a line equal to the (cube root of 2) times the length of
a side of a cube, making it impossible to double a cube with a compass and straight edge. Maybe plane geometry needs one more dimension.
What happens if we extend the geometry to 3D(solid geometry). Is it possible to double a cube in solid geometry using the basic construction tools of solid geometry(whatever is equivalent to a compass, straight-edge)?
 
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Thecla said:
In plane geometry it is impossible to construct a line equal to the (cube root of 2) times the length of
a side of a cube, making it impossible to double a cube with a compass and straight edge. Maybe plane geometry needs one more dimension.
What happens if we extend the geometry to 3D(solid geometry). Is it possible to double a cube in solid geometry using the basic construction tools of solid geometry(whatever is equivalent to a compass, straight-edge)?
The proof, that it is impossible to double the cube doesn't use dimensions. The restrictions are alone due to the allowed means. Therefore the answer is No.
 
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Thecla said:
Is it possible to double a cube in solid geometry using the basic construction tools of solid geometry(whatever is equivalent to a compass, straight-edge)?
Be careful how you phrase your question. The only allowed means are compass and ruler like @fresh_42 said.

Using a marked ruler ( you just need 2 marks on the ruler ) you can construct the cubic root of 2 and trisect any angle.
 
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As @dagmar mentioned earlier a neusis construction could do it too but again it is not a straight edge and compass and so violates the spirit of the problem.

https://en.m.wikipedia.org/wiki/Neusis_construction

Here’s more history on the problem with additional references to search:

https://en.m.wikipedia.org/wiki/Doubling_the_cube

Having said this, why not try to define some three dimensional equivalent and then solve the problem. While it won’t be a solution in the classic sense, it could lead to some interesting and imaginative work. This is how new math or new inventions are often created.
 
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