How the Axiom of Choice Gives Sizeless Sets | Infinite Series

PBS Infinite Series2 minutes read

The Lebesgue measure in mathematics formalizes size, with properties like translation invariance and additivity. Non-measurable sets, created using the axiom of choice, challenge physical intuitions and involve understanding higher dimensions through improved intuition.

Insights

  • The Lebesgue measure in mathematics defines size based on dimensions, with properties like translation invariance and countable additivity.
  • Non-measurable sets, like S created by the Banach-Tarski paradox, challenge traditional notions of size and rely on the axiom of choice, illustrating complex mathematical concepts beyond simple visualization.

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Recent questions

  • What is the Lebesgue measure in mathematics?

    The Lebesgue measure formalizes size, representing length, area, and volume in different dimensions.

  • What are some properties of the Lebesgue measure?

    The Lebesgue measure exhibits translation invariance, additivity, and countable additivity.

  • Why do countable collections of points have a size of 0?

    Countable collections, such as all integers, have a size of 0 due to countable additivity.

  • Do intervals with uncountably many points have a simple size?

    Intervals with uncountably many points, like 0 to 1, do not have a size that is the sum of the sizes of the points.

  • How is a non-measurable set created in mathematics?

    Non-measurable sets, like set S, are formed by sorting numbers into bins based on rational differences and selecting one representative from each bin.

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Summary

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"Lebesgue Measure and Non-Measurable Sets"

  • Size in mathematics is formalized as the Lebesgue measure, representing length in one dimension, area in two dimensions, and volume in three dimensions.
  • Properties of the Lebesgue measure include translation invariance, additivity, and countable additivity.
  • Countable collections of points, like all integers, have a size of 0 due to countable additivity.
  • Intervals with uncountably many points, like 0 to 1, do not have a size that is simply the sum of the sizes of the points.
  • A set without a size, or non-measurable set, can be created by sorting numbers in an interval into bins based on rational differences.
  • The set S, formed by selecting one representative from each bin, is non-measurable and has no size.
  • The axiom of choice is used to create non-measurable sets like S, allowing for the selection of one element from each set.
  • The Banach-Tarski paradox demonstrates the doubling of a solid sphere by breaking it into non-measurable pieces and reassembling them using the axiom of choice.
  • The Banach-Tarski paradox relies on non-measurable sets and the axiom of choice, challenging physical intuitions.
  • Understanding higher dimensions, like the fourth dimension, involves improving intuition rather than literal visualization, aiding in mathematical analysis.
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