Computable Normal Numbers: Is There a Known Answer?

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Discussion Overview

The discussion revolves around the existence of computable normal numbers, specifically whether any known examples exist and the implications of their existence on mathematical conjectures. The scope includes theoretical aspects of normal numbers and computability.

Discussion Character

  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant questions the clarity of Wikipedia regarding known computable normal numbers and references a paper that may not be peer-reviewed.
  • Another participant introduces the Champernowne constant as an example of a known normal number, asserting its computability and noting that it is normal in base 10.
  • A later reply clarifies the definition of "computable" and discusses the existence of a super-exponential-time algorithm for computing Sierpinski's construction, while inquiring about polynomial-time computable normal numbers.
  • One participant speculates that the existence of a polynomial-time computable normal number would not significantly impact existing mathematical conjectures, suggesting that many familiar constants are conjectured to be absolutely normal.

Areas of Agreement / Disagreement

Participants express differing views on the existence of computable normal numbers and their implications, with no consensus reached on whether a polynomial-time computable normal number is known.

Contextual Notes

Unresolved issues include the definitions of computability and normality, the status of the referenced paper, and the implications of the existence of computable normal numbers on conjectures.

Who May Find This Useful

Readers interested in theoretical computer science, number theory, and the properties of normal numbers may find this discussion relevant.

Dragonfall
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Wikipedia is not very clear on this. Is there a known computable normal number?

I found this paper:

http://www.glyc.dc.uba.ar/santiago/papers/absnor.pdf

But I'm not sure if it's been peer reviewed.
 
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What do you mean with "computable"?

Anyway, consider the Campernowne constant. It is just

0.123456789101112131415161718192021222324...

This is known to be normal (one of the very few explicit numbers known to be normal, although it is also known that "most" numbers are normal). And it will probably also satisfy your criterium of computability.

http://en.wikipedia.org/wiki/Champernowne_constant

Now, your paper (which certainly is peer-reviewed and correct!) shows the existence not only of a computable normal number, but of an computable absolutely normal number. This means that it is normal in any integer base ##\geq 2##. Champernowne's constant is only known to be normal in base ##10##. I don't think any other examples of absolutely normal computable numbers are known, but I'm not an expert.
 
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Yes, I meant "absolutely normal". Computable means digits are enumerable by a Turing machine or uniform family of circuits. That paper presents a super-exponential-time algorithm for computing Sierpinski's construction.

Is there a known polynomial-time computable normal number?

How many conjectures will the existence of such a number ruin?
 
Dragonfall said:
...

How many conjectures will the existence of such a number ruin?

Very few of significance, I expect. (In fact, it's conjectured that most of the computable mathematical constants we're familiar with pi or Euler's number are absolutely normal.)
 
Good point.
 

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