The set consisting of random numbers with random lengths

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Discussion Overview

The discussion revolves around the concept of generating random integers with random lengths and whether this process can produce all possible integers. Participants explore the implications of such a generation method, particularly focusing on the probabilities involved and the nature of randomness in this context.

Discussion Character

  • Exploratory
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants propose that the set of random integers with random lengths could produce all possible integers, but they acknowledge the lack of a proof for this assertion.
  • Others argue that all integers have the same probability of being produced, which is zero in finite time, raising questions about the implications of selecting a random length first.
  • A participant suggests that the probability of any particular integer escaping production is zero, referencing countable additivity in probability theory.
  • Some express skepticism about the feasibility of picking an integer at random, questioning the uniformity of the probability distribution and the conditions under which integers can be generated.
  • There is a discussion about the potential for generating numbers multiple times and how this affects the probability of producing specific integers.

Areas of Agreement / Disagreement

Participants do not reach a consensus; multiple competing views remain regarding the nature of randomness, the feasibility of generating all integers, and the implications of probability distributions.

Contextual Notes

Participants highlight limitations in defining how integers are selected at random, the implications of uniform versus non-uniform distributions, and the challenges of generating integers within finite time constraints.

serp777
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Does the set of random integers with random lengths (the number of digits), which hypothetically would generate random numbers with random lengths for eternity, produce all possible integers? It seems to me that this is a natural conclusion but I've never seen a proof of this. A more incredible statement would be that there are integers which could not be produced via this process.
 
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I don't see how you can construct an integer that can escape being produced. All integers have the same probability of being produced (namely zero) in a finite time.
I'm not sure how things change if e.g. you first pick a random length (infinitely many possibilities) and subsequently pick a random integer of that length (a finite number of choices).
 
serp777 said:
Does the set of random integers with random lengths (the number of digits), which hypothetically would generate random numbers with random lengths for eternity, produce all possible integers? It seems to me that this is a natural conclusion but I've never seen a proof of this. A more incredible statement would be that there are integers which could not be produced via this process.
First tell me how you would create that random number generator. If you want to create a random number in a finite time, you will only get random numbers in a finite range...
 
I am not sure that this stands up to rigorous scrutiny but...

As BvU points out, the probability that any particular integer escapes being produced is zero. The probability that any particular integer escapes being produced while all lesser integers are produced is also zero. The case that at least one integer escapes being produced is the infinite union of the cases where some integer escapes being produced while all lower integers are produced. Those component cases are disjoint by construction. By countable additivity, the probability of the union is the sum of the probabilities of all of the component cases. That sum is zero.
 
I like phinds' almost standard referral to the Hilbert Hotel for a nice confrontation with infinities
 
How do you even pick an integer at random? There is no way!
 
micromass said:
How do you even pick an integer at random? There is no way!
It is not possible to pick an integer at random such that all integers are possible and the probability distribution is uniform.

My reading of the problem in #1 is that the requirement that the distribution be uniform has been relaxed but the requirement that the distribution have a non-zero probability for each and every integer has been retained. A procedure such as "flip a coin and count the number of tails prior to the first heads" is almost certain to work for this.
 
jbriggs444 said:
It is not possible to pick an integer at random such that all integers are possible and the probability distribution is uniform.

My reading of the problem in #1 is that the requirement that the distribution be uniform has been relaxed but the requirement that the distribution have a non-zero probability for each and every integer has been retained. A procedure such as "flip a coin and count the number of tails prior to the first heads" is almost certain to work for this.

Sure. But many people not familiar with probability seem to use the word "at random" to mean "uniform probabilities". If the OP doesn't say this, he needs to specify exactly how he does this random number selection.
 
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Does the randomness allow for numbers to be generated twice? If not, it should be exactly the same as trying to enumerate the set of integers, which is infinite. If it does, on the other hand, it just makes things worse as the probability of a particular integer to be generated is even smaller.
 

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