Why does cantors theorem not prove the interval (0,1) in Q uncountable?

In summary, the conversation is about a difficult question involving Cantor's procedure. The person asking for help has been studying for exams and is struggling to find a solution. Another person offers to help, suggesting taking a break and providing more context for the question. They also wish the person good luck on their exams.
  • #1
carheadford
1
0
This is a 'just for fun' question at the end of my online lecture notes..
My brain is fried from studying for exams, I can't figure it out and it is driving me mad!
Anyone care to help me out?
 
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  • #2
Not every number which can be constructed through Cantor's procedure is rational; so, you would need to show that you can always construct a rational number which is not on the list.
 
  • #3
Sure, I'll give it a shot! Can you provide some more context or information about the question? Maybe that will help me come up with a solution. Also, don't stress too much about it, sometimes taking a break and coming back to a problem with a fresh mind can make all the difference. Good luck on your exams!
 

1. Why does Cantor's theorem not prove the interval (0,1) in Q uncountable?

Cantor's theorem, also known as the Cantor diagonal argument, is a mathematical proof that shows that the real numbers are uncountable. However, this proof does not apply to the interval (0,1) in the rational numbers (Q). This is because the rational numbers are countable, meaning there is a one-to-one correspondence between the rational numbers and the natural numbers.

2. How is the interval (0,1) in Q countable?

The interval (0,1) in Q is countable because it can be put into a one-to-one correspondence with the natural numbers. This means that for every rational number in the interval, there is a unique natural number assigned to it and vice versa. This is different from the real numbers, where there is no such correspondence and therefore they are uncountable.

3. Can Cantor's theorem be used to prove the uncountability of the interval (0,1) in Q?

No, Cantor's theorem cannot be used to prove the uncountability of the interval (0,1) in Q. This is because the theorem relies on the fact that there are infinitely many digits in a real number, which is not true for rational numbers. Additionally, the diagonal argument used in the proof does not apply to the rational numbers.

4. What is the difference between countable and uncountable sets?

A countable set is a set that can be put into a one-to-one correspondence with the natural numbers. This means that every element in the set can be mapped to a unique natural number and vice versa. An uncountable set, on the other hand, cannot be put into a one-to-one correspondence with the natural numbers. This means that there is no way to count or list all the elements in an uncountable set.

5. Are there any other proofs for the uncountability of the interval (0,1) in Q?

Yes, there are other proofs for the uncountability of the interval (0,1) in Q. One example is the Dedekind cut, which shows that there are real numbers that cannot be expressed as a ratio of two integers. This concept is not applicable to rational numbers, and thus it proves the uncountability of the interval (0,1) in Q.

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