Why does every subfield of Complex number have a copy of Q?

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Discussion Overview

The discussion revolves around the question of why every subfield of the complex numbers contains a copy of the rational numbers. Participants explore the properties of fields, the assumptions made in proofs, and the implications of field characteristics.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants assert that if ##F## is a subfield of ##\Bbb C##, then it must contain the elements ##0## and ##1##, but question the validity of assuming this without proof.
  • Concerns are raised about the possibility of trivial subfields and whether the assumption of non-triviality is justified.
  • Participants discuss the need for a formal argument to demonstrate that all rational numbers can be constructed within ##F##, emphasizing the importance of avoiding cycles that could limit the field's elements.
  • There is a discussion about the characteristics of fields, specifically noting that fields of characteristic zero contain the rational numbers, while ##\mathbb{Z}_2##, which has characteristic two, cannot be a subfield of ##\mathbb{C}##.
  • Some participants suggest starting with the element ##1## and constructing other elements to show that all natural numbers and their inverses can be included in ##F##.
  • Clarifications are made regarding the meaning of operations like ##p \cdot n## and the distinction between different mathematical structures such as fields and rings.

Areas of Agreement / Disagreement

Participants express differing views on the assumptions made in the original proof and the necessity of providing arguments for certain claims. There is no consensus on the sufficiency of the initial proof or the handling of trivial fields.

Contextual Notes

Participants highlight the importance of addressing cycles in fields and the implications of field characteristics on the existence of rational numbers. The discussion remains open-ended regarding the completeness of the arguments presented.

  • #31
WWGD said:
But werebn't we talking about subfields?
Yes, but we also got picky. ##\mathbb{Z}_7## is a field and ##\{0,1,2,3,4,5,6\} \subset \mathbb{C}##. And yes it is no subfield, because it cannot be embedded as a field into ##\mathbb{C}##. So in the same way you take this embedding for granted, @Buffu may take ##0,1 \in F##, the additional closure or other axioms for granted, which reduces the entire exercise to: Obvious. I only wanted to say, that this property in the meaning / definition of subfield is used same as the axioms of a field are used.
 
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  • #32
FactChecker said:
That is why I asked if you were supposed to be learning how to do proofs. We could take the entire thing for granted, but that is not a proof. We know that the axioms are true. If you are learning how to do math proofs, you have to refer to the things you know in writing where they apply and are used.

I will mention every axiom used from next time when writing proofs :).
 
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  • #33
Buffu said:
I will mention every axiom used from next time when writing proofs :).
At least it will do no harm, except ...
Just a (not completely serious hint) in case you will turn in a paper for your master's degree or similar: Write it down in a way that you understand all steps. Make a copy for yourself. Then wipe out every second step and hand it over :wink:.
 
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  • #34
Buffu said:
I will mention every axiom used from next time when writing proofs :).
Good. The first few years of proofs should include all the steps. You will have a lot of time to learn which steps to skip. A thesis can skip some steps and an article for publication must skip a lot.
 
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