What is the relationship between p-adic and l-adic numbers?

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Discussion Overview

The discussion revolves around the relationship between p-adic and l-adic numbers, exploring their definitions, properties, and distinctions. It includes questions about the nature of p-adic norms, the inclusion of fields, and the relationship between p-adic fields and Galois fields, as well as inquiries into p-adic integrals and differentiation.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants question why the p-adic object requires a prime number p and how the p-adic norm is defined, suggesting that alternative definitions would not satisfy norm properties.
  • There is a discussion about the relationship between the rational numbers Q, real numbers R, and p-adic numbers Q_p, with some stating that neither Q is contained in R nor R in Q_p.
  • Some participants propose that l-adic numbers are essentially the same as p-adic numbers when l equals p, while others clarify that l represents a prime number different from the characteristic of a base field.
  • Questions are raised about the relationship between p-adic fields and Galois fields, with some noting that Galois fields are finite while p-adic fields are infinite for each prime p.
  • Inquiries are made regarding the definition of p-adic integrals and differentiation, as well as potential connections between q-analogues of functions and p-adic numbers.

Areas of Agreement / Disagreement

Participants express differing views on the definitions and properties of p-adic and l-adic numbers, as well as their relationships to other mathematical structures. The discussion remains unresolved with multiple competing perspectives presented.

Contextual Notes

Some claims depend on specific definitions and assumptions regarding norms and field characteristics, which may not be universally accepted or resolved in the discussion.

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1.Why the object requires prime number p?
2.Why the p-adic norm of x is defined by |x|_{p}=p^{-m}(x=\frac{p^{m}r}{s}),not |x|_{p}=p^{m}?
3.Q_{p}\subset R or R \subset Q_{p}?
4.What is the difference between p-adic and l-adic? what is the letter "l" stands for?
 
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navigator said:
1.Why the object requires prime number p?
2.Why the p-adic norm of x is defined by |x|_{p}=p^{-m}(x=\frac{p^{m}r}{s}),not |x|_{p}=p^{m}?
3.Q_{p}\subset R or R \subset Q_{p}?
4.What is the difference between p-adic and l-adic? what is the letter "l" stands for?

1) You can still form the p-adic integers when p is not prime. However, |x|_p wouldn't be a norm (|xy|_p=|x|_p|y|_p wouldn't be true), and the p-adic integers will not be an integral domain (there are zero divisors).
2) the alternative you suggest wouldn't satisfy |x+y|<=|x|+|y|, so it isn't a norm.
3) neither. Q < R and Q < Q_p.
4) l-adic is the same as p-adic, if l=p ! l is just some prime number.
 
Thank you.
One more question here is: What is the relationship between p-adic field and Galois field?
 
navigator said:
Thank you.
One more question here is: What is the relationship between p-adic field and Galois field?

They're quite different. A Galois field is just any field with a finite number of elements; the p-adics form an an infinite field for each prime p.
 
can you define a p-adic integral of any function f(x) where x- is always a p-adic number

Can you define a p-adic differentiation ? in similar manner

Is there any relationship between the q-analogue of a function and the p-adic set of numbers?
 
In arithmetic geometry, one usually uses the letter, p, to denote the characteristic of a base field and "l" for a prime number different from the char.

For example, l-adic etale cohomology. p-adic crystalline cohomology.
 
i once heard a guy talking about galois fields. I asked him what the heck it was. he said it is a finite field.

So, if a finite field has q elements, then q is a power of some prime p. there is a subfield F_p in it. Z_p=inv.lim. F_p^n.
 

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