Understanding P-adic Numbers: A Primer

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In summary, p-adic numbers are a completion of the rational numbers for each prime number, in addition to the usual completion, the real numbers. They are often used in number theory and have many applications in math and physics. They are interesting for their properties and can be used to solve real problems. One example is the Hasse-Minkowski Theorem. There are also many articles in physics that use p-adic numbers in their research.
  • #1
kowalski
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I'm reading the book "Numbers" by Ebbinghaus et al. (Springer Verlag); I can't understand what's the main idea about "p-adic numbers", and what kind of problems can be solved with this sistem of numbers. Can you explain it to me in (as simple as possible...) few words?.
 
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Often used in number theory. There is one completion of the rational numbers for each prime p ... plus the usual completion, the real numbers, which is taken to correspond to a fictitious prime called "infinity".
 
  • #3
i. Do you mean that there are infinite "real numbers, say R_p" (one for each prime p) apart from the usual reals R?. Why are they interesting, what propierties does they have?.

ii. Can you give a (no too esoteric) example of the use of p-adics in Number Theory?. Do they solve 'real' problems, or problems originated in their own existence?.

iii. Any applications out of Number Theory? (math or physics?). [As there are very useful applications of complex, quaternionic and octonions in (theoretical) physics].
 
  • #4
kowalski said:
i. Do you mean that there are infinite "real numbers, say R_p" (one for each prime p) apart from the usual reals R?.

Yes, except they are not called "real numbers" they are called "p-adic numbers". Probably it is more common to write [itex]\mathbb{Q}_p[/itex] for the p-adic numbers, and then maybe correspondingly write [itex]\mathbb{Q}_\infty[/itex] for the real numbers.

Why are they interesting, what propierties does they have?.

ii. Can you give a (no too esoteric) example of the use of p-adics in Number Theory?. Do they solve 'real' problems, or problems originated in their own existence?.

Why not do some reading about them?

iii. Any applications out of Number Theory? (math or physics?).

Google Scholar finds about 400 articles in physics published during 2009 with "p-adic" in the title or abstract. (And only 128 articles for "octonions".)
 
  • #5
kowalski said:
ii. Can you give a (no too esoteric) example of the use of p-adics in Number Theory?.
You could start with the Hasse-Minkowsky Theorem.
 
  • #6
Thank you very much, g_edgar and Petek. I will tray this references. I'm very surprised to know that there are such a number of papers in physics with 'p-adics' in their title !. K.
 

1. What are p-adic numbers?

P-adic numbers are a type of number that extend the concept of the real numbers. They were first introduced by mathematician Kurt Hensel in the early 20th century and are based on the idea of p-adic valuation, where p is a prime number.

2. How do p-adic numbers differ from real numbers?

P-adic numbers differ from real numbers in several ways. One of the main differences is that p-adic numbers are based on a different metric, called the p-adic metric, which is used to measure the distance between numbers. This metric leads to some unique properties of p-adic numbers, such as the fact that they can have infinitely many decimal places to the left of the decimal point.

3. What are some applications of p-adic numbers?

P-adic numbers have various applications in mathematics, physics, and computer science. They are used in number theory, algebraic geometry, and cryptography. In physics, p-adic numbers have been used to study string theory and quantum mechanics. They are also used in computer science for error-correcting codes and in algorithms for solving problems in finite fields.

4. How do I perform arithmetic operations with p-adic numbers?

The arithmetic operations with p-adic numbers are very similar to those with real numbers. Addition, subtraction, and multiplication are carried out in the same way as with real numbers. Division, however, is defined differently due to the unique properties of p-adic numbers. It involves finding a reciprocal, which can be done using the p-adic valuation. Some basic rules for arithmetic with p-adic numbers include: adding or subtracting two p-adic numbers results in a p-adic number, multiplying two p-adic numbers results in a p-adic number, and dividing two p-adic numbers results in a p-adic number if the divisor is not divisible by the prime p.

5. How can I learn more about p-adic numbers?

There are many resources available for learning more about p-adic numbers. Some suggestions include reading textbooks on number theory or algebraic geometry, taking a course in number theory or abstract algebra, or attending lectures or seminars on p-adic numbers. Additionally, there are many online resources, such as videos and articles, that can provide an introduction to p-adic numbers. It may also be helpful to consult with a mathematician or join a math forum to ask questions and discuss p-adic numbers with others.

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