Thursday, 8 November 2018

abstract algebra - A field of order 32



I was working on this problem from an old qual exam and here is the
question. In particular this is not for homework.




True or False: There are no fields of order 32. Justify your answer.





Attempt: From general theory I know that any finite field has prime power order
and conversely given any prime power there exists a finite field of that order. So of course such fields exist. But now I need to explicitly construct such a field.
If I could somehow construct Z2[x]/(p(x)) where p(x) is a polynomial of degree 5 which is irreducible over Z2 I am done. But wait, how do I come up with a degree 5 polynomial that is irreducible over Z2. My normal methods don't work here because p(x) does not have order 2 or 3. In which case it is easy to check for irreducibility.



My question is in these kinds of situations, is there a general way to proceed.



Note: I have not learnt Galois' theory or anything like that. Does this problem require more machinery to solve?




Please help.


Answer



No more machinery. Make yourself a table of irreducible polynomials of degrees up to 5 by thinking about how to recognize polynomials over Z2 with 0 or 1 as a root, then proceeding by doing a sieve of Eratosthenes (crossing out polynomials that are divisible by lower-degree irreducibles).


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