Which Fields Can Be Ordered?
Every ordered field is a formally real field, i.e., 0 cannot be written as a sum of nonzero squares.
Conversely, every formally real field can be equipped with a compatible total order, that will turn it into an ordered field. (This order is often not uniquely determined.)
Finite fields and more generally fields of finite characteristic cannot be turned into ordered fields, because in characteristic p, the element -1 can be written as a sum of (p-1) squares 12. The complex numbers also cannot be turned into an ordered field, as −1 is a square (of the imaginary number i) and would thus be positive. Also, the p-adic numbers cannot be ordered, since Q2 contains a square root of −7 and Qp (p > 2) contains a square root of 1 − p.
Read more about this topic: Ordered Field
Famous quotes containing the word fields:
“Within the regions of the air,
Compassed about with heavens fair,
Great tracts of land there may be found
Enriched with fields and fertile ground;
Where many numerous hosts
In those far distant coasts,
For other great and glorious ends,
Inhabit, my yet unknown friends.”
—Thomas Traherne (16361674)