[Math] Question about the definition of a field…

field-theory

Just out of curiosity – when we define a field, why bother mention multiplication, when its nothing more then repeating the same addition operation?

Here's the definition we were taught in calculus for physicists class:

A field F is a non-empty set on which two binary operations are
defined: an operation which we call addition, and denote by +, and an
operation which we call multiplication and denote by $\cdot$ (or by
nothing, as in a b = ab). The operations on elements of a field
satisfy nine defining properties, which we list now…

And then of course you have the axioms of field.

Best Answer

For an abstract field, $+$ and $\times$ are just symbols for two binary operations which need not be related in any way except by the distributive requirement(i.e. $a\times(b+c)=(a\times b)+(a \times c) $). We use $+$ and $\times$ because they represent operations in the fields we know and love best, the rational numbers, the real numbers and the complex numbers. You could use $\heartsuit $ and $\clubsuit $ , if you like them better.But, as Arturo pointed out, to think of multiplication as repeated addition in even these fields is dangerous. So, if your fields had elements which were say,sequences, it becomes worse, how do I add something like $(0,1,0,\cdots)$ to itself $(1,1,1\cdots)$ times?

But, this idea of "adding" elements $n$(for a natural integer) times has been thought about before and you might consider reading this to see how different things are in abstract fields. http://en.wikipedia.org/wiki/Characteristic_(algebra)

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