Re: Why is time scalar?

>I understand that as far as we know, the direction of time can
>not be reversed, but it obviously does have a direction -
>forward - so why isn't it considered vector instead.

Elizabeth,

Think about it this way: we use vectors as a mathematical tool to keep track of directions. In physics, we typically have three directions of interest (although having two is common, but more anon), and so we use vectors with three numbers in them: . When we are only interested in two directions (like a tabletop), we use vectors with two numbers in them: .

And so, when we're only interested in one direction, we use a "vector" with one number in it, which is....a scalar! So a scalar is just a vector at its "most basic."

In relativity theory, it is common to use four-vectors, since it is impossible to ignore the interaction that time coordinates have with space coordinates, and so you see vectors like with four "directions" in them, and time does get involved with vector notation ("vector notation" meaning its more intuitive notion of keeping track of more than one direction).

-Greg Billock