# Is time Scalar or Vector

In http://en.wikipedia.org/wiki/Time_in_physics its said that time is a scalar quantity. But its hard to understand that how ? As stated that we consider only the magnitude of time then its a scalar. But on basis of time we define yesterday, today and tomorrow then what it will be ?

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If it was a vector, what would its direction be? –  m.buettner Apr 2 '13 at 10:54

To pick up on twistor59's point, time is not a vector but a time interval is.

The confusion arises because you have to define carefully what you mean by the word time. In special relativity we label spacetime points by their co-ordinates $(t, x, y, z)$, where $t$ is the time co-ordinate. The numbers $t$, $x$, etc are not themselves vectors because they just label positions in spacetime. So in this sense the time co-ordinate, $t$, is not a vector any more than the spatial co-ordinates are.

But we often use the word time to mean a time interval, and in this sense the time is the vector joining the spacetime points $(t, x, y, z)$ and $(t + t', x, y, z)$, where $t'$ is the time interval you measure with your stopwatch between the two points. The interval between the two points is $(t', 0, 0, 0)$ and this is a vector.

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Yep good point. Wiki could do with a little bit of caveating of their sentence in order to avoid these confusions. –  twistor59 Apr 2 '13 at 13:30