# Units time?

1. Dec 8, 2009

### alejandrito29

In a space time with metrics :
$$ds^2=f(t)(-dt^2+dx^2+dy^2+dz^2)$$

which is the unit that measures time t?

second?, meter of time?

2. Dec 8, 2009

### Staff: Mentor

For dimensional consistency it would have to be the same units that dx, dy, and dz are measured in.

3. Dec 8, 2009

### alejandrito29

then , if dx,dy and dz are in meters, then t is in meters of time???

4. Dec 8, 2009

5. Dec 8, 2009

### DrGreg

A "metre of time" is the time it takes for light to travel one metre, i.e. (1/299792458) seconds.

Or you could measure dx, dy and dz in light-seconds and then dt is in seconds.

6. Dec 10, 2009

### Matterwave

to be explicit, a c^2 should appear before dt^2 to explicitly convert time into units of distance. But, in relativistic units c=1 so we just omit the c and it's understood.