1. Jun 10, 2006

### Best of the Worst

T = root((t2 - t1)^2 - (x2 - x1)^2)

As I understand it, T is proper time as measured in someone's intertial frame, and (x2 - x1)^2 is their movement through space... but in what frame is (t2 - t1)^2 measured?

2. Jun 10, 2006

### pervect

Staff Emeritus
t1,x1 and t2,x2 are both measured in somenone (anyone's) inertial frame.

Regardless of which inertial frame you chose to measure t1,x1,t2, and x2, the result T will be the same - it will be invariant.

3. Jun 10, 2006

### Best of the Worst

Awesome. Thank you kindly ;).

4. Jun 11, 2006

### pmb_phy

$\Delta$s2 = (t2 - t1)2 - (x2 - x1)2
may be either positive, negative or zero. $\Delta$s2 may be either a proper time or a proper distance according to its sign.