Minkowski Terminology

1. Oct 19, 2006

actionintegral

Hey friends,

When using phrases such as time-like and space-like, is it proper form to use the phrase light-like? Or is there a more professional expression?

2. Oct 19, 2006

HallsofIvy

Staff Emeritus
"Space" and "time" are dimensions so it makes sense to talk about "space-like" and "time-like" regions of Minkowski space. Light is not a dimension and so there is no such thing as a "light-like" region. You may be thinking of a "light-path", the path light would follow, which is the boundary between "space-like" and "time-like" regions.

3. Oct 19, 2006

actionintegral

What if I said:

The set of events between event A and event B is timelike.
The set of events between event A and event C is spacelike.
The set of events between event A and event D is a light-path.

Is that the way "it" is said?

4. Oct 19, 2006

nakurusil

You can find this expressions in older books , like Tolman's when it comes to describing the metric being >0, <0 and exactly 0.

5. Oct 19, 2006

robphy

Timelike, Spacelike, and Lightlike (or Null) are still in common use.
They are used to describe the nature of the causal relation between a pair of events in spacetime. (Example: Event A is lightlike-related to Event B.) They are also used to describe the sign of the Minkowski square-norm of a 4-vector. A lightlike (or null) vector has square-norm equal to zero, without the vector itself necessarily being the zero vector.

6. Oct 19, 2006

pervect

Staff Emeritus
I would personally suggest space-like, time-like, and null. As in "space-like geodesics, time-like geodesics, null geodesics". If you were talking about intervals, it would be space-like intervals, time-like intervals, and null intervals. (I haven't seen "null interval" actually used much, so "light-like" interval might be just as good.)

7. Oct 19, 2006

Thrice

Yeah I always heard it as null.

8. Oct 20, 2006

Meir Achuz

I think "light-like" is OK to describe an interval on the light cone.
It is no better or worse that T-L or S-L, and consistent with their usage.