Is Light-Like an Appropriate Term in Minkowski Space Terminology?

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Discussion Overview

The discussion revolves around the appropriateness of the term "light-like" in the context of Minkowski space terminology, particularly in relation to the established terms "time-like" and "space-like." Participants explore whether "light-like" is a suitable term or if alternative expressions are preferred.

Discussion Character

  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants argue that "light-like" is not a proper term since light is not a dimension, suggesting that "light-path" may be a more accurate description of the boundary between "space-like" and "time-like" regions.
  • Others assert that "timelike," "spacelike," and "lightlike" (or "null") are still commonly used terms to describe causal relations between events in spacetime.
  • A participant proposes that the set of events can be described as timelike, spacelike, or light-path, questioning if this is the correct usage.
  • Some suggest using "null" instead of "light-like," indicating that both terms may be acceptable in certain contexts.
  • Another participant mentions that "light-like" is appropriate for describing intervals on the light cone and is consistent with the usage of "time-like" and "space-like."

Areas of Agreement / Disagreement

Participants express differing views on the appropriateness of the term "light-like," with no consensus reached on whether it is the best term to use. Some support its use, while others prefer alternatives like "null."

Contextual Notes

There are references to older literature that may influence the terminology used, and participants note variations in usage across different contexts, such as intervals and geodesics.

actionintegral
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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?
 
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"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.
 
HallsofIvy said:
You may be thinking of a "light-path",

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?
 
actionintegral said:
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?

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

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.)
 
Yeah I always heard it as null.
 
actionintegral said:
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?
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.
 

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