How can an event which has length and time have L = 0?

  • Thread starter Thread starter rgtr
  • Start date Start date
  • Tags Tags
    Length Time
AI Thread Summary
An event in physics is defined by four coordinates (x, y, z, t) and does not possess length or duration in the traditional sense. The confusion arises from equating an event with a physical object, which requires dimensions greater than zero. When an event has a length L of 0, it indicates that it occurs at a single point in space and time, rather than spanning a distance. The discussion clarifies that while events can be described in terms of their position and time, they do not have physical dimensions like length or duration. Ultimately, the distinction between events and physical objects is crucial for understanding this concept.
rgtr
Messages
90
Reaction score
8
Homework Statement
How can an event which has length and time have L = 0.
Relevant Equations
No equation.
I apologize if this is a stupid question I just always thought length involves 2 points to have a length at different locations.
 
Physics news on Phys.org
rgtr said:
Homework Statement:: How can an event which has length and time have L = 0.
Relevant Equations:: No equation.

I apologize if this is a stupid question I just always thought length involves 2 points to have a length at different locations.
I agree with what what little you've said ##-## it looks to me like you haven't actually posed a well-formed question ##-## yes, to have a length dimension, you need at least one point to start with, and another for extension, right? What question was posed to you?
 
Your question is a bit vague.
You've specified one data point, L, which you have set to 0.
No problem so far, but it doesn't say much.

An event is a point, defined by four coordinates such as x, y, z, t.

If you are deciding that one of those dimensions, say, x, has a value of L, which is equal to zero. then you only need three more to define an event.I suspect what is happening is that you are confusing an event (a point x, y, z, t) with a physically extant object (Δx>0, Δy>0, Δz>0 ,Δt>0).
 
Last edited:
Wow, @DaveC426913, I think that you're not wrong to go to 4d, but I wanted to be gentle and stay 1d and 2d for a minute first. :wink:
 
sysprog said:
Wow, @DaveC426913, I think that you're not wrong to go to 4d, but I wanted to be gentle and stay 1d and 2d for a minute first. :wink:
I've been on PF a long time. If I had described an event with any less than 4 coordinates, I'd bet my pretty blue bonnet someone would step in with "Welll, ACKtually..."

:oldbiggrin:[EDIT]
Aaaaaaand I just noticed that this is a homework question, so I really should have stayed within the confines of the question as-posed.
 
  • Like
  • Haha
Likes robphy, rgtr and sysprog
Is the entire homework question "How can an event which has length and time have L = 0.".
 
DaveC426913 said:
. . . an event with any less than 4 coordinates . . .
Maybe it should have been said as 'fewer than' rather than "less than", given that "4" is a number of co-ordinates in your remark here, and not an amount ##-## yes, I'm being fussy ##\dots## :wink:
 
hmmm27 said:
Is the entire homework question "How can an event which has length and time have L = 0.".
I imagine, as apparently you do, that we haven't been given the entirety of the original question.
 
  • Like
Likes hmmm27
rgtr said:
Homework Statement:: How can an event which has length and time have L = 0.
Relevant Equations:: No equation.

I apologize if this is a stupid question I just always thought length involves 2 points to have a length at different locations.
An event has "position", not "length". It answers the question: "where was it?", not "how big was it?"
An event has "time", not "duration". It answers the question: "when was it?", not "how long did it take?"
 
  • #10
hmmm27 said:
Is the entire homework question "How can an event which has length and time have L = 0.".
Not exactly I was reading a book and just was confused by this.
 
  • #11
rgtr said:
Not exactly I was reading a book and just was confused by this.
So - for context - what was the (book) question/statement that elicited the confusion ?
 
  • Like
Likes jbriggs444 and sysprog
  • #12
rgtr said:
Not exactly I was reading a book and just was confused by this.
What book? You have a book that says an event has a length of zero but also has a length L (that is not zero)?
 
  • #14
rgtr said:
Not exactly I was reading a book and just was confused by this.
Thanks for now having given us that link to the book chapter https://scholar.harvard.edu/files/david-morin/files/relativity_chap_1.pdf ##-## it said parenthethically on page 13 of 70:

(The one exception is when ℓ ′ = 0, in which case the two events happen at the same place and same time in all frames.)​
That refers to two events; not to a single event, as your question, "How can an event which has length and time have L = 0" seems to attempt to do ##-## as @jbriggs444 pointed out, a single location doesn't have length, and a single event doesn't have duration (I'll add for the sake of attempted funniness: unless maybe the event is e.g. a social event, such as a dinner party, or the Oscars, or a slap).
 
  • Like
Likes rgtr
Back
Top