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

[rgtr]

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.

 

[sysprog]

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?

 

[DaveC426913]

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).

 

[sysprog]

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.

 

[DaveC426913]

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.

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..."

[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.

 

[hmmm27]

Is the entire homework question "How can an event which has length and time have L = 0.".

 

[sysprog]

. . . 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 $\dots$

 

[sysprog]

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.

 

[jbriggs444]

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?"

 

[rgtr]

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.

 

[hmmm27]

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 ?

 

[Mister T]

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)?

 

[rgtr]

I obviously must have misread the book.

"
(The one exception is when ℓ′ = 0, in which case
the two events happen at the same place and same time in all frames.
"
Here is the book https://scholar.harvard.edu/files/david-morin/files/relativity_chap_1.pdf

 

[sysprog]

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).