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Simultaneity and t=0 - SRT

Mashuna said:
Why pick t=0? It's just another reference point. Derive all your other t's from t=42 if you like.
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you have to be at t=0 to derive t=1687 or t=42

other wise what the hell does the 1687 or the 42 mean?
 
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Actually don't bother with it... the thead has been answered. It has been stated that according to SRT 't' can be anything you want it to be and that it is arbitary.

thats all I need to know...
 
ozziemate said:
and 42 units from what?
or
84 units from what?
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well, depending which way you go, either 42 is 42 units from 84 or 0, and 84 is 84 units from 168 or zero. But there's no special significance in that. You may as well say that 42 is 20 units from 22 or 62.
 
Mashuna said:
well, depending which way you go, either 42 is 42 units from 84 or 0, and 84 is 84 units from 168 or zero. But there's no special significance in that. You may as well say that 42 is 20 units from 22 or 62.
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just to clarify the point so we are mnot talking at cross purposes [ i am not talking about duration for example.

when you start a stop watch in real life say at a sporting event what does t=? at the time you start it?
 
ozziemate said:
and 42 units from what?
or
84 units from what?
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From whatever you want. It's all arbitrary. There's no law that says a system must originate at zero -- that's just a convention. For example, I could say that I started writing this post at 1223287116 and it is now 1223287138. I could have just as easily said 0 and 22, 143 and 165, or -3842 and -3820. It doesn't matter as long as whatever system I use is consistent within the context of its purpose.
 
ozziemate said:
Actually don't bother with it... the thead has been answered. It has been stated that according to SRT 't' can be anything you want it to be and that it is arbitary.

thats all I need to know...
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You may also want to know that all of the spacetime coordinates (x, y, z and t) are anything you want them to be and they are arbitary.
 
ozziemate said:
just to clarify the point so we are mnot talking at cross purposes [ i am not talking about duration for example.

when you start a stop watch in real life say at a sporting event what does t=? at the time you start it?
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Generally 0, for convenience. There's no reason why it has to though, is there? I mean, you say you're not talking about duration, but the example you give (timing a sporting event), is specifically to measure duration.
 
If your reset button is broken, the watch could read any value. It's still just as useful - just subtract the starting time and you get the duration you want. I don't have a timer on my (old) watch, so I just wait until the minute figure switches and start running then. It works, and it's physically equivalent.
 
Mashuna said:
Generally 0, for convenience. There's no reason why it has to though, is there? I mean, you say you're not talking about duration, but the example you give (timing a sporting event), is specifically to measure duration.
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no just the starting point of a timed duration.... the pohysical moment that the stop watch is started...as in "click" event of action
 
ozziemate said:
no just the starting point of a timed duration.... the pohysical moment that the stop watch is started...as in "click" event of action
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In which case, at the "click" event, the starting point is whatever the current reading on the stopwatch is. Usually 0 for convenience, but as Armillary Sphere states, it doesn't really matter.
 
Is there another term used to describe what I am talking about regarding t=0
 
The problem is that "t=0" is ambiguous, the way you're using it. If you look at the examples of Einstein, he typically says "let x=x0 and t=t0 be the event that ..." and then describe what event he's talking about. If you then switch to talking about another event, you can use x=x1, t=t1 and so forth. The key thing here is that it becomes possible to look at the differences x1-x0 and t1-t0 in a meaningful way.

The absolute values of all these things x0, x1, t0, t1 and so forth lack meaning, but their differences are highly interesting, and that's what SR is interested in describing.
 
ArmillarySphere said:
The problem is that "t=0" is ambiguous, the way you're using it. If you look at the examples of Einstein, he typically says "let x=x0 and t=t0 be the event that ..." and then describe what event he's talking about. If you then switch to talking about another event, you can use x=x1, t=t1 and so forth. The key thing here is that it becomes possible to look at the differences x1-x0 and t1-t0 in a meaningful way.

The absolute values of all these things x0, x1, t0, t1 and so forth lack meaning, but their differences are highly interesting, and that's what SR is interested in describing.
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I am not disagreeing with your assessment when I say this, but I disagree that the t=0 is unimportant.

Possibly it is unimportant to SRT but that is just SRT.

It is something that has bugged me for ages and how confusing this issue is when dealing with non-simultaneity or relative momenets of recording events for relative v observers...
Now that you all have explained the SRT position which I find rather intriguing It starts to make sense why I have had so much difficulty in the past.
 
ozziemate said:
Actually the op needs to be rephrased a little to read:

"If we have two or more observers [ RF's ] at relative v is t=0 for light events simultaneous for both or all of them?"
- the correction in bold.
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Events can have three types of seperation, and all observers will agree on the nature of the seperation.

They can be seperated so that they can be seen by some observers to be in the same place, but no observers can see them at the same time.

They can be sperated so that they can be seen by some observers at the same time, but no observers can see them in the same place.

Or they can be seen as to be sperated by all observers as if a light ray traveled from one event to the other. This is not reverseible, light from event A reached event B when it happened to all observers.

t=0 is just like x=0, you can define the values of your coordiante system how ever you want.
 
ArmillarySphere said:
If your reset button is broken, the watch could read any value. It's still just as useful - just subtract the starting time and you get the duration you want. I don't have a timer on my (old) watch, so I just wait until the minute figure switches and start running then. It works, and it's physically equivalent.
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Ah, but it's much easier to do the math in your head when one of the two numbers is 0 :)
 
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