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Lorentz contraction 
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#37
Nov1509, 04:10 PM

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#38
Nov1509, 04:15 PM

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PF Gold
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I think it is perhaps worth pointing out that some people have a false impression about what Lorentz contraction is. They may think that "when something accelerates it gets shorter". Or to be a bit more precise, if Alice measures (=x) something at rest (relative to Alice) and then later measures (=y) the same thing in motion, the length contracts. There may then be some debate over whether or not the "things" this applies to are just solid objects, or gaps between objects, or "space itself".
The above description of Lorentz contraction is wrong. In many circumstances, what I said above is true, but reason it is true is not simply Lorentz contraction alone; it is Lorentz contraction plus some other reason combined. A more accurate description of Lorentz contraction is that when inertial observer Bob measures the length z between two things both at rest relative to Bob, and another inertial observer Alice in relative motion measures the length y between the same two things at the same time, Alice measures a shorter distance than Bob. So, the situation I described in the first paragraph will arise if there is a reason why Alice's initial "rest distance" x between the two things beforehand is the same as the Bob's final "rest distance" z. For example if the the two things are the two ends of a rigid object that doesn't break into pieces as a result of the acceleration. The attached illustration emphasises my point. The transformation of x to y is not Lorentz contraction. The transformation of z to y is Lorentz contraction. If there is a reason why x = z, then the transformation of x to y will be a contraction. But if there's no reason, then contraction need not occur. 


#39
Nov1509, 04:23 PM

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#40
Nov1509, 04:34 PM

P: 687

In the theoretical instantaneous at rest frame, this is where the various papers prove one way or another the string snaps. But, I want to focus on the launch frame. This frame is not seeing the distance change between the ships.. Question, does the launch frame conclude based on observations that the string breaks? If so, what is the math from the launch frame to show this. 


#41
Nov1509, 04:45 PM

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 In the string rest frame the distances between the atoms/molecules are increased by stretching the string.  In the launch frame the range of the bonding interactions is decreased as the atoms/molecules are contracted 


#42
Nov1509, 04:48 PM

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#43
Nov1509, 04:50 PM

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Is this not correct? 


#44
Nov1509, 04:55 PM

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Do you have such calculations or mainstream articles strictly from the launch frame? 


#45
Nov1509, 04:58 PM

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EDIT: Oh I see what you mean. No you are not correct. You don't need the rest frame of the string to conclude that the string will snap. In the launch frame you observe constant atom distances, but decreasing range of bonding forces. 


#46
Nov1509, 05:27 PM

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#47
Nov1509, 05:51 PM

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Let me ask you this. If you have two rockets at a distance d with a string of length d between them and the rockets at in the same frame moving relative v to a stationary observer, would the string break? 


#48
Nov1509, 05:57 PM

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#49
Nov1509, 06:05 PM

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Say that the string is very weak and brittle. 


#50
Nov1509, 06:12 PM

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[EDIT] I have just noticed noticed that what I said is basically what Dr Greg said in post #33. Sorry about that. The posts in this thread are coming so fast, I missed a few. 


#51
Nov1509, 06:18 PM

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Next, at any instant t in the two rocket and string frame, all three are at rest? 


#52
Nov1509, 06:24 PM

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#53
Nov1509, 06:25 PM

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Matheinste. 


#54
Nov1509, 06:27 PM

P: 3,967




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