🚀 go-pugleaf

Rudolf Drabek a �crit :
> On 7 Mrz., 12:06, Denis Feldmann <feldmann.denis.asuppri...@neuf.fr>
> wrote:
>> Rudolf Drabek a �crit :
>>
>>
>>
>>> On 6 Mrz., 21:31, Denis Feldmann <feldmann.denis.asuppri...@neuf.fr>
>>> wrote:
>>>> Rudolf Drabek a �crit :
>>>>> I'm not good in understanding SR.
>>>>> I only want to know if I look to the situation from the pole's frame:
>>>>> So the distance between the barn doors is in any case too short, that
>>>>> the pole can fit into the barn.
>>>>> SR is symmetrical for time dilatation and length contraction, but not
>>>>> for this situation.
>>>>> Who can help me out.
>>>> Easy: the whole scenario insist on *simultaneously closing the doors*,
>>>> and simultaneity is not an absolute concept, so there is no
>>>> contradiction. But, of course, any serious student of SR knows that, or
>>>> can redemonstrate it to him(her)self convincingly, so you will only find
>>>> crank answers here...
>>> I wanted to point out, that there are two scenarios and each one is
>>> *true* for the corresponding observer.
>> No, not really
>>
>>   Einstein spended a lot of time
>>
>>> on that point regarding syncing clocks and simultaneity, here similar
>>> problems can be seen.
>>> I can accept two truth, only the symmetry is lost, which is a major
>>> part of SR.
>> No, you canot : it is obviously impossible to put the rod in the barn,
>> so this scenario must have a flaw, and indeed trying to close the door
>> simultaneously *and* enclose the rod is not possible. Do the (simple)
>> calculation to check that...
> 
> In practice it's indeed hard to close the doors in the correct timing,
> but possible.
> You have some time for delays, even at gamma = 2
> A detector for the beginning of the pole, o.k.
> Then 2 equally long actuator lines for the doors, to be shut in a few
> ns and open again.
> But I made the assumtion, that I know the length of the pole.


No, no amount of assumption will change the situation : the problem is 
that the definition of length is *not* what you think it is...
> 
> It is clear that the experiment would fail, if the contracted pole has
> exactly the length of the distance of the barn doors. I have no time
> for a reaction.
> 
> But my question is more philisophic in the direction of two different
> truth.
> It' clear that the pole appears contracted acc. to SR. for the barn
> owner but for the pole owner sitting on it, the barn appears
> contracted.

Of course, but there is *no* appearance here. It is real, as the twin 
paradox will show you : for the traveller, the short barns are passed in 
less time that they "should", and the travel is quick (ie there has been 
time dilatation), for the barns, the traveller is contracted, but this 
doesnt make him gain speed...




> 
> But let's stop now.

Good. All this is getting really boring :-)


> 
> 
> 
>>> So, who can help me out?
>>> Length contr. is a consequence of c=const in all frames and not more.
>> Sure
>