Re: So... Lerentz Contractions are *physical* not observered?

mgconsolidated@xxxxxxxxxxxxxx wrote:

Can anyone provide / point to a definitive answer on whether Lorentz
contractions are physical or an observered effect. I thought they were
purely an observed effect of SR until I read the "passing trains"
paradox.

The summary seems to go along the lines of....

Get two trains 100 metres long each heading towards each other on a
single track
Put a passing point between them 80 metres long
At non-reletavistic speeds you simply can't get one train past the
other - however you try, they crash
At relatavistic speeds, each train will observe the passing point less
than 80 metres, but will observe the other train significantly
shorter, due to its much greater speed (relative to themselves) and
there will be no crash

The only sniff of a problem I can see with the above is that you can't
ignore GR in this case, as the original measurements were taken in the
same frame of reference, and the second measurements taken following
acceleration.

Thanks very much
Matt


According to SR, if the picture looks like this:

|
| <- track
|
( ) <- pullout
|
|
|

and if the trains' speeds are identical and large enough, and if both trains reach the pull-outs simultaneously as determined in the track frame, then the trains won't collide (i.e., from the perspective of the tracks, both trains will simultaneously be entirely on the pull-outs). (And, obviously, it only takes one perspective to determine whether or not there's a collision).

.

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