On Monday, December 14, 2020 at 4:08:16 PM UTC-5, Luigi Fortunati wrote:
> Bruce Scott sabato 12/12/2020 alle ore 19:13:37 ha scritto:
> >> The bridge and the train have the same length at rest.
> >> The bridge collapses only if the entire weight of the train rests on
> >> it.
> > [...]
> >> [Moderator's note: This is essentially the same puzzle as the ladder
> >> paradox, which even has its own Wikipedia entry. In fact, it is closer
> >> to the "man falling into grate" version originally discussed by the
> >> late, great Wolfgang Rindler. -P.H.]
> > The version we got in class (way back when) was the train entering the
> > barn with the doors opening/closing just in time. The answer, of
> > course, is relativity of simultaneity.
> But does the bridge collapse or does it not collapse?
> [Moderator's note: Answer per moderator's note here, as this has been
> solved long ago. The bridge collapses. Forget the complication of the
> bridge and the weight of the train causing it to break; just have a gap
> where the bridge should be. Does the train fall into the gap? Yes.
> See the "paradox" due to Rindler above. Check this out:
I think that some of the
> confusion comes from first assuming that when the train is on the bridge
> or the gap then it will fall, but in practice if the train were moving
> that fast then it would just sail over the gap. But if you assume that
> it would fall when positioned over the gap, you also have to assume that
> gravity is strong enough to pull it down. -P.H.]
Simultaneity says that if the bridge collapses in one frame of relativity
that it collapses in all frames. Sort of like that a life destruction
cannot alter to a many universes model.
Say a train is given a barn door pair to travel thru. And the train has
explosives in it, triggered by closed doors firing them if the train
trigger is centered in it. The train velocity to trigger is findable
by trial and error? But in fact the train is never at c. Meaning
that the trigger never fires. Indicating that the barn viewer
can never know when the barn doors are closed.