My question concerns an aspect of the pole-barn paradox that, to my knowledge, has not been discussed so far. So rejecting the question as "duplicate" is incorrect, in my view. Here is the edited version:
Einstein's 1905 postulates entail that unlimitedly long objects can be trapped, in a compressed state, inside unlimitedly short containers:
"These are the props. You own a barn, 40m long, with automatic doors at either end, that can be opened and closed simultaneously by a switch. You also have a pole, 80m long, which of course won't fit in the barn. [...] So, as the pole passes through the barn, there is an instant when it is completely within the barn. At that instant, you close both doors simultaneously, with your switch. [...] If it does not explode under the strain and it is sufficiently elastic it will come to rest and start to spring back to its natural shape but since it is too big for the barn the other end is now going to crash into the back door and the rod will be TRAPPED IN A COMPRESSED STATE inside the barn." http://math.ucr.edu/home/baez/physics/Relativity/SR/barn_pole.html
One of the comments on the previous version of the question is as follows:
"Note that the pole is not compressed by the Lorentz-FitzGerald contraction, it's compressed by colliding with the back door at 0.866c"
Not true. The compression occurs before colliding - the long object is still flying inside the short container when the doors are closed. That is, the compression is purely relativistic. Then the trapped object will "start to spring back to its natural shape". How much energy will be released if a 1 km object, compressed to 1 cm, restores its original length? Even the question sounds absurd, let alone the answer.
If such trapping is absurd, we have reductio ad absurdum: the absurdity of the logical consequence shows that at least one of the postulates is false. Is trapping unlimitedly long objects, in a compressed state, inside unlimitedly short containers absurd?