Summary

Portrait of Max von Laue Max von Laue On the Discussion Concerning Rigid Bodies in the Theory of Relativity

Now, in Newton's mechanics there is of course another definition of rigidity, which fits even better to the physical state of facts; there, one considers the rigid body as the limiting case of a deformable body with a very great elasticity coefficient. This passage to the limit can in any case also be executed in the theory of relativity, although it wouldn't lead to the rigid body, but to a body deformable as less as possible, which possibly has especially simple properties as well.
Source: Wikisource

Portrait of Max von Laue Max von Laue On the Discussion Concerning Rigid Bodies in the Theory of Relativity

All three proposals have the (quite justified) idea in common, that a rigid body, contrary to the infinitely many degrees of freedom of the deformable ones, has only a finite number of them (there, the body is of course imagined as a continuum) . We now want to show, that the relativity principle excludes this possibility due to dynamical causes, so that any attempt in that direction is hopeless from the outset.
Source: Wikisource

Portrait of Max von Laue Max von Laue On the Discussion Concerning Rigid Bodies in the Theory of Relativity

The motion of the body at instant then has surely degrees of freedom. Because a part of it which is not yet belonging to any of these intersections, is still at rest in , while in the parts represented by the intersections, a motion dominates that is independent from the other disturbances, and which naturally has at least one degree of freedom. The number of disturbance points, however, can be arbitrarily increased; thus the number of kinematic degrees of freedom of a body has no upper limit.
Source: Wikisource

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