It was also claimed that special relativity cannot handle acceleration, which would lead to contradictions in some situations. However, this assessment is not correct, since acceleration actually can be described in the framework of special relativity (see Acceleration (special relativity), Proper reference frame (flat spacetime), Hyperbolic motion, Rindler coordinates, Born coordinates). Paradoxes relying on insufficient understanding of these facts were discovered in the early years of relativity. For example, Max Born (1909) tried to combine the concept of rigid bodies with special relativity. That this model was insufficient was shown by Paul Ehrenfest (1909), who demonstrated that a rotating rigid body would, according to Born's definition, undergo a contraction of the circumference without contraction of the radius, which is impossible (Ehrenfest paradox). Max von Laue (1911) showed that rigid bodies cannot exist in special relativity, since the propagation of signals cannot exceed the speed of light, so an accelerating and rotating body will undergo deformations.