Kat, who has been diagnosed with cancer, has 4 years to live. She volunteers on a space mission to Alpha Centauri (4.37 lightyears away), travels at 0.866c, and arrives there ~5.0 years later. According to classical SR, Kat's time slows to a half and ages only ~2.5 years, arriving in Alpha Centauri, fairly bright eyed and bushy tailed, with ~1.5 years more of life.

But... also according to SR, during the space flight, inside the rocket (Kat's inertial frame), its internal clock registers time normally, and ~5.0 years pass by for Kat before the landing at Alpha Centauri. She is dead on arrival.

As Schrodinger would ask, is Kat alive or dead, when the rocket is opened at Alpha Centauri? According to SR, she is alive and dead at the same time. But there is no superposition in relativity, so therefore, we have a contradiction, and relativity must be false, as some 'nuts' have already known.