For a deductive theory, demonstrating an absurdity implies that a postulate is false - the theory can be falsified in this way. For a non-deductive model (empirical concoction), demonstrating an absurdity has no consequences because there are no postulates. So in Einstein's general relativity we find the absurdity ("idiocy" is more precise) that the speed of light DECREASES as the light falls towards the source of gravity - in the gravitational field of the Earth the acceleration of falling photons is NEGATIVE, -2g. This is not deduced from postulates - the absurdity is a fudge factor Einstein and his mathematical friends had to introduce to make the gravitational redshift and gravitational time dilation compatible:
Albert Einstein: "Second, this consequence shows that the law of the constancy of the speed of light no longer holds, according to the general theory of relativity, in spaces that have gravitational fields. As a simple geometric consideration shows, the curvature of light rays occurs only in spaces where the speed of light is spatially variable."
"The change in speed of light with change in height is dc/dh=g/c."
"Contrary to intuition, the speed of light (properly defined) decreases as the black hole is approached."
"Einstein wrote this paper in 1911 in German. [...] ...you will find in section 3 of that paper Einstein's derivation of the variable speed of light in a gravitational potential, eqn (3). The result is: c'=c0(1+φ/c^2) where φ is the gravitational potential relative to the point where the speed of light c0 is measured. Simply put: Light appears to travel slower in stronger gravitational fields (near bigger mass). [...] You can find a more sophisticated derivation later by Einstein (1955) from the full theory of general relativity in the weak field approximation. [...] Namely the 1955 approximation shows a variation in km/sec twice as much as first predicted in 1911."
"Specifically, Einstein wrote in 1911 that the speed of light at a place with the gravitational potential φ would be c(1+φ/c^2), where c is the nominal speed of light in the absence of gravity. In geometrical units we define c=1, so Einstein's 1911 formula can be written simply as c'=1+φ. However, this formula for the speed of light (not to mention this whole approach to gravity) turned out to be incorrect, as Einstein realized during the years leading up to 1915 and the completion of the general theory. [...] ...we have c_r =1+2φ, which corresponds to Einstein's 1911 equation, except that we have a factor of 2 instead of 1 on the potential term."
Einstein's general relativity is an empirical concoction (not even wrong) so the idea of falsification is totally irrelevant. In contrast, special relativity is deductive and can be falsified both logically (reductio ad absurdum) and experimentally.
The logical falsification of special relativity is easy because all consequences of Einstein's 1905 false light postulate are absurd. For instance, length contraction implies that unlimitedly long objects can gloriously be trapped, "in a compressed state", inside unlimitedly short containers:
John Baez: "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."
See, at 7:12 in the video below, how the train is trapped "in a compressed state" inside the tunnel:
"Einstein's Relativistic Train in a Tunnel Paradox: Special Relativity"
It is not difficult to realize that trapping unlimitedly long objects inside unlimitedly short containers implies unlimited compressibility and drastically violates the law of conservation of energy. The unlimitedly compressed object, in trying to restore its original volume ("spring back to its natural shape"), would produce an enormous amount of work the energy for which comes from nowhere.
At 9:01 in the above video Sarah sees the train falling through the hole, and in order to save Einstein's relativity, the authors of the video inform the gullible world that Adam as well sees the train falling through the hole. However Adam can only see this if the train undergoes an absurd bending first, as shown at 9:53 in the video and in this picture:Loading Image...
Clearly we have reductio ad absurdum: An absurd bending is required - it does occur in Adam's reference frame but doesn't in Sarah's. Conclusion: The underlying premise, Einstein's 1905 constant-speed-of-light postulate, is false.