Conjectures that have been disproved with extremely large counterexamples I would like to migrate this Math Question into physics. The question is:


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*Are there conjectures in Physics which have been disproved with extremely large counterexamples? If yes, i would like to know some of them.

 A: One of the better examples of such a reversals is the "Steady-State Hypothesis" of Hoyle and Narlikar. Increasing depth and precision in cosmological measurements in the 1960s and 70s, however, emphatically refuted this idea.
A: Lots of properties that were found to hold locally (in space and time) turned out to be only local approximations.  
Flat earth hypothesis - long journey.
Galilean transformations - breaks at large velocities.
Global curvature of spacetime, locally it is flat - large distances.
Spacetime is not expanding - breaks at large distances (Hubble's law)
Classical mechanics - breaks also at extremely small scales (QM).
A: The equivalent in Physics of a counterexample in Mathematics would be a failed experiment. For example: the Michelson Morley experiment is a counterexample to the ether conjecture. But was it big? Can any experiment be "big" in the same sense as Mathematics? Possibly not. 
I make a conjecture: "any physical conjecture can be disproved with a fairly straightforward experiment." 
Actually it's not a conjecture, it's a simple request that any valid physical theory must be disprovable through experiment (which is pretty much an agreed to principle).
A: There have been conjectures and implicit assumptions in physics that have been disproved with extremely small counterexamples.
But for the spirit of the mathematical question, I think an equivalent would be computationally costly simulations that find unsuspected stable configurations, or accelerator experiments at high energies that shatter conjectures in particle physics.
