[Slick]

Galileo proved that light moved faster than sound and he probably was't the first to prove it. No modern phyisics predicted that the sound barrier was impossible to break. The term "sound barrier" was coined in the World War II era when countries were trying to make airplanes go faster than sound. They knew it was possible, but were encountering extreme difficulties as they approached the speed of sound. Aerodynamic forces on the airplanes was so great that it caused many failures, crashes and deaths. Hence the term "barrier".

Regarding the question on "terminal speed of gravity". I find it interesting that you quote from the first article that appears in a google search for "speed of gravity" even though it does not represent the vast majority of scientific acceptance; which is that gravity is transmitted at the speed of light. Their pic is nice too. Instantaneous transmission of gravity is correct under Newtonian physics, but not under relativistic physics. If gravity was transmitted instantaneously, I could vibrate a mass to send signals everywhere in the universe instantaneously using gravity as a carrier. This would violate the theory of relativity. The theory of relativity may one day be proven wrong, or I should say incomplete; because its predictions have been observed and verfied many times over and so far it has been shown to be consistent for all observable tests performed. Indeed, NASA has used and does use relativistic physics in its calculations. Even as "slow" (relative to the speed of light) as our Mars missions have travelled, their trajectories were calculated using relativistic physics. If they relied on Newtonian physics, they would be off course. Until the theory of relativity is shown to be wrong, incomplete or it is replaced by a superior theory that more closely agrees with observation and is tested to verify its correctness, I'll consider Einstein to be correct.