[Moltke]

Physics is not “silly,” in my opinion.

Thanks for making my point. (And your's is not an opinion, it's a fact, Jack.) The silly part is the premise of a 0.9c baseball in a dense atmosphere. It would have burned up long before ever getting to 0.9c. Ever see a small piece of space debris entering the thin outer atmosphere at 0.0000...c? Poof. Shooting star. Gone. You cannot suspend basic physics, go on to construct some "what if?" scenario, and then claim it's still covered by physics.

[1rudeboy]

What premise? Your premise?

We'll suppose it's a normal pitch, except in the instant the pitcher releases the ball, it magically accelerates to 0.9c. [emphasis added]

[ALPAPilot]

You cannot suspend basic physics, go on to construct some "what if?" scenario, and then claim it's still covered by physics.

Then you best burn most physics textbooks and rid the world of such things as frictionless pulleys, massless ropes connecting point masses, frictionless surfaces, continuous mass distributions etc.