Please learn what an argument from authority is. Citing E=mc^2 is only an argument from authority if you say that it's true because Einstein said it. Luckily, we've done a couple of experiments that show it to be true, so you don't need to rely on an argument from authority to prove E=mc^2 is correct. As long as there was no evidence or proof, and all we had was his say-so, then yes. E=mc^2 is not a fundamental formula, please learn what the theory of general relativity actually says. And I'm not sure it's irreducible. Tested? It's a definition! You can't test a definition, that would be circular reasoning. There is no such thing as a "reliable authority" in science. Please look up what science is. Additionally, Newton was a "reliable authority", yet his gravity has now been proven to be (technically) incorrect. A reliable authority is only reliable until they are shown to be incorrect. And Mandelbrot's definition of the word fractals is incorrect when compared to current usage. In other words, Mandelbrot is not even a reliable authority on this, in this case. Please look up what an argument from authority is, and learn why it is a logical fallacy.