We are certain that quantum computing is much faster for simulating quantum phenomenon. And while it is difficult to show that quantum computing is faster for even some classical computations, it can be shown. Here's a skeptical eye on quantum algorithms: "Read the Fine Print" by Scott Aaronson: https://www.nature.com/articles/nphys3272 PDF: https://pdfs.semanticscholar.org/dfe4/d76e3fc27304a984a5daf1...