I am working with engineering equations in a vacuum system and want to emphasize that a certain set of parameters will not work. Usually, this is due to real world effects (friction, pump efficiency factors, wear and tear of bearings, etc), but I want to emphasize that a particular setup wouldn't work even under perfect textbook conditions.
I would like to say it is "theoretically impossible", but that has a ring of just the opposite of what I would like to say! It sounds like:
a safety rating better than 100% is theoretically impossible, but the Tesla Model S did it!
What is a word or phrase to say something is absolutely forbidden by fundamental, physical laws, even under ideal conditions?