Maybe, but this conversation always inevitably ends up in this territory ("But what if aliens are crystals?"). And sure, we can't know. But we're going to have to make some assumptions, and we all do live in one universe, with a common constituent set of physical laws. Aliens that build spaceships probably also have airplanes and an internet. I don't think it's dumb to speculate with some reasonable assumptions, and while I appreciate that this conclusion always comes up and is not wrong, it's uninteresting.