No, this is not an exercise video. It’s a cogent explanation by theoretical physicist Sabine Hossenfelder of “Why the multiverse is religion, not science.” Watch:
It’s hard to disagree with her:
This is not a polemical argument and it’s not meant as an insult. But believing in the multiverse is logically equivalent to believing in god, therefore it’s religion, not science….
Scientists say that something exists if it is useful to describe observations. By “useful” I mean it is simpler than just collecting data. You can postulate the existence of things that are not useful to describe observations, such as gods, but this is no longer science.
Universes besides our own are logically equivalent to gods. They are unobservable by assumption, hence they can exist only in a religious sense. You can believe in them if you want to, but they are not part of science.
But the question she leaves unaddressed here is why scientists would choose, despite the absence of evidence, despite the fact that the multiverse is “unobservable by assumption,” to believe in a multiverse. What’s the motivation?
For my answer, see “Three Things Materialists Can’t Do Without.”