This is easily Sabine Hoffstader’s fringiest video. Please don’t get the wrong idea that this is a point of controversy within physics! As a physicist I’d estimate 99.9% of her colleagues would disagree and I would too. She has no real argument, just vaguely gestures at “maybe the comoving frame makes relativity invalid” and then vaguely gestures at “quantum gravity spoiling everything we know so far about physics”.
As to the second point, quantum gravity is a thing but almost certainly will not upend the special relativistic account of the large scale causal ordering of events. This is for the same reason that it almost certainly won’t change the calculation of the amount of time it takes an apple to drop from a tree —- within the domain of validity of the old theory, its predictions will agree.
As to the second point, quantum gravity is a thing but almost certainly will not upend the special relativistic account of the large scale causal ordering of events. This is for the same reason that it almost certainly won’t change the calculation of the amount of time it takes an apple to drop from a tree —- within the domain of validity of the old theory, its predictions will agree.