Now me, I have a quibble. She says "physicists don't know" but they do, today. They didn't know back then, partly because they weren't actual physicists in the scientific sense, they were more like noblemen-philosophers who wanted to seem learned and spent the time and money making themselves seem learned while being wrong about pretty much everything. It's a miracle any actual advancement of human technology and understanding ever came out of any of them.
To illustrate the point, look again at the Lord Kelvin interview. He says it can't be done, he gives a vague reason with no evidence to support it, no facts, just him wielding the weight of Someone Who Is Listened To.