I had the impression he was saying the exact opposite.

Physics' definition of all fundamental concepts is exactly that - purely abstract, conceptual. Physics tells us absolutely nothing about the nature of things, nor does it explain anything. "mass" as defined by physics is basically a quantitative statement about the relationships between various aspects of our experience.

I notice you've zoomed in on Casper's questioning of "mass" as some kind of fundamental reality but missed the more important mention of force and energy.

As Richard Feynmann said, "We have to admit that we have no idea what 'energy' is."

This seems SO hard to grasp but it's so incredibly obvious when you think about it.

The astonishing thing, to me, is that scientists can go through their whole careers being mere technicians and never think about this.

Steven Weinberg won the Nobel Prize in physics in 1977. It was not until 25 years later that he even gave a moment's thought to what physics is actually all about. This thought was triggered by an esteemed colleague mentioning to him, "You know Steven, science doesn't really explain anything, it only describes."

This is really all Casper is telling us, but we are so attached to the idea that scientific knowledge is the only kind of knowledge we've got dozens of commenters writing about red herrings and various digressions having nothing to do with the article.

To be fair, Weinberg never got clear about it either. HE wrote an article for the New York Review of Books, "Does Science Explain Everything? Anything?"

And he concluded (almost), "no." But then this was too much for him. In an expression of what can only be called scientific fundamentalism (or more simply, scientism), he wrote, "Well, I don't care what the word "explain" has meant for thousands of years. We scientists can use the word any way we want, and I say we DO explain everything.

Jerry Falwell and Pat Robertson couldn't have said it better.