[atdixon]

It might help to imagine a different world.

One in which Mary steps out of her room, sees a rose, and absolutely nothing new is added to her understandings.

She already had it all sorted out in her study. In many people’s understanding of “naturalism” that wouldn’t be any surprise.

But that’s not this world.

[theresistor]

If she truly possesses all physical knowledge, then she knows exactly what every possible rose looks like from every possible angle, in every possible setting and lighting. She knows in excruciating detail, at the level of every individual atom, how the scent of the rose will reach her brain, and exactly what responses it will trigger.

And indeed had she that knowledge, nothing new would be added by seeing one in person.

The implausible part is presupposing any person could ever have a complete enough understanding of all physical knowledge to achieve that.