It would have been so cool if, instead of suggesting that the 2D fragments are dark matter, they would have been proposed as the solution to the missing baryon problem.
This problem is about the discrepancy between the amount of baryonic ("regular" matter) observed nowadays, as compared to the detections from soon after the Big Bang. According to those measurements from the early universe, there should be more baryons than seen at recent times. Some 30% was missing!
I saw "was", because these days it's pretty much solved, but at the time that the books were published, it was not. So having that matter become invisible because it has collapsed into 2D fragments would have been a beautiful solution 😌
Since it's not at all clear from the original post: this was about the Remembrance of Earth's Past trilogy. The fragments = dark matter thing just doesn't make sense












