A sentence that I don't understand in novel The Three Body Problem

Here is the context from the novel The Three Body Problem by Liu Cixin:

“Have we succeeded?” the princeps asked. “Is that the proton unfolded into two dimensions?”

The science consul replied, “Princeps, it’s still a failure. I just received the report from the accelerator control center. The unfolding left one too many dimensions in, and the proton was unfolded into three dimensions.”

The bold part is the one I don’t understand. I can’t identify the grammatical structure of the sentence as well as the meaning of it.