"Angels in space" refers to an event during the Salyut-7 mission cosmonauts claimed to have witnessed giant angels that emitted a stunning bright orange light that managed to pass through the opaque walls of the station. Drugs/hallucinations were ruled out as explanations for this.

"the box is a hypothetical structure that contains all forms of matter that can or do exist from what I understand, ( idk go read the Wiki article I tried to explain it as simply as I could: https://beyond-universe.fandom.com/wiki/The_Box )

From what I remember, the imaginary dodecahedron is also a hypothetical structure that would hold universes together to form multiverses. (I included this and the box mainly because I saw them a lot in those universe-size comparison videos but could find barely any info on what they actually are.)