What does "of matter" mean?

[Super Sonic]

"In fact, the physical Universe of matter represents only a very
small percentage of the entire, greater Universe as a whole."

Could anyone explain me the highlighted phrase please? Thanks in advance.

[BobK]

I think this is a problem not of language but of particle physics. You know what 'matter' means, but it's not so easy to grasp the concepts of Antimatter - Wikipedia, the free encyclopedia and Dark matter; - Wikipedia, the free encyclopedia. I can't, for example. The sentence refers to 'the physical Universe of matter' - that is, things and their relationships; this doesn't refer to the whole Universe - so I think the use of 'Universe' (especially the capital U) is not helpful; it would be clearer if it were reworded like this:

In fact, the Universe as a whole largely consists of stuff we don't know about; physical matter represents only a very small percentage of it."

b

[Barb_D]

Most of the universe is empty space. The parts that actually have matter (the scientific definition of matter) are very small, compared to the entire universe.

[Super Sonic]

Thank you two, but I am not sure I quite get it:(

[Anglika]

matter = (in physics) that which occupies space and possesses mass.

So this sentence is saying that those objects in Outer Space [the cosmos] which possess mass and occupy physical space form only a very small part of the entire Universe, which chiefly consists of space.

[BobK]

matter = (in physics) that which occupies space and possesses mass.

So this sentence is saying that those objects in Outer Space [the cosmos] which possess mass and occupy physical space form only a very small part of the entire Universe, which chiefly consists of space.

... As I said, I think this is a problem of physics rather than English. Dark Matter is not the same as space. If I were a theoretical physicist I could quantify just how much is not known about what makes up the Cosmos; all I know is it's a lot.

b

PS
Here's the beginning of the Wikipedia article:

In astrophysics and cosmology, dark matter refers to hypothetical matter of unknown composition that does not emit or reflect enough electromagnetic radiation to be observed directly, but whose presence can be inferred from gravitational effects on visible matter.

(For the link to the whole thing see my previous post.)

There's nothing hypothetical about 'space' but Dark Matter is something else.