tldr, energy density of the universe remains same while the universe is expanding, so yes space is being created, and yes physical distances between things are

tldr, energy density of the universe remains same while the universe is expanding, so yes space is being created, and yes physical distances between things are changing (outside of the local influence of gravity that is, so no distance between earth and moon is not changing for example). Now a longish answer, space is like a stage or a backdrop, it's not made of anything, yet we can model the behavior of radiation and matter within space, also we cannot talk only about space, we have to talk about both space and time since they are intertwined. So spacetime has geometry, ie it can be curved by presence of matter, and space tells matter how it can move (geodesics), As for the expansion of space itself, Hubble observations found that every star outside the local group is moving away from earth and not only are they moving away from earth but they are speeding up as they move away from us, also we observe that the acceleration is proportional to the distance to those stars, for example a star 100 light years away is racing away 2x faster than a star 50 light years away (we inferred this based on the redshifting of the light coming from these stars that are moving away from us), based on these observations, we can conclude that the space between stars itself is expanding at rate proportional to the distance between stars, ie something like the opposite of positive pressure is pushing stars away and the further they are from each other the stronger the push away, we have some sort of always accelerating negative pressure affecting everything. This negative pressure is referred to as dark energy and it is responsible for this expansion of space. To put it another way outside of local cluster of galaxies, gravity is losing the battle against this negative pressure expanding force we call dark energy and eventually everything would be so far away that light from these distinct racing away stars won't ever make it to earth no matter how long we wait, which is why the author ends with future astronomers would see a barren universe. disclaimer: I am no physicist, just another nerd who's watched a lot of documentaries and thinks he understands a thing or two about this stuff but could totally be drawing the wrong analogy or incorrect in some technical way for the above explanation, so I am happy to be corrected and learn.