But dark matter was also important because electromagnetic radiation initially prevented ordinary matter from developing structure on scales smaller than about a hundred times the size of a galaxy. Only by hitchhiking with dark matter did galaxy-sized objects and the seeds of stars in our Universe have time to form.
Again, the numbers don't match. Things would not be able to be more than 100 times the size of our galaxy could not form, and therefore our galaxy could not form despite being the size of our galaxy and not 100 times larger.
There is obviously a big simplification going on here, with some process being completely elided because this is aimed at non-physicists, but the inclusion of numbers make this missing process necessary to understanding the text.
Is this some metatextual metaphor for the measurements that showed dark matter and dark energy were needed, or is this just poor communication?
Either drop the numbers, or explain the simplification in a footnote. Or just don't simplify it this much.
