Question: if there was no dark matter how would all the universe be arranged

Monique Henson answered on 18 Nov 2015:

Good question! Without dark matter, we wouldn’t see structures around us today. There wouldn’t be enough gravity to hold together galaxies or even larger structures like galaxy clusters.

But what if there was still the same amount of matter in the Universe, but it was all normal matter rather than dark matter? Well, people originally thought dark matter might be like normal matter, but be too faint for us to see. There are a couple of problems with this: firstly, our ideas about the Big Bang theory wouldn’t produce enough of the right type of normal matter. Secondly, it would change the way the Universe looks. When we look at the sky, we can describe mathematically how the density of matter changes across the night sky. We can make a map of the whole sky, looking at where there is matter and where there isn’t. If all dark matter was normal matter, this map would look different. It would have more wiggles (the technical term is baryon acoustic oscillations). As we don’t see more wiggles, we know that dark matter isn’t different to normal matter.