But there are clues as to what was happening inside those dense hydrogen clouds. Look back even further in time to a moment just 380,000 years after the big bang, and the universe was filled not with/ darkness but with light. 

 

 

 

Its faint after glow is still visible to astronomers today. 

 

 

 

In fact, this picture is amazing. This is a picture of the early universe. This is an image of the after-glow of the big bang. 

 

 

 

At this time, the universe was the same everywhere, filled with hot atmosphere of matter and radiation. But the seeds of the very different universe we see today had already been sown. 

 

 

 

Everywhere we look around us in the universe, we see structure, we see galaxies all over the place. Where do these galaxies come from? There is a big clue to this, buried in this picture. If you look closely you can see that there are red spots and there are blue spots. These red regions are / regions 

 

 

 

where there is basically / more stuff and the blue regions are the regions where there is less stuff. 

 

 

 

This image reveals that there were tiny variations in the density of the gas which filled the early universe, minute ripples that would grow with time. 

 

 

 

We think that these ripples, these primordial ripples are the seeds to all future structure. These ripples eventually grew into what became the first galaxies. 

 

 

 

But how could something so small grow into something so big? 

 

 

 

It’s gravity that amplifies these ripples. In fact, we need an additional source of gravity to amplify those ripples, to form galaxies like we see today. And that additional gravity comes to form dark matter.