It is an amazing thing that we can use observations to constrain the geometry of the universe. This video explains how we use the characteristic features in the Cosmic Microwave Background (CMB) radiation to constrain the geometry. But to do this we need some understanding of the intrinsic (underlying), or the average size of these features. These cosmic ripples in the CMB help us to do this. The ripples were set up when the universe was a hot fluid of plasma, when it was so hot that all electrons and protons were in a 'soupy' mix. This animation shows how the ripples imprint themselves on the CMB.

One of the ways we detect dark matter is by how it distorts light. Just like the kind of lenses made of glass that we wear in glasses, dark matter acts like a gravitational lens and bends light around it. This causes the light from background galaxies to be smudged, smeared, and stretched. How much it is stretched depends on the distance between us, the foreground galaxies doing the lensing and the background galaxies, and also the mass of the lensing galaxies. You can read more about this lensing here.

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