Abstract
We can now take a closer look at how structure on large scales in the universe forms, having discussed the ingredients for this process in the previous two chapters. These ingredients are the different types of matter and how they behave, and the forces governing the evolution and interaction of the various matter species, in particular gravity.
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Notes
- 1.
Even if the dark matter would interact through the weak interaction, this interaction is too weak to be relevant here.
- 2.
As mentioned above, there is five times as much dark matter as there are baryons, and of the baryons only about 10% are luminous, that is in form of stars or extremely hot gas.
- 3.
This is a simplified example, we neglect air resistance, the fact that the ball is elastic and also not a point particle, and many other effects.
- 4.
The Jeans length of the photon-baryon fluid is too large for the fluid to be able to collapse.
- 5.
We should stress that is a much simplified model, the actual gravitational well is three dimensional, whereas the bowl is two dimensional—recall the rubber sheet analogy in Sect. 6.4.2.2.
- 6.
This can be shown explicitly by studying the governing equations.
- 7.
The size of the box in Fig. 2.2 is 430 million lightyears or 140 million parsecs, the results are shown starting at redshift 6 or 650 million years, z =  2 or 2.9 billion years, and z =  0 today.
- 8.
Electrons and protons can interact through the electromagnetic force, as discussed in Sect. 6.2.
- 9.
A sound wave in air also doesn’t move fluid material, in this case air, with it. Air just gets compressed—gets denser—, and then rarefied, as the wave travels through it.
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Malik, K.A., Matravers, D.R. (2019). How Does the Structure in the Universe Form?. In: How Cosmologists Explain the Universe to Friends and Family. Astronomers' Universe. Springer, Cham. https://doi.org/10.1007/978-3-030-32734-7_7
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DOI: https://doi.org/10.1007/978-3-030-32734-7_7
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