Moment of beginning of space-time about 13.7 billion years ago. The time at which all the material and energy in the expanding Universe was coincident

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1 Big Bang Moment of beginning of space-time about 13.7 billion years ago The time at which all the material and energy in the expanding Universe was coincident Only moment in the history of the Universe when energy was created Hot Big Bang Theory describes the behaviour of the components of the Universe in the moments following the explosion.

2 Expanding Universe 1920s Hubble measured greater redshifts for galaxies at greater distances and determined that the Universe must be expanding

3 The Hubble constant is the gradient of this line and is a measure of how fast the Universe is expanding. Today the Hubble diagram is normally constructed with type Ia supernovae.

4 Cosmology Timeline 1950s Big Bang nucleosynthesis theory and helium abundance predictions 1965 Cosmic microwave background discovered

5 At this point the Hot Big Bang theory became widely accepted. 1960s development of the standard model of particle physics

6 1970s opening up of the infrared and x-ray sky discovery of dark matter

7 1982 inflation theory 1991 discovery of anisotropies in the microwave background

8 1997 discovery of the accelerating Universe from the supernova Ia Hubble diagram evidence for dark energy

9 2015 gravitational waves detected from intermediate mass black holes

10 Dark matter and galaxy formation We know dark matter exists because of many astronomical measurements like measurements of the outer parts of galaxies. We can also infer it exists because extra mass is required to create galaxies by gravity.

11 Current observational cosmology research Square Kilometre Array Large Synoptic Survey Telescope

12 James Webb Space Telescope

13 Inflation theory

14 Cosmological simulations Q continuum 2.5 PB of data

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16 Special Relativity

17 General Relativity Equivalence principle

18 Tests of general relativity Precession of the perihelion of Mercury Gravitational redshift Gravitational lensing

19 Standard Model of Particle Physics Feynman diagram beta decay

20 Beyond the standard model Symmetry Breaking

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22 Evidence for Dark Matter Galaxy rotation curves Galaxy formation from primordial fluctuations Galaxy clustering Cluster galaxy dynamics Gravitational lensing X-ray halos Dark matter is present on all scales. The ratio of dark matter : stars in galaxies is typically about 1:10. The ratio of dark matter : x-ray gas in clusters is typically about 1:6.

23 Galaxy rotation curves

24 Galaxy formation simulations

25 Galaxy clustering

26 Galaxy cluster dynamics Coma cluster at 90 Mpc

27 Gravitational lensing Observed in both strong and weak regimes

28 Cluster x-ray gas

29 Baryonic dark matter Baryons cannot make up most of dark matter because they cool by dissipation and would always collapse into the central disk. Stars in the Milky Way disk are kept in place by more mass than is observed in the stars, so the implication is some of the disc material must be dark. Baryonic dark matter cannot be gas (or it would be observed at radio and submillimetre wavelengths) or stellar remnants (then it would overproduce metals). It is probably brown dwarfs or Jupiters. The MACHO microlensing experiment estimates of fraction of 20% of disk dark matter.

30 Neutrinos Neutrinos are an attractive candidate for dark matter because we know they exist and were produced in the Big Bang. But there are problems. 1. Neutrino dark matter is hot, meaning that it would thermally diffuse out of perturbations in the early universe so galaxies with dark matter halos would never form. A sterile neutrino would produce warm dark matter, but neutrinos cannot produce cold dark matter required for galaxy formation. 2. Neutrinos are fermions so cannot be packed arbitrarily closely together. The maximum local dark matter density allowed for neutrinos is lower than the measure dark matter density in the centre of dwarf spheroidal galaxies.

31 Cold dark matter There are a large number of candidates, most of which have no or little chance of direct detection. Some candidates are 1 WIMPs are weakly interacting massive particles so might produce weak electromagnetic signatures. 2 Axions are predicted to exist from quantum field theory and may have negligible free streaming, even if light. 3 Supersymmetric particles which probably do not interact with normal matter in any detectable way.