Cosmology

1. Cosmology Steve King Physics CSG Day at Southampton University 5/6/7 13.7Gyr ABB

3. Copernicus Kepler Galileo Newton Revolutionaries These men taught us that the Earth is not the centre of the Universe

4. Newfangled Cosmology Hubble Space Telescope

5. The Universe Age 700 million years

6. Cosmological Principle • Our position in the Universe is not special • -all points in the Universe are equivalent just as all points on the surface of the Earth are equivalent • the Universe looks the same wherever you are • - cosmological principle is an approximate property of the global Universe, which only applies on the largest distance scales

7. You are here The Milky Way Spiral Galaxy

8. You are here The Milky Way Local Group: satellites

9. You are here The Milky Way Local Group: including Andromeda galaxy N.B. Large galaxies separated by about 1,000,000 pc = 1 Mpc

10. You are here The Virgo Supercluster: containing Virgo Cluster and our Local Group Each dot is a bright galaxy. Milky Way is dot in the exact centre.

11. You are here Our Neighbouring Superclusters: Virgo Supercluster at the centre Note the presence of filaments and voids in an irregular cellular pattern.

12. You are here On the largest distance scales the Universe appears smooth, with no further structures

13. Homogeneity and Isotropy The fact that the Universe is smooth on the largest distance scales (bigger than a billion light years) supports the cosmological principle. In fact the Universe appears to have two separate features: Homogeneous– the same at each point (c.f. homogenised milk) Isotropic – the same in all directions Very small departures from homogeneity are clearly present due to the irregular cellular large scale structure of the Universe.

14. The Expansion of the Universe Hubble’s Law: all galaxies are moving away from us with a speed of recession v proportional to the distance of the galaxy d Hubble’s constant

15. How is the galactic speed v measured? – from redshift z of absorption and emission lines (Doppler effect) How is galactic distance d measured? – from the apparent luminosity of “standard candles” in the galaxy (e.g. Cepheid variables, type Ia supernovae,…) What is the interpretation of Hubble’s law? – the Universe is expanding at a constant rate

16. If the Universe is expanding at a constant rate then every galaxy will be moving away from every other galaxy in accordance with Hubble’s law

17. This implies that in the distant past the Universe would have been much smaller than now. We infer that the Universe started from a small, dense, hot region from some initial explosion called the Big Bang. Modern Cosmology

18. History of the Universe\_PC START.exe

20. H H H H H H H H H H H H H H The Universe Age 380,000 years just after the atoms were formed and the Universe becomes transparent -- henceforth these Big Bang photons travel unhindered through the Universe ? e ? ? ? e He e e e e e e

21. As the Universe expands, the Big Bang photons in the visible spectrum get redshifted into microwave photons

22. Cosmic microwave background The Big Bang photons from the time of atom formation (380,000 yrs) are observed as microwave background radiation, with a Black Body spectrum corresponding to a temperature of about 3 K = -270o C (redshifted from a temperature of about 3,000 K )

23. In 1965 Penzias and Wilson discovered the CMB as an irremovable background hiss in their antenna Penzias & Wilson Nobel Prize 1978

24. About 1% of TV White Noise is due to CMB

25. These days more sophisticated equipment is used to make temperature maps of the sky

26. John Mather, NASA GSFC Overall PI of COBE and PI of FIRAS George Smoot, Berkley PI of DMR The first people to make a temperature map of the sky COBE Nobel Prize 2006

27. Temperature Maps Earth Universe

28. COBE 1992 WMAP 2006

29. We can learn a lot from these temperature maps

30. The Standard Cosmological Model Requirements: • Flat Universe • Dark Energy • Dark Matter WOW!!

31. …means the Universe is flat

32. Why did nature choose this one?

33. This could be due to an exponential inflation

34. Atoms only make up 4% of the mass of the Universe The rest is unknown Dark Energy (fluid like) and Dark Matter (particle like)

35. A Final Word on Dark Energy Could the Dark Energy be Einstein’s Cosmological Constant? ``My biggest blunder…”

37. Dark Matter has been ``seen’’ Seeing is believing! Do you believe in Dark Matter?

38. The Bullet Cluster of Galaxies

39. How Dark Matter Evolves This computer simulation takes the CMB temperature fluctuations as seeds of density fluctuations which evolve in time to give long filaments of dark matter

40. By the time the Universe is 100 million years old it is dominated by filaments of dark matter around which the galaxy clusters and superclusters will form

41. Who is the dark matter particle? An excellent candidate for dark matter is the spin ½ partner to the photon called the photino

42. The photino could be discovered at the CERN Large Hadron Collider which starts later this year Atlas particle_event_full_ns.mov

43. How Did it All Begin? Some believe it was a vacuum quantum fluctuation quickly followed by inflation . .

44. Conclusion • Cosmology has now entered a precision era • Landau’s adage that cosmologists are “often in error never in doubt” is undoubtedly no longer true! • There is now a Standard Model of the Universe consisting of 74% Dark Energy which looks like Einstein’s Cosmological Constant • But only 4% is atoms • The remaining 22% is Dark Matter consisting of particles which could be discovered soon at CERN (with the help of Southampton students!)

45. Appendices • Parsecs • Spherical Harmonics • Angular Power Spectrum • Fluids in the Early Universe • Sound Waves • First Peak = Geometry • Second Peak = Baryons • Third Peak = Dark Matter

46. Stars: main source of visible light from nuclear fusion in stars Sun is typical: 1 Parsec ~ 3.26 light years ~ 3 × 1016 meters Sun Earth

48. We want to understand this