The Search for the Complete History of the Cosmos. Neil Turok

Transcription

1 The Search for the Complete History of the Cosmos Neil Turok * The Big Bang * Dark Matter and Energy * Precision Tests * A Cyclic Universe? * Future Probes

2 BIG Questions * What are the Laws of Nature? * What is the Universe made of? * How big/curved is the Universe? * How fast is it expanding? * How did galaxies, stars and planets form? * How did the Universe begin? * How will it end?

3 Unreasonable effectiveness Of Theory

4 Big Bang Cosmology Assume: Hot, uniform, expanding initial state + laws of gravity, thermal, nuclear + particle physics Evidence: Uniform Expansion Hot Radiation filling space Light Element Abundances

5 Uniform Expansion: Speed oc distance (Hubble, 1930)

6 Uniform Expansion Velocity (km/sec) (Supernovae, Reiss et al. 1997) V/D~ 65 5 km s -1 Mpc Distance (Mpc)

7 COBE Maps the Sky (1992) Near-perfect black-body spectrum Intensity Error Bars (X 400) Planck (1905) : origin of quantum mechanics

8 Primordial Abundances e.g. Deuterium QSO (black hole) Intensity gas cloud (12.5 billion yrs ago) - D fits big bang prediction Wavelength

9 Seeing the Dark Matter gravitational lensing

10 Empty space: Dark Energy (Λ) * Only visible to gravity * Energy doesn t grow with speed (Lor.Inv.) * Negative pressure: gravity is repulsive! Simplest way to look for it: acceleration of cosmic expansion Supernovae surveys (1999): Λ> 0!

11 Cosmic Concordance (late 90s) Einstein: Best Fit: Expansion Rate = Density + Curvature Flat Universe, fractional densities Ω DE ~.7, Ω DM ~.25, Ω ord ~.05, Ω ν ~.003, Ω rad ~ small, growing mode, scale-invariant, density variations Fits a wide array of observations: many alternative models ruled out

12 Looking Back to the Beginning 13.6 billion lt yrs 300,000 lt yrs

13 The Wilkinson-MAP Satellite (2003)

14 The Wilkinson-MAP Satellite

15 The Cosmic Microwave Sky (~20 resolution)

16 Comparison with COBE (7 o resolution) (1/3 o resolution)

17 Theory versus Reality Fluctuation Level: Temperature Polarisation <TE> predicted by Coulson et al (l = 2π/θ) Angle on Sky (Degrees)

18 Polarisation of the Cosmic Radiation

19 CMB Polarisation Observed Kovac et al Sum Difference 100 Declination (arcmin) uk Right Ascension (arcmin) Right Ascension (arcmin) 100

20 TQ correlation T Q θ Coulson, Crittenden, NT 1994

21 Forward with Newton yrs today

22 Galaxy Clustering Real Simulated

23 Back to the BIG Puzzles Why is the Universe so big, flat and smooth? What produced the density variations? Conventional answer (since 1981): INFLATION -a temporary phase of dark energy domination in the early Universe

24 Inflation Go! V(φ)=Λ Stop! φ Most remarkable side effect: Quantum fluctuations in φ lead to Hawking 1982 small, growing, near-scale invariant density variations (form anticipated by Harrison,Peebles,Z eldovich, 70s)

25 Inflation de Sitter: Vacuum energy =dynamite! Lorentz invariance implies P=-ρ Scale factor Density.. a = - a (4π G/3) (ρ + 3P).. ρ = - 3 (a/a) (ρ + P) ρ=const, a ~ Exp(Ht) Explains flatness, homogeneity, expansion Vacuum energy ρ=λ produces `free lunch

26 Doubts about Inflation Start the Universe `by hand Initial singularity? not removed What is φ? Mystery of Λ doubled -> Λ today ~ Λ inflation -> perhaps we need a new approach

27 Brane Worlds String theory -> Extra Dimensions Old idea: Kaluza-Klein `hose-pipe Brane string New idea: we live on a `brane embedded in higher dimensions: - Bulk + Brane

28 Brane Collision = Big Bang? Khoury et al. (2001)

29 The Cyclic Universe Steinhardt, NT 2002 branes V d Field-theory d M-theory

30 The Cyclic Universe Beginning at the present epoch V d dark energy dominates, branes stretch &.

31 The Cyclic Universe V d Matter diluted away homogeneity & isotropy established (low energy inflating phase)

32 The Cyclic Universe V d Vacuum energy decays away, branes pulled towards each other

33 The Cyclic Universe Quantum ripples on branes amplified ->Scale invariant variations! V d

34 The Cyclic Universe BIG CRUNCH V d collision! but only the extra dimension collapses

35 The Cyclic Universe Brane ripples Density perturbations in ensuing hot big bang V d

36 contraction expansion (of extra dimension) The Cyclic Universe BIG CRUNCH BIG BOUNCE V d

37 The Cyclic Universe V d New era of expanding and cooling

38 Conventional???? inflation Cyclic bang radiation cold future???? Λ uninvited guest matter dark energy contraction crunch Λ is key player big bounce

39 Key Observational Test Inflation -> long wavelength gravitational waves. Cyclic model -> none... falsifiable

40 Gravity Waves from Inflation φ 2 inflation dust Lewis et al 2001

41 Walking the Planck -ESA 2007

42 -> will distinguish cyclic model from inflation (bet with Hawking) Polarisation Windows -sensitive only to component of polarisation produced by gravitational waves but not by density variations

43 Conclusions * We live in a golden age for cosmology * Standard theory works but isn t complete * Potential connections to superstring theory * From philosophy to physics