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Dr Martin Hendry University of Glasgow

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Why are we here?…. The period of inflation in the very early Universe was invoked to explain some apparent fine tuning problems. If the Universe is now inflating, this presents a new set of fine tuning problems

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Dark Energy Cold Dark Matter Atoms State of the Universe – Nov 2003

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Dark Energy Cold Dark Matter Atoms State of the Universe – Nov 2003 Why does 96% of the Universe consist of strange matter and energy?

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From Lineweaver (1998)

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General Relativity:- Geometry matter / energy Spacetime tells matter how to move and matter tells spacetime how to curve Einsteins Field Equations Einstein tensor Ricci tensor Metric tensor Curvature scalar Energy-momentum tensor of gravitating mass-energy

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General Relativity:- Geometry matter / energy Spacetime tells matter how to move and matter tells spacetime how to curve Einsteins Field Equations Treating the Universe as a perfect fluid, can solve equations to determine the pressure and density, and how they evolve

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Einstein originally sought static solution but this isnt possible, for normal pressure and density He added a cosmological constant to the field equations Can tune to give static Universe, but unstable (and Hubble expansion made idea redundant anyway!)

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Einsteins greatest blunder?

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But what is ?… Particle physics motivates as energy density of the vacuum but scaling arguments suggest:- So historically it was easier to believe

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Re-expressing Friedmanns Equations At any time Dimensionless matter density Dimensionless vacuum energy density Dimensionless curvature density

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Re-expressing Friedmanns Equations At any time If the Universe is flat then Dimensionless matter density Dimensionless vacuum energy density Dimensionless curvature density

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Dark Energy Cold Dark Matter Atoms State of the Universe – Nov 2003

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From Lineweaver (1998)

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Value of Present-day If the Concordance Model is right, we live at a special epoch. Why?…

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Hydrogen fusion – fuelling a stars nuclear furnace E = mc 2

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P-P chain, converting hydrogen to helium

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This has led to more general Dark Energy or Quintessence models: Evolving scalar field which tracks the matter density Convenient parametrisation: Equation of State Can we measure w(z) ? Matter 0 Radiation 1/3 Curvature -1/3 Lambda Quintessence w(z) Pressure Density

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SNIa at z = 0.5 Adapted from Schmidt (2002) At low redshift, SN1a essentially measure the deceleration parameter

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SNIa at z = 1.0 Adapted from Schmidt (2002) At low redshift, SN1a essentially measure the deceleration parameter

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SNIa at 0.5

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Tegmark et al (1998) SNIa measure:- CMBR measures:- Together, can constrain:-

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Can we distinguish a constant term from quintessence?… Not from current ground- based SN observations (combined with e.g. LSS) Adapted from Schmidt (2002)

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Can we distinguish a constant term from quintessence?… Not from current ground- based SN observations (combined with e.g. LSS)… …or from future ground- based observations (even with LSS + CMBR) Adapted from Schmidt (2002)

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Can we distinguish a constant term from quintessence?… Not from current ground- based SN observations (combined with e.g. LSS)… …or from future ground- based observations (even with LSS + CMBR) Adapted from Schmidt (2002)

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Can we distinguish a constant term from quintessence?… Not from current ground- based SN observations (combined with e.g. LSS)… …or from future ground- based observations (even with LSS + CMBR) Main goal of the SNAP satellite (launch ~2010?) Adapted from Schmidt (2002)

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