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## Dr Martin Hendry University of Glasgow

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**Why are**we here? Dr Martin Hendry University of Glasgow**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**Atoms**Cold Dark Matter Dark Energy State of the Universe – Nov 2003**Atoms**Cold Dark Matter Dark Energy State of the Universe – Nov 2003 Why does 96% of the Universe consist of ‘strange’ matter and energy?**General Relativity:-**Geometry matter / energy “Spacetime tells matter how to move and matter tells spacetime how to curve” Einstein’s Field Equations Ricci tensor Metric tensor Einstein tensor Energy-momentum tensor of gravitating mass-energy Curvature scalar**General Relativity:-**Geometry matter / energy “Spacetime tells matter how to move and matter tells spacetime how to curve” Einstein’s Field Equations Treating the Universe as a perfect fluid, can solve equations to determine the pressure and density, and how they evolve**Einstein originally sought static solution but this isn’t**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!)**But what is ?…**Particle physics motivates as energy density of the vacuum but scaling arguments suggest:- So historically it was easier to believe**Re-expressing Friedmann’s Equations**At any time Dimensionless matter density Dimensionless curvature density Dimensionless vacuum energy density**Re-expressing Friedmann’s Equations**At any time If the Universe is flat then Dimensionless matter density Dimensionless curvature density Dimensionless vacuum energy density**Atoms**Cold Dark Matter Dark Energy State of the Universe – Nov 2003**Value of**Present-day If the Concordance Model is right, we live at a special epoch. Why?…**Hydrogen fusion – fuelling a star’s nuclear furnace**E = mc 2**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) ? Pressure Density**SNIa at z = 0.5**At low redshift, SN1a essentially measure the deceleration parameter Adapted from Schmidt (2002)**SNIa at z = 1.0**At low redshift, SN1a essentially measure the deceleration parameter Adapted from Schmidt (2002)**SNIa at 0.5<z<1.0**At low redshift, SN1a essentially measure the deceleration parameter Adapted from Schmidt (2002)**SNIa measure:-**CMBR measures:- Together, can constrain:- Tegmark et al (1998)**Can we distinguish a constant L term from quintessence?…**Not from current ground-based SN observations (combined with e.g. LSS) Adapted from Schmidt (2002)**Can we distinguish a constant L 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)**Can we distinguish a constant L 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)**Can we distinguish a constant L 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)