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

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

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

From Lineweaver (1998)

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

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

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!)

Einsteins greatest blunder?

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 Friedmanns Equations At any time Dimensionless matter density Dimensionless vacuum energy density Dimensionless curvature density

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

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

From Lineweaver (1998)

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

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

P-P chain, converting hydrogen to helium

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

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

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

SNIa at 0.5<z<1.0 Adapted from Schmidt (2002) At low redshift, SN1a essentially measure the deceleration parameter

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

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

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)

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)

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)