Dr Martin HendryUniversity 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

Ato

ms

State of the Universe – Nov 2003

Dark Energy

Cold Dark Matter

Ato

ms

State of the Universe – Nov 2003

Why does 96% of the Universe consist of ‘strange’ matter and energy?

CDM

From Lineweaver (1998)

General Relativity:-

Geometry matter / energy

“Spacetime tells matter how to move and matter tells spacetime how to curve”

Einstein’s Field Equations

TGRgRG 82

1

Einstein tensor Ricci tensor Metric tensorCurvature 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”

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!)

Einstein’s 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

12010theory)(

obs)(

0

Re-expressing Friedmann’s Equations

At any time

1 km

Dimensionless matter density

Dimensionless vacuum energy density

Dimensionless curvature density

Re-expressing Friedmann’s Equations

At any time

If the Universe is flat then

1 km

Dimensionless matter density

Dimensionless vacuum energy density

Dimensionless curvature density

0k

Dark Energy

Cold Dark Matter

Ato

ms

State of the Universe – Nov 2003

State of the Universe – Nov 2003

m

CDM

From Lineweaver (1998)

m

Value of

Present-day 0/ RR

If the Concordance Model is right, we live at a special epoch. Why?…

Hydrogen fusion – fuelling a star’s 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) ?

wP Matter 0Radiation 1/3Curvature -1/3‘Lambda’ -1Quintessence w(z)

iw

Pressure

Density

SNIa at z = 0.5

Adapted from Schmidt (2002)

mq2

10

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

mq2

10

SNIa at 0.5<z<1.0

Adapted from Schmidt (2002)

At low redshift, SN1a essentially measure the deceleration parameter

mq2

10

Tegmark et al (1998)

SNIa measure:-

CMBR measures:-

Together, can constrain:-

mq2

10

mk 1

,m

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)