dr martin hendry university of glasgow. why are we here?…. the period of inflation in the very...
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Dr Martin HendryUniversity 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
Ato
ms
State of the Universe – Nov 2003
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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?
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CDM
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”
Einstein’s Field Equations
TGRgRG 82
1
Einstein tensor Ricci tensor Metric tensorCurvature 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”
Einstein’s 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 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!)
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Einstein’s 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
12010theory)(
obs)(
0
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Re-expressing Friedmann’s Equations
At any time
1 km
Dimensionless matter density
Dimensionless vacuum energy density
Dimensionless curvature density
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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
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Dark Energy
Cold Dark Matter
Ato
ms
State of the Universe – Nov 2003
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State of the Universe – Nov 2003
m
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CDM
From Lineweaver (1998)
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m
Value of
Present-day 0/ RR
If the Concordance Model is right, we live at a special epoch. Why?…
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Hydrogen fusion – fuelling a star’s 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) ?
wP Matter 0Radiation 1/3Curvature -1/3‘Lambda’ -1Quintessence w(z)
iw
Pressure
Density
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SNIa at z = 0.5
Adapted from Schmidt (2002)
mq2
10
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
mq2
10
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SNIa at 0.5<z<1.0
Adapted from Schmidt (2002)
At low redshift, SN1a essentially measure the deceleration parameter
mq2
10
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Tegmark et al (1998)
SNIa measure:-
CMBR measures:-
Together, can constrain:-
mq2
10
mk 1
,m
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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)