bob nichol - nobel prize public talk
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TRANSCRIPT
The Nobel Prize in Physics 2011
Bob Nichol (ICG Portsmouth)
“majority of its surface area is only about 10 feet above sea level”
General Relativity Primer
Cosmology Primer I Assumptions
Cosmological Principle; not special place, time or physics Homogeneous and isotropic; defines “simple” FRW metric
Assume GR and FRW metric; solve to get Friedmann’s equations (including Einstein’s Cosmological Constant)
€
H 2 ≡˙ a a⎛
⎝ ⎜ ⎞
⎠ ⎟
2
=8π3ρ −
kR2 −
Λ3
Cosmology Primer II
Hubble discovered the expansion of the Universe in 1929
Einstein dropped his cosmological constant
Next 70 years was the search for two numbers! “Hubbles’ Constant” Density of matter
!
"0 #$0$c
=8%G3H0
2 $0
Distance from us
Re
cess
ion
Ve
loci
ty
€
Ω0 =1 for a flat universe
Distances and SNeIa
n
Thermonuclear explosions of White Dwarf stars
White Dwarf accretes mass from or merges with a companion star, growing to a critical mass ~1.4Msun (Chandrasekhar)
A violent explosion is triggered at or near the center, and the star is completely incinerated within seconds. In the core, light elements are burned in fusion reactions to produce ~0.6Msun Nickel. The radioactive decay of Nickel and Cobalt makes it shine for a couple of months
Standardizable Candles
A"er correc(on, σ~ 0.16 mag (~8% distance error)
Kim et al. 1997
Industrial Astronomy
Sciama Building
Only ~1 SNe per ~100 years in our Galaxy
SN Hubble Diagram (circa 1999)
Sciama Building
ICG only UK institute in SDSS-III
a=1/(1+z)
W
€
Ω0 =ΩM +ΩΛ
€
Ω0 =ΩM +ΩΛ
Nobel Prize 2011 "for the discovery of the accelerating expansion of the Universe
through observations of distant supernovae"
Baryon Acoustic Oscillations
Initial fluctuation in DM. Sound wave driven out by intense pressure at 0.57c.
Initial fluctuation in DM. Sound wave driven out by intense pressure at 0.57c. Photons free stream, while baryons
remain still as pressure is gone
Today. Baryons and DM in equilibrium. The final configuration is the original peak at the center and an echo (the sound horizon) ~150Mpc in radius
Illustrations by Martin White
Standard Rulers in the Sky
WMAP 1st year data
First year WMAP power spectrum
150Mpc
Flat Universe
WMAP 1st year data
“Ruler” is 150Mpc and distance to CMB is known to high accuracy (z=1089)
Today
Densities known to ~10%
Energy of Nothingness!
Coincidence problem?
Log[a0/a(t)] €
ρDE ~ a−3(1+w )
€
wi(z) ≡piρi
Cosmological Constant
€
ρDE ~ a−3(1+w )
(10120 too small)