The Nobel prize in Physics 2006:
Cosmology becomes
precision science
Hans Kristian Eriksen
Institute of Theoretical Astrophysics
Onsala, June 2012
The Nobel prize in Physics 2006
Press release from the Nobel
committee 3. oktober 2006:
”Pictures of a newborn universe.
This year the Physics Prize is awarded for work
that looks back into the infancy of the Universe
and attempts to gain some understanding of the
origin of galaxies and stars. It is based on
measurements made with the help of the COBE
satellite launched by NASA in 1989.
... These measurements marked the inception of
cosmology as a precise science...
... The success of COBE was the outcome of
prodigious team work involving more than 1,000
researchers, engineers and other participants.
John Mather coordinated the entire process and
also had primary responsibility for the experiment that revealed the blackbody form of the
microwave background radiation measured by
COBE. George Smoot had main responsibility
for measuring the small variations in the
temperature of the radiation.”
John Mather
George Smoot
Cosmology in five slides
Two things are infinite: The universe and
human stupidity; and I’m not sure about the
universe.
Albert Einstein
What is the universe?
•
How do we mathematically
describe the properties of
space?
•
How many stars and galaxies
are there?
•
Is there matter we cannot see?
•
Could the universe be dominated
by unknown dark forces?
How did structures form?
What does the universe look like?
Summary
• Cosmology is the study of the universe as a
whole
• Our goal is to understand
–
–
–
–
how the universe was created
how it evolved
what it consists of
how old it is
Summary
”I want to know God’s thoughts; the rest are details.”
Albert Einstein
Cosmology before 1965
What kind of theory is this, that was conceived by
a priest and endorsed by the pope?
Fred Hoyle about Big Bang
Einstein’s General Relativity
Einstein publishes in 1916 a new
theory of gravity (GR) that corrects
Newton’s theory from 1687
GR summarized in one equation:
E ¹ º = · T¹ º
Geometry
Contents
GR summarized in one sentence:
Matter tells space how to curve,
and space tells matter how to
move
”The greatest blunder of my life”
•
The universe is dominated by
gravitational forces
•
GR is therefore the appropriate theory
to describe the universe as a whole
•
”Problem”: GR does not allow static
solutions!
– The universe must either expand or
contract
– Einstein was convinced that the
universe was static, and therefore
”corrected” his theory by adding a
term
1925: Edwin Hubble publishes
measurements of galaxy velocities
relative to us – and finds that the
universe expands!!
Creation in a hot Big Bang?
George Gamow (1948) –
”The origins of elements”
•
•
•
•
If the universe expands today, it must
have been smaller earlier
The tempertaure of a compressing
gas increases
Very early the temperature must have
been very high; the universe can only
have contained free elementary
particles and photons
Predictions from Gamow’s theory:
– There must be roughly 75%
hydrogen and 25% helium in the
universe
– The universe must be filled with
electromagnetic radiation with a
temperature of about 5°K
– The radiation must be nearly
isotropic, ie., equally hot in all
directions
– The intensity must follow a black
body (or Planck) spectrum
Still, could the universe really be static?
•
The idea of a creation was (and still is)
philosophically troublesome from many:
– The laws of physics breaks down
– Physics is easily mixed with religion
•
Fred Hoyle (1948) – Steady State-modellen:
– The universe has always looked the way it
does today
• There was no beginning and no end
• The density is always the same
– The expansion of space must therefore be
accompanied by creation of new matter
• About one atom per m3 per billion years
•
•
No observations could distinguish between Big Bang and Steady
State in the 50’s, and the discussion was very heated
Arguments revolved around esthetics and philosophy, and partially
religion
The cosmic microwave background –
an echo from the Big Bang
Boys – we’ve been scooped...
Robert Dicke
Radiation from the Big Bang
•
The universe started as a
hot gas of electrons, protons
and photons
– Frequenc collisions lead to
thermodynamic equlibrium
– Photons could only move a
few meters before hitting an
electron
Today
•
This gas expanded and
cooled quickly
•
When the temperature fell
below 3000°K, electrons and
protons combined into
neutral hydrogen
•
Without free electrons,
photons could move freely
through the universe!
The importance of the CMB
Two important properties:
•
Frequency dependency:
–
–
–
•
Photons and electrons in thermodynamic
equilibrium sets up a Planck spectrum
Big Bang  Planck spectrum with
T = 2-5°K
Steady State does not easily explain such
radiation
Spatial temperature variations
–
–
–
–
The temperature is primarily given by the
density of the gas
Small temperature variations correspond
to small density fluctuations
Regions with high density 380,000 years
after the Big Bang formed the starting
point for later galaxy formation
A CMB map is a picture of the matter
distribution in the universe shortly after
the Big Bang!
The first detection of the CMB
•
In 1964 Arno Penzias og Robert Wilson,
two scientists at Bell Laboratories, studied
the radiation from the Milky Way at radio
wavelengths
•
The measurements were made with a 6
meter horn antenna in New Jersey
•
No matter where they pointed the
telescope, they found an excess noise
term of 3.5°K!
•
A similar experiment was at the same time
prepared by Dicke, Peebles og Wilkinson,
three Princeton scientists, to measure the
radiation from the Big Bang!
•
Penzias and Wilson accidentally heard
about this, and called Dicke...
– “Boys, we’ve been scooped.”
•
Penzias and Wilson won the Nobel prize
in Physics in 1978
Arno Penzias
Robert Wilson
The frequency spectrum
•
Big Bang got a boost from Penzias and
Wilson’s discovery
–
–
•
Groups all over the world started
measuring at at different wavelengths
–
•
All results were consistent with a Planck
spectrum, but uncertainties were large
Major surprise in 1988!
–
–
–
–
•
But only if the intensity actually follows
the Planck spectrum!
If not, Big Bang is in real trouble!
Matsumoto et al. launches a rocket
based experiment
Formally by far the most sensitive so far
And they find T0 = 3.175 ± 0.027 K!!
17σ away from other results!!
Clear violation of Big Bang predictions!
–
–
–
Is Big Bang dead?
Is there something wrong with the
experiment?
More than 100 papers the next year tried
to establish a theory for this result!
Group
Year
λ (cm)
T0
Penzias and Wilson
1965
7.35
3.5 ± 1.0
Howell et al.
1966
20.7
2.8 ± 0.6
Roll and Wilkinson
1967
3.2
3.0 ± 0.5
Welch et al.
1967
1.58
2.0 ± 0.8
Kislyakov et al.
1971
0.36
2.4 ± 0.7
Mandolesi et al.
1986
6.3
2.70 ± 0.07
Temperature fluctuations
•
•
Scientists also started looking for variations in the
temperature
Usually quantified by ΔT / T0 for a given angular
scale
–
•
Example: ΔT / T0 = 10-5 at 90 degrees means that the
average difference between two points separated by
90 degrees on the sky is ΔT = 10-5 · 2.74 K = 27.4 μK
Theoretical calculations showed that ΔT / T0 had to
be larger than 10-6 for there to be enough time for
galaxies to form since the Big Bang!
Scale
1964
T0
3.5±1.0 K
180°
 0.2
90°
1°
0.1°
0.01°
Temperature fluctuations
•
•
Scientists also started looking for variations in the
temperature
Usually quantified by ΔT / T0 for a given angular
scale
–
•
Example: ΔT / T0 = 10-5 at 90 degrees means that the
average difference between two points separated by
90 degrees on the sky is ΔT = 10-5 · 2.74 K = 27.4 μK
Theoretical calculations showed that ΔT / T0 had to
be larger than 10-6 for there to be enough time for
galaxies to form since the Big Bang!
Scale
1964
1969
T0
3.5±1.0 K
~ 5%
180°
 0.2
0.002
90°
 0.011
1°
 3-5·10-4
0.1°
 3·10-3
0.01°
Temperature fluctuations
•
•
Scientists also started looking for variations in the
temperature
Usually quantified by ΔT / T0 for a given angular
scale
–
•
Example: ΔT / T0 = 10-5 at 90 degrees means that the
average difference between two points separated by
90 degrees on the sky is ΔT = 10-5 · 2.74 K = 27.4 μK
Theoretical calculations showed that ΔT / T0 had to
be larger than 10-6 for there to be enough time for
galaxies to form since the Big Bang!
Scale
1964
1969
T0
3.5±1.0 K
~ 5%
180°
 0.2
0.002
Dipole
discovered
90°
 0.011
3·10-4
announced!
1°
 3-5·10-4
 10-4
0.1°
 3·10-3
 10-4
0.01°
1979
 0.05
Temperature fluctuations
•
•
Scientists also started looking for variations in the
temperature
Usually quantified by ΔT / T0 for a given angular
scale
–
•
Example: ΔT / T0 = 10-5 at 90 degrees means that the
average difference between two points separated by
90 degrees on the sky is ΔT = 10-5 · 2.74 K = 27.4 μK
Theoretical calculations showed that ΔT / T0 had to
be larger than 10-6 for there to be enough time for
galaxies to form since the Big Bang!
Scale
1964
1969
T0
3.5±1.0 K
~ 5%
180°
 0.2
0.002
Dipole
discovered
Amplitude
+ direction
90°
 0.011
3·10-4
announced!
 3·10-5
1°
 3-5·10-4
 10-4
 3-5·10-5
0.1°
 3·10-3
 10-4
 3-5·10-5
 0.05
 10-4
0.01°
1979
1984
~ 2%
Temperature fluctuations
•
•
Scientists also started looking for variations in the
temperature
Usually quantified by ΔT / T0 for a given angular
scale
–
•
Example: ΔT / T0 = 10-5 at 90 degrees means that the
average difference between two points separated by
90 degrees on the sky is ΔT = 10-5 · 2.74 K = 27.4 μK
Theoretical calculations showed that ΔT / T0 had to
be larger than 10-6 for there to be enough time for
galaxies to form since the Big Bang!
Scale
1964
1969
T0
3.5±1.0 K
~ 5%
180°
 0.2
0.002
Dipole
discovered
Amplitude
+ direction
90°
 0.011
3·10-4
announced!
 3·10-5
 2·10-5
1°
 3-5·10-4
 10-4
 3-5·10-5
 10-5
0.1°
 3·10-3
 10-4
 3-5·10-5
 1.7·10-5
 0.05
 10-4
 3-5·10-5
0.01°
1979
1984
1988
~ 2%
Matsumoto
et al?!
COBE –
precision cosmology is born
The scientific discovery of the century, if not
all time!
Stephen Hawking about COBE
Challenge from NASA
• NASA released on June 15th 1974 an ”announcement of opportunity” to
the research community
– If we give you 5-10 million dollars and a rocket, what do you do with it?
– No limitations on research topic
• 121 groups responded, of which three suggested CMB observations:
– Massachusetts Institute of Technology, led by John Mather
• Three instruments, measuring 1) spectrum, 2) fluctuations, and 3) galactic dust
• Estimated cost: Between $2.9 and $4.85 million
– Actual cost: ~ $350 million...
– UC Berkeley, led by George Smoot
• Small rocket, satellite smaller than 200 kg
– Jet Propulsion Laboratory, California, led by Samuel Gulkis
• Very conservative proposal, everything based on existing technology
• NASA arranges a ”shotgun marriage”:
– The CMB proposals are approved, but NASA decides who will join!
– The core group is Mather, Weiss and Wilkinson (MIT), Smoot and Hauser
(Berkeley) and Gulkis (JPL)
One satellite, three instruments
COBE:
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•
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Base for three instruments
Weight: 2270 kg
Polar orbit
–
–
•
FIRAS:
•
•
Period: 103 minutes
Altitude: 900 km
Lifetime: 4 years
Target: CMB spectrum
Leader: John Mather
DIRBE:
•
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Target: Galactic dust
Leader: Mike Hauser
DMR:
•
•
Target: CMB fluctuations
Leader: George Smoot
Preparations and constructions
•
•
Building COBE started at Goddard Space Flight
Center (GSFC) in 1982
Launch scheduled with the space shuttle in 1989
•
First version of COBE ready in January 1986
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–
•
January 27th 1986: Challenger explodes shortly
after take-off
–
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–
•
Six astronauts killed, one teacher
All planned launches are indefinitely halted
No way COBE will be launched by a shuttle
Only option: A medium sized Delta rocket
–
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–
•
Infrastructure only, no instruments
Dimensions: 6 meters long, 5 meters wide, 4800 kg
Complete rebuild required
New dimensions: 6 meters long, 2.6 meters wide,
2300 kg!
In 1988, 300 scientists, engineers and support
personell worked on rebuilding COBE
Ready for launch in June 1989
Launch and early observations
•
Launch on November 19th 2898 at
Vandenberg, California
–
An earthquake at 7.1 on Richter’s scale hit on
October 16th; COBE escaped undamaged
•
•
After one hour, COBE was in a perfect orbit
Worked flawlessly through the four years of
observations
•
First FIRAS spectrum was found after nine
minutes of observations!
DIRBE produced a beautifully detailed
image of our own galaxy
DMR needed two years of observations to
produce robust results
•
•
Black body radiation or not?
•
Recall that:
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–
–
•
Big Bang
 Planck-spektrum
Steady State  not Planck-spektrum
Matsumoto et al. found descrepancies in 1988...
The COBE team reserved time at the annual
American Astronomical Society meeting in
January 1990
–
Indicated something big was coming
•
The conference room was packed with more
than 2000 excited spectators
•
John Mather walked onto the stage:
”Here is our spectrum.”
•
A few seconds of silence, then everybody gets
up and give the COBE team standing ovations!
•
A very strong confirmation of the Big Bang
theory
– The Steady State model is dead
Results from DMR – the first structures
•
The DMR results were ready in
spring 1992, and were presented
on April 23rd
•
George Smoot led the presentation
this time
– Showed a picture with red and blue
spots
– A journalist asked what this picture
means, and Smoot replied:
”If you’re religious, it’s like
looking at God.”
•
The oldest and largest structures in
the universe had been found, and
were in preferct agreement with
the Steady State theory
•
Stephen Hawking:
”The greatest discovery of the
century, if not all time!”
•
Cosmology turned into precision
science
Reward
• The Nobel prize in Physics 2006 was
given jointly to John Mather and George
Smoot
"for their discovery of the blackbody
form and anisotropy of the cosmic
microwave back-ground radiation”
• 10 million Swedish kroner were split
equally between the laureates
The next generations –
WMAP and Planck
Every astronomer will remember where he or she was
when they first heard the WMAP results. I certainly will.
Prof. John Bahcall’s (Princeton)
WMAP – the successor of COBEs
•
COBE only provided very general answers:
– Big Bang, not Steady State
– The starting point for galaxy formations was
primordial fluctuations from the Big Bang
• Most details could not be addressed
– What physical processed worked in the
early universe?
– How much matter and energy is there?
• WMAP was approved by NASA in 1996:
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–
–
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Centered on the COBE team at Goddard
Launched on June 30th, 2001
Higher resolution and lower noise
Observations from the 2. Lagrange point
• Far away from Earth, very little heat
radiation
• Thermally very stable
WMAP vs. DMR
WMAP
•
•
•
•
had 33 times the resolution of DMR
had 45 times the sensitivity of DMR
observed at five frequency bands
was located in a much better place
than DMR
Highlights from WMAP
Main products from WMAP:
•
•
Full-sky CMB maps at five frequencies
Complete statistical description on
angular scales down to ~0.2°
From these we find that the universe
•
•
is 13.7 ± 0.2 billion years old
consists of
–
–
4% atoms
22% dark matter
•
–
74% dark energy
•
•
But we don’t know what this is…
And we have no idea what this is!
probably started with a short period of
exponential expansion called inflation
Planck – Europe steals the show
• ESA decided in 1996 to build
Planck
– Goal: Measure the primoridal
temp-erature fluctuations once
and for all
– 15 countries involved
– Costs more than 600 million
euros
– Launched on May 14th 2009
– First cosmological results will
be published in January 2013
• Planck vs. WMAP
– Three times higher resolution
– Ten times lower noise
– Nine frequencies from 30 to
850 GHz
• Will be able to separate
cosmological signal from Milky
Way contamination
Planck – going all the distance
COBE
WMAP
Planck
= All important
information!
The future
Prediction is very difficult, especially if it’s about the future.
Niels Bohr
CMB polarization and gravity waves
•
The CMB not only has a temperature, but also polarization
– Just like ordinary light
•
Polarization is created by local
quadrupoles in the temperature field
•
Gravity waves create local quadrupoles by (stretching space + Doppler
shift)
– Lots of other effects, too, but this is
the cool one 
•
Therefore, we can in principle
observe gravity waves from the Big
Bang by looking for a particular
signature in the CMB polarization
– But the amplitude is low, probably at
~100 nK RMS compared to a 3K
carrier signal
QUIET – looking for gravity waves
•
Inflation predicts the existence of gravity waves
– Such waves have never been directly observed
– If you want to find them, a good place to look is in
the CMB polarization field
•
QUIET is one experiment that aims to find these
– Located in the Atacama desert in Chile
• One of the driest places on the Earth
– Employs ~100 extremely sensitive radiometers
•
The world’s most sensitive CMB array with
published results
• Very good systematic properties
– First results released in December 2010
– Second data release scheduled to happen in ~1
month
QUIET – looking for gravity waves
The Nobel prize in Physics 2039
Announcement from from the Nobel
committee on October 3rd 2039:
”Pictures of a newborn universe.
This year the Nobel prize in physics is given to
work that looks back to the very first second of
the universe, This work is made by a satellite
called CMBPol, launched in 2025 in a joint
experiment between ESA and NASA.
... These measurements showed that all
structures in the universe wwere created in a
quantum mechanical process called inflation...
Jane Doe
... The success of CMBPol was the result of a
joint effort incluiding more than 1500 scientists,
engineers and support personel. Jane Doe from
NASA lead the instrumentation team, and Otto
Normalverbraucher led the analysis team.
Working together, these two branches eventually
revealed the minute polarization signal set up by
primordial gravitational waves.”
Otto Normalverbraucher
CMB project:
Detecting the first structures in
the universe!
Inventory
•
•
•
•
The four-year DMR sky maps
Noise specification
Beam information
A Galactic mask
• An partially completed Fortran 90 computer program
The CMB likelihood
• CMB is Gaussian:
L (µ) /
e¡
• Conceptually simple –
surprisingly difficult in practice
1
2
p
d t C ( µ) ¡
jC (µ)j
1d
Strength of perturbations
Simple case: The 2D likelihood
NON-ZERO Q
=
PRIMORDIAL FLUCTUATIONS
Shape of power spectrum
Primary goals
1.
Compute the 2D q-n likelihood
•
•
•
2.
First method:
Second method:
Third method:
Simple grid evaluation
Metropolis MCMC (if time)
Gibbs sampling (if still time)
Figure out whether q is non-zero or not
•
How large fluctuations in terms of ΔT / T0 do you find?
3.
Write a Nobel prize winning Letter
4.
Present results at the end of the summer school