The Nobel prize in Physics 2006:

Cosmology becomes precision science

Hans Kristian EriksenInstitute of Theoretical Astrophysics

Onsala, June 2012

The Nobel prize in Physics 2006

John Mather

George Smoot

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 experi-ment 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.”

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 publishes in 1916 a newtheory of gravity (GR) that corrects Newton’s theory from 1687

GR summarized in one equation:

GR summarized in one sentence: Matter tells space how to curve, and space tells matter how to move

Einstein’s General Relativity

Geometry Contents

E ¹ º = · T¹ º

”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

• 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!

Today

Time Temp.

The importance of the CMBTwo important properties:

• Frequency dependency:– Photons and electrons in thermodynamic

equilibrium sets up a Planck spectrum

– Big Bang Planck spectrum withT = 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– But only if the intensity actually follows

the Planck spectrum!– If not, Big Bang is in real trouble!

• 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!– 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

Scale 1964

T0 3.5±1.0 K

180° 0.2

90°

1°

0.1°

0.01°

• 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 1979

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° 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 1979 1984

T0 3.5±1.0 K ~ 5% ~ 2%

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

0.01° 0.05 10-4

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 1979 1984 1988

T0 3.5±1.0 K ~ 5% ~ 2% Matsumoto et al?!

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

0.01° 0.05 10-4 3-5·10-5

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!

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:• Base for three instruments

• Weight: 2270 kg

• Polar orbit– Period: 103 minutes– Altitude: 900 km

• Lifetime: 4 yearsFIRAS:• Target: CMB spectrum

• Leader: John Mather

DIRBE:• 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– Infrastructure only, no instruments– Dimensions: 6 meters long, 5 meters wide, 4800 kg

• January 27th 1986: Challenger explodes shortly after take-off

– 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– 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:

– 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:– 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

Atoms

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• But we don’t know what this is…

– 74% dark energy• 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 distanceCOBE 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 tempera-

ture, but also polarization– Just like ordinary light

• Polarization is created by local quadrupoles in the temperature field

• Gravity waves create local quadru-poles 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

Jane Doe

Otto Normalverbraucher

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...

... 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.”

CMB project:

Detecting the first structures in the universe!

Plagiarize th

is!

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:

• Conceptually simple – surprisingly difficult in practice

L(µ) /e¡ 1

2 dtC (µ)¡ 1d

pjC(µ)j

Simple case: The 2D likelihoodS

tren

gth

of p

ertu

rbat

ions

Shape of power spectrum

NON-ZERO Q =

PRIMORDIAL FLUCTUATIONS

Primary goals

1. Compute the 2D q-n likelihood• First method: Simple grid evaluation• Second method: Metropolis MCMC (if time)• Third method: Gibbs sampling (if still time)

2. 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