Tak Kaneko, Astrophysics, Cavendish,

1
The Cosmic Microwave Background Radiation

• Tak Kaneko
• Astrophysics Group, Cavendish Laboratory,
• University of Cambridge
• Amateur Astronomy Talk 5th July 2005

2
CMB Situation in 1999

• From http//ulysse.iap.fr/CMB/index.htm

3
CMB Situation in 2004

• From the WMAP Science Team http//lambda.gsfc.nas
  a.gov/product/map/

4
1948 Relic of the Big Bang

• Alpher and Herman proposed that it should be
  possible to detect the afterglow of the big bang
  (ie. The CMB).
• But their proposal was largely ignored

5
CMB Spray Can Analogy

• When you spray deoderant, it feels cold.
• This is because the gas cools as it expands on
  being released from the spray can.
• Similarly, in the early Universe, energy was
  concentrated in a small space so it was hotter.

6
CMB Redshift Explanation

• The early Universe 30,000 years after the big
  bang was
• Hot (3000K)
• Filled with radiation.
• As the Universe expanded, the fabric of spacetime
  was stretched 1,000-fold.

7
CMB Redshift Explantion

• This stretches the wavelength of light
  1,000-fold.
• Longer wavelengths are less energetic and
  colder (think X-ray vs radio).
• We should be able to observe these colder light
  permeating the Universe.

8
The Surface of Last Scattering

• The CMB dates from 379,000 years after the big
  bang and is called the surface of last
  scattering.
• It reaches us largely unimpeded, so it is 13
  billion year old light.
• We cannot see beyond the CMB using
  light/radio/X-rays. The surface of last
  scattering is like the surface of the sun.

9
Cosmology in the Early 1960s

• By the early 1960s, cosmologists were divided
  5050 between the big bang camp and the
  steady-state camp.

10
Renewed Interest in the CMB

• 1964-65 Robert Dicke realises it should be
  possible to detect the relic of the big bang.
• James Peebles calculates the necessary conditions
  in the early Universe.

Dicke and Peebles.
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Dicke, Roll and Wilkinson

• Roll and Wilkinson made and instrument and before
  they could get any data
• Arno Penzias was told about Dicke and Peebles
  work by Bernard Burke from MIT in a chance
  meeting.

David Wilkinson
12
Penzias and Wilson

• Penzias Wilson at the Bell Labs began
  converting a communications antenna in 1963.
• They were unable to account for around 10 of the
  noise.

13
The Excess Noise

• They checked everything Galactic and
  extragalactic sources, emissions from New York
  City, interference from the ground, pigeon
  nesting in the antenna

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Well boys. Weve been Scooped. -Dicke

• Dicke visited Penzias Wilson and realised that
  their noise was the CMB.
• Penzias Wilson measured a CMB temperature of
  3K, compared to Alphers prediction of 5K.

Penzias Wilson receiving the 1978 Nobel Prize.
15
Post-1965

• Most cosmologists switched to the big bang camp.
• The CMB had a characteristic temperature of 3K
  and uniform in all direction.
• But, the early universe couldnt have been
  completely uniform, otherwise we wouldnt have
  structures today like galaxies and human beings.

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Part II Ripples in the Sky
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Structure Formation

• For galaxies and human beings to form, there must
  have been seeds of imperfections in the early
  Universe.

http//uchicago.edu/lss/filaments.html
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Ripples in the CMB

• Late 1960s Peeble Yu in Princeton and
  Zeldovich Sunyaev in Russia independently
  realised that the early universe would have
  contained sound waves.
• The sound waves (or density variation) would have
  imprinted themselves on the CMB.

19
1992 COBE

• NASAs COBE satellite determined the CMB
  temperature to 2.7K and detected structures in
  the CMB to 1 part in 100,000.

20
A Few Problems

• What seeded the variations in the CMB?
• Two patches of the CMB a few degree apart were
  never in causal contact. So how come they have
  the same temperature?

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Flatness Problem

• Mass energy in the Universe curves spacetime.
• The geometry can be inferred by measuring the
  angles of a triangle.
• Peculiarly, the Universe is very close to being
  flat.

22
1981 Guth Inflation

• In the first 1000 billionth of a second, the
  Universe may have undergone rapid expansion.
• This solves the horizon problem and the flatness
  problem.
• Quantum fluctuation seeded the Universe with tiny
  imperfections.

23
High Resolution Imaging
CAT, Cambridge
CBI, Atacama Desert
Boomerang, Antartica

• Starting the late 1990s, a number of ground-based
  instruments detected the CMB anisotropies.

24
2003 WMAP

• Launched in 2001
• Improved the resolution of the CMB.

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CMB Power Spectrum
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What WMAP Tells us

• The Universe is 13.7 Byrs old (to 1)
• CMB dates from 379,000 years after the big bang.
• Universe is close to being flat.
• First stars formed 200 million years after the
  big bang.

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Inflation Put to the Test

• Fits the observations remarkably well.
• But requires massive extrapolation of the laws of
  physics to explain why and how inflation happens.
• Still open to debate. (Inc)

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Part III The Future
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CMB Polarisation

• Inflation predict that gravitational waves were
  produced during the rapid expansion.
• Gravitational waves would have left
  characteristic (B-mode) polarisation patterns in
  the CMB.

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CMB Polarisation
Simulated image from http//cosmologist.info/lensp
ix/
31
CMB Polarisation Current Status
32
Planck Satellite

• European Space Agencys new CMB satellite.
• Launch in 2007

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Planck Expected Sensitivity
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Summary

• The CMB has dramatically advanced our
  understanding of the Cosmos.
• The big bang paradigm has so far passed tests
  drawn from many corners of astronomy physics
  (A)
• Inflation seems to fit observations so far but
  requires huge extrapolation of the laws of
  physics (Inc).
• Other problems remain The nature of dark matter
  and dark energy.
• Adopted from James Peebles article in Scientific
  American, The Once and Future Cosmos

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Bonus Slides
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1998 Supernovae 1A Results infer accelerating
expansion
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Hubble Deep Field North South
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(No Transcript)
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Geometry of The Universe
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Horizon Problem
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DASI CMB Polarisation