Cosmic Microwave Background The Edge of Our Perception

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Cosmic Microwave BackgroundThe Edge of Our
Perception

• by Nathan Wiley
• PH2010

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Abstract

• The cosmic microwave background is our view of
  the earliest form of the Universe. My
  presentation will first study the big bang and
  it's direct relation to the CMB. I will then
  show the steps through which this radiation
  progressed to become how we perceive it today. I
  will then in more detail, describe how we view
  this background. Finally, I will describe two
  major tools used to measure and observe the
  background radiation.

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OutlineCosmic Microwave Background

• The accidental discovery
• The origin of the universe
• The Big Bang
• How it relates to CMB
• Surface of Last Scattering
• The creation of atoms
• An opaque Universe
• The expansion of the Universe
• Hubble's Law and constant
• Relativistic redshift
• Tools of Discovery

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Accidents Happen

• Electric current (1791) Luigi Galvani and
  experimenting with frog legs
• X-rays (1895) Wilhelm Roentgen and a
  barium-coated screen
• Penicillin (1928) Alexander Flemming and a messy
  laboratory
• Cosmic Radiation Background (1964) Robert Wilson
  trying to improve Bell Telephone reception

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Accidents Happen

• Arno Penzias and Robert Wilson detect a hiss in
  their telecommunications equipment, on task to
  try and eliminate it. They analyze the Milky
  Way's microwave spectrum to test.
• The noise comes from any direction in the sky,
  night or day, and has the same magnitude
  everywhere.
• After confirming their finds with home base at
  Bell Laboratories and Princeton University, and
  refining of their finds, Penzias and Wilson
  realize that they have stumbled upon the earliest
  image of our Universe
• In 1978 they are awarded the Nobel Prize in
  physics.

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And it begins...

• The big bang the Universe originates as a
  singularity infinitely dense and hot
• In the period of time 10-35 to 10-32 seconds
  after the big bang, the universe expanded without
  check, to a factor of 1050 of its original size
• As the Universe expands, the radiation put forth
  becomes redshifted into the microwave range of
  the EM spectrum

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The Creation of Atomsmore beginnings

• At one hundred millionth it's present size, the
  average temperature was about 280 million Kelvin
• Gamma ray radiation broke apart nuclei before
  they had a chance to form larger particles.
  Hydrogen is completely ionized into protons and
  electrons.
• Photons scatter off of wandering electrons
  relatively easily. This creates a dense fog
  environment.

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The Transparent Universekind of

• Only certain wavelengths of radiation interact
  with matter (spectral lines)
• Light of all other wavelengths is then free to
  travel indefinitely (hence, transparent)
• The result is an almost completely uniform
  picture, at a temperature of 2.725 Kelvin /-
  .002 K

• Variations in intensity of the CMB are at a level
  of one part in one hundred thousand.

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The Universe Is Expanding!

• As a direct result of the big bang, the Universe
  is expanding in every direction. Space itself is
  expanding, not just the matter contained inside.
• Early 1900s observations by Slipher, Lowell and
  Hubble found that nearly every spiral galaxy had
  a red shifted spectrum, the consequence being
  that all galaxies are receding from our galaxy.

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A Different Approach
The Balloon Model
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Another Different Approach

• At increasingly large distances, astronomers tend
  to refer to distance in terms of an object's red
  shift. This is preferred, because it is a
  directly observable property, whereas distance
  must be computed from red shift using Hubble's
  constant.

• Redshift observed wavelength true
  wavelength / true wavelength
• Redshift recessional velocity / speed of
  light
• Recessional velocity Hubble's constant
  distance (Hubble's Law)

• Hubble's constant is generally accepted to be 71
  km/s/Mpc. The problem here is that its value has
  been measured by various research groups, using
  different galaxies as reference points, and using
  a wide variety of distance measuring techniques.

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Another Different Approach

• By computing redshift from observed spectrum, and
  then recessional velocity from redshift, we can
  thus use Hubble's Law to calculate distance!
• -- This technique is used to measure the farthest
  of the farthest away objects in our Universe.
• As the recessional velocity approaches the speed
  of light, relativistic properties begin to occur,
  and the previous equations are simply not enough.
• For example, the redshift as velocity approaches
  C is actually infinity, and not 1 as the quations
  would suggest.

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A Final Problem

• At incredibly large distances and velocities,
  another problem occurs, and simply referring to
  an object's redshift is not sufficient.
• For close sources, the given distance (and thus
  time, because of the constant speed of light), is
  simply how long ago the object emitted the
  radiation we see.
• At the immense distances previously mentioned,
  the expansion of the Universe must be taken into
  account. For example, a galaxy now located 14
  billion light years away was much closer when it
  initially emitted the light.

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The Tools

• Cosmic Background Explorer (COBE)
• Diffuse Infrared Background Experiment (DIRBE)
• Differential Microwave Radiometer (DMR)
• Far Infrared Absolute Spectrophotometer (FIRAS)
• Wilkinson Microwave Anisotropy Probe (WMAP)

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Bibliography

• The Science Book, Cassell and Co. 2001
• Physics for Scientists and Engineers, Knight.
  2004
• Astronomy A Beginner's Guide to the Universe,
  Chaisson, McMillan. 2004
• Hinshaw, Gary Wilkinson Microwave Anisotropy
  Probe Mission http//map.gsfc.nasa.gov/m_mm.html
• Greason, Michael R. Legacy Archive for Microwave
  Background Data Analysishttp//lambda.gsfc.nasa.g
  ov/product/cobe/
• Gedny, LarryUnexpected Scientific Discoveries
  Are Often The Most Important http//www.gi.alask
  a.edu/ScienceForum/ASF7/741.html
• Weisstein, Eric W. Relativistic Redshift
  http//scienceworld.wolfram.com/physics/Relativist
  icRedshift.html
• Scott, Douglas Astronomy POD FAQs
  http//www.astro.ubc.ca/people/scott/faq_basic.htm
  l