Understanding the Cosmic Microwave Background (CMB)

ObjectivesStudents are always curious about how the universe started and how it is changing. TheCosmic Microwave Background is pivotal to exploring those questions. Students will beable to describe how the Cosmic Microwave Background is evidence of the Big BangTheory and that the slight variations in temperature (color) are the seeds of the large scalestructures that evolved over cosmic time. They will be able to state the rule thatdecreasing temperature increases density and that more dense areas have larger gravityand therefore attract more matter. They will also be able to describe that these lowtemperature, high density areas in the CMB are the starting points of structure formationin the Universe.

Appropriate CoursesIn addition to Earth Science (Standard below above), these lessons are also appropriatefor High School Physics. Although the state standards in Physics do not includecosmology or the CMB, this really is an application of e-m waves and their relationshipto temperature, and temperature to density.

State Standard AlignmentThis discusses both the evidence for the "big bang" and its connection to large scalestructures. In doing so it addresses the Earth Science standard discussing the Earth'sPlace in the Universe:

Standard 2. Earth-based and space-based astronomy reveal the structure, scale,and changes in stars, galaxies, and the universe over time. As a basis forunderstanding this concept: g. Students know how the red-shift from distantgalaxies and the cosmic background radiation provide evidence for the "big bang"model that suggests that the universe has been expanding for 10 to 20 billionyears.

ResourcesAll the materials needed are: the internet, colored crayons, and a zerox machine.

ImplementationStudents will go through the following http://www.universeadventure.org/ sections:under Evidence for the Big Bang the following two pages: CMB Radiations (AccidentalDiscovery) and Origins of the CMB. Then students will complete the activity sheetcoloring the CMB and answering questions about the density differences.

AssesmentCompletion of the worksheet and a post test.

Lesson Plan: Lesson about the Cosmic Microwave Background (CMB)I. Prerequisites: Students should understand that density is mass / volume. Studentsshould know that gravity increases with mass and decreases with distance. Studentsshould understand that (except for water at 4 degrees C) as materials cool they becomedenser. Students should understand that the Universe started as a much smaller hot denseregion that expanded outward in an event called the Big Bang.

II. Instructional Procedures:1) Pass out Class Discussion Handout to accompany the review of concepts #2-7

(see page 4).2) Review the concept of density. Remind students that density is mass / volume.3) Discuss the fact that as material cools down it becomes denser since its volume

decreases. (If brought up remind students that water is the exception to thissince it is most dense at 4 degrees C. That is why ice at 0 degrees C floats eventhough it is colder than liquid water.)

4) Discuss the fact that everything with mass attracts everything else with massand the greater the mass the greater the gravitational attraction.

5) Remind students that scientific evidence supports the Big Bang Theory whichstates that the Universe started out as a very small hot dense area of energy thathas over the last 13.7 billion years expanded and cooled into the stars, planets,and the galaxies we see today.

6) Tell students that the CMB (Cosmic Microwave Background) is like a babypicture of our early Universe. It is evidence that supports the Big Bang Theory.

7) Discuss that microwaves are a type of electromagnetic wave meaning they carryenergy just like visible light. They are the waves that carry energy that cookfood in microwave ovens. Microwaves are longer wavelengths than visiblelight. Cosmic Microwaves are the energy that spread out from the Big Bang.

8) Have students color in the CMB coloring page (page 7). This will help themsee the variations in the CMB. These variations lead to galaxies such as ourown Milky Way, and clusters of galaxies. Different colors can be substitutedbut remember that blue light is higher energy than red light. Students could alsodesign their own way to designate the differences using one color.

9) Have students go to the http://www.Universeadventure.org website: (Smoot, George, et al.) The Universe Adventure Lawrence Berkeley National Laboratory. Copyright © 2005 Lawrence Berkeley National Laboratory Physics Division | Last Update: August 2, 2007

http://www.universeadventure.org) Once at the site have them go to the section labeled Evidence for the Big Bang. In that section have them go through the pages labeled Cosmic Microwave Background (Accidental Discovery) and Origins of the CMB. If students do not have computers you could assign reading from their text or copy the included text from those pages from the website (see pages 12-17). For students that need a guided questions to answer while going through the website or reading have them complete the Website Questions handout (see pages 5-6).

10) Then have students complete the Understanding the Cosmic MicrowaveBackground sheet (see page 8). A comment on question 4: you may wish toskip this if you don’t have access to the website since the text version doesn’tshow this part. Also, this may be too detailed if students don’t have anunderstanding of red-shift.

11) Discuss the correct answers. Answer keys on pages 10-11.

III. Assessment/ Evaluation: Give the following quiz (see page 9 for handout copy): 1) When something is cooled it becomes: a) more dense b) less dense .

2) As mass increases gravity? a) increases b) decreases c) remains constant.3) The Cosmic Microwave Background is important because: a) it cooks my food, b) is evidence of the Big Bang, c) has neat colors4) More dense areas have: a) less gravity so matter collect there b) more gravity so matter collects there c) no gravity so matter collects there.5) Colder regions in the CMB are: a) areas were no matter exists b) areas that are less dense so matter collects, c) areas were matter collects due to increased density, d) are more dense areas were matter can’t collect.6) The starting points in the Universe for structures such as stars are:

a) cold, dense, high gravity regions, b) warm, dense, low gravityregions, c) cold, low density, low graivty regions.

IV. Follow-up Activities:1) Have students write a paragraph describing how the slight variations in the temperatures in the CMB lead to large scale structure formation.2) Have students make a flip book showing structure formation.3) Go through other sections of the Universeadventure.org website. Such as in the section on Evidence for the Big Bang go through the pages on Red-shift then complete the Rubber Band activity accessed through the teacher section on the title page of the website. This will help students understand the expansion of the Universe.4) Explore more of the Universeadventure.org website and the teaching materials there to learn more about the Big Bang and the History of our Universe.5) For highly motivated students they could read Wrinkles in Time by George Smoot and report back to the class.

V. Worksheets, Answer Keys, and Copy of Website pages. p. 4 Class Discussion Worksheet p. 5-6 Website Questions p. 7 CMB Coloring Page p. 8 Understanding the Cosmic Microwave Background p. 9 Quiz p. 10-11 Answer Keys p. 12-17 Copy of Website pages

Class Discussion - Student Worksheet NAME __________________________

1) The equation for density is:

2) An example of something a) More dense than water is b) less dense than water

3) In my own words density means:

4) As things cool down their size (volume) ________________ so they become

_______________dense.

5) Everything with matter will _____________everything else with matter.

6) In my own words gravity means:

7) List ways to increase gravity.

8) What is the Big Bang Theory?

9) What evidence is there to support this theory?

10) What is a wave?

11) What type of wave are Cosmic Microwaves?

Website Questions NAME____________________________

Answer these as you go through the following pages in the Universedaventure.orgEvidence section: http://www.universeadventure.org/big_bang/cmb-discovery.htmand http://www.universeadventure.org/big_bang/cmb-origins.htm

1) What was the accidental discovery of Penzias and Wilson?

2) Why was this discovery important to Astrophysics?

3) How long after the Big Bang was the CMB formed?

4) What were the conditions of the early Universe at the time the CMB formed?

5) What is the temperature of the CMB now?

6) What made the Universe cool down as demonstrated in the CMB?

7) What do the differences in color in the CMB represent?

8) The light from the CMB really came from a process called decoupling in which

__________________ separated from _________________. This separation

occurred because the Universe __________________which cooled the Universe

enough that ______________could form when electrons bond to nuclei.

9) The original light was at a temperature of _______K (________degrees F).Sketch what happened to the wavelengths of light as the temperature cooled dueto the expansion of the Universe. Hotter - - - - - - - - - - - - - - - - Cooler

10) This stretching of wavelengths is called the _______________ because redwavelengths of light are longer than yellow or green or blue.

11) The age of the Universe is ______________________.

12) The anisotropies on the CMB represent tiny ______________ in ____________

which are really fluctuations (changes) in ______________________.

13) The colder areas are more dense and denser areas have more ______________ so

they can attract more matter leading to the formation of ___________________.

14) Explain why the CMB and maps of the Earth are shaped like ovals.

15) Why is the CMB so important?

16) Why are the anisotropies so significant?

Understanding the Cosmic Microwave Background1.a) When did the CMB form?

b) What is the Cosmic Microwave Background?

c) What significant event happened in cosmic history to produce the CMB?

2. How do temperature & density relate—why?

3. Although the discovery that the CMB is virtually the same temperatureeverywhere was significant; the slight variations in temperature are nowof great interest—why? What do these “wrinkles in time” have to dowith the history of the universe?

4. Below are some other pictures of the CMB. Why do they appear sodifferent from the one you colored? What are the differences?

CMB Quiz Name_______________________Date__________________

1) When something is cooled it becomes: a) more dense b) less dense.

2) As mass increases gravity? a) increases b) decreases c) remains constant.

3) The Cosmic Microwave Background is important because:a) it cooks my food b) is evidence of the Big Bang c) has neat colors

4) More dense areas have:a) less gravity so matter collect thereb) more gravity so matter collects therec) no gravity so matter collects there

5) Colder regions in the CMB are:a) areas were no matter existsb) areas that are less dense so matter collectsc) areas were matter collects due to increased densityd) are more dense areas were matter can’t collect

6) The starting points in the Universe for structures such as stars are:a) cold, dense, high gravity regionsb) warm, dense, low gravity regionsc) cold, low density, low graivty regions.

Answers to Student Worksheet – Class Discussion1) Density = Mass / Volume2) a) cement, books, most rocks b) Styrofoam, oil, beach ball, air3) Density is how much matter (stuff) is per space.4) Decreases (shrinks), more5) Attract6) Gravity is the attraction (or pull) that everything has on everything else.7) You can increase gravity by increasing mass or bringing things closer together.8) The Big Bang Theory states that the Universe was once a smaller more dense

hotter area that has expanded over time.9) The evidence to support this theory is the Cosmic Microwave Background.

(Other evidence not specifically addressed in this lesson include: a) expansion ofthe Universe b) elemental abundances c) evolution of stars and galaxies. Thee arediscussed in further detail in other website pages.)

10) A wave is a transfer of energy.11) Cosmic Microwaves are a type of electromagnetic wave. (These include visible

light.)

Answers to Website Questions1) Penzias and Wilson discovered microwave radiation (CMB) coming from all

directions from space.2) This discovery was important to Astrophysics because it supplied evidence for the

Big Bang Theory.3) The CMB was formed about 380,000 years after the Big Bang.4) The early Universe was hot and dense.5) The CMB is 2.7 K now.6) The Universe and the expanded which caused the energy to spread out as shown

in the waves stretching.7) The differences in the colors of the CMB represent small differences in

temperature.8) Matter, light, expanded, atoms.9) 3000 K, (5000 F) hotter should be small wavelengths, cooler should be longer wavelengths10) Red-shift11) 14 billion years (14.7)12) Variations (differences), temperature, density.13) Gravity, stars and galaxies.14) These maps are shaped like ovals because it is the way to represent a sphere on a

flat piece of paper.15) The CMB is so important because it is evidence that supports the Big Bang.16) Anisotropies are significant because these slight differences are the seeds of star

and galaxy formation.

Answers to the Understanding the Cosmic Microwave Background worksheet:1) The CMB is the Cosmic Microwave Background. It is the baby picture of the

early Universe since it is the waves that spread out from the Big Bang. The BigBang occurred 13.7 billion years ago.

2) As temperature decreases substances become more dense (except for water at 4degrees C.) Decreasing temperature makes objects decrease in volume. Sincedensity is mass/ volume, if the volume decreases the density increases.

3) The slight variations in temperature lead to areas that are denser and these coldermore dense regions have a slightly larger gravity so they collect more matterleading to large-scale structures such as stars.

4) The first picture demonstrates the CMB before the effect of the direction ofmotion is removed. When moving towards light the light appears blue shifted asseen in the lower left, when moving away the light is red shifted as seen in the topright.The second picture still shows the light from the Milky Way (our galaxy) whichwe look through to see the CMB.

Answers to the quiz 1- a 2-a 3-b 4-b 5-c 6-a

Smoot, George, et al.The Universe AdventureLawrence Berkeley National Laboratory.Copyright © 2005 Lawrence Berkeley National Laboratory PhysicsDivision | Last Update: August 2, 2007http://www.universeadventure.org

The Universe Adventure

Cosmic Microwave Background Radiation

"Once you eliminate the impossible, whatever is left, no matter how improbable, it mustbe the truth." -Sir Arthur Conan Doyle, Sherlock Holmes

Accidental Discovery

In 1964, Bell Laboratory scientists Arno Penzias and Robert Wilson were trying to detectsources of radiation that might potentially harm satellites. Their data, however, showedbackground noise from a microwave signal corresponding to a temperature ofapproximately 2.7 K that appeared to be emitted from every direction. This apparentaberration was recognized by scientists at Princeton as remnant radiation from the earliestobservable moment in the evolution of the universe, now called the Cosmic MicrowaveBackground.

Arno Penzias and Robert Wilson with the Horn Antenna used to discover the CosmicMicrowave Background.

Their discovery was a tremendous one for astrophysics, providing a glimpse of theearliest observable moment in the evolution of the Universe.

What is the CMB?

The Cosmic Microwave Background, or CMB, is ancient radiation leftover from a timeroughly 380,000 years after the Big Bang when the hot, dense plasma that permeated theUniverse cooled with the expansion of space. At a nearly uniform temperature of 2.7Kelvin, the CMB fills the entire Universe and can be detected everywhere we look. If thehuman eye could see microwaves, the entire sky would glow with nearly equal brightnessin every direction.

A map of the Cosmic Microwave Background. The different spots of color correspond todifferent temperatures and in turn, different densities.

Here are some questions about the CMB that we will answer in this section:

• Where did it come from?• Why is it so cold?• Why is the map different colors?• Why is the map of the CMB an oval?

The Universe Adventure

Origins of the CMB

The first light radiated after decoupling is now known as the CMB.

During the first 380,000 years after the Big Bang, the universe was so hot that all matterexisted as plasma. During this time, photons could not travel undisturbed through theplasma; instead, the photons constantly interacted with the charged electrons andbaryons. This is a phenomenon known as Thompson Scattering. As a result, the universewas opaque. As the universe expanded and cooled, electrons began to bind to nuclei,forming atoms. The introduction of neutral matter allowed light to pass freely withoutscattering. This separation of light and matter is known as decoupling.

The light first radiated from this process is what we now see as the Cosmic MicrowaveBackground. Similarly, in the video below, the precipitate in a solution of magnesiumhydroxide scatters light from a flashlight, making it opaque to radiation.

Movie: The Last Scattering | Download

Why is the CMB so Cold?

Light from the CMB was red-shifted as the universe expanded, cooling it over time.

The CMB is a perfect example of red-shift. Originally, light from the CMB had a muchshorter wavelength corresponding to a temperature of about 3,000 K (nearly 5,000° F).As the universe expanded, the light was stretched into longer and longer wavelengths.

By the time the light reaches us, 14 billion years later, we observe it as microwaves at afrigid 2.7 K (-450° F). This is why CMB is so cold now.

What do the Colors on the CMB Map Represent?

Although the temperature of the CMB is almost completely uniform at 2.7° K, there arevery tiny variations, or anisotropies, in the temperature on the order of 10-5 K. Theanisotropies appear on the map as cooler blue and warmer red patches. But what do theseminute fluctuations mean?

Map of the CMB created from data gathered by the Wilkinson Microwave AnisotropyProbe (WMAP).

These anisotropies in the temperature map correspond to areas of various densityfluctuations in the early universe. Eventually, gravity would draw these fluctuations intoeven denser ones. After billions of years, these minute ripples in the early universeevolved, through gravitational attraction, into the planets, stars, galaxies, and clusters ofgalaxies that we see today.

Why are Maps of the CMB Shaped like Ovals?

The spherical map of the CMB translates to an oval in the same way a globe translates toa familiar oval map when flattened.

The CMB is shaped like an oval for the same reason that many maps of the world areovals. You can't take a sphere and make it flat without tearing it, because a sphere isfatter in the middle than at the top and bottom.

To see why this is true, peel and orange and try to flatten it. The only way you canaccomplish this is by tearing the peel, or distorting it. Instead of "tearing" the map of theCMB, it is depicted as an oval, which is the shape with the least angular distortion of theoriginal sphere.

The Predictive Power of the CMB

In 1992, physicists used the orbiting COBE satellite to make the first detailedmeasurements of the CMB anisotropy.

The CMB is one of the strongest pieces of evidence for the Big Bang model. The theorymakes highly accurate predictions about the size and types of anisotropies in the CMB aswell as its nearly perfect black body spectrum, all of which have been verified byexperiment and observation. The discovery of the CMB in the 1960's marked the end forseveral competing cosmological models including the Steady State theory.

With the information attained from the CMB, we can understand the formation of thestructure and matter of the universe.