# Day 14 The Very Big – The Cosmos

 Дата канвертавання 24.04.2016 Памер 26.21 Kb.
Day 8.14 The Very Big – The Cosmos
1) The spectral lines of the galaxies tell us what elements the stars contain and how they are moving relative to us. Use the red shift of the lines to determine the velocity of each galaxy.
 Galaxy Distance (x1020 km) Ca-K Ca-H reference lines Velocity (km/s) NGC 1357 7.7 2100 NGC 3147 13.6 NGC 3368 3.4 NGC 5548 22.1 NGC 6764 10.0 NGC 6745 19.7 Velocity Scale (km/s) 6000

2) Plot the velocity of the galaxy on the y-axis and the distance to the galaxy on the x-axis.

3) Almost of the galaxies are moving away from us and the farthest ones are moving fastest. Explain why, using a model of paper clips (galaxies) linked by elastic bands (space).

It is not because we are special. Every galaxy appears to be moving away from every other galaxy because space is expanding. The galaxies don’t expand because gravity overcomes this.

4) Explain how to use this data to determine the age of the universe.

The age is just distance/time or the inverse of the slope.

5) The theory that describes how the universe has expanded was named the ‘Big Bang’ by Fred Hoyle, a British astronomer with a competing model. Explain why the name is a poor descriptor.

It isn’t a noisy expansion of matter into existing space. It is just space itself expanding.

6) According to the Big Bang theory the early universe was denser, brighter, hotter and more uniform.

a) Explain why the universe used to be much denser using a balloon and a marker.

Draw a dark circle and then inflate the balloon. The circle gets bigger and so the ink becomes more spread out and fainter.

b) Explain why the universe used to be much brighter using a flashlight.

The light from the flashlight that is farther away forms a bigger spot of light, where the light is spread out over a larger area like the marker circle above.

c) The universe used to be much hotter. The early universe was mostly made of light. Explain why stretching light would make the universe cooler using a Slinky.

The wavelength increases and so the frequency os and energy is smaller. E = hf.

d) The universe used to be much more uniform. Right now, the universe contains galaxies of stars and huge empty spaces in between the galaxies. The earlier, hotter universe would have been much more uniform. Explain why, using salad dressing that has separated.

A hotter temperature means that the particles are moving faster and therefore colliding more often and harder. This breaks up any structure.

7) According to the Big Bang theory the early universe was too hot for electrons and protons to stick together as atoms. It was a soup containing electrons, protons and light. However, once the temperature went below 3000 degrees K, the electrons and protons joined to form hydrogen that does not interact with the light. The light could now pass unimpeded and the universe became transparent. You are going to act out what happens as the universe cooled. You can use props, but no words. How will you do this?

8) According to the Big Bang theory, this light should be hitting the Earth from all directions. The original light has stretched 1000 times and should now have a peak wavelength of 1-mm which corresponds to a temperature of 3 K or -270o C. This light is called the Cosmic Microwave Background (CMB). Watch Minute Physics: Picture of the Big Bang http://www.youtube.com/watch?v=_mZQ-5-KYHw Describe a part of the video helped you understand something better or something new that you learnt.

9) The images above show temperature measurements of a small section of the CMB made by three different satellites. In 1992, COBE measured the CMB temperature to be 2.73 K. In 2003 WMAP measured it at 2.726 K and in 2013 Planck found that it was 2.72547 K. The variations in shade represent differences in temperature of +/ 0.00002 degrees.

1. The Big Bang predicted that the CMB should be uniform temperature. Only the first image looks uniform. Why do the later ones look different?

COBE showed that the CMB was smooth as predicted. Then the technology improved with better spatial and temperature resolution. And this showed that there was some variation.

1. Your friend says that variation of the third image proves that the Big Bang theory is wrong. Explain how the third image still shows a very uniform CMB. Using the ‘smoothness’ of the Earth as an analogy.

The Big Bang predicted smoothness – but not perfect smoothness. We are seeing a temperature variation of just 1 in 10,000. The surface of the earth is 100 times rougher and it still looks smooth from space. They knew that there had to be some variation and WMAP was able to confirm this.

1. The early universe was very uniform but the present universe is not. It is made of galaxies and clusters of galaxies with large empty spaces in between them. Where did this structure come from? The Big Bang theory predicts that there must have been some tiny variation in the early universe to provide the seeds that grew to form the galaxies that we see now. Which of the images supports this prediction? Explain.

The variation that resulted in the galaxies can be seen in the smallest dots which can only be seen in the Planck image which came out in the spring of 2013.

1. The CMB images show how temperature and density varied. This variation resulted in galaxy formation. Gravity pulls matter closer and light pressure pushes it apart. Galaxies can’t form unless the original density is high enough.

1. Predict what will happen to the tiny variations in density as the universe evolves.

2. Observe a simulation at http://cosmicweb.uchicago.edu/filaments.html

3. Model this using magnetic marbles. Take magnetic marbles and see how many you can place on a 20 cm by 20 cm piece of cardboard without them clumping together.

1. Astrophysicists cannot test their theories with experiments, so they make computer models and test these. You will use a simplified version to determine the density of the early universe. Go to http://www.learner.org/courses/physics/interactive/lab_interactives/cosmic.html

1. The picture on the bottom right shows what the distribution of galaxies and empty spaces of our universe looks like. What does it look like the most?

1. Swiss cheese B) sand on a beach C) a sponge D) cobwebs

1. The graph on the top right shows what the density of our universe is like.
The horizontal axis is density and the vertical axis shows how much

of the universe has that particular density. Label the graph on the right

where is shows that a small amount of universe is low density, a small

amount is high density and most of it is medium density.

1. Set the initial conditions on the graph (bottom left) for completely uniform

(slider at far left) and the maximum density (slider at very bottom). Compare

the universe that results to our present universe. Use both the image and the

1. What initial conditions match our universe?

1. The space between galaxies keeps getting bigger and bigger.

1. Explain why we should expect the expansion to slowdown.

2. The expansion is speeding up. How is this ‘explained’ by dark energy? Minute Physics 2011 Nobel Prize http://www.youtube.com/watch?v=v6o2bUPdxV0&list=PLED25F943F8D6081C

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