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Doing Science

Unit Six: Investigating the Universe
Doing Science

3. Back Through Time and Space to the Cosmic Background

In 1948, a physicist named George Gamow was investigating possible origins of the elements assuming a big bang model. He reasoned that very soon after the big bang, when the universe was small enough, it would be hot and dense enough for elementary particles to fuse into larger nuclei. He then realized that when the hot and dense early universe expanded sufficiently, atoms would form and the remaining photons would fly freely through the expanding universe. Gamow hypothesized that this would result in a highly redshifted microwave "echo" that should be detectable in any direction. Gamow's work went unrecognized at the time, but in 1964, Arno Penzias and Robert Wilson, two engineers from Bell Labs, detected a background hiss in every direction with a large antenna they was building as part of the brand-new satellite communications industry. The "hiss" turned out to be Gamow's "echo" of the big bang. The "Echo," now commonly called the Cosmic Microwave Background (CMB), has been intensively studied since 1948 as the earliest source of information about the origin of the universe, and the origin of galaxies. In this Doing Science, you will gather images that show the universe from the present back to its beginnings and explore its connection to the modern structure of the universe.

Collect the following images:

  1. Color Image of the Universe today: Follow the links to get the best resolution image possible. (This and subsequent images are all in the Mollweide projection, a useful way to present data from a sphere, like the sky or the surface of Earth onto a flat surface.)
  2. Three images from the 2MASS survey at the University of Massachusetts: Click on IPAC Image Gallery: The Infrared Milky Way, the Infrared Universe, and the Galaxies of the Infrared Sky. These images show the Milky Way in infrared, and thousands of galaxies beyond. The third image of the set is color coded to show galaxies at increasing distance, and thus farther back in time to the big bang. Follow the Full size Image links to get the largest version you can comfortably download to your computer.
  3. The CMB Background from the WMAP mission: Click on Outreach/Media and download The Microwave Sky. Choose the largest version you can download.

Your Report:
Open the five images in ImageJ or similar program that you can use to resize each of the images to the same dimensions. Overlay the images in the order above and create a movie that takes the viewer from the present to the distant past. Provide an explanation of how each image fits into the history of the Universe. Maps an images that will help you tell your story are:

Time Line of the Universe at

Microwave Sky Overlay at; and

The CMB Spectrum at: and

Slide 29 at

Compare the distribution of the galaxies in Galaxies of the Infrared Sky with The Microwave Sky image. How does the distribution of the fluctuations in the microwave background compare with the distribution of galaxies?

Measurements indicate that the redshift of the CMB is z = 1089. What was the size and density of the universe at that time? About how long after the Big Bang did the CMB form?

Compile your report and present it to your class in the form of a PowerPoint presentation.