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Announcements

Announcements. Our final exam period is Monday May 6 @ 1:30pm. Will do project presentations first then Exam 4. Exam 4 will be all essay, probably five out of nine. It will cover Chapters 12 – 17. Sample essay questions will be posted by the end of the week. Measuring Large Scale Structure.

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Announcements

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  1. Announcements Our final exam period is Monday May 6 @ 1:30pm. Will do project presentations first then Exam 4. Exam 4 will be all essay, probably five out of nine. It will cover Chapters 12 – 17. Sample essay questions will be posted by the end of the week.

  2. Measuring Large Scale Structure Simulations show us what the models predict but how does that compare to reality?

  3. Galaxy Surveys Galaxy surveys examine slices of the sky and measure the location on the celestial sphere and the “z”. The 2dF survey is done from the Anglo-Australian telescope

  4. The 2MASS The 2 Micron All Sky Survey is another galaxy survey done in near infrared

  5. The Sloan Digital Sky Survey has also done a galaxy plot The SDSS pioneered a novel approach to taking the spectra of large numbers of objects simultaneously

  6. Sky Surveys in other wavelengths Infrared surveys tend to show more of the gas and dust in our galaxy than other galaxies and how they are distributed

  7. The Chandra COSMOS Survey Chandra observes in x-ray so it tends to show the active galaxies. Getting distances from x-ray data is difficult, though, so correlations analysis must be done to get 3-D structure

  8. So far, the observed structure matches the simulations well

  9. Inflation!

  10. The Horizon Problem Observations from WMAP and Planck show that the CBR is uniform to about one part in 105 over the entire sky

  11. How large is our horizon? For non-expanding space-time just construct a light cone and find the time since the Big Bang. Anything within the light cone is within our horizon. Anything outside the light cone is stuff we cannot see.

  12. Complicating factor to the simple light-cone For non-expanding space-time the space-time interval between light-like lines is zero so In an expanding universe governed by the Robertson-Walker metric the zero space-time interval is given by

  13. Even in a flat universe (k = 0) we need to know R(t) For the Einstein-De Sitter model R is proportional to t2/3 so the “horizon” (maximum separation between causally connected objects) is Using H = 72 km/s/Mpc gives an horizon of 8 x 109 parsecs

  14. So, what was the horizon for stuff at the “Surface of Last Scattering” Same kind of analysis gives rh = 106 lightyears. That corresponds to approximately 1° on our sky

  15. The Horizon Problem Re-visited There should be no fluctuations larger than about 1° according to calculations but the entire sky varies by only one part in 105. This is the Horizon Problem

  16. The Flatness Problem Many different cosmological measurements indicate

  17. Why is W = 1 a problem? For simplicity, consider a universe with only matter (L= 0) The second term depends on 1/(H2R2). Since R now is so much different that R far in the past, for W to be close to one now it would have to have been extraordinarily close to one in the past. The solution: k = 0…a flat universe.

  18. Why is there structure? What caused these fluctuations? If the universe was originally a small, hot, dense plasma why is there any variation at all?

  19. The relic problem Why is most of the ordinary matter in the universe made from just these few particles? Why aren’t there magnetic monopoles and other exotic particles?

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