== Build a Universe! (enable the FlashPlayer) == https://wmap.gsfc.nasa.gov/resources/camb_tool/index.html 1. Find the parameters that match the data points 2. Record the behaviour of the power spectrum, when you vary a parameter * For example: What happens when you reduce the “Spectral Index”? What happens when you increase “Atoms”? * Tip: Where to start? Start by varying one parameter away from the best-fitting parameter you found in (1) * Explore the behaviours of as many parameters as you have time to explore 3. Document your findings in the shared note. * I have not yet taught you how the power spectrum depends on the parameters. So, collect data yourself now; it helps you understand physics later. ------------ 1. What are the best-fitting parameters? - Omega_B ["Atom"] = 4% - Omega_D ["Cold Dark Matter"] = 22% - Omega_Lambda ["Dark Energy"] = 74% - Hubble Constant = 73 - Reionization Redshift = 11 - Spectral Index = 0.95 ------------ 2. What happens when you vary: 1. Omega_B ["Atom"] - higher Omega_B leads to higher power fluctuations shortward of ~0.5 deg and lower longward - changes relative height of the peaks - higher OmegaB means more baryons, so photons oscillate in deeper potentail wells, which means bigger difference between peak heights (?) - 3rd peak is higher than 2nd when atom content increases. --> odd/even peaks different 2. Omega_D ["Cold Dark Matter"] - higher Omega_D, higher the second peak compared to the first one - changes relative sizes of the peaks - changes amplitude of the power spectrum - changes amplitud: higher Omega_D, weaker fluctuations -Peak location shifts to the left when Omega_D increases 3. Omega_Lambda ["Dark Energy"] - shift on the angle across the sky (so shifts the whole spectrum in x direction) - changes frequency of the peaks - does not affect photon-baryon physics, so it does not affect ratios between the peaks, but simply shifts the C(l) - Lower Omega_Lambda, lower the angle across the sky of the power spectrum. 4. Hubble Constant - changes power fluctuations for the same angle across the sky while maintaining the overall shape - for angles < 2 degree the increase / decrease is less severe - peaks become shifted in x direction 5. Reionization Redshift - shifts the power spectrum in the y direction while maintaining the shape - higher reionization redshift leads to overall damping of the power - peaks does not become shifted in x direction 6. Spectral Index (n=1 is the scale invariant; see Lecture 4, page 37) - Changing the spectral index changes the intensity of first peak only. - Changes the tilt of the power spectrum - Impacts features on scales > 0.5deg - Changes the intensities of all the peaks, being the change in the first peak more dominant