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EXERCISE 14
(a) What was the temperature of the cosmic background when the light we see from LPIF13 left that quasar, at z=2.58? Was it still a "microwave" background at that time? (b) The human eye is sensitive to light with wavelengths ranging from about 400 nm to 700 nm. At what redshift did the "color temperature" of the cosmic background drop to a wavelength below the threshold where humans could see it? (c) At the time of matter-energy decoupling, electromagnetic radiation was finally able to travel through the universe without being "hitched" to matter. Thus, the universe is said to become "transparent" at this epoch in cosmic history, which occurred at a redshift of approximately z = 1100. hat was the background temperature of the universe? How does that compare to the temperature of the surfaces of stars? With this in mind, can you give a possible explanation of why decoupling might have occurred at z = 1100 and not much earlier or later? |