{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

solution_4 - ASTRONOMY 294Z The History of the Universe...

Info icon This preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
ASTRONOMY 294Z: The History of the Universe Professor Barbara Ryden SOLUTIONS TO PROBLEM SET # 4 1) [20 points] Today, the average density of matter in the universe is ρ = 3 × 10 - 27 kg / m 3 . If the matter consisted entirely of hydrogen atoms, how many hydrogen atoms (on average) would be contained in a cubic meter of the universe? If the matter consisted entirely of regulation baseballs (of mass M = 0 . 145 kg apiece), how many baseballs (on average) would be contained in a cubic astronomical unit of the universe? The mass of a single hydrogen atom is m = 1 . 7 × 10 - 27 kg. In order for the mass density to be ρ = 3 × 10 - 27 kg / m 3 , the number of hydrogen atoms per cubic meter would have to be n = ρ m = 3 × 10 - 27 kg / m 3 1 . 7 × 10 - 27 kg = 1 . 76 / m 3 . (1) Fewer than two atoms, on average, per cubic meter of space – that’s a very low density. The mass of a single baseball is M = 0 . 145 kg. In order for the mass density to be ρ = 3 × 10 - 27 kg / m 3 , the number of baseballs per cubic AU would have to be n = ρ M = ˆ 3 × 10 - 27 kg / m 3 0 . 145 kg ! ˆ 1 . 5 × 10 11 m 1 AU ! 3 = 69 , 800 , 000 / AU 3 . (2)
Image of page 1

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
2) [20 points] The temperature of the cosmic background light today is T 3 K . At the time the universe became transparent, the temperature of the cosmic background light was T 3000 K . This means that the universe has
Image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern