Universe: Stars And Galaxies
6th Edition
ISBN: 9781319115098
Author: Roger Freedman, Robert Geller, William J. Kaufmann
Publisher: W. H. Freeman
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Chapter 25, Problem 55Q
To determine
Whether there can be other universes, regions of space, and time that have no connection with our universe and should astronomers be concerned with such possibilities.
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Students have asked these similar questions
mathematician Archimedes, responding to a claim that the number of grains of sand was infinite,
calculated that the number of grains of sand needed to fill the universe was on the order of 1063. Our
understanding of the size of the universe has changed since then, and we now know that the
observable universe alone is a sphere with a radius of 1026 m. Estimating the size of a grain of sand,
A) Approximately how many grains of sand would fill the observable universe?
B) How many times larger or smaller is this number than Archimedes' result?
Assume the observable Universe is charge neutral, and that it contains n nuclei (hydrogen plus helium nuclei, ignoring other elements). Take the helium mass fraction as 1/4. How many electrons are there in the observable Universe? Enter your answer in scientific notation with one decimal place.
Value: n = 4*1080
Observations of distant galaxies show
they appear older than they really are.
the size of the visible universe is getting smaller.
O galaxies move but they remain at constant distances from one another.
O they are moving away from us.
O they are all located inside the Milky Way Galaxy.
Chapter 25 Solutions
Universe: Stars And Galaxies
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- Where are you in the Universe? If you had to give directions to your location in the Universe, what directions would you give?arrow_forwardIn which type of model universe is space-time infinite in extent and positively curved? List all possibilities.arrow_forwardIn which type of model universe is space-time infinite in extent and open? List all possibilities.arrow_forward
- What is the spatial radius of curvature for a hypothetical closed universe at a moment of time with given values below. Give the answer in units of Mpc, to the nearest integer (not in scientific notation - e.g., 1234). Values: H = 51 km s-1 Mpc-1 ρ = 2.9x10-26 kg m-3arrow_forwardUsing our example from the previous unit, let's try to determine the Hubble time for this example universe. You were given that a good representative galaxy receded at a speed of 4000 km/s and was found to be 20 Mpc away. With that in mind, what would the age of that universe be in years (aka what is that universe's Hubble time)? Go ahead and take the number of kilometers per Mpc to be approximately 3.1*10^19 km/Mpc. While this problem may look scary at first, this is really just bringing you full circle to one of the unit conversion problems you encountered at the beginning of this course.arrow_forwardYour friends are talking about Olber's Paradox: Friend 1: When the universe was quite young, it was also quite small, and therefore light was trapped inside the universe. This is why we don't see light from the edge of the universe in every direction. Friend 2: No, Olber's Paradox describes only light from stars, not from galaxies, and why you can't use light from distant stars to see at night. Friend 3: You're both right and you're both wrong. The paradox concerns itself with the expansion of the universe, and explains why light from the early universe was able to be released. Are any of them right, in part or in whole?arrow_forward
- Does the universe have a center? Explain.arrow_forwardA light-year is the distance that light can travel in one year. Similarly, we can define a light-second, light-day, etc. as the distance that light can travel in other time intervals. Calculate the distance represented by each of the following: (Assume that the speed of light is 3 x 10^8m/s) 5 light-minutes 6 light-days 6 light-days, but this time answer in miles (enter just the number with no units)arrow_forwardPhysics 17 & 19 please.arrow_forward
- I asked the following question and was given the attached solution: Suppose that the universe were full of spherical objects, each of mass m and radius r . If the objects were distributed uniformly throughout the universe, what number density (#/m3) of spherical objects would be required to make the density equal to the critical density of our Universe? Values: m = 4 kg r = 0.0407 m Answer must be in scientific notation and include zero decimal places (1 sig fig --- e.g., 1234 should be written as 1*10^3) I don't follow the work and I got the wrong answer, so please help and show your work as I do not follow along easily thanksarrow_forwardRecent findings in astrophysics suggest that the observable universe can be modeled as a sphere of radius R=13.7x109 light-years=13.0 x 1025m with an average total mass density of about 1x10-26 kg/m3 Only about 4% of total mass is due to “ordinary” matter (such as protons, neutrons, and electrons). Estimate how much ordinary matter (in kg) there is in the observable universe. (For the light-year, see Problem 19.)arrow_forwardThe visible section of the Universe is a sphere centered on the bridge of your nose, with radius 13.7 billion light-years. (a) Explain why the visible Universe is getting larger, with its radius increasing by one light-year in every year. (b) Find the rate at which the volume of the visible section of the Universe is increasing.arrow_forward
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