Universe
11th Edition
ISBN: 9781319039448
Author: Robert Geller, Roger Freedman, William J. Kaufmann
Publisher: W. H. Freeman
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Chapter 25, Problem 27Q
To determine
The background temperature, if the mass density of
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What would be your estimate for the age of the universe if you measured Hubbleʹs constant to be 33 km/s/Mly? You can assume that the expansion rate has remained unchanged during the history of the universe.
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Using Ho = 20.8 km/s/Mly and assuming the expansion rate has been
constant, find out how long the universe has been expanding.
Chapter 25 Solutions
Universe
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- In which model universe does the average density of the Universe equal the critical density?arrow_forwardSome theorists expected that observations would show that the density of matter in the universe is just equal to the critical density. Do the current observations support this hypothesis?arrow_forwardThe critical mass density needed to just halt the expansion of the universe is approximately 10-26 kg/m3. Find the number of neutrinos per cubic meterneeded to close the universe if their average mass is 7 eV/c2 and they have negligible kinetic energies.arrow_forward
- What will happen if the density of the universe is less than the critical density?arrow_forwardSuppose 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 = 10 kg r = 0.0399 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)arrow_forwardThe present number density of electrons in the Universe is the same as that of protons, about 0.2 m-3. Consider a time long before the formation of the microwave background, when the scale factor was x times smaller than its present value. What was the number density of electrons then? Value: x = 12×106arrow_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_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_forward1. The current (critical) density of our universe is pe = 10-26kg/m³. Assume the universe is filled with cubes with equal size that each contain one person of m = 100kg. What would the length of the side of such a cube have to be in order to give the correct critical density? How many hydrogen atoms would you need in a box of 1 m³ to reach the critical density? The matter we know, which consists mostly of hydrogen, constitutes only 4.8% of the current critical energy density of our universe. So how many hydrogen atoms are actually in a box of 1 m3 in our universe? Deep space is very empty and a much better vacuum than we can obtain on earth in a laboratory.arrow_forward
- The mass of the neutrino plays an important role in the universe. Suppose the mass of two neutrinos in the universe is 4.8×10-³5 kg and the current Hubble’s constant is 72 km/s/Mpc. The critical density of the universe is five times the average density of the universe. Estimate the number of neutrons present per cubic meter in the universe. (a) 2.1×10⁹ (b) 4.1×10² (c) 1.1x10° (d) 8.1×107arrow_forwardCalculate the temperature of the universe when photons can no longer disassociate deuterons. Use the mean value of the distribution.arrow_forwardThe critical mass density needed to just halt the expansion of the universe is approximately 10-26 kg/m3. Convert this to eV/c2.m3 .arrow_forward
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