Universe
11th Edition
ISBN: 9781319039448
Author: Robert Geller, Roger Freedman, William J. Kaufmann
Publisher: W. H. Freeman
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Question
Chapter 25, Problem 14Q
(a)
To determine
The value of redshift, when the value of representative distance between galaxies is increased by
(b)
To determine
The density and compare the representative distance between galaxies to present value of distance, if the value of redshift is 8.
(c)
To determine
The comparision for density of dark energy for
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(a) Calculate the approximate age of the universe from the average value of the Hubble constant, H0 = 20km/s ⋅ Mly . To do this, calculate the time it would take to travel 1 Mly at a constant expansion rate of 20 km/s. (b) If deceleration is taken into account, would the actual age of the universe be greater or less than that found here? Explain.
According to the version of the Big Bang Theory without a Cosmological Constant (and without Dark Energy of any kind), what would be the maximum possible age of the universe in Gyr (Gigayears, meaning billions of years) if the Hubble Constant had the following values? Another way of asking the question would be: What is the Hubble Time in Gyr, given the following values of H0? H0 = 50 km/s/Mpc H0 = 75 km/s/Mpc H0 = 100 km/s/Mpc answer to two significant figures.
Using 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.
Chapter 25 Solutions
Universe
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Need a deep-dive on the concept behind this application? Look no further. Learn more about this topic, physics and related others by exploring similar questions and additional content below.Similar questions
- Why cant an open universe have a center? How can a closed universe not have a center?arrow_forwardTo get an idea of how empty deep space is on the average, perform the following calculations: (a) Find the volume our Sun would occupy if it had an average density equal to the critical density of 10-26 kg / m3 thought necessary to halt the expansion of the universe. (b) Find the radius of a sphere of this volume in light years. (c) What would this radius be if the density were that of luminous matter, which is approximately 5% that of the critical density? (d) Compare the radius found in part (c) with the 4-ly average separation of stars in the arms of the Milky Way.arrow_forwardIf the universe had a density equal to its estimated critical density of 9= 10-30 g/cm3, and if it were composed entirely of one-solar-mass stars (mass 2.0 x1030 kg) distributed uniformly across the universe, what would be the distance between stars? Compare your result with the density of stars in the neighborhood of the sun and comment on the result.arrow_forward
- The 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(a) What Hubble constant corresponds to an approximate age of the universe of 1010 y? To get an approximate value, assume the expansion rate is constant and calculate the speed at which two galaxies must move apart to be separated by 1 Mly (present average galactic separation) in a time of1010 y. (b) Similarly, what Hubble constant corresponds to a universe approximately 2×1010 -y old?arrow_forwardI 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_forward
- Consider the following line element, ds² = -dt² + a² (t) (dx² + dy²) + b²(t) dz², where a(t) and b(t) are distinct functions. State whether or not this line element obeys the Cosmological Principle, if applied to describe the universe on large scales. Justify your answer.arrow_forwardSuppose a hypothetical universe is expanding (at some moment in time) at a rate of H. At this same moment the density of this Universe is ρ. (a) Confirm for yourself that this is a closed universe, given the values below. (b) Determine, and enter below, the spatial radius of curvature for this closed universe (at the same moment in time at which the values above are given). Values: H = 56 km s-1 Mpc-1 ρ = 4.9x10-25 kg m-3 Give your answer for (b) in units of Mpc, to the nearest integer (not in scientific notation - e.g., 1234).arrow_forwardCompute a numerical value (in units of protons/m3) for the critical density of our Universe. Howdoes it compare to the density of hydrogen gas at standard temperature and pressure?arrow_forward
- 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 = 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_forwardAssuming that the Hubble constant is, in fact, constant over the age of the universe, what is the Hubble look-back time (effectively the age of the universe in this case) if the Hubble constant is measured to be 50 km/s/Mpc (Please give your answer in units of billions of years; i.e. 10 billion years should be answered as 10)? Keep in mind that this is not the observed measurement of the Hubble constant (70 km/s/Mpc) and is only a value given for this problem. That said, it is not incredibly different so you should expect your answer to still be on the scale of billions of years.arrow_forwardBy what factor would the critical density of the universe today change if the Hubble constant today measured at 5 times greater than what we previously thought?arrow_forward
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