Astronomy
1st Edition
ISBN: 9781938168284
Author: Andrew Fraknoi; David Morrison; Sidney C. Wolff
Publisher: OpenStax
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Textbook Question
Chapter 29, Problem 29E
There is still some uncertainty in the Hubble constant. (a) Current estimates range from about 19.9 km/s per million light-years to 23 km/s per million light-years. Assume that the Hubble constant has been constant since the Big Bang. What is the possible range in the ages of the universe? Use the equation in the text,
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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?
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.
Explain how the Hubble constant, H0, can be used to make an estimate for the age of the Universe. Use the value of H0 = 0.07×103 kms-1/Mpc to estimate the Universe’s age. Comment on the significance of your answer.
Chapter 29 Solutions
Astronomy
Ch. 29 - What are the basic observations about the universe...Ch. 29 - Describe some possible futures for the universe...Ch. 29 - What does the term Hubble time mean in cosmology,...Ch. 29 - Which formed first: hydrogen nuclei or hydrogen...Ch. 29 - Describe at least two characteristics of the...Ch. 29 - Describe two properties of the universe that are...Ch. 29 - Why do astronomers believe there must be dark...Ch. 29 - What is dark energy and what evidence do...Ch. 29 - Thinking about the ideas of space and time in...Ch. 29 - Astronomers have found that there is more helium...
Ch. 29 - Describe the anthropic principle. What are some...Ch. 29 - Describe the evidence that the expansion of the...Ch. 29 - What is the most useful probe of the early...Ch. 29 - What are the advantages and disadvantages of using...Ch. 29 - Would acceleration of the universe occur if it...Ch. 29 - Suppose the universe expands forever. Describe...Ch. 29 - Some theorists expected that observations would...Ch. 29 - There are a variety of ways of estimating the ages...Ch. 29 - Since the time of Copernicus, each revolution in...Ch. 29 - The anthropic principle suggests that in some...Ch. 29 - Penzias and Wilson’s discovery of the Cosmic...Ch. 29 - Construct a timeline for the universe and indicate...Ch. 29 - Suppose the Hubble constant were not 22 but 33...Ch. 29 - Assume that the average galaxy contains...Ch. 29 - The CMB contains roughly 400 million photons per...Ch. 29 - Following up on Exercise 29.27 calculate the...Ch. 29 - Continuing the thinking in Exercise 29.27 and...Ch. 29 - Continuing the thinking in the last three...Ch. 29 - There is still some uncertainty in the Hubble...Ch. 29 - It is possible to derive the age of the 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
- 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. Values: n = 1*10^80arrow_forwardAssume 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*1080arrow_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
- 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_forwardOur galaxy is approximately 100,000 light years in diameter and 2,000 light years thick through the plane of the galaxy. If we were to compare the ratio of the diameter galaxy and its thickness to the ratio of the diameter of a CD and its thickness (CD has a diameter of 12 cm and thickness of 0.6 mm), what would be the factor differentiating those ratios? Put differently, if the galaxy were scaled down to the diameter of a CD, how many times thicker or thinner would the galaxy be than the CD? (For example if it would be twice as thick, you would answer 2 and if it were twice as thin you would answer 0.5 (aka 1/2))arrow_forwardHow would I calculate the age of the universe in billions of years from the Hubble constant (73.48 +/- 1.66 km/s/Mpc)? I know I need to use basic unit conversion but I’m not sure which numbers to use.arrow_forward
- What is the estimated age of the Universe (in years) if the Hubble constant is 80 km/s/Mpc?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_forwardAssume 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.arrow_forward
- 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.arrow_forwardThe Universe is approximately 13.8 Billion years old. What is the volume of the visible universe in m3?arrow_forwardPerhaps the most fundamental problem in all of astronomy is the determination of distance to the various objects in the cosmos. Which of the following seems least reasonable regarding the various measurement techniques: Group of answer choices The Hubble Law relates the recessional speed of distant objects (measured with the Doppler Effect) to distance. Hubble law is most useful for determining the distance to nearby objects, while parallax is most useful for the more distant objects. We can determine the position of a star on the H-R diagram through spectral analysis and then figure out the distance by comparing absolute luminosity (from H-R diagram) to apparent brightness. The distance to nearby stars can be determined by measuring parallax. The distance to the planets in our solar can be determined by measuring the time for a radar signal to reach a planet, bounce off, and return.arrow_forward
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