Physics of Everyday Phenomena
9th Edition
ISBN: 9781259894008
Author: W. Thomas Griffith, Juliet Brosing Professor
Publisher: McGraw-Hill Education
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Textbook Question
Chapter 21, Problem 8CQ
How do we know that the universe is expanding? Explain.
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Does the universe have a center? Explain.
1. 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.
Olbers’s paradox deals with which of these questions?
a.
Is the universe accelerating?
b.
Why is the sky dark at night?
c.
Is the universe expanding?
d.
Why does the sun shine so brightly?
e.
none of the above
Chapter 21 Solutions
Physics of Everyday Phenomena
Ch. 21 - Prob. 1CQCh. 21 - Prob. 2CQCh. 21 - Prob. 3CQCh. 21 - Prob. 4CQCh. 21 - Prob. 5CQCh. 21 - Prob. 6CQCh. 21 - Prob. 7CQCh. 21 - How do we know that the universe is expanding?...Ch. 21 - Prob. 9CQCh. 21 - Prob. 10CQ
Ch. 21 - Prob. 11CQCh. 21 - Prob. 12CQCh. 21 - Describe two astronomical discoveries that provide...Ch. 21 - Prob. 14CQCh. 21 - Prob. 15CQCh. 21 - Prob. 16CQCh. 21 - Prob. 17CQCh. 21 - Prob. 18CQCh. 21 - Prob. 19CQCh. 21 - Prob. 20CQCh. 21 - Prob. 21CQCh. 21 - Prob. 22CQCh. 21 - Prob. 23CQCh. 21 - Prob. 24CQCh. 21 - Prob. 25CQCh. 21 - Prob. 26CQCh. 21 - Prob. 27CQCh. 21 - Prob. 28CQCh. 21 - The average distance from the sun to Venus is...Ch. 21 - Prob. 2ECh. 21 - The nearest star to our sun is a red dwarf named...
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- 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, T0=1H , and make sure you use consistent units. (b) Twenty years ago, estimates for the Hubble constant ranged from 50 to 100 km/s per Mps. What are the possible ages for the universe from those values? Can you rule out some of these possibilities on the basis of other evidence?arrow_forward(a) Calculate The approximate age of the universe from the average value of the Hubble constant, 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.arrow_forwardDoes an elliptical galaxy rotate like a spiral galaxy? Explain.arrow_forward
- Why cant an open universe have a center? How can a closed universe not have a center?arrow_forwardExplain the differences among the observable universe expanding, the Universe expanding, and the Universe's expansion accelerating.arrow_forwardGalaxies are found in the “walls” of huge voids; very few galaxies are found in the voids themselves. The text says that the structure of filaments and voids has been present in the universe since shortly after the expansion began 13.8 billion years ago. In science, we always have to check to see whether some conclusion is contradicted by any other information we have. In this case, we can ask whether the voids would have filled up with galaxies in roughly 14 billion years. Observations show that in addition to the motion associated with the expansion of the universe, the galaxies in the walls of the voids are moving in random directions at typical speeds of 300 km/s. At least some of them will be moving into the voids. How far into the void will a galaxy move in 14 billion years? Is it a reasonable hypothesis that the voids have existed for 14 billion years?arrow_forward
- The mass density of our universe is measured to be about 10-29 kg/m3. If an arbitrary point is chosen as the center, how large is the radius of a spherical surface centered at the point so that the mass enclosed in the surface will become a blackhole observed by someone outside the surface? A. 4.2 trillion light years B. 420 billion light years C. 42 billion light years D. 4.2 billion light years Is the answer D? Thanks!arrow_forwardThe matter density in the Universe today is Pm = -27 kg m-3. What would 2.7 x 10 be the value of the density parameter, 2o, if the Hubble constant had the value Ho = 38 km/s/Mpc? Assume the Universe does not contain dark energy and choose the option below that best matches your answer. Select one: O a. 0.1 O b. 2. О с. 1. O d. 0.7 О е. 0.5arrow_forwardWe know that dark matter must exist in galaxies. If not, many of the stars in a galaxy would ... a.Expand and go supernova due to the expansion of the Universe b.Fly away from the galaxy because the stars’ velocities are so large, and the galaxy would not have enough gravity to hold onto them c.Orbit the center of the galaxy normally d.Spiral in toward the center of the galaxy because most of the galaxy’s mass would be toward the centerarrow_forward
- In the standard model, about when after the Big Bang did the universe become transparent to radiation? O a.10:35 , O b.10435 O C:3x 105 y O d.103 sarrow_forwardIf a galaxy is 9.0 Mpc away from Earth and recedes at 488 km/s, what is H0 (in km/s/Mpc)? km/s/Mpc What is the Hubble time (in yr)? years How old (in yr) would the universe be, assuming space-time is flat and the expansion of the universe has not been accelerating? How would acceleration change your answer? A.If the expansion of the Universe has been accelerating, the Universe could be substantially younger than the value entered above. BIf the expansion of the Universe has been accelerating, the Universe could be substantially older than the value entered above.arrow_forwardThe history of the universe described by the Big Bang theory is separated into different eras. During which era was the predominant temperature of the Universe about 1 million Kelvin?a.The Plank Erab.The GUT Erac.The Electroweak Erad.The Era of Nucleie.The Era of AtomsSome planets have very strong magnetic fields. What features must a planet have to cause this?a.both rapid rotation and a conducting liquid coreb.only a rapid rotationc.only a liquid conducting cored.both a rapid rotation and a solid metallic coree.only a metallic corearrow_forward
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