What can change the expansion rate of the Universe over time? O Gravity: Attractive forces increase the expansion rate by pulling mass together making gravity stronger. O Gravity decreases the expansion rate, while electromagnetic forces are always repulsive and speed-up expansion. O Attractive forces such as gravity decrease the expansion rate. Repulsive forces would speed-up expansion by pushing spacetime apart. O Nothing, since the expansion rate remains always constant, and it is measured from Hubble's law.

What can change the expansion rate of the Universe over time? O Gravity: Attractive forces increase the expansion rate by pulling mass together making gravity stronger. O Gravity decreases the expansion rate, while electromagnetic forces are always repulsive and speed-up expansion. O Attractive forces such as gravity decrease the expansion rate. Repulsive forces would speed-up expansion by pushing spacetime apart. O Nothing, since the expansion rate remains always constant, and it is measured from Hubble's law.

Principles of Physics: A Calculus-Based Text

5th Edition

ISBN:9781133104261

Author:Raymond A. Serway, John W. Jewett

Publisher:Raymond A. Serway, John W. Jewett

Chapter31: Particle Physics

Section: Chapter Questions

Problem 47P

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(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 of 1010 y. (b) Similarly, what Hubble constant corresponds to a universe approximately 21010years old?
(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 0.307 Mpc at a constant expansion rate of 20 km/s. (b) If somehow acceleration occurs, would the actual age of the universe be greater or less than that found here? Explain.
Galaxies 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?
3. Consider the following two universes: Universe I: flat, matter-dominated with no cosmological constant or radiation, in which a(t) = (t/to)2/3. Universe II: flat, radiation-dominated with no cosmological constant or matter, in which a(t) = (t/to) ¹/². a. Which universe is expanding the fastest? b. For each case, use the Hubble law to show that to = 3/(2H₁) and to = 1/(2H₁) for universes I and II respectively. c. Based on the previous question, which universe would be the youngest assuming a given Ho value?
What can change the expansion rate of the Universe over time? Gravity: Attractive forces increase the expansion rate by pulling mass together making gravity stronger. Gravity decreases the expansion rate, while electromagnetic forces are always repulsive and speed-up expansion. Attractive forces such as gravity decrease the expansion rate. Repulsive forces would speed-up expansion by pushing spacetime apart. Nothing, since the expansion rate remains always constant, and it is measured from Hubble's law.
The 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. 0.5
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.
Does Hubble's Law work well for galaxies in the Local Group (such as Andromeda)? No, because dark energy is accelerating the universe's expansion over those distances. No, because we do not know the precise value of Ho. No, because Hubble did not know the Local Group existed when he discovered his law. Yes, it works well for all galaxies. No, because galaxies in the Local Group are bound gravitationally together.
3. The formula for Hubble's Law using the velocity v is valid only for velocities much smaller than the speed of light (c). For velocities which are greater, the following formula is used where 1+v/e - 1. 1-v/c The largest redshift measured for a quasar (as of 1997) is z = 4.89 Solving the above equation for v, we can compute the recessional velocity for a quasar. - 1- Velocity= +z)² -1 (1+z) + 1 Velocity = km/sec. Calculate how far the quasar is in light years by knowing that distance = velocity/Ho. Make the appropriate units conversions. Distance = velocity/Ho=C Mpc) = light years %3D
Problem 3. Consider a flat, single component universe. 1. For a light source at redshift z that is observed at time to, show that z changes at a rate dz dto = = Ho(1 + 2) — Ho(1+2)³(¹+w)/2 (2.1) 2. For what values of w does the observed redshift increase with time? 3. Assuming the single component is matter and Ho = 68 km/s/Mpc, you observe a galaxy at z = 1. Using Equation 2.1, determine how long you will have to keep observing the galaxy in order to see its redshift change by 1 part in 106.
. The temperature of background radiation left over from the Big Bang during the creation of the universe is 3 K. What is the temperature of the universe a) in °C? b) in °F?
Question A7 Consider the following line element, ds² = - dt² + a² (t) (da² + 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.