Modern Physics
3rd Edition
ISBN: 9781111794378
Author: Raymond A. Serway, Clement J. Moses, Curt A. Moyer
Publisher: Cengage Learning
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Chapter 16, Problem 13P
(a)
To determine
To prove that the age of the universe is equal to inverse of Hubble’s constant.
(b)
To determine
The value of
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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.
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)
(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.
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- To 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_forward(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 itwould 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_forwardIf the average density of the Universe is small compared with the critical density, the expansion of the Universe described by Hubble's law proceeds with speeds that are nearly constant over time. Calculate t since the big bang, assuming H = 22.0 km/s/Mly.arrow_forward
- Name: Hubble Distances Redshift z parameter The relativistic redshift is parametrized by z and given by Δ In terms of the scale factor, 2= X do - de de 1+z= ao a (2) Problem 01. Find the redshift z for a Hydrogen spectral line originally at 656 nm which has been observed at a wavelength of 1.64 μm. Astro 001 Fall 2022 Problem 02. How much smaller was the universe when this light was emitted? U₁ = DHO Using the redshift to measure the velocity, we find D~ (1) 0.1 Hubble's Law Hubble's Law states that the recession velocity of a redshifted galaxy is given by the product of the distance and the Hubble constant. (3) ZC Ho where c = 3 x 108 m/s and Ho = 2.3 x 10-18 s in standard units. The standard measurement of the Hubble constant is Ho = 71 (km/s)/Mpc. Problem 03. What is the distance in Mpc and ly to the galaxy measured in problem 01? 1 pc = 3.26 ly.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_forwardThe time before which we don’t know what happened in the universe (10-43 s) is called the Planck time. The theory needed is a quantum theory of gravity and concerns the three fundamental constants h, G, and c. (a) Use dimensional analysis to determine the exponents m, n, l if the Planck time tP = hmGncl . (b) Calculate the Planck time using the expression you found in (a).arrow_forward
- Consider a universe identical to ours, but where the only difference is that the mass of the proton and the one of the neutron are the same. What would have been the neutron fraction 39 seconds after the Big Bang? Consider for the neutron a mean lifetime of 886 s. Enter your answer to 3 decimal places. Answer:arrow_forwardTwo distant galaxies are observed to have redshifts z1 = 0.05 and z2 = 0.15, and distances d1 = 220.60 Mpc and d2 = 661.75 Mpc, respectively. Assuming the motion of the galaxies is due to the Hubble flow, determine the value of the Hubble constant, H0. Show how the value of H0 can be used to estimate the age of the Universe, describing any assumptions that you make. Use the value of H0 you have obtained to estimate the age of the Universe, expressing your answer in Gyr.arrow_forwardHubble's law can be stated in vector form as v = HR. Outside the local group of galaxies, all objects are moving away from us with velocities proportional to their positions relative to us. In this form, it sounds as if our location in the Universe is specially privileged. Prove that Hubble's law is equally true for an observer elsewhere in the Uni- verse. Proceed as follows. Assume we are at the origin of coordinates, one galaxy cluster is at location R, and has velocity v, = HR relative to us, and another galaxy cluster has position vector R, and velocity v, = HR, Suppose the speeds are nonrelativistic. Consider the frame of reference of an observer in the first of these galaxy clusters. (a) Show that our velocity relative to her, together with the position vector of our galaxy cluster from hers, satisfies Hubble's law. (b) Show that the position and velocity of cluster 2 rel- ative to cluster 1 satisfy Hubble's law.arrow_forward
- Consider the energy-momentum tensorT_µν = (ρ + p) u_µ u_ν + p g_µνapplied to the matter/energy distribution in the universe on large scales, and assume an equation of state of the form p = wρ, with w a constant. Determine the type of matter/energy dominating the universe if the energy-momentum tensor is traceless, that is, T^µ_µ = 0.arrow_forward(a) Let L be the diameter of our galaxy.Suppose that a person in a spaceship of massm wants to travel across the galaxy at constantspeed, taking proper time τ. Find the kineticenergy of the spaceship. (b) Your friend is impa-tient, and wants to make the voyage in an hour.For L = 105 light years, estimate the energy inunits of megatons of TNT (1 megaton=4×109 J).arrow_forwardAssume a power law for the scale factor a = Ctn, where C is a constant. (a) For what values of n are the universe accelerating and decelerating? (b) For deceleration, what is the dependence of H on time?arrow_forward
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