Universe: Stars And Galaxies
6th Edition
ISBN: 9781319115098
Author: Roger Freedman, Robert Geller, William J. Kaufmann
Publisher: W. H. Freeman
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Chapter 25, Problem 35Q
To determine
(a)
The reason for the
To determine
(b)
The radiation temperature at
To determine
(c)
The redshift at which the radiation temperature is equal to
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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.
The geometry of spacetime in the Universe on large scales is determined by the mean energy density of the matter in the Universe, ρ. The critical density of the Universe is denoted by ρ0 and can be used to define the parameter Ω0 = ρ/ρ0. Describe the geometry of space when: (i) Ω0 < 1; (ii) Ω0 = 1; (iii) Ω0 > 1. Explain how measurements of the angular sizes of the hot- and cold-spots in the CMB projected on the sky can inform us about the geometry of spacetime in our Universe. What do measurements of these angular sizes by the WMAP and PLANCK satellites tell us about the value of Ω0?
If we were to analyze the magnetic flux lines of a current-carrying conductor, oriented
perpendicularly to a magnetic field between two bar magnets, the interaction would look
something like this:
S
N
S
N
This interaction of magnetic flux lines (the bar magnets' straight lines versus the wire's cireles)
will produce a mechanical force on the wire (called the Lorentz force). Which direction will
this force act?
Also, determine the direction of current through the conductor (seen from an end-view in
the above illustration) necessary to produce the circular magnetic flux shown.
Chapter 25 Solutions
Universe: Stars And Galaxies
Ch. 25 - Prob. 1QCh. 25 - Prob. 2QCh. 25 - Prob. 3QCh. 25 - Prob. 4QCh. 25 - Prob. 5QCh. 25 - Prob. 6QCh. 25 - Prob. 7QCh. 25 - Prob. 8QCh. 25 - Prob. 9QCh. 25 - Prob. 10Q
Ch. 25 - Prob. 11QCh. 25 - Prob. 12QCh. 25 - Prob. 13QCh. 25 - Prob. 14QCh. 25 - Prob. 15QCh. 25 - Prob. 16QCh. 25 - Prob. 17QCh. 25 - Prob. 18QCh. 25 - Prob. 19QCh. 25 - Prob. 20QCh. 25 - Prob. 21QCh. 25 - Prob. 22QCh. 25 - Prob. 23QCh. 25 - Prob. 24QCh. 25 - Prob. 25QCh. 25 - Prob. 26QCh. 25 - Prob. 27QCh. 25 - Prob. 28QCh. 25 - Prob. 29QCh. 25 - Prob. 30QCh. 25 - Prob. 31QCh. 25 - Prob. 32QCh. 25 - Prob. 33QCh. 25 - Prob. 34QCh. 25 - Prob. 35QCh. 25 - Prob. 36QCh. 25 - Prob. 37QCh. 25 - Prob. 38QCh. 25 - Prob. 39QCh. 25 - Prob. 40QCh. 25 - Prob. 41QCh. 25 - Prob. 42QCh. 25 - Prob. 43QCh. 25 - Prob. 44QCh. 25 - Prob. 45QCh. 25 - Prob. 46QCh. 25 - Prob. 47QCh. 25 - Prob. 48QCh. 25 - Prob. 49QCh. 25 - Prob. 50QCh. 25 - Prob. 51QCh. 25 - Prob. 52QCh. 25 - Prob. 53QCh. 25 - Prob. 54QCh. 25 - Prob. 55Q
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- esc a) 10 points) Gravitational Time Dilation. The escape velocity from the surface (radius r) of a star or planet of mass M is given by the formula v = (2GM/r). Use this expression to write the time-dilation fraction, At/t, in terms of the ratio of vesc to the speed of light, c. Hint: This is just a simple exercise in substitution. 5.98 x 1024 kg b) (10 points) Extra Lifetime on the Surface of Earth. The Earth has mass MEarth and radius REarth 6.38 x 10 m. What is the fractional time-dilation (At/t) for someone on the Earth's surface? How much longer (At) is a typical lifetime on the surface of Earth, compared to someone in deep space, far away from Earth? Assume a typical human life span of t = 80 years. Iarrow_forwardsuppose you collected a data set in which you measured fall-times for different fall-heights, you plotted the data and fit the mathemathical model, y=Ax^2, to match the physical hypothesis, y=0.5*g*t^2. From the best fit curve you are told that the value of your fit-parameter, A, is for 4.6 m/s^2 +/- 0.4 m/s^2. Determine the value of g +/- delta g for this fit parameter value.arrow_forwardSuppose you are designing a proton decay experiment and you can detect 50 percent of the proton decays in a tank of water. (a) How many kilograms of water would you need to see one decay per month, assuming a lifetime of 1031 y ? (b) How many cubic meters of water is this? (c) If the actual lifetime is 1033 y , how long would you have to wait on an average to see a single proton decay?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 = 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)arrow_forwardThe peak intensity of the CMBR occurs at a wavelength of 1.1 mm. (a) What is the energy in eV of a 1.1-mm photon? (b) There are approximately 109 photons for each massive particle in deep space. Calculate the energy of 109 such photons. (c) If the average massive particle in space has a mass half that of a proton, what energy would be created by converting its mass to energy? (d) Does this imply that space is “matter dominated”? Explain briefly.arrow_forwardConsider the case where an electron and a positron annihilate each other and produce photons. Assume that these two particles collide head-on with equal, but slow, speeds. Is it possible that only one photon is produced? If yes, how? If not, is it possible that only two photons are produced? If yes, how? Is it possible that the produced photons have different energies? Explain your reasoning based on the conservation laws of physics.arrow_forward
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