Chapter 34: Q11CQ (page 1237)
If the smallest meaningful time interval is greater than zero, will the lines in Figure below ever meet?
Short Answer
The lines in the given figure will never meet.
Chapter 34: Q11CQ (page 1237)
If the smallest meaningful time interval is greater than zero, will the lines in Figure below ever meet?
The lines in the given figure will never meet.
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Get started for freeThe critical mass density needed to just halt the expansion of the universe is approximately\({\rm{1}}{{\rm{0}}^{{\rm{ - 26}}}}{\rm{ kg/}}{{\rm{m}}^{\rm{3}}}\). (a) Convert this to\({\rm{eV/}}{{\rm{c}}^{\rm{2}}} \cdot {{\rm{m}}^{\rm{3}}}\). (b) Find the number of neutrinos per cubic meter needed to close the universe if their average mass is\({\rm{7 eV/}}{{\rm{c}}^{\rm{2}}}\)and they have negligible kinetic energies.
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\({\rm{1}}{{\rm{0}}^{{\rm{ - 26}}}}{\rm{kg/}}{{\rm{m}}^{\rm{3}}}\)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\({\rm{5 \% }}\)that of the critical density? (d) Compare the radius found in part (c) with the\({\rm{4 - ly}}\)average separation of stars in the arms of the Milky Way.
Show that the velocity of a star orbiting its galaxy in a circular orbit is inversely proportional to the square root of its orbital radius, assuming the mass of the stars inside its orbit acts like a single mass at the center of the galaxy. You may use an equation from a previous chapter to support your conclusion, but you must justify its use and define all terms used.
(a) What is the approximate speed relative to us of a galaxy near the edge of the known universe, some\({\rm{10 Gly}}\)away? (b) What fraction of the speed of light is this? Note that we have observed galaxies moving away from us at greater than\({\rm{0}}{\rm{.9c}}\).
Black holes with masses smaller than those formed in supernovas may have been created in the Big Bang. Calculate the radius of one that has a mass equal to the Earth’s.
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