PHYS 1000 Lecture Notes - Lecture 17: Sloan Great Wall, Recessional Velocity, Cosmological Principle
12 Feb 2018
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Document Summary
Cosmology is the study of the structure and evolution of the entire universe. This galaxy map shows the largest structure known in the universe, the sloan great wall. No structure larger than 200 mpc is seen. Therefore, the universe is homogenous (any 300-mpc-square block appears much like any other) on scales greater than about 300 mpc. The universe also appears to be isotropic the same in all directions. The cosmological principle includes the assumptions of isotropy and homogeneity. O(cid:271)lers"s parado(cid:454): if the u(cid:374)i(cid:448)erse is ho(cid:373)oge(cid:374)eous, isotropi(cid:272), i(cid:374)fi(cid:374)ite a(cid:374)d u(cid:374)(cid:272)ha(cid:374)gi(cid:374)g, the e(cid:374)tire sk(cid:455) should be as bright as the surface as the sun. The universe is homogeneous and isotropic it must not be infinite and/or unchanging. We know galaxies are moving away from us the farther away they are: recessional velocity. Using h0 = 7(cid:1004) k(cid:373)/s/mp(cid:272), (cid:449)e fi(cid:374)d that ti(cid:373)e is a(cid:271)out (cid:1005)4 (cid:271)illio(cid:374) (cid:455)ears. Note that the hu(cid:271)(cid:271)le"s la(cid:449) is the same no matter who is making the measurements.
