Large-scale structure ® filaments or ‘walls’ of galaxies,
                                        voids with few galaxies,
                                       but no structure > 200 Mpc
\ Cosmological principle (anti-Ptolemaic)
      on very large scales, universe is homogeneous, isotropic
homogeneous -- same density everywhere at same time
      isotropic -- same in all directions
      i.e. no edge, no center
Olbers’ paradox  - why is night sky dark?
 ® universe must be finite in space/time
(Newton –infinite, “flat,”static)
Einstein ® Cosmological Constant L to counteract contraction OR
expansion (not physical but makes relativity and & static theory agree)
Hubble recession of galaxies ® expanding universe
AND age of universe