ASTR 340 Lecture Notes - Lecture 13: Peculiar Velocity, Cosmological Constant, Edwin Hubble
Document Summary
Astr340: lec 13&14: expansion of the universe + cosmological principles. Doppler effect: related to frequency, wavelength, and speed. 1913: slipher: first results on radial velocity or speed of andromeda galaxy. 1920: edwin hubble: showed that nebulae were other galaxies. George"s lemaitre: 1927- put 2 and 2 together. Hubble spent time gathering data but confirmed that velocity increases as distance increases (hubble & humason 1931) Assuming the universe is homogeneous and isotropic: only 3 geometries: spherical, flat, hyperbolic. Einstein creates cosmological constant; hubble realizes the universe is expanding. Hubbles law says that speed is proportional to distance. Redshift not due to velocity of galaxies, but due to stretching of spacetime. Peculiar velocity: galaxies have motions due to other reasons besides expansion of space. Redshift is related to the ratio of the size of the universe when light is observed versus when it is emitted: allows measurement of time, because the universe had a size r then z = t.
