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Chaos Game 
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Miscel laneous 
Physics Quiz 
The Expanding Universe
Cosmological Redshift
The discovery of the linear
relationship between redshift, interpreted
as recessional velocity, and distance yields
a straightforward mathematical expression
for Hubble's Law as follows:Photons propagating
through the expanding space are stretched
between their point of emission emission
(em) and their point of observation (obs),
creating an increase
in wavelength: the
cosmological redshift.
(1+z) is the factor by which
the universe has expanded while the photon
was travelling towards the observer. If t_{obs}
is the present time, then a(t_{obs})=1,
and the cosmic scale factor at the time of
emission is
e. g.:
for a cosmological redshift of z=3 the cosmic scale factor at the time of emission was a=1/4. v = recession velocity,
in km/sec
H_{0} = Hubble Parameter (today), H0 = (70 +/ 7) km/sec/Mpc D = (comoving) distance from the galaxy to the observer, in Mpc H_{0} may be interpreted as the rate of expansion of the Universe, and the "Hubble time" 1/H_{0} as the current age of the universe. 
