Space
itself is expanding, causing every objects to become separated without
changing their positions in space. This is know as the cosmological
redshift. All sufficiently distant light sources generally more than few
million light-years away show redshift corresponding to the rate of
increase in their distance from Earth which is known as Hubble's Law.
Hubble's
law formally known as the Hubble-Lemaitre's law, is the observation in
physical cosmology that :
- All objects observed in deep space are found to have a Doppler shift (redshift) which interpreted as a relative velocity to Earth and to each other.
- This Doppler shift measured velocity of various galaxies moving away from the Earth is approximately proportional to their distance from the Earth and all other interstellar bodies.
In
effect, the space-time volume of the observable universe is expanding
and Hubble's Law is considered as the first observational basis for
the expansion of the universe and is evidence often cited in support
of the Big Bang model.
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| George Lemaitre |
George
Lemaitre first noted in 1927 that an expanding universe could be
traced back in time to an originating single point and independently
derived that the universe might be expanding, observed the
proportionality between relative velocity of and distance to distant
bodies and suggested an estimated value of the proportionality
constant, which when corrected by Edwin Hubble became known as the
Hubble constant.
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| Edwin Hubble |
The
motion of astronomical objects due to this expansion is known as the
Hubble Flow, which is expressed by the equation
ᴠ= H₀×D,
where
H₀ is the constant of proportionality called Hubble constant,
D is
the proper distance between the objects which can change over time,
v is
the relative velocity between them.
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