The Cosmological Redshift
A subtle point:
- the cosmological redshift of galaxy spectra is not a simple
a Doppler shift
- Doppler shifts result from sources of waves moving
THROUGH space; here distances between sources of waves (i.e.,
galaxies emitting light)
increase because space itself is
- as photons travel through the universe they are
STRETCHED as the fabric of spacetime expands!
Stretched Photon (Balloon Analogy)
Q: What happens to the energy of a photon
when you increase its wavelength?
A: The photon loses energy!
Consequence: as the
universe expands the density of "radiant
energy", i.e. light, in the universe decreases faster
than the density of "mass energy".)
energy density = energy per unit volume
At the present day, there is roughly 20,000 times more
energy density in the form of mass/matter
. We live at a time when
the universe is "Matter Dominated".
In the far distant past there would have been a time when there was
more energy density in the form of
This would have been a time when the universe was
Q: Where are the "fossil photons" from the Big Bang?
90% of the radiant energy in the universe at the present day - but
you can't see them with your eyes...)
On to Cosmic Microwave Background Radiation or back to