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R. Barrett and P. P. Delsanto
same in all directions. In our balloon analogy, in this case the speck representing the earth does not move across the surface of the balloon; the balloon
expands carrying the earth with it. However, the real earth is not stationary,
but moves around the sun, the sun moves within the galaxy, and the galaxy
moves through the cosmos. This motion introduces a further shift of frequencies (red or blue, depending on the direction of the earth’s motion relative to
the incoming radiation) superimposed on that of the CMB. This additional
shift is a true Doppler frequency shift due to the earth’s motion through
space, unlike the cosmic red shift due to the expanding universe. From the
observed anisotropy in the CMB relic radiation, the “absolute” velocity of the
earth (i.e. the velocity with respect to the background) can be estimated, and
is found to be 371 km/s in the direction of the constellation Leo.
Once we know its origin, we may as well subtract this Doppler anisotropy,
so that we are left only with the primordial anisotropies. The study of the
latter is extremely important in many aspects, which we cannot discuss here.
However, a quick qualitative remark is that the tiny density fluctuations
present at the recombination era are the “seeds” of the future galaxies. In
fact, any density excess, via a gravitational positive feedback, would tend to
grow, attracting matter from the surrounding less dense regions and in the
process give rise to large scale structure.
Also, the pattern of density fluctuations of the last scattering surface carries
the imprint of what happened before that era. Nothing else can arrive to
us from earlier times closer to the Big Bang. The last scattering surface
acts as a bright impenetrable curtain that prevents us from plunging deeper
towards the singularity. The history of the universe before the recombination
may be inferred to some extent from the accepted laws of physics, but not
observed. This is certainly true for the information carried by known physical interactions. Various non-standard theories predict the existence of other
“messengers” from the very early times of the universe. Besides these, it has
been conjectured that gravitational waves could also exist as a relic of the prerecombination era. However at present no observational evidence exists for
any of this.
10.7 The Universe, as It Was Known at the End
of the 20 th Century
Let us now assemble facts and theories to construct a consistent cosmology, as
it was accepted at the end of the twentieth century. General relativity was the
R. Barrett and P. P. Delsanto
same in all directions. In our balloon analogy, in this case the speck representing the earth does not move across the surface of the balloon; the balloon
expands carrying the earth with it. However, the real earth is not stationary,
but moves around the sun, the sun moves within the galaxy, and the galaxy
moves through the cosmos. This motion introduces a further shift of frequencies (red or blue, depending on the direction of the earth’s motion relative to
the incoming radiation) superimposed on that of the CMB. This additional
shift is a true Doppler frequency shift due to the earth’s motion through
space, unlike the cosmic red shift due to the expanding universe. From the
observed anisotropy in the CMB relic radiation, the “absolute” velocity of the
earth (i.e. the velocity with respect to the background) can be estimated, and
is found to be 371 km/s in the direction of the constellation Leo.
Once we know its origin, we may as well subtract this Doppler anisotropy,
so that we are left only with the primordial anisotropies. The study of the
latter is extremely important in many aspects, which we cannot discuss here.
However, a quick qualitative remark is that the tiny density fluctuations
present at the recombination era are the “seeds” of the future galaxies. In
fact, any density excess, via a gravitational positive feedback, would tend to
grow, attracting matter from the surrounding less dense regions and in the
process give rise to large scale structure.
Also, the pattern of density fluctuations of the last scattering surface carries
the imprint of what happened before that era. Nothing else can arrive to
us from earlier times closer to the Big Bang. The last scattering surface
acts as a bright impenetrable curtain that prevents us from plunging deeper
towards the singularity. The history of the universe before the recombination
may be inferred to some extent from the accepted laws of physics, but not
observed. This is certainly true for the information carried by known physical interactions. Various non-standard theories predict the existence of other
“messengers” from the very early times of the universe. Besides these, it has
been conjectured that gravitational waves could also exist as a relic of the prerecombination era. However at present no observational evidence exists for
any of this.
10.7 The Universe, as It Was Known at the End
of the 20 th Century
Let us now assemble facts and theories to construct a consistent cosmology, as
it was accepted at the end of the twentieth century. General relativity was the