10 How the World Began
211
basic conceptual framework, and the expanding universe had been well established in the FLRW formalism. A consistent chain of physical events may be
described using known physics (including quantum mechanics for nuclear
and sub-nuclear forces) from very close to the initial Big Bang up to the
present time. Not everything is clear and understood, but the fundamental
pillars are well established.
The initial singularity of the Big Bang remains outside the domain of
physics, since nobody knows what to do with an infinite energy density.
Immediately following the Big Bang, we don’t even know what the laws of
physics were. At these incredible energies, the four forces may well be unified
into a single force. We expect gravity to play a dominant role because of the
enormous densities, and consequent curvature of space–time, in this region,
but so far it has stubbornly resisted all of our attempts to bring it into the
framework of quantum physics.
Despite these difficulties, theorists have proposed a mechanism to explain
the puzzling homogeneity of the Cosmic Microwave Background that we
discussed in the previous Section. Allan Guth and Andrei Linde in the 1980s
conjectured that in the period leading up to 10 –32 s after the Big Bang, the
universe underwent an exponential expansion. This might seem an inconceivably short time period, but the Big Bang was proposed as initiating at a
singularity, which is, as we have seen, a point with zero volume in space–time.
Such was the expansion rate that the scale of spatial distances increased by a
factor of at least 10 26 . To achieve such an enormous rate, the recession velocities of the components of the universe, would have been well above the speed
of light. As discussed earlier, these superluminal velocities are not a contradiction of relativity, because it was space–time itself that was expanding. This
period of expansion was called inflation by Guth and Linde.
The development of inflation theory is highly mathematical, and beyond
the scope of this book. However, a few qualitative observations are possible.
The period of exponential expansion smooths out any density fluctuations present at the beginning of inflation. As a consequence, the CMB is
incredibly homogeneous, as we have already seen. However, tiny residual
inhomogeneities (see Fig. 10.9) do remain. Once the inflationary expansion is over, these inhomogeneities are frozen into the fabric of the universe
because the regions containing them can no longer interact with each other.
Such interactions would require faster-than-light travel, which is forbidden
by Relativity.
To explain this period of inflation, Guth and Linde proposed a new field,
called the inflaton, to describe matter/energy. As the expansion proceeds, the
energy density decreases until the inflaton field decomposes, and the more
211
basic conceptual framework, and the expanding universe had been well established in the FLRW formalism. A consistent chain of physical events may be
described using known physics (including quantum mechanics for nuclear
and sub-nuclear forces) from very close to the initial Big Bang up to the
present time. Not everything is clear and understood, but the fundamental
pillars are well established.
The initial singularity of the Big Bang remains outside the domain of
physics, since nobody knows what to do with an infinite energy density.
Immediately following the Big Bang, we don’t even know what the laws of
physics were. At these incredible energies, the four forces may well be unified
into a single force. We expect gravity to play a dominant role because of the
enormous densities, and consequent curvature of space–time, in this region,
but so far it has stubbornly resisted all of our attempts to bring it into the
framework of quantum physics.
Despite these difficulties, theorists have proposed a mechanism to explain
the puzzling homogeneity of the Cosmic Microwave Background that we
discussed in the previous Section. Allan Guth and Andrei Linde in the 1980s
conjectured that in the period leading up to 10 –32 s after the Big Bang, the
universe underwent an exponential expansion. This might seem an inconceivably short time period, but the Big Bang was proposed as initiating at a
singularity, which is, as we have seen, a point with zero volume in space–time.
Such was the expansion rate that the scale of spatial distances increased by a
factor of at least 10 26 . To achieve such an enormous rate, the recession velocities of the components of the universe, would have been well above the speed
of light. As discussed earlier, these superluminal velocities are not a contradiction of relativity, because it was space–time itself that was expanding. This
period of expansion was called inflation by Guth and Linde.
The development of inflation theory is highly mathematical, and beyond
the scope of this book. However, a few qualitative observations are possible.
The period of exponential expansion smooths out any density fluctuations present at the beginning of inflation. As a consequence, the CMB is
incredibly homogeneous, as we have already seen. However, tiny residual
inhomogeneities (see Fig. 10.9) do remain. Once the inflationary expansion is over, these inhomogeneities are frozen into the fabric of the universe
because the regions containing them can no longer interact with each other.
Such interactions would require faster-than-light travel, which is forbidden
by Relativity.
To explain this period of inflation, Guth and Linde proposed a new field,
called the inflaton, to describe matter/energy. As the expansion proceeds, the
energy density decreases until the inflaton field decomposes, and the more