18.5 Condensation of Nucleons
279
think of nucleons condensing from a quark gluon plasma at this time, about 10
−6 s.
The stuff of the universe before this time is a dense hot plasma of quarks and gluons
and leptons (e and μ and τ and their neutrinos) and many photons (Quigg 2006).
High energy particle experimentalists are now trying to create quark gluon plasmas
at accelerator laboratories by colliding heavy nuclei. The results are interesting for
their relevance to early universe physics.
A question under current debate is why the universe appears to be composed
almost entirely of matter and very little anti-matter. One might naively expect a
mixture of roughly 50% matter and 50% anti-matter, but this is definitely not observed
(Moskowitz 2019; Peebles 1993).
18.6 Inflation
Recall the horizon or isotropy puzzle, which we discussed in Sect. 17.3: it is difficult
to see how the universe could have been as homogeneous and isotropic as it appears to
have been at the time of decoupling. But also recall that we noted in Exercise 17.5 that
the exponentially expanding de Sitter model universe has no horizon. Many theorists
believe that a period of very rapid expansion of the universe, described roughly by
the de Sitter model, provides the best resolution of the horizon puzzle; this very rapid
expansion is called inflation. It is postulated to have occurred well before the quark
gluon plasma era, say at about 10
−36 s. There are many versions of inflation theory,
and it is better to consider it a general scenario rather than a single theory. Most
versions postulate a scalar field called the inflaton as the dominant ingredient of the
universe. It is now the most widely accepted solution of the horizon puzzle and we
will discuss it in Chap. 19. It is also relevant to the spectrum of the CMB radiation,
which provides an observational test (Freedman 2006; Linde 2007).
The end of the inflation era is widely called reheating, at which time the particles
and fields that later filled the universe were somehow formed after inflation. There
is little observational information concerning this transition, but much theoretical
speculation (Kofman 1996).
18.7 Planck Era
Finally we run the clock backwards for the final time to such high temperature and energy that we simply do not know what happens but can only make
informed guesses. Perhaps interesting and strange things happen when the temperature approaches kT = 10
17 GeV, at which time it is believed by many theorists
that the strong, electromagnetic and weak forces become equal. There are many
possibilities.
However, one thing seems to be clear about very early times: at about
kT = 10
19 GeV and 10
−43 s the description of gravity by general relativity is no
279
think of nucleons condensing from a quark gluon plasma at this time, about 10
−6 s.
The stuff of the universe before this time is a dense hot plasma of quarks and gluons
and leptons (e and μ and τ and their neutrinos) and many photons (Quigg 2006).
High energy particle experimentalists are now trying to create quark gluon plasmas
at accelerator laboratories by colliding heavy nuclei. The results are interesting for
their relevance to early universe physics.
A question under current debate is why the universe appears to be composed
almost entirely of matter and very little anti-matter. One might naively expect a
mixture of roughly 50% matter and 50% anti-matter, but this is definitely not observed
(Moskowitz 2019; Peebles 1993).
18.6 Inflation
Recall the horizon or isotropy puzzle, which we discussed in Sect. 17.3: it is difficult
to see how the universe could have been as homogeneous and isotropic as it appears to
have been at the time of decoupling. But also recall that we noted in Exercise 17.5 that
the exponentially expanding de Sitter model universe has no horizon. Many theorists
believe that a period of very rapid expansion of the universe, described roughly by
the de Sitter model, provides the best resolution of the horizon puzzle; this very rapid
expansion is called inflation. It is postulated to have occurred well before the quark
gluon plasma era, say at about 10
−36 s. There are many versions of inflation theory,
and it is better to consider it a general scenario rather than a single theory. Most
versions postulate a scalar field called the inflaton as the dominant ingredient of the
universe. It is now the most widely accepted solution of the horizon puzzle and we
will discuss it in Chap. 19. It is also relevant to the spectrum of the CMB radiation,
which provides an observational test (Freedman 2006; Linde 2007).
The end of the inflation era is widely called reheating, at which time the particles
and fields that later filled the universe were somehow formed after inflation. There
is little observational information concerning this transition, but much theoretical
speculation (Kofman 1996).
18.7 Planck Era
Finally we run the clock backwards for the final time to such high temperature and energy that we simply do not know what happens but can only make
informed guesses. Perhaps interesting and strange things happen when the temperature approaches kT = 10
17 GeV, at which time it is believed by many theorists
that the strong, electromagnetic and weak forces become equal. There are many
possibilities.
However, one thing seems to be clear about very early times: at about
kT = 10
19 GeV and 10
−43 s the description of gravity by general relativity is no