280
18 A Brief Historical Overview of the Universe
longer valid since we must take account of quantum effects. Indeed, according to
general ideas of quantum theory spacetime itself undergoes large quantum fluctuations and is not describable in classical terms (Adler 2010). This time period is called
the Planck era since Planck was the first to realize that the fundamental constants
h, c, G define a natural scale; this very small scale is likely to be the relevant one for
this earliest phase of the universe.
At this point we must finally give up on running the cosmic clock backwards,
since we do not have a believable quantum theory of gravity. We likely do not even
know if times earlier than the Planck time have meaning. We will discuss some basic
concepts and speculations concerning quantum theory and gravity and the Planck
scale in Chap. 19.
Exercises
There are none of the usual exercises for this descriptive and qualitative chapter.
The reader interested in more information may read Weinberg’s well-known little
book The First Three Minutes, which is clear and informative but a little out of
date (Weinberg 1988). Another source of more recent information is Wikipedia; it
contains much information, but since it is not peer reviewed there is no guarantee of
its accuracy. More dependable discussions are in the readable undergraduate text by
Liddle (2003) and the authoritative text by Peebles (1993).
18 A Brief Historical Overview of the Universe
longer valid since we must take account of quantum effects. Indeed, according to
general ideas of quantum theory spacetime itself undergoes large quantum fluctuations and is not describable in classical terms (Adler 2010). This time period is called
the Planck era since Planck was the first to realize that the fundamental constants
h, c, G define a natural scale; this very small scale is likely to be the relevant one for
this earliest phase of the universe.
At this point we must finally give up on running the cosmic clock backwards,
since we do not have a believable quantum theory of gravity. We likely do not even
know if times earlier than the Planck time have meaning. We will discuss some basic
concepts and speculations concerning quantum theory and gravity and the Planck
scale in Chap. 19.
Exercises
There are none of the usual exercises for this descriptive and qualitative chapter.
The reader interested in more information may read Weinberg’s well-known little
book The First Three Minutes, which is clear and informative but a little out of
date (Weinberg 1988). Another source of more recent information is Wikipedia; it
contains much information, but since it is not peer reviewed there is no guarantee of
its accuracy. More dependable discussions are in the readable undergraduate text by
Liddle (2003) and the authoritative text by Peebles (1993).