Chapter 16
Some Properties of the LCDM Universe
Abstract In the last half century of so there have been great advances in cosmological observations, making cosmology a thriving mix of theory and observations. In
this chapter we will discuss how we understand from LCDM theory the expansion of
the universe, its age, and the behavior of its dominant constituents, the dark energy
and cold dark matter. We will also relate and compare the theory with the observed
values of various cosmological parameters such as the Hubble constant. Despite the
impressive agreement between theory and observation the basic physical nature of
the dark matter is not yet known.
16.1 Diverse Cosmological Observations
In its first half century relativistic cosmology was based on very few observations,
some of which we discussed in Chaps. 13 and 14. Sandage is quoted as saying that
observational cosmology was the search for two numbers, the Hubble constant and
the deceleration parameter (Sandage 1961). That viewpoint changed greatly in the
latter half of the twentieth century and the early twenty- first century. The field of
observational cosmology exploded and is now in the mainstream of physics and
astronomy; there are many ways being used to gather information about the largescale universe, many researchers are doing observations and theory and simulations,
and there are many references to their work. This book is about the ideas and basic
mathematics of the theory so we can only give a sketch of the observations being done
and the kind of information they give us about the universe. Fortunately there are
numerous references for the interested reader on the observations; a rather extensive
set of references is given in the NASA website (NASA 2019).
Here are just some examples of interesting ways to gather information about the
large-scale universe:
1. Velocity and distance measurements of galaxies and supernovas: Since Hubble’s
work early in the twentieth century a great deal of effort has gone into extending
the distance scale to obtain more accurate values for the Hubble constant, the
most important number in cosmology, and also the deceleration parameter that
we discussed in Chap. 13.
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
R. J. Adler, General Relativity and Cosmology, Graduate Texts in Physics,
https://doi.org/10.1007/978-3-030-61574-1_16
247
Some Properties of the LCDM Universe
Abstract In the last half century of so there have been great advances in cosmological observations, making cosmology a thriving mix of theory and observations. In
this chapter we will discuss how we understand from LCDM theory the expansion of
the universe, its age, and the behavior of its dominant constituents, the dark energy
and cold dark matter. We will also relate and compare the theory with the observed
values of various cosmological parameters such as the Hubble constant. Despite the
impressive agreement between theory and observation the basic physical nature of
the dark matter is not yet known.
16.1 Diverse Cosmological Observations
In its first half century relativistic cosmology was based on very few observations,
some of which we discussed in Chaps. 13 and 14. Sandage is quoted as saying that
observational cosmology was the search for two numbers, the Hubble constant and
the deceleration parameter (Sandage 1961). That viewpoint changed greatly in the
latter half of the twentieth century and the early twenty- first century. The field of
observational cosmology exploded and is now in the mainstream of physics and
astronomy; there are many ways being used to gather information about the largescale universe, many researchers are doing observations and theory and simulations,
and there are many references to their work. This book is about the ideas and basic
mathematics of the theory so we can only give a sketch of the observations being done
and the kind of information they give us about the universe. Fortunately there are
numerous references for the interested reader on the observations; a rather extensive
set of references is given in the NASA website (NASA 2019).
Here are just some examples of interesting ways to gather information about the
large-scale universe:
1. Velocity and distance measurements of galaxies and supernovas: Since Hubble’s
work early in the twentieth century a great deal of effort has gone into extending
the distance scale to obtain more accurate values for the Hubble constant, the
most important number in cosmology, and also the deceleration parameter that
we discussed in Chap. 13.
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
R. J. Adler, General Relativity and Cosmology, Graduate Texts in Physics,
https://doi.org/10.1007/978-3-030-61574-1_16
247