16.1 Diverse Cosmological Observations
251
in measuring the redshift the time rate dz/ dt might be measurable in the near future
and thus yield information on the Hubble constant and the present matter density
(Martins 2016; Eikenberry 2019).
There are many pulsars whose timing is being monitored to extreme accuracy. If a
long wavelength gravitational wave passes by a number of such pulsars it will move
them slightly and alter the timing of the electromagnetic pulses we receive from
them; a system of pulsars can thus be used as a gravitational wave detector. This
could be especially interesting for wavelengths much longer than can be detected
using earth-based detectors such as LIGO or even LISA. Such measurements may
become feasible in the near future (Lommen 2017).
16.2 Cosmological Parameter Values
In Table 16.1 we list approximate values for some important cosmological parameters. They are obtained from analyses of a variety of observation, some of which
are discussed in the previous section. Some of the values are fairly rough estimates.
Some are continually being remeasured, and some remain controversial—such as
the Hubble constant. (It may be helpful to remember that 1 Mpc = 3.09 × 10
22 m.)
Table 16.1 Values of diverse cosmological parameters and numbers
Hubble constant (our own error estimate)
H 0 = 70 ± 5 (km/s)/Mpc
Hubble time
T H = 1/H 0 = 1.40 × 10 10 year
Cosmological constant
= (0.964 × 10 10 ly)
−2
Asymptotic Hubble function
H ∞ =
c 2 /3 = 59 (km/s)/Mpc
Asymptotic Hubble time, de Sitter time
T dS = 1/H ∞ = 1.67 × 10 10 year
Age of the universe
t 0 = 1.35 × 10 10 year
Deceleration parameter
q 0 = −0.55
Cold dark matter energy density ratio, present
dmo = 0.25
Baryonic matter energy density ratio, present
b0 = 0.05
Total matter energy density ratio, present
m0 = 0.30
Cosmological constant energy density ratio, present
V0 = 0.70
Radiation energy density ratio, at present
r 0 = 3.8 × 10 −5
Curvature effective energy density ratio, present
k0 = 0
Total energy density ratio according to GR
T = m + V + k = 1.0
Critical energy density
ρ cr = 8.28 × 10 −10 J/m 3
Time of matter and dark energy density equality
t e = 9.9 × 10 9 year
Time of decoupling
t d = 380,000 year
251
in measuring the redshift the time rate dz/ dt might be measurable in the near future
and thus yield information on the Hubble constant and the present matter density
(Martins 2016; Eikenberry 2019).
There are many pulsars whose timing is being monitored to extreme accuracy. If a
long wavelength gravitational wave passes by a number of such pulsars it will move
them slightly and alter the timing of the electromagnetic pulses we receive from
them; a system of pulsars can thus be used as a gravitational wave detector. This
could be especially interesting for wavelengths much longer than can be detected
using earth-based detectors such as LIGO or even LISA. Such measurements may
become feasible in the near future (Lommen 2017).
16.2 Cosmological Parameter Values
In Table 16.1 we list approximate values for some important cosmological parameters. They are obtained from analyses of a variety of observation, some of which
are discussed in the previous section. Some of the values are fairly rough estimates.
Some are continually being remeasured, and some remain controversial—such as
the Hubble constant. (It may be helpful to remember that 1 Mpc = 3.09 × 10
22 m.)
Table 16.1 Values of diverse cosmological parameters and numbers
Hubble constant (our own error estimate)
H 0 = 70 ± 5 (km/s)/Mpc
Hubble time
T H = 1/H 0 = 1.40 × 10 10 year
Cosmological constant
= (0.964 × 10 10 ly)
−2
Asymptotic Hubble function
H ∞ =
c 2 /3 = 59 (km/s)/Mpc
Asymptotic Hubble time, de Sitter time
T dS = 1/H ∞ = 1.67 × 10 10 year
Age of the universe
t 0 = 1.35 × 10 10 year
Deceleration parameter
q 0 = −0.55
Cold dark matter energy density ratio, present
dmo = 0.25
Baryonic matter energy density ratio, present
b0 = 0.05
Total matter energy density ratio, present
m0 = 0.30
Cosmological constant energy density ratio, present
V0 = 0.70
Radiation energy density ratio, at present
r 0 = 3.8 × 10 −5
Curvature effective energy density ratio, present
k0 = 0
Total energy density ratio according to GR
T = m + V + k = 1.0
Critical energy density
ρ cr = 8.28 × 10 −10 J/m 3
Time of matter and dark energy density equality
t e = 9.9 × 10 9 year
Time of decoupling
t d = 380,000 year