6.4 KiB
| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Cosmic age problem | 2/2 | https://en.wikipedia.org/wiki/Cosmic_age_problem | reference | science, encyclopedia | 2026-05-05T09:33:53.430171+00:00 | kb-cron |
=== Late 1990s: probable solution === The age problem was eventually thought to be resolved by several developments between 1995 and 2003: firstly, a large program with the Hubble Space Telescope measured the Hubble constant at 72 (km/s)/Mpc with 10 percent uncertainty. Secondly, measurements of parallax by the Hipparcos spacecraft in 1995 revised globular cluster distances upwards by 5-10 percent; this made their stars brighter than previously estimated and therefore younger, shifting their age estimates down to around 12-13 billion years. Finally, from 1998 to 2003 a number of new cosmological observations including supernovae, cosmic microwave background observations and large galaxy redshift surveys led to the acceptance of dark energy and the establishment of the Lambda-CDM model as the standard model of cosmology. The presence of dark energy implies that the universe was expanding more slowly at around half its present age than today, which makes the universe older for a given value of the Hubble constant. The combination of the three results above essentially removed the discrepancy between estimated globular cluster ages and the age of the universe. More recent measurements from WMAP and the Planck spacecraft lead to an estimate of the age of the universe of 13.80 billion years with only 0.3 percent uncertainty (based on the standard Lambda-CDM model), and modern age measurements for globular clusters and other objects are currently smaller than this value (within the measurement uncertainties). A substantial majority of cosmologists therefore believe the age problem is now resolved. New research from teams, including one led by Nobel laureate Adam Riess of the Space Telescope Science Institute in Baltimore, has found the universe to be between 12.5 and 13 billion years old, disagreeing with the Planck findings. Whether this stems merely from errors in data gathering, or is related to the as yet unexplained aspects of physics, such as Dark Energy or Dark Matter, has yet to be confirmed.
== Dynamical modeling of the universe == In this section, we wish to explore the effect of the dynamical modeling of the universe on the estimate of the universe's age. We will assume the modern observed Hubble value
H
0
≈
70
{\displaystyle H_{0}\approx 70}
km/s/Mpc so that the discussion below focuses on the effect of the dynamical modeling and less on the effect of the historical accuracy of the Hubble constant. The 1932 Einstein-de Sitter model of the universe assumes that the universe is filled with only matter and has vanishing curvature. This model received some popularity in the 1980s and offers an explicit solution for the scale factor (see, e.g., D. Baumann 2022)
a
(
t
)
=
(
t
t
0
)
2
/
3
,
{\displaystyle a(t)=\left({\frac {t}{t_{0}}}\right)^{2/3}~,}
where
t
0
{\displaystyle t_{0}}
is the universe's current age. This then implies that the age of the universe is directly related to the Hubble constant
t
0
=
2
3
H
0
−
1
.
{\displaystyle t_{0}={\frac {2}{3}}H_{0}^{-1}~.}
Substituting in the Hubble constant, the universe has an age of
t
0
≈
9
{\displaystyle t_{0}\approx 9}
billion years, in disagreement with, e.g., the age of the oldest stars. If one then allows for dark energy in the form of a cosmological constant
Λ
{\displaystyle \Lambda }
in addition to matter, this two-component model predicts the following relationship between age and the Hubble constant
t
0
=
2
3
H
0
−
1
⋅
1
Ω
Λ
sinh
−
1
(
Ω
Λ
Ω
m
)
.
{\displaystyle t_{0}={\frac {2}{3}}H_{0}^{-1}\cdot {\frac {1}{\sqrt {\Omega _{\Lambda }}}}\sinh ^{-1}\left({\sqrt {\frac {\Omega _{\Lambda }}{\Omega _{m}}}}\right)~.}
Plugging in observed values of the density parameters
(
Ω
Λ
≈
0.7
,
Ω
m
≈
0.3
)
{\displaystyle (\Omega _{\Lambda }\approx 0.7,~\Omega _{m}\approx 0.3)}
results in an age of the universe
t
0
≈
14
{\displaystyle t_{0}\approx 14}
billion years, now consistent with stellar age observations.
== References ==
== External links == http://map.gsfc.nasa.gov/universe/uni_age.html