World age

As a world age in the modern is cosmology , the age of the visible universe called. Astronomic it is since the Big Bang past time and is according to current knowledge - which is also the data of the Planck space telescope includes - ${\ displaystyle t_ {0}}$

(13.787 ± 0.020) billion years or (4.354 ± 0.007) × 10 ¹⁷ seconds.

This currently longest researched period contrasts with the physically shortest period, the Planck time (approx. 10 ⁻⁴³ seconds). The time continuum extends over about 60 powers of ten .

World age and Hubble constant

The age of the world is approximately the reciprocal of the Hubble constant , which can be determined from the increasing redshift of distant galaxies : ${\ displaystyle t_ {0}}$ ${\ displaystyle H_ {0}}$ ${\ displaystyle z}$

{\ displaystyle t_ {0} \ approx {\ frac {1} {H_ {0}}}}

(Details see Hubble time )

The underlying phenomenon of the expansion of space was discovered in the 1920s by Carl Wilhelm Wirtz and Abbé Georges Lemaître .

In 1929, the US astronomer Edwin Hubble and his colleagues found that there is an approximately linear relationship between expansion and distance: the greater the distance of the galaxy being observed , the greater the apparent rate of cosmic expansion . ${\ displaystyle {\ dot {a}}}$ ${\ displaystyle r}$

{\ displaystyle H_ {0} \ approx {\ frac {\ dot {a}} {a}} = {\ frac {c \, z} {r}}}

at the speed of light . ${\ displaystyle c}$

However, for this fundamental quantity of cosmology, Hubble received the far too high value of 500 km s ⁻¹ Mpc ⁻¹ , which would have meant a world age of only 2 billion years. It was soon recognized that this contradicted geological knowledge, in particular the determination of the age of rocks, which was already possible at that time .

Development of the estimates

Since 1950, the assumed age of the world has moved between 4 and 20 billion years. Within a few years the value of the Hubble constant could be corrected to around 50 to 100 km s ⁻¹ Mpc ⁻¹ . The related cosmologist debate began around 1970 and lasted through the late 1990s.

More recent methods provided values between 72 and 77 km s ⁻¹ Mpc ⁻¹ for H ₀ , which would limit the fluctuation range of the world age to 13.3 to 14 billion years. Today, however, it is assumed that the Hubble “constant” changes over time, which is why one speaks of the Hubble parameter . However, whether the cosmic expansion will slow down or accelerate in the long term has not yet been finally clarified. This topic is related to fundamental questions about the structure of the cosmos , especially its geometry (flat versus hyperbolic universe) and the proportions of dark matter and dark energy . The most recent value published in 2016 for is 67.74 ± 0.46 (km / s) / Mpc. ${\ displaystyle H_ {0}}$

Individual evidence

↑ ^a ^b Planck Collaboration: Planck 2015 results. XIII. Cosmological parameters . In: Astronomy & Astrophysics . 2016, arxiv : 1502.01589 .
↑ Planck Collaboration: Planck 2018 results. VI. Cosmological parameters . See PDF, page 15, Table 2, Age / Gyr, last column. In: Astronomy & Astrophysics . 2018, arxiv : 1807.06209 .

[PlanckI-1] Planck Collaboration: Planck 2015 results. XIII. Cosmological parameters . In: Astronomy & Astrophysics . 2016, arxiv : 1502.01589 .

[Planck_2018-2] Planck Collaboration: Planck 2018 results. VI. Cosmological parameters . See PDF, page 15, Table 2, Age / Gyr, last column. In: Astronomy & Astrophysics . 2018, arxiv : 1807.06209 .