Cosmic Age Test In Inhomogeneous Cosmological Models Mimicking LambdaCDM On The Light-cone

In the usual evolving cosmic models, cosmic age is defined to be the scale factor going from 0 to its present value. For some cosmological model, for example Newton's cosmological model, the rank model and the steady cosmological model, the cosmic age is of no sense. Usually, Hubble age is the reliable up band of the cosmic age and it can be used to estimate the cosmic age. If we look back in time, the cosmic density is increasing. By some finite time t 0, the cosmic density is increasing to be infinite. If we set the cosmic age to be 0 when its density is infinite, t 0 is the cosmic age. So our universe has a finite age. Different cosmological models will give different cosmic age. Which cosmological model is better in describing our universe? We must compare the prediction of the models with the astrophysical observation. The model which can match the astrophysical observation well is better than others. Cosmic age is one kind of quantities which can be used to compare with the experiment.Since cosmic age can not be measured directly, what is measured is the age of the old object. If we assume the object is formed at time of t 1 and its age at present time isÏ„. So the cosmic age is t₀ = t₁+Ï„.The object is very old, so t₁<<Ï„. We can useÏ„to estimate the cosmic age. Since Rutherford, people began to use radioelement to measure the age of the remnant of the old object. Since the cosmic age is about 10Ga, so the life of the radioelement that were used to measure the cosmic age must have the same dimension. The radioelement that were used to measure the cosmic age are (233)_Th(life timeÏ„=20.3Ga);(235)^U (Ï„=1.02Ga);(238)^U (Ï„=6.45Ga). Since 1980s, the cooling of the neutron star is used to conclude the age of the Milk Way. At the beginning of the neutron star formation, the temperature in the neutron star is still very high. So it can give off the light. With the time pass by, the temperature falls. The luminosity of the neutron star is depressed. So the dimmer the neutron star is, the older it is. As the cooling of the neutron star is slower than the burning of the nuclei, the age of the dim neutron star is the age of the star. For this reason, the age of the Milk Way can be estimated by the dimmest neutron star in it. The more important thing is the age of the globular cluster. The globular cluster is one of the oldest objects in the Milk Way. Before we use the age of the Milk Way to estimate the age of the universe, we should calculate the formation time of the Milk Way. It is manifested that the impact of the formation time of the Milk Way is not very significant.Different cosmological models will give different range of the cosmic age. We compare the age of the LambdaCDM model and the LTB model. We find the age of the LTB model is 2 years younger than that of the LambdaCDM model.