8.-DARK ENERGY. REDSHIFT OF TYPE IA SUPERNOVA

Several observations made of Type Ia supernovas lead to the suspicion that the universe expands quickly. This deduction is based on the fact that the distance obtained by redshift measurement is shorter than what it should be judging by the intensity of the light received (Type Ia supernovas all have the same absolute magnitude). The astrophysic proposes like cause of this quick expansion what denominates dark energy, even not discovered and that the model of the Living Universe makes unnecessary its introduction like we will see.

According to classic cosmology, the redshift observed for objects in the universe is due to the lengthening of photon wavelengths during their trip through the cosmos. This is usually expressed as 1 + z = λ_o / λ_e, where λ_o is the observed wavelength and λ_e the emitted wavelength.

The expansion dynamics of the universe is expressed by means of the expansion or scale factor a(t). We can define a(t₀) = 1, where t₀ is the present. The expansion factor may be used as a reference between the expansion at an instant t and current expansion by means of the equation R_h(t) = a(t) R_h0, where R_h0 is the current Hubble radius. The equation for the evolution of the expansion factor is the following:

(da(t)/dt)² - 8/3 π G ρ(R_h) a(t)² = constant     (8.1)

Depending on the evolution of the expansion factor, the redshift can be expressed as:

1 + z = a(t_o) / a(t_e)

The model proposed in this article enables the evolution of factor a(t) to be easily calculated without the need of solving equation (8.1); indeed, at any moment, according to this model, R_h(t) = c t, at the present R_h0(t) = c t₀, where a(t) = c t / c t₀, that is:

a(t) = H₀ t     (8.2)

Where H₀ is the current Hubble Constant.

The deceleration parameter q can be defined as:

q = - a(t) (d²a(t)/dt²)/(da(t)/dt)²     (8.3)

It is easy to see that in this model the deceleration parameter has a permanent value of zero. If the redshift study of Type Ia supernovas is carried out considering a model with a positive deceleration parameter, it is natural to interpret a null real parameter of deceleration, just as the Living Universe model proposes, as an accelerated expansion of the universe.

_{© Jorge Ales, 2002. http://www.livinguniverseweb.com}