These results are robust – data from any one method can be removed without compromising the constraints – and they are not substantially weakened by dropping the assumption of spatial flatness." The use of Hubbles law allows us to map the distribution of galaxies and clusters of galaxies far away from us. This implies that the Universe began accelerating at redshift z ∼ 0.4 and age t ∼ 10 Gyr. The recession-distance relationship is interpreted as an overall expansion of the. v H x d where v is the galaxys radial outward velocity, d is the galaxys distance from Earth, and H is the constant of proportionality called the Hubble constant. He interpreted the redshift as being caused by the receding velocity of the galaxies. Hubble compared the distances to galaxies to their redshift and found a linear relationship. 44: "Taken together, all the current data provide strong evidence for the existence of dark energy they constrain the fraction of critical density contributed by dark energy, 0.76 ± 0.02, and the equation-of-state parameter, w ≈ −1 ± 0.1 (stat) ☐.1 (sys), assuming that w is constant. Hubble's Law of cosmological expansion was first formulated by Edwin Hubble in 1929. When the redshift is small (much less than 1), then we can approximate the velocity of the moving object that is emitting light with the equation. But the stretching or compressing of wavelengths because of the relative motion of two objects was. During the radiation-dominated era, a(t) ∝ t 1/2 during the matter-dominated era, a(t) ∝ t 2/3 and for the dark-energy-dominated era, assuming w = −1, asymptotically a(t) ∝ exp(Ht)." The cosmological redshift and blueshift was discovered by Edwin Hubble about a century ago. The evolution of the scale factor is controlled by the dominant energy form: a(t) ∝ t 2/3(1+w) (for constant w). 6: "The Universe has gone through three distinct eras: radiation-dominated, z ≳ 3000 matter-dominated, 3000 ≳ z ≳ 0.5 and dark-energy dominated, z ≲ 0.5. The relative expansion of the universe is parametrized by a dimensionless scale factor a, is ≈70.88 km s −1 Mpc −1 (The Hubble time is 13.79 billion years).
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