The Expansion of the universe
Throughout centuries humans needed to examine , investigate, find out, postulate a theory or just get to know how everything in the universe just begun, how the universe we is made or is it created by god or what really happened. Physicist and cosmologists brought up dozens of theories and today we rely on or just tend to believe on the big bang theory. And thus going further relying on this theory when we think ahead, we wanted to know about the shape of the universe and going further in the journey we wanted to know whether the size of the universe is the same or is getting smaller or is it getting larger and larger, thinking a step ahead, it is getting larger (expanding) then is it expanding at a constant rate or is it expanding with an accelerating rate.
In 1929 Edwin Hubble suggested that the universe is expanding. In 1929, the article published by Edwin Hubble investigated the relation between distance and radial velocities of interstellar objects. He obtained this remarkable observational relation from the data he gathered from 24 nearby galaxies. Although the readings he took were quite off according to the present, it was comparative accurate than what the mankind was capable during those days. He saw there is a linear relationship between those two quantities and thus proposed the law 𝑣=𝐻0𝑑 where 𝐻0 is the Hubble’s constant.
The Hubble’s constant is usually given in the units’ km/s/Mpc. The Hubble’s constant is a constant that changes with time (we can use the Friedman’s equation to further understand about this statement). At present it is about 70 km/s/Mpc. So, we calling this a constant is little misleading. Hence the cosmologists call this the Hubble’s Parameter.
Expansion and Redshift
Redshift is a phenomenon of which the wavelength of the electromagnetic radiation from an object is increased. When we consider it astronomically, let’s say the universe is expanding, so we can say that the objects are going away from us. So we can realize according to Doppler’s law, that the wavelength should be increased. And thus the radiations should be red shifted. Actually in the real observations we see there is redshift so we can say the objects are moving away from us. So the space itself is expanding. Therefore it is very solid evidence to support Hubble’s idea about expansion of the universe.