Why Hubble is famous?

 

The topic of Expansion of the Universe doesn’t start without mentioning the name of the American Scientist Edwin Powell Hubble. He is considered as the father of observational cosmology for his significant contributions that revolutionized our understanding of the Universe. While everyone knows that he discovered that the Universe is expanding, and provided the evidence for Lemaitre’s model of ‘Primordial Soup’ [nascent version of the modern Big Bang Theory], there are peels of factoids which remain un-discussed. To start with, Hubble was not the first person to find observational evidence for the expansion of the Universe.

In 1920s, Vesto Slipher, another American astronomer, used spectra of stars to measure the velocities of nearby galaxies [during that time, galaxies were not well-defined]. His method of observation was based on Doppler Effect. Waves of light from a star moving toward Earth are compressed, shortening the wavelength and making the light bluer. Light waves from an object moving away from us are stretched, making the wavelength longer and the light redder. By measuring the lengthening or compression of the light waves from distant galaxies, Slipher was able to determine whether they were moving toward us or away from us and at what speed (Krauss & Scherrer, 2008). Slipher concluded that almost all the galaxies were moving away from us.

But Hubble, not Slipher, is credited with the discovery of expanding Universe. Well, this isn’t a scientific conspiracy, because Hubble did two things which justify his fame. Hubble determined the distances of the galaxies along with the velocities. And this extra parameter led to important implications:

1. First Hubble showed that galaxies were so far away that they really were independent collections of stars, just like our own galaxy
2. Second, he discovered that the velocity of recession of a galaxy is directly proportional to the distance of the galaxy. [The proportionality constant, Hubble Constant, gives the most reliable measurement for the age of the Universe.]

So, not only did he change the notion that our galaxy is the ‘island universe’ surrounded by eternity of void, he also gave results which match the theoretical expansion rates. His discoveries strengthen the view that in past there must have been something which caused the expansion to begin with, as proposed by Big Bang theory. Hubble also calculated this epoch of expansion to be around 2 billion years [current estimates are 13.75 billion years].

He had won many awards, including the Gold medal from Royal Astronomical Society (Ravindranath, 2009). Many would argue that he would have been a strong contender for the Nobel Prize, if Astronomy was considered a part of Physics, rather than a field of its own. In 1990, the Hubble Space Telescope (HST) was launched. HST is among the most powerful optical telescopes (more on that later).

 

Citations

Krauss, L. M., & Scherrer, R. J. (2008, March). The End of Cosmology. Scientific American.

Ravindranath, S. (2009, March). Edwin Powell Hubble. Resonance.