Observational Evidence for the Big Bang

It All Started With a Bang 

The majority of evidence suggests that the universe was created 13.7 billion years ago; it started from an infinitely dense and infinitely small singularity. The universe expanded and created the first particles, elements and eventually stars, galaxies and planets. This theory is called the Big Bang theory. The opposing, less supported theory is called the Steady State theory. These two are the predominant competing ideologies of how the universe began. The latter is aptly named, for it suggests that the universe has been in a ‘steady’ state since the beginning. There is much evidence that suggests the Big Bang theory is more suitable; this blog will discuss the three most important pieces. 

http://cosmictimes.gsfc.nasa.gov/online_edition/1955Cosmic/origin.html

The first is called the Red Shift. In 1912, it was determined that the majority of galaxies were moving away from us, thus the universe is expanding. When the universe expands the light expands with it, shifting the wavelength of light towards the red end of the spectrum, hence the name ‘Red Shift’. The common analogy used to explain this is the sound waves of a siren. When an ambulance gets closer and closer to you the sound it makes becomes higher pitch; conversely when it moves farther and farther away the siren emits a lower pitch frequency. The same is true for light, except instead of pitch it changes color. 

http://calgary.rasc.ca/redshift.htm

The second piece of evidence is the distribution of elements. Physicists have calculated what the elemental make-up of the universe might look like moments after a big bang, roughly  ¾ hydrogen and ¼ helium with trace amounts of a few other elements. This matches what has been measured in existing stars.

http://wmap.gsfc.nasa.gov/universe/bb_cosmo_fluct.html




https://www.youtube.com/watch?v=xtrYF_hxxUM

The third piece of evidence is called Cosmic Microwave Background Radiation, or CMB. In the 1960’s Penzias and Wilson were building a radio receiver and came across a source of excess noise.  Eventually it was realized that the noise was a result of leftover radiation from the big bang. Nearer to the Big Bang this radiation was significantly hotter (thousands of degrees K). Today CMB is only 2.725 degrees above absolute zero which is why it shows up as microwaves on the electromagnetic spectrum.

If you are interested in the Big Bang Theory in a quick snapshot take a look at this video. 

Sources: 

https://storiesbywilliams.com/2013/12/08/evidence-for-the-big-bang/

http://map.gsfc.nasa.gov/universe/bb_tests_cmb.html

https://www.scientificamerican.com/article/what-is-the-cosmic-microw/