Observations leading to the Big Bang theory

(1) Expansion of the visible universe.
The discovery of the red shift in the visible spectrum of our surrounding stars and galaxies revealed the universe is generally expanding.

Redshifts for galaxies and brown dwarfs measured around the infrared 2 micron wavelength during the 2MASS (2 Micron All-Skye) survey by a consortium of IPAC, NASA and NSF.
How much do we know about the universe? Auguste Comte, a French philosopher, wrote in 1825 that all we would ever know about the stars is that they are points of light we could never reach. However, around the same time, Joseph von Fraunhofer determined the chemical composition of a star by analyzing its light using a prism and spectroscope. Ian D. Bush composed a rhyme about this:

Twinkle, twinkle little star
I don’t wonder what you are
For by spectroscopic ken
I know that you are hydrogen

Redshifts for the hydrogen absorption line spectrum

From this we not only know the chemical composition of the outer fringes of a star, but, when it was discovered that the spectral lines of most faraway light sources were shifted towards the red end of the spectrum, we could also determine the speed of those sources relative to our observation post on Earth.

George Lemaitre proposed his idea of a universe expanding from a primeval atom as a solution of Einstein’s general relativity formulas. He published his paper as early as 1927 . It is interesting to note that he was an ordained priest and taught at the Catholic University of Leuven in Belgium. He was dedicated to his religion as well as to science, becoming president of the Pontifical Academy of Sciences in 1960.

Fred Hoyle, a noted English astronomer, was the proponent of a static universe, as were Eddington, De Sitter and Einstein. Hoyle mocked Lemaitre’s idea by giving it the pejorative name of “the Big Bang.” It was a catchy name however, and today it is used and the theory adhered to by the established astrophysical community. In reality the Big Bang theory explains many observations and is considered the best fitting model of our world.

It was Hubble who discovered the tool to quantify the expansion by means of the redshift of the visible electromagnetic spectrum of stars and galaxies.

(2) the Cosmic Microwave Background (CMB) radiation.
A background noise in the microwave portion of the electromagnetic spectrum is interpreted as the last remnant of the Big Bang.

Credit: NASA / WMAP Science Team
Temperature fluctuations in the CMB, measured over nine years by NASA's WMAP team
The subsequent detection of the Cosmic Microwave Background radiation is touted as very strong supporting evidence of the Big Bang. According to the theory, this is the last thing soon after the big explosion that we can see, and it marks the end of the opaque plasma stage associated with the generation of matter: the synthesis of atoms from the elementary particles (quarks, leptons and bosons). Photons could escape and form the image from 13.8 billion years ago we now observe.

(3) Einstein embraced the theory.
One of the greatest scientists in the history of mankind subscribed to the theory.
Although Einstein initially believed in a steady state model he later embraced the Big Bang theory. His field equations were proven right time and again. His latest triumph came in 2016, when scientists were able to detect a gravity wave caused by the collision of two black holes. Admittedly the effect is minute and does not seem to affect our daily lives.

One of the early confirmations of Einstein’s general relativity theory and his field equations came when it was tested to describe the precession of Mercury’s orbit around the sun. Orbits of one celestial body around another are generally elliptical, where the more massive body resides in one of the two foci of the ellipse. This is called a Kepler orbit. Mercury’s orbit has a relatively high eccentricity: 0.2 (the Earth's orbit eccentricty is 0.02 and is closer to a perfect circle). The point on Mercury’s path closest to the Sun is called the perihelion. If no other planets were exerting gravitational pull on Mercury, this perihelion would always be the same point in space after each revolution. In reality the perihelion shows precession: after each revolution the perihelion is a little advanced from the previous. Using Newton's equations to calculate the precession as a result of all the surrounding planets could never completely explain its magnitude. Einstein’s prediction, that space is curved around massive bodies, closed the gap and triumphantly confirmed his field equations. The precession is measured by radar to be one sixths of a degree of arc per century or to be more precise 574.10 arc seconds per century. Of this 531.6” are caused by planetary pull. General relativity (Einstein’s field equations) added 42.98” for a total of 574.61”. Admittedly this is half a second too large, but that falls well within the accuracy of the radar measurements calculated as +/- 0.65

Credit: Marcia Stark, astrologer
Mercury is a small dot in retrograde transit before the sun

Created by the National Center for Supercomputing Applications (NCSA). Copyright 2016 Board of Trustees of the University of Illinois.
Mercury’s orbit around the sun (left) and the precession of the perihelion (right)

© Peter van Bemmel

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