In 1842 the Austrian scientist Doppler unveiled the frequency shift phenomenon.
An example of it is the siren of a passing by emergency vehicle, the pitch of its siren changes. Similarly the frequency of a light wave decreases when the distance from the observer to light source is increasing, a phenomenon called red shift; a red shift is a reduction of the frequency that amounts to a loss of energy as compared to the energy emitted by the source.
In 1915 Einstein published his general relativity theory; in 1917 he applied his theory to the Universe and introduced the so-called cosmological constant to make it comply with a static Universe, as was thought to be at the time. It turned out that the following experiments showed such modification was wrong and he later stated it was its "biggest blunder".
In 1927, Lemaitre, a Belgium scientist and Catholic priest published a paper linking mathematically Einstein General Relativity to an expansion of the Universe.
And a couple years later in 1929 Hubble, an outstanding astronomer, discovered far away galaxies are emitting red shifted lights, and the farther the galaxies the redder the shift.
Applying the Doppler shift to Huble's measures, by 1930, most scientists concluded the Universe is expanding and in addition the more distant the galaxies the faster their recession with respect to each other.
Then going backward in time the Universe had to start from a dimensionless point given the name Big bang. As of today this is confirmed by the red shift observed on the so-called Cosmic Microwave Background, which is now considered to have been emitted soon after the Big bang.
A Universe that does not expand
Whether in favor of big-bang or not, in all logic the only alternative, on which we could all agree, is that there should be no Universe at all; there should be no time, no space, not a thing whatsoever; and to render things even more confusing, Einstein's 1917 theory, which is advocating a still Universe, is as true mathematically as his 1915 theory, in which the Universe was expanding instead.
In the end we're all caught between a rock and a hard place.
Getting back to the redshifts used in science to justify expansion, considering instead the gravity surrounding far away material objects, galaxies and Cosmic background, these very redshifts justify a non expanding Universe.
In this drawing a blue heavy quazar on the right is represented; its gravity is affecting its surrounding space-time, as described by Einstein's general relativity, and graphically represented here as usually done with a stretched grid.
The "DISTANCE quasar earth" represented by the top arrow "Dqe" remains constant in this interpretation.
The quasar is emitting a blue light of frequency "F1" which through its own gravity is shifted toward the red frequency "F2" before hitting the observer eye at left on Earth.
Because its gravity is small with respect to the far away objects and galaxies considered, our Earth doesn't annihilate or compensate in reverse the redshifts observed. And because the redshifts observed remain constant, the red and blue shifts produced by our Earth's local motions are negligible. An observed red shift, instead of indicating the object is speeding away from us, may indicate a large body of matter remaining more or less at a constant distance from us.
And why would far remote galaxies recess faster from each other than close by galaxies do? The question actually being why would the farther the galaxies the redder the shift? In the above drawing, the closer to the quasar, the higher the gravity the less the red shift, and the farther from it the less the gravity the higher the redshift; gravity is providing a straight forward, simple, physical answer to that question; in comparison the expansion, supposedly occurring in accordance to the measured red shifts, involves a mysterious dark energy and requires a deviation of the gravitational laws from general relativity; namely speeds faster than light.
Let's face it, gravity's explanation goes along this Simplicity is the ultimate sophistication saying from Leonardo da Vinci.
Nowadays in science, the galaxies are no longer moving away from each other, space in between the galaxies instead is expanding; so the question becomes: How are space increases related to distances increases, the later creating the redshifts? When the emergency car is departing from me, even though the distance between it and me increases, I know the road and the space it occupies is not increasing in length. This new inconsistency is elegantly solved considering gravity.
Gravity has the advantage to dismiss such controversies and to provide a physical cause to the redshift measures; gravity is a cause at work right now everywhere and measurable; the cause of Big bang is non measurable as it supposedly occurred 13.8 billions years ago.
A major drawback to a non expanding Universe is our human conviction that all things including the Universe must have a beginning. This conviction of ours no doubts is due to our human very thinking as that thinking, because it did not occur before our birth, had seemingly a begining; yet this thinking of ours is integral part of our material body; and that body had a physical cause that is the union of our parents, followed by the pregnancy of our respective mothers; as such our conviction that things have a beginning, in the sense of coming out of nothing, must be shaken-off!
More recently, the Big Bang is now preceded by “inflation”, which itself had no beginning, even in science Big Bang lost its charm.
In this drawing a blue heavy quazar on the right is represented; its gravity is affecting its surrounding space-time, as described by Einstein's general relativity, and graphically represented here as usually done with a stretched grid.