1. The 3 proofs of the Big Bang

2. Proof 1. An expanding universe
Edwin Hubble, in the 1920’s, hypothesized that the Universe was expanding, and he measured the distance between galaxies and the speed at which they were moving apart.
If galaxies are expanding, then galaxies must have been closer together in the past. If you keep going back in time, then eventually, everything must have started with a singularity.
This idea led directly to the proposal of the Big Bang Theory in by Georges Lemaitre.

3. Things are not expanding at the same rate: objects that are further away are moving away from us MORE QUICKLY than objects that are closer to us.
You can model this Expanding Universe with a simple balloon. Let’s do that now.

4. Hubble's law: Galaxies are moving away from each other, and the further away the galaxy, the faster it is moving away from us.

5. The Doppler Effect
Think about the sound a siren makes as it approaches you and then passes you. What you are hearing is the Doppler Effect.
The Doppler Effect is the change in wavelength of a wave as an object is moving towards or further away from an observer.
If an object is moving towards you, the wavelength shortens (gets squished) and the sound goes up in pitch.
If an object is moving away from you, the wavelength lengthens (gets stretched) and the sound goes down in pitch.

7. Red Shifted Light Spectrum
The Doppler Effect refers to sound and LIGHT wavelengths.
Using a Spectroscope, astronomers can look at the light wavelengths coming from a star.
Every star has a different light spectrum, depending on the concentration of elements in that star. Here is what our sun’s light spectrum looks like.
The little black lines represent the presence of specific elements.

8. However, if a star is moving away from us, the wavelengths of light would lengthen, just like what happens to sound as a police car moves away from us.
If a star happened to be moving towards us, the wavelengths would shorten.
Almost all stars and galaxies appear to be moving away from us.

9. When a galaxy or star is moving away from us, the light is RED-SHIFTED on the spectrum, meaning the element lines (the black ones) are shifted towards the red end of the spectrum.
BLUE-SHIFTING occurs if a star or galaxy is moving towards us.
By studying the incoming light of stars and galaxies over time, scientists are able to say that galaxies are expanding from one another at an ever increasing rate.
THUS, PROOF 1 of the Big Bang Theory is the Law of Expanding Galaxies.

11. Proof 2. Cosmic Microwave Background Radiation
In 1963, scientists discovered that anywhere they looked in space, there was Cosmic Microwave Background Radiation. Initially, they struggled to explain this phenomenon.
For the first years of the Universe, it was too hot for light to escape the plasma that existed everywhere.
When the temperature cooled enough, a massive “blast” of light from everywhere, all at once, started travelling through space. For a period, the Universe was actually orange.
Over time, these light wavelengths got Red-Shifted as the Universe was expanding. They stretched so far, that the light wavelengths moved beyond visible light, into microwaves, which appear black to human eyes.
Thus, the Universe became dark.

12. In 1992, the COBE satellite was able to take this picture of the Universe’s CMBR.

13. In 2003, the WMAP satellite took this image:

14. And finally in 2013, the Planck satellite took this one:

15. The red areas represent areas of greater density, areas where more gas existed and allowed stars, planets and galaxies to form.
Blue areas represent less dense areas, where there was not enough matter to form any solid objects. These are areas of empty space.
Proof #2. Cosmologists predicted that there would be “leftover” microwaves in space. The Cosmic Microwave Background Radiation (CMBR) data proved their hypothesis and is the 2nd major proof of the Big Bang.

16. Proof 3. Presence of light elements
The presence of enormous amount of Hydrogen, 75% of the Universe and Helium, 24% of the Universe supports the Big Bang Theory.
As these are the most basic elements, it is logical that they were formed in the earliest days of the Universe and that they would make it the majority of the Universe.
This was predicted by cosmologists, and was proven to be true.

17. This is the atomic structure of a Hydrogen atom. Pretty simple, huh?
This is the structure of a helium atom. Still basic, but it was more complex for the Universe to create.

18. And this is the atomic structure of plutonium, the most complex naturally occurring element. Seems logical that the Universe need more time to create this, doesn’t it?
The incredibly mathematical predictions of the Big Bang called for a Universe filled predominantly with H and He, hydrogen and helium.
The Big Bang is the only model that calls for significant amount of He. All other models could not account for the Helium in our Universe.

19. In review…
The Big Bang is the most widely accepted theory for the creation of the Universe. There are currently no other models that have any credible proof.
Cosmologists can say the Big Bang occurred because of 3 proofs:
1. The expansion of galaxies.
2. Cosmic Microwave Background Radiation
3. The presence of Hydrogen and Helium
Amazingly, almost all of our knowledge on the creation of our Universe has been learned in the last 50 years.