Is the Big Bang Theory really true? No one knows for sure, but there is a lot of evidence to support it. The sign of a good hypothesis is that it predicts things that haven’t been discovered yet. Let’s take a look at a few of the things the Big Bang theory predicted we would discover .
In 1929, Edwin Hubble discovered that the distant stars and galaxies were moving away from us. He, also, discovered that the speed in which the stars and galaxies move away from us is determined by how far they are from us. The stars and galaxies that are farther from us move at a faster speed than the stars that are close to us. In fact, the speed is proportional to their distance from us.
Look at the diagram above. Star PINK is two light years from us, Star WHITE is one light year from us, and Star YELLOW is .5 light years from us. After a certain amount of time, Star PINK is four light years from us, Star WHITE is two light years from us, and Star YELLOW is one light year from us. Star PINK moved two light years in the same amount of time that Star WHITE moved one light year and Star YELLOW moved .5 light years. That means that Star PINK is moving twice as fast as Star WHITE because it is twice as far away from us and four times as fast as Star YELLOW because it is four times as far away from us. Their speeds are proportional to their distance. That is how real stars behave.
It is reasonable to assume that if you reverse the direction that these stars are traveling (that is, go backwards in time) they would all join each other at a single point at the same time. If you know how far away the stars are and how fast these stars are traveling, you could calculate how long it would take them to reach that meeting point. In our universe, the meeting time would be reached in 13.7 to 13.8 billion years.
Matter heats up as it is compressed. Scientist figured that if the Big Bang theory was true, the universe would have had to have been incredibly hot in its early phases. So hot that electrons could not interact with protons and, that as the universe cooled, the only atoms that could form would be hydrogen and helium (and a smidge of lithium). This would mean that the universe would be almost all hydrogen and helium. As it turns out, 98% of the universe is made of hydrogen and helium. The 2% of heavier atoms were made in stars after the early formation of the universe. Scientists, also, predicted that energy would be released in a very specific wave length at the moment protons were able to interact with electrons to form hydrogen and helium. They predicted that this energy would come from everywhere in the universe. This energy was discovered, in the 1960s.
If you are interested in learning more about why so many scientists think the Big Bang theory is true, WATCH THIS TED TALK VIDEO AFTER WATCHING OUR VIDEO ABOUT THE FORMATION OF THE UNIVERSE.