Science is not about believing in what you like or want. It is about theories, mathematical derivations, facts, data; all of which, accumulated and simulated together lead to the most probable conclusion.
We don’t just believe everything. Science really doesn’t work that way. Science doesn’t work on beliefs. It doesn’t work on the ideas like “Regret is better than what if”.
If we start doing that, we’ll end up creating a black hole on the surface of Earth which will eventually annihilate the entire planet and then everything around.
So, how do we know the Big Bang happened?
The Universe is expanding
When we look at the night sky, the stars we can see are within our own galaxy. But there are also some fuzzy patches which we need a telescope to see clearly. These are other galaxies – much, much further away than the stars.
A general idea would be that some of them are moving away and some are moving towards us. But that’s not the case. Almost all the galaxies are moving further away from each other.
We know the galaxies are moving away because of an effect called red-shift – similar to the way that a car sounds more
high-pitched as it approaches you, and low-pitched as it moves away.
If most galaxies are moving away from us, it follows that the Universe is expanding. (It does not mean that Earth is at the centre of the Universe.)
If the Universe is expanding, that suggests it used to be smaller and more compact. And if you go back far enough, then there was a moment in the past when all the matter in the Universe was packed into a point, a singularity, and exploded outwards. That moment was the Big Bang. We can even work out when it happened, from the current size of the Universe and the speed at which it is moving – about 14 billion years ago.
We can see the afterglow of the Big Bang. We can’t see it with the naked eye, but some of our telescopes can. Our eyes actually only see a fraction of the light in the Universe. Just as the visible light, there are other kinds of light, such as X-rays, infrared light, ultraviolet light, radio waves and microwaves. They have shorter or longer wavelengths than visible light.
After the Big Bang, the whole Universe was flooded with incredibly bright light. As the Universe has expanded, that light has been stretched so that it is now microwaves.
A microwave telescope can see this ancient light from the very beginning of the Universe. In fact, a view through a microwave telescope shows the whole sky filled with a glow, day and night. Unlike light coming from a star, it is the same wherever you look, and wherever you are. This glow is called the Cosmic Microwave Background.
What does the Cosmic Microwave Background look like?
We can see gas clouds in the early Universe. Looking out into space is like looking back in time. That is because light from objects that are far away takes longer to reach us than light from objects nearby. If an object is a million light years away, we are seeing it as it looked a million years ago.
Modern telescopes are so powerful that they can view objects many billions of light years away, close to the time of the Big Bang. For example; The Hubble Telescope.
If the Big Bang did happen, then we’d expect those distant views to reveal clouds of gas which had not yet turned into stars and galaxies. And those gas clouds should be made of stuff, very different as compared to the modern Universe. That is because most of the chemical elements in the modern Universe are made inside stars. The earliest gas clouds should contain almost no complex elements. Instead they should be made almost entirely of the most basic elements, hydrogen and helium.
Gas clouds were found in the distant Universe some time ago. Some of them are around 12 billion years old. Even at this incredible distance, we can tell what they are made of by using a technique called spectroscopy to analyse light that passes through them.
This shows that they are mostly hydrogen and helium – exactly as the Big Bang theory predicts.
P.S. Facts, when analyzed with correct logic and reasoning, yield true results.