The generally accepted theory of the origin of the universe in science is the “Big Bang theory”. Here we need to understand the phrase “generally accepted”. Science never pretends to know what it does not know. It is not science at all.

We have experimental evidence that the universe we observe today is expanding. Similarly, the universe as seen today has various properties. For example, the way it expands, the density of its atomic shells, and why there are so many hydrogen and helium atoms need to be answered.

There is no place in science for saying "that's the way it is". A clear scientific theory is therefore needed to explain the properties of the universe we currently observe. That's where the big bang theory comes in.

Consider a very simple example to understand this:

Suppose you pick up a tennis ball and throw it. Doesn't it fall a certain distance? Now if you calculate how far it has fallen, you can see how much force you used to throw it. We can calculate this using the Earth's gravity and Newton's laws.

Now let's look at the opposite. The ball is thrown and here it is. We don't know from where and how far it was thrown, nor do we know the magnitude of Earth's gravity. Now the question is, how to find out how much force this ball was thrown from where?

This is where something called “theory” comes into play. Theory is not law. Theory presents us with a picture. That is, it is from here that the ball must have been thrown with such force. This is because theory tells us that Earth's gravitational force can be roughly calculated to be this much (1. We have to do experiments to calculate it. 2. Note that gravity is just an example here). And the theory is based on the sand pits caused by the ball falling and its current position.

You can compare it to detective work in a crime branch. Scientific theorists are detectives of this nature.

So they theorize and postulate many possibilities. Whichever theory clearly captures the state of the ball currently lying on the ground is accepted. The theory will then be verified through experiments. If the results obtained during the experiment are not in accordance with the theory, changes are made to the theory to reflect this. If the experimental results completely contradict the theory, the theory itself is abandoned! Or the doctrine will be fully perfected. After that it can become a rule. This is the scientific method.

Well, let's get back to the big bang, the only theory that most accurately describes what we have observed is the big bang theory.