Does the Universe have a beginning, or is it just being there from eternity? If it is just being there, then it seems to be easier to assume that it has no external cause as discussed previously. In that case, it is just there!
However, science seems to favor the idea that the Universe does have a beginning.
There are several reasons that convince me to make the above claim. The first one would be the famous Big Bang theory.
What is the Big Bang? According to NASA, “It is the idea that the universe began as just a single point, then expanded and stretched to grow as large as it is right now”. How long does it take to grow from a point to the current size? The same article from NASA says, “the universe is 13,800,000,000 years old”.
We see that the article says the universe “began” as a point. It is 13.8 billion years “old”. The universe is not from the eternity past. It is not just there. It has a beginning!
Isn’t it a crazy idea to claim that the vast universe comes from a tiny point? I think the simplest way to think about this Big Bang idea is to start from an observation in astronomy. That observation was made by Edward Hubble about 90 years ago, and Hubble’s finding has been verified over and over again ever since. The observation is: our neighboring galaxies are moving away from us at high speed. It is now a widely accepted fact that in general any two galaxies in the universe are running away from each other. The further apart they are to begin with, the faster they are running away from each other.
Now, if the galaxies are running away from each other today, then what happened yesterday? They were closer to each other yesterday. Winding the clock backward further and further, we can perceive a time when all galaxies were really close to each other. It is so close that it can be, as said before, idealized as a “point”.
Please be cautioned that no one claims to understand the true starting point of the universe at Big Bang. There is a known limitation of our knowledge at the extreme physical conditions expected to be present at the very early universe. However, most people would consider the Big Bang model to be trustworthy starting at 10^-43 second after the universe was "born". What is 10^-43 second? It is 0.00.....01 second, with 42 zeros between the decimal point and the number "1" at the end.