How do you explain the big bang theory?

The big bang theory is the consensus cosmological framework for explaining the origin, properties, and evolution of the universe. According to this theory, the universe began almost 14 billion years ago in an extremely hot and dense state, from which it has cooled and expanded since.

What is the Big Bang theory in simple terms?

The Short Answer:

The big bang is how astronomers explain the way the universe began. 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—and it is still stretching!