THE BIG BANG THEORY

People have always sought out ‘big-picture’ theories that explain how the universe began, what it looks like on the largest scales and how it evolves over time. In the past, such theories were often based more on human imagination than anything else. But our present best contender, the Big Bang theory, is much better than that. It’s based on a mixture of observational evidence and a mathematical understanding of how space and matter behave on very large scales, and most astronomers believe it probably comes quite close to the truth.

There are two reasons we no longer need to rely on pure imagination to visualise the evolution of the universe. First there’s the fact that we can actually see into the distant past. That’s because light travels at a finite speed, so when a telescope shows us a galaxy a billion light years away, we’re seeing it as it was a billion years ago. The second important factor is the universality of the laws of physics. This means we can study physics in laboratories here on Earth and know that exactly the same principles must apply to the rest of the universe as well.

Putting state-of-the-art observations and some very sophisticated physics together is what’s given us the Big Bang theory. According to this, the universe began approximately 13.8 billion years ago as an infinitesimally tiny point, smaller than the smallest