Why do scientists think the Universe began with the Big Bang?

Scientists think that the Universe began long ago (several billion years ago indeed!). If that’s right – then no one was around to watch it happen and we can’t make it happen again. So why do scientists think the Big Bang theory is probably right?

Science is all about observations. We can’t observe the Big Bang happening but luckily, there are useful observations to be made by looking at what is here today. These observations do not ‘prove’ that the theory is right. For the moment, however, most scientists seem to think the case is convincing.

What Astronomers see

What are the observations that support the Big Bang theory?

One is that scientists have noticed that the light that comes to us from any star that is a long way away is redder than we might expect. It’s called the ‘red shift’, There’s an explanation of the red shift on this site ‘ What is the Red Shift?‘.
The further the star is from us, the greater the red shift. Scientists have argued about why this happens.

The most popular idea today is that it is happening because the stars are moving apart and are getting further from us. If this is so, then it follows that billions of years ago, the Universe was smaller. If scientists trace the expansion right back until the Universe is as small as possible, this suggests it started in one spot, about 14 billion years ago.

It’s an interesting theory, but is it right? Here’s what Professor Jim Al-Khalili thinks (watch the video below).