No one really knows the answer to this question. It's quite possible that there are more than one, in fact there may be infinitely many, popping in and out of existence like bubbles in a bubble bath. The following articles will introduce you to the topic. (If you would like to get away from your computer or smart phone, then you can also download our Universes ebook).

To get a very rough overview, start with the article

• What is a universe?

To go a little further, see the following articles:

• Are there parallel universes? explores the possibility that reality consists of many parallel branches, with you existing in lots of different ones — scary!
• From planets to universes is an article by Astronomer Royal Martin Rees exploring the idea of a multiverse.
• What happened before the Big Bang? also looks at the multiverse, and our own Universe within it, in a little more detail.
• Bang, crunch, freeze and the multiverse looks at the past and future of our Universe, and the multiverse as a prediction of string theory.
• The multiverse: science or speculation? How can we prove that the world consists of many different universes when, by definition, we will never be able to see them? This article asks whether speculating about the multiverse can count as science.

If you really want to get stuck in, then try this:

• Playing games in many worlds explores how betting on events happening in parallel worlds makes (potential) sense of a quantum mechanical puzzle.