How did our universe begin and how will it end?
The vast majority of scientists accept the Big Bang theory for the origin of the universe. According to this model the universe is about 13,700 million years old.
At the beginning of the universe, all the material that we can observe with our telescopes today (known as the observable universe) was confined to a very small space. Every point and everything that would become the space, matter and energy in the present-day Universe was contained within this entity – in our familiar three dimensions nothing exists outside it.
If we go as far back as the Big Bang (the starting point for our current theory of the history of the universe) this material was squeezed tightly together and was extremely hot – leading to the full name of the theory as the 'Hot Big Bang'. After the Hot Big Bang, the universe expanded at an enormous rate, eventually becoming the cosmos that we inhabit today.
In the contemporary universe astronomers can see that virtually all galaxies (large collections of stars like our own Milky Way) are moving away from each other. This implies that the whole universe is expanding and that the volume of space is getting larger. Scientists are still not exactly sure how the universe will end, although there are several different ideas.