Scientists believe that the Universe began from a Big Bang which has essentially no size or as small as a dot with huge amounts of energy and radiation in it. The Universe then cooled and exapanded to the form which we see today over billions of years. According to current theories it is still exanding.

Professor Alan H Guth is from Massachusetts Institute of Technology and won this year's Isaac Newton medal from the Institute of Physics. Click here to watch his talk on Inflationary Cosmology: Is Our Universe Part of a Multiverse?