It was first suggested by the general theory of relativity and is backed up by physics in the examination of the galactic spectrum; the regular movement towards the red section of their spectrum may be explained by the distancing of one galaxy from another.Thus the size of the Universe is probably constantly increasing and this increase will become bigger the further away the galaxies are from us.

The speeds at which these celestial bodies are moving may, in the course of this perpetual expansion, go from fractions of the speed of light to speeds faster than this. 
The following verse of the Qur'an (sura 51, verse 47) where God is speaking, may perhaps be compared with modern ideas:

"The heaven, We have built it with power. Verily. We are expanding it." 

'Heaven' is the translation of the word sama' and this is exactly the extra-terrestrial world that is meant. 'We are expanding it' is the translation of the plural present participle musi'una of the verb ausa'a meaning 'to make wider, more spacious, to extend, to expand'. 
Ramidullah in his translation of the Qur'an talks of the widening of the heavens and space, but he includes a question mark. There are those who arm themselves with authorized scientific opinion in their commentaries and give the meaning stated here. This is true in the case of the Muntakab, a book of commentaries edited by the Supreme Council for Islamic Affairs, Cairo. It refers to the expansion of the Universe in totally unambiguous terms.