Quran Sura 7 verse 54 states:
“Indeed, your Lord is Allaah, Who created the heavens and the earth in Six Days, and then He rose over (Istawa) the Throne (really in a manner that suits His Majesty)”.
Aishaaa1, remember that even the Christians and Jews believe that it took 6 days - the 7th day, in the Bible, is one of which they claim Allah rested (which sounds distictly fishy - why would an all powerful deity need to rest???)
Interestingly enough, for insolent mods, the Quran says in two verses, (22:47 and 32:5), that the measure of one day in the sight of Allah is equal to 1,000 years of our reckoning. In another verse (70:4) it says that the measure of one day in the sight of Allah is equal to 50,000 years of our reckoning.
These verses generally mean that the time of Allah (swt) is incomparable to the earthly time. Which means that whilst to Allah SWT it took 6 days to make the heavens and the earth, these 6 days could have lasted a very long time in human terms- potentially even billions of years. We humans cannot comprehend how long a day of Allah SWT is.
In addition, consider the verse
"Do not the unbelievers see that the heavens and the earth were joined together, then we
clove them asunder . . .” (Qur’an 21:30).
Clearly, this proves that whatever matter is found in the heavens and the earth was once as one - a situation that would have been found at the moment of the scientists' proposed Big Bang, as this theory requires that all matter was once in the same place.
It is well within the power of Allah SWT to have created this universe with a Big Bang, and then created the objects within it over the time that followed, completing it in his 6 days - which, as I mentioned, could be billions of our years. Hence there is no apparent direct conflict between what scientists currently hold to be true and Islam.
Having said that, Allah SWT could have created the universe in another manner. We simply don't know in depth the details of the Creation.