After speaking to Muslims, I find that for many of them, the reasoning
goes as follows.
1) We follow Islam because the Quran came from Allah.
2) We know it came from Allah because of the many scientific facts in the Quran that we now know to be true.
3) These facts could only have been known by Allah at the time of the Prophet (pbuh) 650 AD.
The problem with this logic, is that 3) isn't correct.
Dozens of examples are given. I don't want this post to be too long, so I'll look at three of them that are commonly given.
1) The Big Bang. The Quran 21:30 tells us that the Big Bang happened, but scientists have only recently rediscovered this.
Not so. The Ancient Greeks proposed this. Anaxagoras in the 5th century BC
proposed this, 1000 years before the time of the Prophet. And the Hindu Rigveda proposed this also, 2000 years before Mohammed (pbuh).
But how could an illiterate Mohammed (pbuh) have read the writings of the ancient Greeks?
He had Companions. Not everyone in that region was illiterate. And people talk to each other. The origin of the universe is an interesting question, and would have been discussed often.
2) The different stages of development of the human fetus. How, before X-rays and ultrasound, could they have known about that? Quran 23:12-14
Because of miscarriages. And the Ancient Greeks, 1000 years before the Quran was revealed knew this. And the Bhagavata Purana, 100 years before the Apostle of Allah, gave an accurate account of the development of the fetus.
3. The waters salt and fresh, not mixing, Quran 55:19:20. This explains that you can have water that is salt, and water that is fresh, side by side, not mixing.
If you live by the coast, near a river, then you can go out in a boat and see this for yourself. It isn't hard to check. Fishermen would have known abuot this for thousands of years. But how would an illiterate man, not living by the coast, have known abut this?
Again - people talk to each other.
And, by the way, if you think that salt water and fresh water can never mix (as suggested by the Quran), try it yourself. Take a half glass of fresh water and a half glass of salt water, pour them into a single glass, stir well, and taste. It will be half as salty as the original salt water. And you don't need to take my word for this, you can try it yourself.
So here's my suggestion to Muslims. Look through the Quran, and find some true scientific fact that could only have had a divine origin. And I will undertake to show you that this fact was already well known at the time of the Prophet (pbuh).