The Quran is not just a miracle for the Arabs, but the miracles of the Quran are still shown to people till now. The Quran contains facts that were not known to people 1400 years ago. This is what God said in the Quran:
We will show them Our signs in the horizons and within themselves until it becomes clear to them that it is the truth. But is it not sufficient concerning your Lord that He is, over all things, a Witness? (Holy Quran 41:53)
Expansion of the Universe
The Quran tells about the expansion of the Universe where it says:
And the heaven We constructed with strength, and indeed, We are [its] expander. (Holy Quran 51:47)
This is a fact discovered in the 20th century by Edwin Hubble. No one in the seventh century could have known this fact unless this was a revelation from God.
The Mountains have Roots and their effect on Earth Stability
Allah says in the Quran regarding mountains:
Have We not made the earth a resting place? And the mountains as stakes? (Holy Quran 78:6-7)
And He has cast into the earth firmly set mountains, lest it shift with you, and [made] rivers and roads, that you may be guided, (Holy Quran 16:15)
These verses show two scientific facts. The first scientific fact shown here is that mountains have deep roots in the earth’s crust as shown in the following picture:
The second fact is that these roots help in stabilizing the earth through mass equilibrium in order to keep the upper dense earth layer (lithosphere) floating on the lower less dense layer (asthenosphere). This is called isostasy, where Archimedes principle is applied between the lithosphere and asthenosphere. If the mountains didn’t have these roots with their given density, this isostatic equilibrium won’t have been achieved and a great disturbance on earth would have occurred. Prophet Muhammad couldn’t have known this information recently discovered.
Allah says in the Holy Quran:
And it is He who has released [simultaneously] the two seas, one fresh and sweet and one salty and bitter, and He placed between them a barrier and prohibiting partition. (Holy Quran 25:53)
These are called the estuaries. An estuary is a partly enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. This partition (zone of separation) has a different salinity from the fresh water and from the salt water. This acts as a buffer zone between a sea and a river.
Prophet Muhammad couldn’t have known this phenomenon in an environment that has never seen rivers meeting with seas. The human eye cannot see the difference between the two seas that meet; rather the two seas appear to us as one homogeneous sea. This could have been nothing but a revelation from God.
Actually there are many other scientific miracles in the Quran regarding embryology, human body, astronomy, geography and other sciences. These may be explained in detail in this website talking about scientific miracles in the Quran and the Sunna.
The below video is a witness made by many scientists confirming the miracles in the Holy Quran.