Allah be he exalted says: (Or [the state of a disbeliever] is like the darkness in a vast deep sea, overwhelmed with waves topped by waves, topped by dark clouds, (layers of) darkness upon darkness: if a man stretches out his hand, he can hardly see it! And he for whom Allah has not appointed light, for him there is no light.) [Surat An-Nur, verse: 40].

The explanation of the verse:

God be he blessed and exalted talks in this Quranic text about those who disbelieved in God's verses and denied His meeting and disclaimed the Prophet. So those people and their works that they have done in their lives are like a man that runs behind a mirage, panting behind it and when he reaches it he found nothing but his bad work. And this unbeliever is like a man living in the darkness of a deep sea and can hardly see anything because of the accumulated darkness.

Al-Imam Al-Qurtuby may Allah have mercy on him said: (in a vast deep sea) is the sea that we couldn't see its bottom and vast means the sea when the waves clash. And it was recently discovered that there are interior waves in the deep sees.

Scientific fact:

When scientists went down to the depths of the oceans, they found that deep sees have great darkness. And at the depth of one kilometer one could hardly see something and the darkness increases if the surface sea waves are high as they contribute in blocking the sunlight.

They have also found that at the depths of the deep sees, there are internal waves that no one could see unless he goes down to depths of more than one thousand meters and these waves could be harder than the surface waves.

The point of inimitability:

In this Quranic text there are two scientific signs:

1-Talking about the darkness in the deep sees and this is what scientists have recently discovered and it wasn't known at the time of the coming down of Quran.

2-Referring to the internal deep waves and it was also recently discovered by scientists and it was mentioned in the verse as Almighty God says: (overwhelmed with waves topped by waves).