Gravity

I met one of the biggest astrophysicists in the world, at the Sheraton Frankfurt airport hotel. He is the professor: Jurgen von der Lipper who was working as the head of Into space agency which was established by European Union to compete NASA .
He told me about how researches are conducted in the space because of weightlessness.
And he gave a simple example to explain that . He said that if we throw a small stone in an empty cup,the stone will fall down at 230 kilometers per hour , which is the speed of gravity .However, if a cup is full of water the stone will fall at a slower rate and if it was honey it would fall even slower and so on.
I asked him “What is gravity?”

He said “No one knows, it is like Electricity ,physical phenomena we discovered it centuries ago.We benefit from it and use it but no one knows what it is or how it works. We haven’t any in depth knowledge of it. All we know is that it is a phenomena associated with cosmic in general.” I told him that Quran has mentioned it 1400 years ago he replied”It is impossible!”, and asked surprisingly “What was mentioned in Quran?”
I told him that The Glorious Quran declares that the cause of gravity is density of rocks in the center of the earth.

{When the earth is shaking to her utmost convulsion and the earth throws out its burdens}(Az Zalzalah 1-2)
{and when the earth stretched ,and casts out what is in it and become void}(Al Inshiqaq 3-4)
{The day when mankind shall be like scattered moths,and mountains shall be like carded wool}(Al Qariah 4-5)

when the earth vacate what is inside of rocks and metals so crustal cant hold what is on its surface Then all things above it will fly people,trees,animals,rivers, and also the heaviest thing above it mountains

{And every soul shall come with it a driver and a witness}(qaf 21)

in this verse allah tells us that on the day of judgement allah exchange the angels who write good and bad deeds with witness angel and driver who drive people to fire or paradise because after destroying the earth there is no gravity and no one can move from his place Now the question is why does quran mention that?
Only if it is from god