# why gravity exists? [closed]

I always have a doubt on gravity , why does gravity exists ?

is there any scientific explanation on gravity ?

I know that Gravity exists , i can feel it. But Who is creating all these rules ?

secondly i am curious about the bigbang theory , how its possible From Nothing TO Something

I know the stack rules , but curiosity is the main reason.

Thanks

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This site works best when you have a specific question and we can provide a specific answer. As it stands your question is too general to answer without writing a massive essay. You really need to do some reading around and come back with specific questions. There are loads of easily Googlable articles on general relativity. For info on the Big Bang search this site for "FLRW metric" and you'll find lots of relevant questions and answers. – John Rennie Mar 10 at 7:15
@JohnRennie this is what i expected :) there are many article saying about gravity , but no article saying about why its exists.I am not asking about how gravity works or its rules. in my understanding gravity is coming from atomic level itself,but if you go through it you will end up with something called unknown physics,which is exists before bigbang. In this point everything is converted to divine (Just remember what stephen hawkings said about this). – Red Mar 10 at 7:46
@JohnRennie well ,well,well. Again one theory,now just assume we know about everything ,what exists before bigbang etc ,so what ? does it says who created all these universal laws? my question comes after a discussion with one of ma astro-researcher friend who quoted Science/Universe/laws is a playground for humans which is written and directed by God. And thanks for the links :) – Red Mar 10 at 8:08
Physicists are like engineers in that we are principally interested in what works, and we test what works by doing experiments. We have been known to drink beer and chatter late into the night about pre-Big Bang conditions and other esoterica, but in the morning we go back to the day job. – John Rennie Mar 10 at 8:45
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## closed as not a real question by John Rennie, Manishearth♦Mar 10 at 7:28

It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, see the FAQ.

The first good theory of gravity was Newton's Law of Gravitation, which was proposed in the 1600's. It says that any two masses are attracted to each other by a force which follows the following equation:

$$F=G\frac{m_1 m_2}{r^2}$$

where $G$ is the gravitational constant and $r$ is the distance between the two masses. Along with Newton's Second Law, $F=ma$, this tells us how masses will behave when they are placed near each other.

As time went on, it was observed that Newton's Law appeared to fail in certain circumstances, for example with the precession of the planet Mercury. Fast forward a few hundred years, and Einstein proposes General Relativity. This theory says that gravity is a consequence of the geometry of space and time. It says the metric of spacetime is related to the energy and momentum density in spacetime by the Einstein Field Equations:

$$R_{\mu \nu}-\frac{1}{2}g_{\mu \nu}R=\frac{8\pi G}{c^4}~T_{\mu \nu}$$

Along with the geodesic equation, a sort of generalization of Newton's First Law to curved spaces, this tells us how objects will move. (As a technical aside, the geodesic equation is actually derivable from the Field Equations.) General Relativity accounts for phenomena which is unexplainable by Newton's theory, such as the precession of Mercury and gravitational time dilation.

We now know that the world is, as far as we can tell, fundamentally quantum mechanical. General Relativity is a classical theory, so a theory of quantum gravity is required to explain phenomena where there is a strong gravitational field yet things are really small, such as in the singularity of a black hole. Unfortunately, gravity is very difficult to quantize unlike the other three fundamental forces. We currently have no complete and accepted theory of quantum gravity. String Theory provides probably the best lead so far.

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This theory explain what is exists now , but i am asking why it exists. – Red Mar 10 at 7:37
@Red if you're looking for a philosophical answer, then from a scientific point of view, youtube.com/watch?v=iMDTcMD6pOw "If you want to know the way nature works we look at it carefully... that's the way it looks!"-Richard Feynman. From a religious point of view, it's creation :) – Raindrop Mar 10 at 11:51