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I've always wondered how our planet Earth or any other large spheroid-shaped thing in our universe has gravity?

Does it have a small black hole on its core causing it to have gravitational force?

Take our planet as an example: what causes it to have gravity?

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    $\begingroup$ Mass. Mass and a very small amount of energy to be more precise. $\endgroup$ – Rob Jeffries Nov 30 '16 at 20:01
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    $\begingroup$ Something worth noting: science never describes the true reason why something happens. It concentrates on predicting the effects of what happens. When one asks science "why," we answer by showing a deeper and more powerful model (such as Newtons' law of universal gravitation or Einstein's relativity). If you want the "real" reason for gravity, turn to philosophy or religion. They'll dare to try to answer such ontological questions. $\endgroup$ – Cort Ammon - Reinstate Monica Nov 30 '16 at 20:32
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    $\begingroup$ @RobJeffries: What "very small amount of energy" are you referring to? $\endgroup$ – Keith Thompson Nov 30 '16 at 20:41
  • $\begingroup$ @KeithThompson Just taking a stab at this, but maybe rotational energy? The rotational energy would be a cause of frame dragging which helps to distort the space-time around the mass and as GR tells us, space-time distortion is gravity. $\endgroup$ – zephyr Dec 1 '16 at 1:38
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    $\begingroup$ The total mass-energy of the Earth is it's rest mass $\times c^2$ plus a negative term due to its potential energy plus a positive term due to the kinetic energy of its constituents. The latter two terms are tiny in comparison to the first. @KeithThompson $\endgroup$ – Rob Jeffries Dec 1 '16 at 16:50
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Anything that has mass will have gravity ( Exhibit a phenomemon called gravitation) not just black holes. One way of understanding gravity was put forth by Newton as his law of gravitation. As @christo said, there is no clear knowledge of why it has gravity.

A more generic way to put it would be to say, anything that has mass curves the space around it. The force or gravity you would feel can be considered as the way you are being forced to follow the curved lines instead of your intended path. This is how Einstein's general theory of relativity explains gravitation.

In quantum mechanics, It is speculated that gravity is caused by exchanging particles called gravitons, think of it like the way you would play catch with your friends. Multiple objects having some mass throwing small balls called gravitons at each other. There is no evidence for the existence of gravitons yet, but it explains a lot of things in the quantum realm.

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Any massive body (i.e., a body having mass) like the stars, planets, moons, and any atom in the universe have, what is called, a gravitational potential which results in its gravity. This is described by Newton's Law of Gravity. Why masses cause gravity, we do not know.

So, in short, the earth's mass causes it to have gravity.

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  • $\begingroup$ Than you for the edit, @AtmosphericPrisonEscape $\endgroup$ – Christo Nov 30 '16 at 14:17
  • $\begingroup$ Well, learn something new! TIL that definition number3 at Merriam-Webster is indeed exactly how you used it here :-) $\endgroup$ – Carl Witthoft Dec 1 '16 at 12:58

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