# Where does gravity come from?

1. Apr 26, 2012

### Snowgooned

So I know that when a massive star stops creating nuclear fusion the star collapses on itself from the gravity and creates a black hole (or nuetron star). So when the star collapses the black hole creates gravity.

From my understanding gravity comes from black holes in the center of galaxies like the milky way.

So my question is where did gravity originally come from if it all comes from black holes?

2. Apr 26, 2012

### phinds

You seem to have no idea at all what gravity is. Black holes do not "create" gravity, ANY object with mass has a property that creates the attraction in space-time of all other bodies that have mass.

EDIT: do you think that the black hole in the center of the Milky Way is what gives you weight here on earth?

3. Apr 27, 2012

### Chimps

Nobody knows where gravity comes from.

Unfortunately our understanding of the universe is not at a stage where that question can be answered. We know it exists and we know it can be predicted, but we can't explain the philosophical aspects which your question implies.

This is the nature of science. We want to understand as much as possble but we have to ask the right questions.

4. Apr 27, 2012

### Drakkith

Staff Emeritus
All objects with mass or energy "create" gravity, not just black holes.

This is incorrect. Mass and energy curve spacetime which results in the effect of gravitation.

While perhaps true on a certain level, we do know a lot about gravity. It really depends on who is asking the question "What is gravity". We can explain that mass and energy cause gravitation, and how it does so, but any underlying "why" is beyond us at the moment.

5. Apr 27, 2012

### Chimps

Yes, that is the point I was rather clumsily trying to make.

I feel that the OP wants a definitive answer which is clearly unrealistic.

6. Apr 27, 2012

### Drakkith

Staff Emeritus
Maybe. We'll have to wait and see if our previous answers satisfied them.

7. Apr 27, 2012

### Mark M

Snowgooned, to compound on the answers that have already been given, gravity is caused by the curvature of spacetime. Essentially, objects with large amounts of mass and energy curve the space through which other objects travel. Similar to the way a perfectly banking road will curve the path of your car, curvatures in spacetime alter the geodesic (the shortest path between to points) of objects near it. Here is an image that may help you visualize this.

8. Apr 28, 2012

### Snowgooned

Well I feel rather dumb. I have honestly just gotten into looking into space and for some reason the more I learn about it the more I want to know how the universe works.

Anyways, I guess it was a bit off for me to think gravity comes from a black hole since all stars have gravity in the first place.

But I do not exactly understand your reply, you say everything that has mass has a pull to anything else that has mass? When I read that the only thing I think of is magnets and how we are stuck to the earth because of gravity. Sorry if I'm being confusing or asking dumb questions.

9. Apr 28, 2012

### Calimero

There are no dumb questions, just dumb answers. For starters you should try to understand Newton's law of universal gravitation. It is simple law, which states that force that two massive objects insert on each other is proportional to product of their masses, and inversely proportional to square of distance between them, multiplied with gravitational constant - G.

$F= G \frac{m1m2}{r^2}$

Now, gravitational constant is tiny number - 0.0000000000667 m3kg-1s-2, so in order to get significant force, mass needs to be huge. From your everyday experience you know that two apples left on the table will never attract each other. It is not because there is no force between them - there is! It is just that that force is incredibly tiny and not nearly enough to overcome other things involved, like friction between apples and table. On the other hand, two apples left floating in the empty space will eventually attract each other.

10. Apr 28, 2012

### phinds

Your statements are, of course, correct, but you use the work "attract" to mean "move toward each other" when in fact it normally means "pull toward each other". They DO always attract in the normal sense, but as you point out, they do NOT always move toward each other.

11. Apr 28, 2012

### phinds

As Calimero says, there are no dumb questions and as you get more and more into physics (particularly cosmology and quantum mechanics) the questions will SEEM more and more weird, as will the answers. BUT ... it's a lot of fun.

12. Apr 28, 2012

### Calimero

Yes, you are completely right, I probably don't need to tell you that English is not my native language :)

13. Apr 28, 2012

### phinds

OH. Your English is so good it never occurred to me that you are not a native speaker.

14. Apr 28, 2012

### Snowgooned

Thank you that helped me out a lot and thanks to everyone else who replied. :)