# Nature of Gravity Discussion

1. Jun 30, 2011

### Goolds

I was thinking a bit about gravity. As is known, Physicists have yet been unable to unify the Theory of Relativity (describing gravity) and Quantum Theory (decribing the other three fundamental forces).
As mass is a measure of a system's energy, the force of gravity (presumably carried by gravitons), increases for that system as it's mass increases.
Knowing that mass and gravitational strength are directly proportional, could it be safe to assume that gravity is quanta of mass that is attracted in a larger degree by more massive objects (though still attracted by less massive objects).
Let us examine a system containing a larger mass and a smaller mass.
The quanta of mass (gravitons) would therefore be removed from the smaller mass by the larger mass, while simultaneously the smaller mass removes an equal magnitude of gravitons from the larger mass, creating a sort of ''gravitational equilibrium'', whenre no net mass is lost by either object.
The greater mass is not accelerated as largely because it has a higher mass, and therefore requires a larger force to accelerate it to the same degree as the smaller mass.
The interaction between the objects would create a force of attraction between them, as the proximity of the gravitons to their parent object would be stronger the closer they are to said object. Therefore the more gravitons removed from the smaller mass, the greater the proximal force of attraction.
And since the force of gravity increases with the mass of an object, this explains why there is a larger acceleration of the smaller object when the larger object's mass increases (more gravitons are removed from the smaller mass, which have a greater net proximal force of attraction on the smaller mass).
Now, this begs the question: Why do the two bodies become more suitable when in closer proximity to each other?
The answer would be that there would be a smaller distance for the gravitons to travel between the constituent particles of the two objects, therefore more energy is conserved.

2. Jun 30, 2011

### SinghRP

I am interested in gravity as well.
At the macroscopic level, gravity iis due to the curvature in spacetie that a mass (matter) creates. The space-time ggemetry is the gravitational field.
Then on the other hand, to every accleration, there is an equal and opposite gravitational field!
At the microscopic level, gravitational interactions are medietd by gravitons. So, won't gravitons be the quanta of space-time geometry field?
Then another problem is that all the other fundaental fields (the strong, the weak, and electromagnetic) are of similar type. But gravity's space-time geometry field is a very different type of field!
They say, I think, that supersymmetry and hidden dimensions yield gravity!
What's going on?

3. Jun 30, 2011

### cosmik debris

Two things, there is no quantum theory of gravity so anything said about it is speculative. Secondly according to GR gravity is spacetime curvature produced by the energy/momentum tensor, so energy as well as mass are important.

4. Jul 1, 2011

### SinghRP

Thanks for the answers. I know those anyway.
But can you tell me, as a physicist, as a physicist, how matter creates and warps space-time?

5. Jul 1, 2011

### cosmik debris

Well from what you said in your other post you don't understand it at all. You stated it is matter/mass that creates the spacetime curvature, this is incomplete, energy also curves spacetime.

Then you said:

This is not true in any way that I can see.

Then you said:

I pointed out that there is no quantum theory of gravity and gravitons are certainly not part of GR.

The question of how is difficult. Physics makes models of reality, the models don't explain why or how really.

6. Jul 2, 2011

### SinghRP

Well, I never said I did not understand at all. What I don't understand is so many theories are floating arond that I can't figure out where physics is going to!
I think physics has become too mathematical to be physics. I recall Feynman: "The glory of mathematics is that you don't have to say what you are talking about." For me, physics comes first, math next. I must have a physical picture, model, etc.

I really don't distinguish between matter and energy. Both can warp space-time. This point is not even worth discussing.

If there is an accleration, there would be a gravitational force opposite to it. That's how they, not I, explain zero gravity. You may find it in Einstein's "Meaning of Relativity," which was my first textbook on relativity.

Quantum gravity. I agree with you here. Now I use reading glasses, I don't care about Planck length?

Please don't find faults with wordings. It's not worth it.

Thanks.

7. Jul 2, 2011

### WannabeNewton

Well the language of physics is math so why use English to explain very abstract concepts? For example your question about how mass warps space - time: this would be very hard to explain in words but I can just tell you "hey this is how mass - energy warps space - time $R_{\mu \nu } - \frac{1}{2}g_{\mu \nu }R = 8\Pi GT_{\mu \nu }$" and your question would be answered very succinctly and without the confusing English.

8. Jul 2, 2011

### SinghRP

By the way you forgot to add the cosmological constant.
I suggest we terminate this discussion.
Thanks anyway.

9. Jul 2, 2011

### bcrowell

Staff Emeritus
In my opinion it would help in these discussions if you would make more of an effort to engage in dialog rather than making brief, nonmathematical pronouncements. It's not helpful when you jump into the end of discussions without looking at what has been said before, and it's not helpful when you claim that what you've said is the last word and should naturally lead to the termination of discussion. Cosmik debris pointed out some mistakes you made (such as "Then on the other hand, to every accleration, there is an equal and opposite gravitational field!"), and it would be gracious of you to admit that that you've made a mistake.

10. Jul 2, 2011

### Naty1

No one has so far claimed via any theory that matter CREATES space time. Matter does warp space-time via the Einstein stress-energy-momentum tensor...but no one knows what THAT mathematical description and not some other formulation is the way nature works.

But Einstein's forumlation fits what we observe, except at extremely high energy gravitational field levels like at the big bang and near the singularity of a black hole....nothing works there inlcuding quantum mechanics.

Other theories postulate that energy vibrations of unseen dimensions or string like vibrations are the foundation of everything around us.

11. Jul 2, 2011

### SinghRP

I don't know where to start.

Matter creating space. This is the latest thinking.

Matter/energy warping space-time. We all know what GR says.

The great astrphhysicist E. A. Milne asked "How matter warps space? We have not answered it yet.

Gravitational field opp. to an acleration. This has been thought-experimented with an elevator acclerating up/down. A body falling toward the earth - it is acclerating downward, a gravitational force acting upward. (Personally I think entrifugal force is fictitious.)

Look, if I have offended someone's sensibility/belief, I apologize. But I DID NOT make any physics mistake. I would think that, in a discussion, I may have some free thoughts to convey to my colleague physicists.

I think, in this round, my involvement in this discussion should be end. It was very nice talking physics with you all.

12. Jul 2, 2011

### bcrowell

Staff Emeritus
No, that's incorrect. If you want to keep claiming that, please provide a reference to a peer-reviewed scientific paper to back it up.

Here you seem to have a muddled and/or oversimplified understanding of how GR handles acceleration.

You have not offended anyone's beliefs. but in my opinion you've simply made some mistakes in physics.

13. Jul 3, 2011

### cosmik debris

I think expecting any answer as to why or how something happens in nature is fraught with difficulty. I've said this many times but physics uses mathematics to create models of the world we inhabit. These models, if they are good ones, make predictions which can be verified by experiment. These experiments either add weight to the correctness of the model or refute it. Why or how doesn't enter into it and seems more in the realm of philosophy than physics.

14. Jul 3, 2011

### Staff: Mentor

I agree generally with this train of thought except that I think the models do answer "how", just not "why". I.e. To me a "how" question is asking for the details of the model while a "why" question is asking for the story behind the model. That could just be my usage of language.

15. Jul 4, 2011

### Naty1

I posted above:

and Crowell posted:

I was just rereading Michio Kaku's HYPERSPACE (1994) and he has some comments that might appear to support "matter creates space" (but actually do not).

Kaku explains (pg 157)

So a string (representing matter,energy, forces) requires certain space-time characteristics, like the number of dimensions, and some curled up dimensions, and these create required symmetries.

Kaku then quotes quotes David Gross, one of the founders of Heterotic string theory, who looks at geometry (spacetime) creating matter:

and Kaku goes on to say

Last edited: Jul 4, 2011
16. Jul 5, 2011

### cosmik debris

Yeah I agree with you too, it depends on how the how question is asked. Often people are wanting to know the exact mechanism. The OP asked it in this way IMHO. He said "how does matter/energy curve spacetime". All you can say really is:

G = T;

Is there an explanation of how this works?

17. Jul 6, 2011

### Goolds

With regards to the Matter Creates Spacetime arguement.

I am no professional physicist (im only studying Advanced Higher Physics at high school), but to me, it seems silly to assume that spacetime would be created independently from matter and energy.
My logic being that an object must have mass and/or energy to interact with the universe, as it could not exist if it can not interact with anything.
So, everything in the universe must have mass and/or energy. This leads me to think that the universe's boundaries (i.e. spacetime) must expand in order to contain an ever-expanding area of mass and energy.
Otherwise you would be saying that it is possible for matter to simply fly out of spacetime. Which, as we know, is impossible, as matter can only exist in the environment created by spacetime.
Hope I made sense to everyone.

18. Jul 6, 2011

### ZapperZ

Staff Emeritus
You need to back up your argument with physics that either has been established, or been published. If you can't, this is a speculative post and in violation of the https://www.physicsforums.com/showthread.php?t=414380" that you had agreed to.

Either this thread sticks with physics, or it will end immediately.

Zz.

Last edited by a moderator: Apr 26, 2017
19. Jul 6, 2011

### Goolds

Are all objects gravitationally aware of every other object in the universe?

20. Jul 6, 2011

### Staff: Mentor

Very few objects are aware at all AFAIK, gravitationally or otherwise. Can you ask your question again, without anthropomorphizing? Are you simply asking about the range of gravity?