What is Gravity?

[michel123456]

I spoke of massive particles first of all, not of gravitons. Anyway, in QED and in GR the exact equations are coupled and non linear. So even photons can scatter photons - there is no superposition principle, to be exact.

 

The same is in GR: any stuff that possesses energy or mass is the field source. And this field gets in the particle equations as well as in the field equations. Linear is the zeroth approximation after equation linearization.

 

 

So, correct me , in everyday langage: the "thing" is not the observed object, the "thing" is the object+field.

[Baby Astronaut]

Astronomers observe BH candidates, not BH. From far distances, with help of indirect observations, and with BH idea in the head one can mistake a massive body without horizon for a BH with a horizon.

........

GR has also pathological solutions - black holes with horizons. It is because the theory fails at short distances, just like classical examples given above. What is observed is not black holes for sure but massive objects.

I don't think so. What about the microlensing effects of black holes passing in front of stars? If they weren't black holes, we'd likely have seen them, especially if so massive.

 

Lone Black Holes Discovered Adrift in the Galaxy

 

 

Also...

 

http://astronomynow.com/081216Dissectingablackholewithnaturalmagnifyingglasses.html

Combining the natural magnifying power of galactic lenses with ESO’s Very Large Telescope, astronomers have scrutinised a supermassive black hole 10 billion light years away.

 

By using a technique known as gravitational lensing – the effect of a foreground galaxy or star magnifying a distant object by bending light with its gravitational field – astronomers can hone in on an object that would otherwise be too distant to observe in much detail. In this case, a team of astronomers were able to study the inner parts of a black hole’s accretion disc with a level of detail a thousand times better than that of the best telescopes in the world, providing the first observational confirmation of the prevalent theoretical models of such discs.

Has the RTG theory accounted for such observed effects?

[Bob_for_short]

I don't think so. What about the microlensing effects of black holes passing in front of stars? If they weren't black holes, we'd likely have seen them, especially if so massive.

 

???

 

RTG admits existence of heavy objects which gravitationally affect light. How could you see them, "especially if so massive"? RTG does not predict a point-like singularity situated inside the horizon. Any heavy body has a radius exceeding the gravitational one in RTG.

...supermassive black hole 10 billion light years away.

 

By using a technique known as gravitational lensing – the effect of a foreground galaxy or star magnifying a distant object by bending light with its gravitational field – astronomers can hone in on an object that would otherwise be too distant to observe in much detail. In this case, a team of astronomers were able to study the inner parts of a black hole’s accretion disc with a level of detail a thousand times better than that of the best telescopes in the world, providing the first observational confirmation of the prevalent theoretical models of such discs. Has the RTG theory accounted for such observed effects?

 

Of course. Light bending is predicted by RTG with no problem.

Edited February 21, 2010 by Bob_for_short

[Baby Astronaut]

???

 

RTG admits existence of heavy objects which gravitationally affect light. How could you see them, "especially if so massive"? RTG does not predict a point-like singularity situated inside the horizon. Any heavy body has a radius exceeding the gravitational one in RTG.

That's my point. If a wandering heavy body passed in front of a star, it'd be closer to us than the star it's passing in front of -- thus larger, and more visible. But instead, we just observe the star's light distort as if doing so on its own.

 

 

Of course. Light bending is predicted by RTG with no problem.

I meant, can it account for such observed effects as described above -- i.e. not just if RTG can predict light's bending.

 

Did you check out the links of post # 52? Reviewing the second link again...

 

In this case, a team of astronomers were able to study the inner parts of a black hole’s accretion disc with a level of detail a thousand times better than that of the best telescopes in the world, providing the first observational confirmation of the prevalent theoretical models of such discs.

 

So, does RTG explanations account for those observations, dealing with accretion disks, not merely light-bending?

[Bob_for_short]

...So, does RTG explanations account for those observations, dealing with accretion disks, not merely light-bending?

I do not know about this particular observation but RTG handles well everything outside the horizon.

[ernst39]

What is gravity?

 

According to Wikipedia: "Gravitation, or gravity, is one of the four fundamental interactions of nature, and is the means by which objects with mass attract one another." The phenomenon of gravitation occurs as an "action-at-a-distance" and there are several possible explanations (theories).

 

1. In the GRT (the current description of gravitation in modern physics), gravity is the result of the "curvature" of space-time by the energy-momentum of matter. The GRT implies that one must assume that space and time are not only pure ideas but active elements of the universe. Understanding the technical details of this succesful theory requires an extensive mathematical knowledge.

 

2. Another point of view is the concept of the "classical" gravitational field (the current description of gravitation in textbooks for calculus-based physics courses for science and engineering students). A mass particle sets up a "gravitational field" and that field then acts on any other mass particle in it: the field mediates in the interaction between masses. The classical field theory regards the field as an element of the real world that requires no further explanation. Understanding the technical details of this theory requires a good knowledge of calculus.

 

3. It is also possible to develop a theory of gravity, starting from the idea that a mass particle emits dot-shaped entities which spread in space. They constitute the gravitational field and mediate in the interaction between masses. These particles should be mass- and energy-less, otherwise the principle of conservation of energy would be violated. Because their only attribute is information (about the position and the velocity of the emitter), we can call them "informatons". This theory of informatons, that regards informatons as elements of the real world, implies that one must assume that the concept "information" can be made suitable for physical theory development by narrowing its everyday meaning and defining it mathematically. The degree of difficulty of this theory corresponds with that of the field theory (2). In the forum SPECULATIONS, there is a treat "Gravitation and Electromagnetism" about the theory of informatons.

 

4. ...

[michel123456]

4. is Le Sage theory. http://en.wikipedia.org/wiki/Le_Sage%27s_theory_of_gravitation which has been dicarded several times, since it comes back every few years, and discarded again.

 

5...

 

I vote for 5.

[ernst39]

(5) = (3) ??

 

I think that the development op a new theory always is achieved by extending the arsenal of physical concepts: e.g. "mass" and "force" (Newton), "curvature of space-time" (GRT), "field" (field theory), ... . This is done by narrowing (via a mathematical definition) the meaning of a concept with which we are familiar from everyday life.

 

This approach forms also the basis of the theory of informatons (3). The concept "information", with which we are all familiar, is made suitable to develop a consistent theory about gravitation (and electromagnetism).

[ions]

thanks for all the answers, but the point is that I'm not a Physicist, I am just a Civil Engineer who is interested in many fields of science including Physics.

I remember some of the basic theories some of you have mentioned like "Relativity theory of gravitation" by Einstein, but I didn't learn about it thoroughly.

I thought the explanation of our Earth core gravity would be easily illustrated & understood, but from all that previous debate, I assume it's rather more complicated than I though or I should restudy physics thoroughly to feed my needs of such questions.

Do anybody have a recommendation for a good comprehensive start?

[KennyC]

thanks for all the answers, but the point is that I'm not a Physicist, I am just a Civil Engineer who is interested in many fields of science including Physics.

I remember some of the basic theories some of you have mentioned like "Relativity theory of gravitation" by Einstein, but I didn't learn about it thoroughly.

I thought the explanation of our Earth core gravity would be easily illustrated & understood, but from all that previous debate, I assume it's rather more complicated than I though or I should restudy physics thoroughly to feed my needs of such questions.

Do anybody have a recommendation for a good comprehensive start?

 

I always think Wikipedia is a good place to start as long as you keep the salt nearby and read other sources as well.

 

http://en.wikipedia.org/wiki/Gravitation

[Bob_for_short]

...I thought the explanation of our Earth core gravity would be easily illustrated & understood, but from all that previous debate, I assume it's rather more complicated than I though or I should restudy physics thoroughly to feed my needs of such questions...

 

You can safely think of gravity in the Newtonian sense because the GR effects are very weak in the Solar system.

[ions]

I understand your point, which 'in short' refers to the scale factor & the variable magnitude of forces according to this scale factor.

thanks

[Bagz]

I think everything here on earth is attracted to the earth and can't escape its gravitational field. This gravitational field is unlike the magnetic field that only attracts metals but rather a centripetal force created by earth's revolution and rotation around the sun. If the earth were sitting still, then everything will float and escape to space or the earth will dismantle itself. I think everything here will float if the earth revolves and rotates at a lesser speed. The lesser the speed, the higher we float.

[lazygamer]

I'm working on a theory of gravity, and it fits with my theory of everything (neither is published as they are not completely done yet).

 

and I can tell you that there are no particles that create gravity, its just that our universe is in 11 dimensions. I'll debunk dark energy, dark matter, particle-gravity and make a few adjustments to M-theory aswell as black-holes and give all of the sollutions for why gravity seems to be different at different scales and why travel from xyz to another xyz value is impossible through black holes (even why our laws of physics seem to be inadequate in black holes). there'll still be lots to figure out, I'll literally make it possible for us to view other paralell universes. and there is quite alot of math to do for everyone to dot the i's and cross the t's between all the laws of physics aswell as figuring out the stuff that comes into view from my theory.

 

When I eventually publish it, be ready (I'll give the LHC a little extra time to find the graviton and the other scientists a little time to find the dark-matter particle, just so they can't say "we haven't looked long enough" when I tell them those things doesn't exist as particles at all).

[Mr Skeptic]

I'm working on a theory of gravity, and it fits with my theory of everything (neither is published as they are not completely done yet).

...

When I eventually publish it, be ready (I'll give the LHC a little extra time to find the graviton and the other scientists a little time to find the dark-matter particle, just so they can't say "we haven't looked long enough" when I tell them those things doesn't exist as particles at all).

 

Just remember to not bother trying to explain anything. No one will care. Scientists care about accurate numerical predictions.

[matterdoc]

Attraction due to gravity is the only part of 'gravitation' considered currently by all. It is the dynamic action of 'gravitation'. Static actions of 'gravitation' is more fundamental and important. Gravitational attraction is a minor by-product of 'gravitation'. Cause of gravitation and explanations on its static actions may be checked at matterdoc.info

[swansont]

Attraction due to gravity is the only part of 'gravitation' considered currently by all. It is the dynamic action of 'gravitation'. Static actions of 'gravitation' is more fundamental and important. Gravitational attraction is a minor by-product of 'gravitation'. Cause of gravitation and explanations on its static actions may be checked at matterdoc.info

 

!

Moderator Note

Attempts at thread hijacking with "alternative" science is against the rules

[zheng sheng ming]

what is gravity? this problem need solve!