# Gravitational force vs. relativity

• crebigsol
In summary, two terrestrial objects B1 and B2 with concentrated mass will experience a drastic disturbance in their physical state when a high speed rocket ship flies by parallel to the line connecting them, according to the theory of relativity. The mass of each object will appear to increase for the observer in the rocket ship, as well as a shortened distance between the objects. This would lead to a predicted increase in gravitational force between the two objects. However, this effect is observer-dependent and would not be observed by an observer at rest next to the two masses. Additionally, the theory of general relativity, which explains the effects of gravity, is incompatible with Newton's equation of universal gravitational force for relativistically moving bodies. In general relativity, the
crebigsol
Suppose two terrestrial objects B1 and B2 have concentrated a high quantity of mass while being reasonably separated by a distance. When a high speed rocket ship flies by in direction more less parallel to the line connecting these two objects, relativity must predict a drastic disturbance in the physical state between B1 and B2. Not only the mass of each of the two objects is seen increased as moving mass by someone in the rocket ship according to relativity, but also the distance between B1 and B2 found shortened by the observer. Gravitational force between them must be predicted by this theory to increase many folds. Indeed, if relativity is valid, the increase is by a factor of {1/[1-(v/c)2]1/2}4
(2, 1/2, and 4 are all in superscript)! Gravitational force thus escalated must force these two objects to collide, or at least to be predicted as having much higher potential of ultimately colliding by this observer. Does relativity reveal what kind of physical effect that a fly-by rocket ship can exert on these two objects? Or does relativity have paragraph rewriting Newton’s equation of universal gravitational force in a moving person’s observation?

crebigsol said:
Suppose two terrestrial objects B1 and B2 have concentrated a high quantity of mass while being reasonably separated by a distance. When a high speed rocket ship flies by in direction more less parallel to the line connecting these two objects, relativity must predict a drastic disturbance in the physical state between B1 and B2. Not only the mass of each of the two objects is seen increased as moving mass by someone in the rocket ship according to relativity, but also the distance between B1 and B2 found shortened by the observer. Gravitational force between them must be predicted by this theory to increase many folds. Indeed, if relativity is valid, the increase is by a factor of {1/[1-(v/c)2]1/2}4
(2, 1/2, and 4 are all in superscript)! Gravitational force thus escalated must force these two objects to collide, or at least to be predicted as having much higher potential of ultimately colliding by this observer. Does relativity reveal what kind of physical effect that a fly-by rocket ship can exert on these two objects? Or does relativity have paragraph rewriting Newton’s equation of universal gravitational force in a moving person’s observation?

You have misinterpreted what the theory of relativity says. It tells you what the observer in the rocket ship measures. An observer at rest next to the two masses would not observe any changes in either their mass or the distance separating them. Your observer in the rocket ship would only observe a contraction of the distance between the two masses. Without actually interacting with them, he would not be able to measure a change in their mass, but that is a different situation from what you describe.

Gravitational force between them must be predicted by this theory to increase many folds. Indeed, if relativity is valid, the increase is by a factor of {1/[1-(v/c)2]1/2}4

I don't know where you learned relativity, but this is wrong.

Gravitational effects are observer independent. That is why general relativity is written in terms of tensors or an equivalent formalism.

Mentz114 said:
I don't know where you learned relativity, but this is wrong.

Gravitational effects are observer independent. That is why general relativity is written in terms of tensors or an equivalent formalism.

Tensor is a mathematical means, not any insight of physics of any kind. An equation of 1+1=2, no matter how correct, tells you nothing about any material state in a physical world. On the ohter hand, without any math, people can explain why on can see his image in a mirror.

Besides, does relativity proposes that gravitational effects are observer independent and tell people why it should?

AEM said:
Your observer in the rocket ship would only observe a contraction of the distance between the two masses. Without actually interacting with them, he would not be able to measure a change in their mass, but that is a different situation from what you describe.

Wouldn't the moving length contraction influence the gravitational effect? If the contraction affects time measurement, why is it exempted from affecting gravitational measurement? Besides, special relativity has mathematical prediction on how moving mass changes, how has it become "Without actually interacting with them, he would not be able to measure a change in their mass"? In fact, it is this prediction leads to the E=mc2

Once again- the moving observer would observe an increase in mass of the two objects and a decrease in the distance between them. An observer in the rest frame of the two masses- and the two masses themselves- would see no change in mass, distance, or gravitational force.

crebigsol said:
Or does relativity have paragraph rewriting Newton’s equation of universal gravitational force in a moving person’s observation?
This is much more than a paragraph, it is the entire theory of General Relativity. Newton's equation is simply not compatible with relativistically moving bodies, although GR does reduce to Newtonian gravity for non-relativistically moving bodies in weak gravitational fields.
crebigsol said:
On the ohter hand, without any math, people can explain why on can see his image in a mirror.
I don't believe this is true.
crebigsol said:
Besides, special relativity has mathematical prediction on how moving mass changes
Don't forget that in GR mass is not the source of gravity; in GR the source of gravity is the stress-energy tensor. This means that gravity couples not only to mass, but also to momentum, pressure, stress, etc.

DaleSpam said:
.I don't believe this is true.QUOTE]

The truth is only a simple concept of reflection, although how precisely the reflection works out does require math. However, math steps in after physiccal explanation not before. Possibly a primitive man can explain why he sees himself while staring at water ssurface. When Archimeda used concave mirrors to burn enemy's ships, possbibly (it means I do not say this with certainty) he had not figured out the mathematical relationship between curvature of the reflecting surface and the focus point.

I don't understand where you're going here. You posted an equation that turned out to be wrong, and now you seem to be complaining that things get quantitative too soon.

I don't understand where you're going here. You posted an equation that turned out to be wrong, and now you seem to be complaining that things get quantitative too soon.

Possibly I have to discontiue this thread because I seem not being able to have a full grasp on how to follow the publishsing mecahnism here. For example, you can quote clearly from what I say, but I am unable to do the same thing. It only creates difficulty between our communicaiton. Thank you for all your time and effort, anyway.

Ah, after I complain, I see I can quote you clearly. But it is ok. I will come back some other time. Thank you.

crebigsol said:
I will come back some other time.
I am glad to hear it. In the meantime you may wish to learn more about the use of tensors in GR as was mentioned previously. The main point is that in GR the source of gravity is not simply mass (a scalar) but energy, and momentum, and pressure, and stress all together (a tensor). And for relativistically moving bodies the mass is not the only significant component of the stress-energy tensor.

## 1. What is the difference between gravitational force and relativity?

Gravitational force is a fundamental force that describes the attraction between two objects with mass. Relativity, on the other hand, is a theory that explains the relationship between space, time, and gravity.

## 2. How does gravitational force affect objects?

Gravitational force causes objects with mass to attract each other. The strength of this force depends on the masses of the objects and the distance between them. The force causes objects to move towards each other, which is why objects fall towards the Earth.

## 3. What is the theory of relativity?

The theory of relativity, developed by Albert Einstein, is a fundamental theory of physics that explains the relationship between space, time, and gravity. It is divided into two parts: special relativity, which deals with objects moving at a constant speed, and general relativity, which deals with objects in accelerating frames of reference.

## 4. How does relativity explain the bending of light around massive objects?

According to general relativity, massive objects, like stars and planets, create a curvature in space-time. This curvature causes light to bend as it travels near the object. This phenomenon, known as gravitational lensing, has been observed and confirmed by scientists.

## 5. What are some practical applications of the theory of relativity?

The theory of relativity has many practical applications, including GPS technology, which relies on the precise measurements of time predicted by the theory. It also helps in understanding the behavior of black holes, the expansion of the universe, and the production of energy in nuclear reactions.

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